Table of Contents
Introduction 3
Purpose 3
Organization of the writing committee 3
Methodology and evidence review 3
Document review and approval 4
Scope of the document 4
Genetic influences on disease and modes of inheritance 4
Different methods of genetic testing 8
Methods to interrogate genetic variation 8
Genome-wide association study and polygenic risk scores 9
Choice of genetic tests and interpretation of variants 12
Background 13
State of genetic testing for inherited arrhythmia syndromes 14
Long QT syndrome 14
Background 15
Summary of the major long QT syndrome genes 15
Prognostic and therapeutic implications of long QT syndrome genetic testing 16
Acquired long QT syndrome 17
Catecholaminergic polymorphic ventricular tachycardia 18
Background 18
Diagnostic implications of catecholaminergic polymorphic ventricular tachycardia
genetic testing 18
Prognostic and therapeutic implications of catecholaminergic polymorphic ventricular
tachycardia genetic testing 19
Brugada syndrome 20
Background 20
Diagnostic implications of Brugada syndrome genetic testing 20
Prognostic and therapeutic implications of Brugada syndrome genetic testing 22
(Progressive) cardiac conduction disease 22
Background 22
Diagnostic implications of genetic testing in cardiac conduction disease/progressive
cardiac conduction disease 22
Prognostic and therapeutic implications of genetic testing 25
Short QT syndrome 25
Background 25
Diagnostic implications of short QT syndrome genetic testing 25
Prognostic and therapeutic implications of short QT syndrome genetic testing 27
Atrial fibrillation 27
Background 27
Genetic forms of atrial fibrillation 27
Sinus node disease 28
Background 29
Diagnostic implications of genetic testing in sinus node dysfunction 29
Prognostic and therapeutic implications of genetic testing 30
Early repolarization syndrome 31
Background 31
Wolff–Parkinson–White syndrome 31
Background 31
Genetics of Wolff–Parkinson–White 31
State of genetic testing for cardiomyopathies 32
Hypertrophic cardiomyopathy 32
Background 32
Diagnostic implications of genetic testing 33
Prognostic and therapeutic implications of genetic testing 35
Dilated cardiomyopathy 35
Background 36
Diagnostic implications of dilated cardiomyopathy genetic testing 36
Prognostic and therapeutic implications of dilated cardiomyopathy genetic testing 37
Arrhythmogenic cardiomyopathy 37
Background 38
Diagnostic implications of arrhythmogenic cardiomyopathy genetic testing 38
Prognostic and therapeutic implications of arrhythmogenic cardiomyopathy genetic
testing 39
Left ventricular non-compaction cardiomyopathy 40
Background 40
Diagnostic implications of left ventricular non-compaction genetic testing 41
Prognostic and therapeutic implications 41
Restrictive cardiomyopathy 41
Background 42
Diagnostic implications of restrictive cardiomyopathy genetic testing 42
Prognostic and therapeutic implications 42
State of genetic testing for sudden cardiac death or survivors of unexplained cardiac
arrest 42
Background 43
State of genetic testing for congenital heart disease 44
Background 45
Antenatal testing 47
Antenatal screening 47
Neonates and infants requiring investigation or procedures for congenital heart disease 47
Patients with congenital heart disease and extracardiac anomalies 47
Familial forms of congenital heart disease 47
Sporadic non-syndromic congenital heart disease 47
Heterotaxy 47
State of genetic testing for coronary artery disease and heart failure 48
Conclusion and future directions 48
Developed in partnership with and endorsed by the European Heart Rhythm Association
(EHRA), a branch of the European Society of Cardiology (ESC), the Heart Rhythm Society
(HRS), the Asia Pacific Heart Rhythm Society (APHRS), and the Latin American Heart
Rhythm Society (LAHRS).
Introduction
Purpose
Genetic testing has advanced significantly since the publication of the 2011 HRS/EHRA
Expert Consensus Statement on the State of Genetic Testing for the Channelopathies
and Cardiomyopathies.
1
In addition to single-gene testing, there is now the ability to perform whole-exome
sequencing (WES) and whole-genome sequencing (WGS). There is growing appreciation
of oligogenic disorders,
2,
3
the role of modifier genes,
2
and the use of genetic testing for risk stratification, even in common cardiac diseases
such as coronary artery disease or atrial fibrillation (AFib), including a proposal
for a score awaiting validation.
4
This document reviews the state of genetic testing at the present time, and addresses
the questions of what tests to perform and when to perform them. It should be noted
that, as articulated in a 1999 Task Force Document by the European Society of Cardiology
(ESC) on the legal value of medical guidelines,
5
‘The guidelines from an international organization, such as the ESC, have no specific
legal territory and have no legally enforcing character. Nonetheless, in so far as
they represent the state-of-the-art, they may be used as indicating deviation from
evidence-based medicine in cases of questioned liability’. In the case of potentially
lethal and treatable conditions such as catecholaminergic polymorphic ventricular
tachycardia (CPVT) or long QT syndrome (LQTS), it is the responsibility of the physician,
preferably in conjunction with an expert genetics team, to communicate to the patient/family
the critical importance of family screening, whether this be facilitated by cascade
genetic testing or by broader clinical family screening.
Organization of the writing committee
The writing committee included chairs and representatives nominated and approved by
European Heart Rhythm Association (EHRA), Heart Rhythm Society (HRS), Asia Pacific
Heart Rhythm Society (APHRS), and Latin American Heart Rhythm Society (LAHRS). Chairs
and authors had no relevant relationship with industry (RWI). Details are available
in Supplementary material online.
Methodology and evidence review
Writing committee members were assigned topics, compiled tables of recommendations
supported by appropriate text and references, and attended periodic virtual meetings.
Writing committee members without relevant RWI drafted recommendations. In the arena
of genetic testing, there are few if any randomized trials to provide the strongest
level of scientific evidence. Recommendations were associated with a green heart symbol
(‘should do this’) if supported by at least strong observational evidence and author
consensus. A yellow heart (‘may do this’) was used if there was some evidence and
general agreement. A red heart (‘do not do this’) indicated evidence or general agreement
not to perform this testing (Table 1
). Writing committee consensus of 80% was required. The recommendations were approved
by an average of 93% of the writing committee members.
Table 1
Scientific rationale of consensus statements
a
Definitions related to a treatment or procedure
Consensus statement instruction
Symbol
Supported by strong observational evidence and authors’ consensus
‘Should do this’
Some evidence and general agreement favour the usefulness/efficacy of a test
‘May do this’
There is evidence or general agreement not to recommend a test
‘Do not do this’
a
The categorization for our consensus document should not be considered directly similar
to the one used for official society guideline recommendations which apply a classification
(I–III) and level of evidence (A, B, and C) to recommendations.
Document review and approval
After review by the writing committee, the recommendations were opened for public
comment. The document was then reviewed by the scientific documents committees of
EHRA, HRS, APHRS, and LAHRS. After revision, the document was sent to external reviewers
nominated by the participating societies. After further revision, the document was
endorsed by the collaborating societies and presented for publication.
Scope of the document
This document addresses essential principles of genetic testing including modes of
inheritance, different testing methodologies, and interpretation of variants. Additionally,
the document presents the state of genetic testing for inherited arrhythmia syndromes,
cardiomyopathies, sudden cardiac death (SCD), congenital heart disease (CHD), coronary
artery disease, and heart failure. A discussion of aortopathies and hyperlipidaemia
is beyond the scope of this document. The authors discuss diagnostic, prognostic,
and therapeutic implications of genetic testing in each of these syndromes, as far
as these are known. The writing committee recognizes that the feasibility of genomic
testing by gene panel testing or by WES or WGS depends on the availability of genomic
technology and on regional reimbursement policy. Therefore, the recommendation ‘should
do this’ can be read as ‘should do this when available’.
Table 2
lists previous guidelines and consensus statements that are considered pertinent for
this document as they all include relevant information for the diagnosis of patients
with inherited cardiovascular conditions (ICCs) and the need for genetic testing.
The terms and abbreviations used in consensus statement are summarized in Table 3
.
Table 2
Relevant clinical practice documents or guidelines
Title
Publication year
Consensus documents/guidelines of scientific societies
APHRS/HRS expert consensus statement on the investigation of decedents with sudden
unexplained death and patients with sudden cardiac arrest, and of their families
6
2021
HRS/EHRA/APHRS/LAHRS Expert Consensus Statement on Catheter Ablation of Ventricular
Arrhythmias
7
2020
Genetic Testing for Inherited Cardiovascular Diseases: A Scientific Statement From
the American Heart Association
8
2020
European Recommendations Integrating Genetic Testing into Multidisciplinary Management
of Sudden Cardiac Death
9
2019
Pre-participation Cardiovascular Evaluation for Athletic Participants to Prevent
Sudden Death: Position Paper from the EHRA and the EACPR, Branches of the ESC
22
2019
HRS Expert Consensus Statement on Evaluation, Risk Stratification, and Management
of Arrhythmogenic Cardiomyopathy
11
2019
AHA/ACC/HRS Guideline for Management of Patients with Ventricular Arrhythmias and
the Prevention of Sudden Cardiac Death
12
2017
ESC Guidelines for the Management of Patients with Ventricular Arrhythmias and the
Prevention of Sudden Cardiac Death
13
2015
EHRA/HRS/APHRS Expert Consensus on Ventricular Arrhythmias
14
2014
HRS/EHRA/APHRS Expert Consensus Statement on the Diagnosis and Management of Patients
with Inherited Primary Arrhythmia Syndromes
15
2013
HRS/EHRA Expert Consensus Statement on the State of Genetic Testing for the Channelopathies
and Cardiomyopathies
1
2011
Genetic counselling and testing in cardiomyopathies: a position statement of the
European Society of Cardiology Working Group on Myocardial and Pericardial Diseases
16
2010
NIH-Clinical Genome Resource Consortium (ClinGen) documents
A Multi-Centred, Evidence-Based Evaluation of Gene Validity in Sudden Arrhythmic
Death Syndromes: CPVT and The Short QT Syndrome
17
2022
International Evidence Based Reappraisal of Genes Associated With Arrhythmogenic
Right Ventricular Cardiomyopathy Using the Clinical Genome Resource Framework
18
2021
Evidence-Based Assessment of Genes in Dilated Cardiomyopathy
19
2021
An International, Multicentred Evidence-Based Reappraisal of Genes Reported to Cause
Congenital Long QT Syndrome
20
2020
Reappraisal of Reported Genes for Sudden Arrhythmic Death: An Evidence-Based Evaluation
of Gene Validity for Brugada Syndrome
21
2018
Evaluating the Clinical Validity of Hypertrophic Cardiomyopathy Genes
10
2017
Table 3
Definitions and abbreviations
Term (abbreviation)
Definition
Sudden cardiac arrest (SCA)
Sudden cessation of cardiac activity with haemodynamic collapse, typically due to
sustained ventricular arrhythmia
Sudden cardiac death (SCD)
Death that occurs within 1 h of onset of symptoms in witnessed cases, and within 24 h
of last being seen alive when it is unwitnessed
Sudden unexplained death (syndrome) [SUD(S)]
Unexplained sudden death occurring in an individual older than 1 year
Sudden unexplained death in infancy (SUDI)
a
Unexplained sudden death occurring in an individual younger than 1 year with negative
pathological and toxicological assessment
Sudden arrhythmic death (syndrome) [SAD(S)]
b
Unexplained sudden death occurring in an individual older than 1 year with negative
pathological and toxicological assessment
Abbreviation
ASO
Allele-specific oligonucleotide
ACMG
American College of Medical Genetics & Genomics
aCGH
Array comparative genomic hybridization
ACM
Arrhythmogenic cardiomyopathy
ALVC
Arrhythmogenic left ventricular cardiomyopathy
ARVC
Arrhythmogenic right ventricular cardiomyopathy
AFib
Atrial fibrillation
ASD
Atrial septal defect
ASS
Atrial stand still
AD
Autosomal dominant
AR
Autosomal recessive
BrS
Brugada syndrome
CRDS
Calcium release deficiency syndrome
CCD
Cardiac conduction disease
RyR2
Cardiac ryanodine receptor
CMR
Cardiovascular magnetic resonance
CPVT
Catecholaminergic polymorphic ventricular tachycardia
CVS
Chorionic villous sample
CMA
Chromosomal microarray
CHD
Congenital heart disease
CNV
Copy number variant
DCM
Dilated cardiomyopathy
ERP
Early repolarization pattern
ECA
Extracardiac anomaly
GWAS
Genome-wide association studies
GRS
Genomic risk scores
HCM
Hypertrophic cardio-myopathy
IVF
Idiopathic ventricular fibrillation
ICD
Implantable cardioverter-defibrillator
ICC
Inherited cardiovascular conditions
JLNS
Jervell and Lange-Nielsen Syndrome
LCSD
Left cardiac sympathetic denervation
LV
Left ventricular
LVH
Left ventricular hypertrophy
LVNC
Left ventricular non-compaction cardiomyopathy
LB
Likely Benign
LP/P
Likely pathogenic/pathogenic
LQTS
Long QT syndrome
MAF
Minor allele frequency
MLPA
Multiplex ligation-dependent probe amplification
NGS
Next-generation sequencing
PRS
Polygenic risk scores
PCR
Polymerase chain reaction
PNP
Polyneuropathy
PCCD
Progressive cardiac conduction disease
RCM
Restrictive cardiomyopathy
siRNA
Short interfering RNA
SQTS
Short QT syndrome
SNP
Single-nucleotide polymorphism
SNV
Single-nucleotide variant
SND
Sinus node dysfunction
SCA
Sudden cardiac arrest
SCD
Sudden cardiac death
TOF
Tetralogy of Fallot
TdP
Torsades de pointes
TKOS
Triadin knockout syndrome
UCA
Unexplained cardiac arrest
UTRs
Untranslated regions
VUS
Variants of uncertain clinical significance
VF
Ventricular fibrillation
VSD
ventricular septal defect
WES
Whole-exome sequencing
WGS
Whole-genome sequencing
WPW
Wolff–Parkinson–White syndrome
X-chr
X-chromosomal
a
Synonymous with ‘sudden unexplained infant death’ (SUID).
b
Synonymous with ‘autopsy-negative sudden unexplained death’.
Genetic influences on disease and modes of inheritance
Research conducted, over the last three decades, has provided considerable insights
into the modes of inheritance of cardiovascular disorders and into the underlying
genes and pathways. These insights were fuelled by developments in technologies for
DNA sequencing and genotyping, statistical genetic approaches, and our increased understanding
of the wide spectrum of genetic variation in the general population. Two broad categories
of cardiovascular disorders are recognized: Mendelian disorders that are caused by
the inheritance of one or two genetic variants and that typically cluster in families,
and disorders with complex inheritance, wherein multiple genetic variants contribute
and for which familial clustering is less pronounced. In both categories non-genetic
factors also contribute to the ultimate phenotypic expression.
Inheritance patterns for monogenic disorders include autosomal dominant (AD), autosomal
recessive (AR), and sex-linked. In AD disorders, the inheritance of a single defective
copy of a gene, either the maternal or the paternal copy, is sufficient to cause the
disorder. In some cases, an AD condition may result from a de novo variant in the
gene and occurs in individuals with no history of the disorder in their family. In
AR disorders, both the maternal and paternal copies need to be defective to produce
the disorder. X-linked disorders are caused by pathogenic variants in genes on the
X chromosome. Two types of X-linked disorders are recognized, X-linked dominant and
X-linked recessive. In females with an X-linked dominant condition, a pathogenic variant
in one of the two copies of the gene is sufficient to cause the condition. In males,
who have only one X chromosome, a pathogenic variant in the only copy of the gene
causes the disorder. In X-linked recessive inheritance, in males, one defective copy
of the gene is sufficient to cause the condition, whereas females are mildy affected
or unaffected if only one copy of the gene is aberrant. A characteristic of both types
of X-linked inheritance is that males cannot pass on the disorder to their sons. Besides
Mendelian inheritance, single-gene disorders may exhibit mitochondrial inheritance.
Because mitochondrial DNA is inherited from the mother, only females can pass on genetic
defects residing on mitochondrial DNA. In rare cases, disease-causing variants may
arise post-zygotically (during development), leading to mosaicism (the occurrence
of genetically distinct cell populations). Mosaicism may be limited to somatic cells,
where there would be no risk of passing the disease-variant to the offspring, or it
may also affect the germ line cell population and in this way the disease variant
may be passed to the offspring.
Disease-associated genetic variants likely lie on a spectrum of population frequency
and phenotype effect size. Mendelian variants, when dominant, are usually characterized
by an ultra-low minor allele frequency (MAF, typically <0.01%) in the population and
have large effect sizes (Figure 1
). Classically, genes underlying Mendelian disorders were identified by linkage studies
that tracked chromosomal regions that are co-inherited with the condition in multiple
affected individuals in families, followed by Sanger sequencing of the linked chromosomal
interval. More recently, next-generation sequencing (NGS) and WES have been successful
in identifying novel genes underlying Mendelian disorders. It is estimated that there
are about 7000 single-gene inherited disorders of which causative genes have been
discovered for over 4000.
23
Accordingly, many genes for hereditary cardiomyopathies, including dilated cardiomyopathy
(DCM), hypertrophic cardiomyopathy (HCM), and arrhythmogenic cardiomyopathy (ACM);
hereditary arrhythmias, such as LQTSs, Brugada syndrome (BrS), short QT syndromes
(SQTSs), and CPVT; and cardiac conduction defects have been identified.
24
Figure 1
The genetic aetiology of cardiovascular diseases. Mendelian disease variants (upper
left panel) are ultra-rare in the population and have large effect sizes, though often
not sufficient in isolation to yield a disease phenotype. Mendelian genes and variants
can be identified through analysis of family pedigrees or burden analysis in case–control
studies and further validated with functional assays. Common variants (upper right
panel) with individually small effect sizes may collectively contribute to disease
burden or modulate the effects of Mendelian variants. Intermediate effect variants
(upper middle panel) are emerging variant classes that usually have population frequencies
and effect sizes between rare Mendelian and common variants and may act to increase
severity and penetrance. Such variants can be identified by demonstrating enrichment
in case cohorts and deleterious effects in established functional assays. These different
variant classes can combine to reach the threshold of disease in patients with rare
cardiovascular diseases and contribute to the variable severity observed in patients.
Diseases such as HCM and LQTS are often Mendelian [1] or near-Mendelian where Mendelian
variants of large effect sizes can combine with other variant classes to cause disease
[2] or act as protective modifiers (e.g. regulatory variants affecting the expression
ratio of the mutant vs. non-mutant alleles) [3]. In contrast, diseases such as BrS
and DCM may exhibit a more complex aetiology where substantial non-Mendelian genetic
and non-genetic factors are required to reach disease threshold in the presence of
a low penetrance rare variant [4] or in a non-Mendelian disease model [5]. blue −,
individual does not harbour the familial rare pathogenic variant; blue +, individual
harbours the familial rare pathogenic variant; green −, individual does not harbour
that intermediate effect variant; green +, individual harbours a given intermediate
effect variant; GWAS, genome-wide association study; MAF, minor allele frequency;
PRS, polygenic risk score; SNP, single-nucleotide polymorphism. Adapted from Walsh
et al.
3
In Mendelian cardiovascular disorders with potentially devastating initial manifestations,
such as SCD or aortic dissection, appropriate and prompt identification of individuals
at risk is imperative.
25
Genetic testing has been recommended for a number of inherited cardiac conditions
for several years and has become a standard aspect of clinical management in affected
families. The primary benefit of genetic testing is to identify at-risk carriers of
the familial pathogenic variant (and non-carriers who are unlikely to develop disease)
through cascade screening, assuming a genetic variant is identified that can be predicted
with confidence to cause the disease. Such clinical genetic testing for these single-gene
disorders has been shown to be cost-effective
26
and can be considered as a success story in the application of genetics into clinical
practice.
Although pathogenic Mendelian genetic variants are characterized by a large effect
size, they may not in isolation be sufficient to yield a disease phenotype. This is
evidenced by incomplete disease penetrance where only a proportion of individuals
in the same family carrying a particular genetic variant shows the disease. Another
feature that characterizes Mendelian disorders is the phenomenon of variable expressivity,
where different disease severity is observed among individuals carrying the same underlying
genetic predisposition. What this means is that, even within pedigrees sharing the
same pathogenic variant, the clinical presentation can vary from a patient having
no clinical manifestation of the disease to another having severe disease. A clearly
pathogenic variant can, therefore, have high diagnostic value, but low prognostic
utility.
27
Besides non-genetic (such as environmental) factors, penetrance and expressivity of
Mendelian genetic defects are influenced by the co-inheritance of other genetic factors
alongside the Mendelian genetic defect, that act to exacerbate or attenuate the effect
of the latter on the phenotype (often referred to as ‘genetic modifiers’, Figure 1
).
Contrary to Mendelian disorders, where a single large-effect variant primarily determines
susceptibility to the disorder, susceptibility to disorders with complex inheritance
rests on the co-inheritance of multiple variants. Such variants are identified by
means of genome-wide association studies (GWAS) that compare the prevalence of millions
of genetic variants genome-wide between affected individuals and controls. Non-Mendelian
genetic risk variants that contribute to cardiovascular disease risk and that are
detectable with current approaches and study sample sizes can be broadly grouped into
two categories. These comprise common variants, typically defined as having a MAF
of >1–5%, which have individually small effect sizes, and intermediate effect variants
(MAF <1–2%) with effect sizes and frequencies between common and Mendelian variants
(Figure 1
).
It is likely that a continuum of genetic complexity exists where at one end of the
spectrum are Mendelian disorders determined primarily by the inheritance of an ultra-rare
large-effect genetic defect, and at the other end are highly polygenic disorders determined
by many genetic variants with additive effect (Figure 1
). While some disorders present primarily with one form of inheritance, different
inheritance patterns may exist for the same disorder.
28
Emerging data suggest that common variants of small effect and intermediate effect
variants may, to varying extents, influence penetrance in individuals with Mendelian
genetic defects by pushing the genetic burden towards the threshold of disease, as
well as influence severity of disease.
29,
30
While their incorporation into genetic testing approaches is expected to increase
the sensitivity of genetic testing, the identification of such modulatory variants
is still a matter of intense research and therefore currently not clinically applicable.
Different methods of genetic testing
Methods to interrogate genetic variation
Genomic technology has enabled efficient and comprehensive assessment of genetic variation
within individuals. We each carry millions of variants in our genome, ranging in size
from substitutions of a single-nucleotide (single-nucleotide variant; SNV, sometimes
termed SNP) to deletions or duplications of an entire chromosome. Smaller variants,
such as SNVs, are more prevalent in our genomes. We each carry about 100 SNVs that
have arisen de novo during our development and are private to us,
31
and thousands of other rare SNVs.
32
The largest structural variants are much less prevalent, for example aneuploidy (the
presence of an abnormal number of chromosomes in a cell), affects about 1 in 300 live
births.
33
Though individually smaller variants are less likely to cause disease than larger
changes that are more likely to disrupt genome function, collectively they probably
account for the majority of phenotypic variability and inherited disease.
34,
35
The largest genetic variants were the first to be detectable and associated with disease,
with an extra copy of chromosome 21 detectable by microscopy, and recognized as causing
Down’s syndrome in 1959.
36
In 1977, Sanger sequencing was developed as a method for directly reading the sequence
of DNA,
37
with the resolution to discover SNVs. It was the most widely used DNA sequencing technology
for more than 30 years, underpinning the human genome project (1990–2003),
38
and remains an important tool today as it is fast, flexible, and remains the gold-standard
for accuracy. However, it is prohibitively costly and laborious for large scale genomics,
or diagnostics of ICCs at scale. The human genome, for example, is made up of ∼3 billion
base pairs, with about 20 000 distinct protein-coding genes. One sequencing reaction
reads out up to ∼1000 base pairs of sequence (equivalent to 1000 base pairs), so that
typically one reaction is required per exon of a gene. Large genes require many reactions
(e.g. RYR2 has 105 exons, TTN has 364 exons). Furthermore, ICCs are genetically heterogeneous,
so that it is often necessary to sequence many genes in an individual patient.
A ‘next generation’ of sequencing technologies became available in the early 2000s
that used diverse strategies to make the sequencing process massively parallel, and
therefore vastly more scalable.
39,
40
Several high-throughput sequencing technologies are now available, each with different
strengths and weaknesses (e.g. emphasizing cost, speed, accuracy or read-length),
and high-throughput sequencing now is the mainstay for first-line sequencing in most
diagnostic contexts.
High-throughput sequencing allows WGS, or with additional sample preparation, restriction
to specific genomic regions of interest: targeted sequencing. The choice of target
represents a trade-off of cost vs. completeness of genetic characterization. The region
of interest may be restricted by gene, and/or by functional annotation (e.g. coding
sequence, promotor region, cis-regulatory element, intron, etc.). Since protein-coding
regions represent about 1% of the genome, but harbour ∼85% of disease-causing variants,
41
targeted sequencing often prioritises these regions. Typical approaches are to sequence
the protein-coding regions of all ∼20 000 annotated genes (WES),
42
or a pre-specified set of genes of interest, such as genes related to a particular
clinical condition (a ‘gene panel’; usually exons only). Data can also be generated
for a large panel of genes, or indeed all genes, but with downstream in silico analysis
restricted to a more focused subset—sometimes described as a ‘virtual panel’. In practice
there is usually also a trade-off between depth and breadth of sequencing, with broader
targets (e.g. WES) leading to reduced sequencing depth and reduced sensitivity in
some areas. That is for a given amount of sequencing, as the number of genes sequenced
increases, the amount of data from each gene decreases. We can focus sequencing on
a narrow region for maximum accuracy, or can spread across a larger region, accepting
that sensitivity will decrease if sequencing is spread too thinly. Currently, more
targeted sequencing often provides more complete data for the selected region. Table 4
summarizes the strengths and limitations of the various genetic testing methods.
Table 4
Different methods of genetic testing
Technology
Strengths
Limitations
Example diagnostic application
Sequencing approaches
Sanger sequencing
Accuracy
Low cost per reaction
Not scalable
Insensitive to large SVs
Single gene test
Single variant testing—for a pre-specified variant during cascade family evaluation
Panel sequencing
Balances reasonably comprehensive coverage (e.g. all genes associated with a particular
phenotype) against cost
Often highly optimized for complete and uniform capture of region of interest
Usually exonic only
Needs updating as knowledge changes (e.g. new gene-disease associations discovered)
First line diagnostic test for proband
WES
Comprehensive coverage of all genes
Off-the-shelf design
Can run a single wet-lab workflow, and introduce specificity at analysis stage
Can update analysis to incorporate new knowledge without regenerating data—adaptable
Enables analyses for secondary findings
Larger target requires more sequencing (c.f. panels)
May be less optimized than more focused panel
More costly and complex to store and process data (c. 10–100× more data than panel)
Will not detect non-coding variants
May not detect all variant classes
Diagnosis in proband for very heterogeneous conditions (e.g paediatric and syndromic
cardiomyopathies)
Second line test if panel negative in specific circumstances, for example with informative
family structure
WGS
Comprehensive genetic characterization—all genes, all elements, all variant types
Will also detect common variants for PRS, pharmacogenetics and other applications
Enables analyses for secondary findings
More costly and complex to store and process data (∼100× more data than WES)
Diagnosis in proband for very heterogeneous conditions
Second line test if panel negative
Definitive and future-proof genetic characterization if funds permit—e.g. hold data
in medical record for iterative targeted interpretation according to clinical needs
Non-sequencing approaches
Allele-specific PCR
Quick, cheap, accurate
Pre-specified variants only
Testing a single variant in a large family (more likely Sanger sequencing now)
Array comparative genomic hybridization
Cheap screening for SVs/CNVs
High-resolution (compared with cytogenetic approaches)
Insensitive to other variant classes
Screening for structural variants, including aneuploidy, e.g. in structural congenital
heart disease
Droplet digital PCR
Low cost, high-sensitivity, detection of genome dose for SV/CNV detection at a pre-specified
locus
Scalability limited by multiplexing of pre-specified PCR amplicons targeting regions
of interest
Confirmation of putative CNVs detected in high-throughput sequence data
DNA SNP arrays
Genome wide
Relatively cheap
Pre-specified variants only
Accuracy poor for many rarer variants
Recreational ancestry analysis
Polygenic risk
Pharmacogenetics
CNV, copy number variant; PCR, polymerase chain reaction; PRS, polygenic risk score;
SNP, single-nucleotide polymorphism; SV, structural variant; WES, whole-exome sequencing;
WGS, whole-genome sequencing.
While exon sequencing typically also targets sufficient immediately adjacent sequence
to detect non-coding variants disrupting known splice sites, it will not detect variants
that create new splice sites at a distance from the usual coding sequence, and usually
omits 5′- and 3′-untranslated regions and other regulatory elements which can harbour
important disease-associated variants.
43,
44
Sequencing methods also differ in their sensitivity for different variant types. All
methods are able to detect the small variants that account for the majority of the
burden of ICCs (SNVs, small insertions and deletions). Larger and more complex variants,
such as deletion of a whole exon, or a complex genomic rearrangement, are often harder
to detect, especially if sequencing does not cover the boundary of the variant (the
breakpoint). They may nonetheless be detectable in high-throughput sequence data through
a change in the number of DNA reads coming from a particular region, or through a
change in allele balance (loss of heterozygosity). Whole-genome sequencing offers
the most comprehensive sensitivity across all variant classes, but development in
computational tools continues to improve detection of structural and copy number variants
(CNVs) from WES and panel sequencing.
45,
46
However, alternative non-sequencing quantification approaches such as multiplex ligation-dependent
probe amplification (MLPA) or array comparative genomic hybridization may be more
sensitive as discussed below.
All sequencing approaches directly read out the DNA sequence(s) present in a sample,
allowing analysis of any variation present, and can be used for both discovery and
detection of variants. There are some notable additional technologies that can determine
the presence or absence of a pre-specified variant, i.e. detection only, that have
important clinical applications.
Polymerase chain reaction (PCR) methods can be used for variant detection. Allele-specific
PCR is cheap and scalable for the detection of a specific variant and quantification
of alleles in a sample, but must first be optimized for each variant to be studied.
Digital PCR (including droplet digital PCR) allows precise quantification of the number
of copies of a target DNA sequence relative to a single-copy reference locus.
47
It is cheap and sensitive to small differences in dose and is an important approach
to confirm the presence of potential new CNVs identified by sequencing.
Other important methods are based on competitive hybridization of DNA to oligonucleotide
probes with a known sequence. DNA single-nucleotide polymorphism (SNP) arrays can
detect millions of variants in parallel, but each variant must be pre-specified and
the hybridization optimized, and not all variants can be assayed accurately. These
have minimal utility for identification of rare variants for Mendelian diagnosis but
are widely used where common variants are important, for example in GWAS, calculating
polygenic risk scores as detailed below, and in pharmacogenetics.
48
Array comparative genomic hybridization (aCGH) is another genome-wide hybridization-based
approach used to detect copy-number changes, of particular importance in congenital
structural heart disease and individuals with syndromic ICCs. MLPA combines PCR and
hybridization methods to quantify specific nucleic acid sequences quickly and efficiently,
and may be used to detect many variant types, but particularly copy number changes.
46
These diverse and complementary methods can then be deployed for different types of
clinical genetic testing. Confirmatory testing refers to genetic analysis of an individual
with a diagnostic clinical phenotype to identify the underlying genetic cause. In
a proband (the first presenting person in a family), there is no pre-specified variant
to search for, so a direct sequencing approach is used to discover any genetic variation
in the genes associated with that condition. For many ICCs, the first line test will
be a high-throughput sequencing gene panel relevant to a specific disease, or a virtual
panel using WES with targeted analysis. If this analysis does not identify an underlying
cause, then more comprehensive genetic characterization, such as WES or WGS, may be
used to interrogate additional genes, look for variant types not examined by the first
line test, or assess for non-coding variants. This kind of comprehensive testing is
appropriate only in experienced centres and with cautious interpretation of any variants
identified. Having established the causative variant in one family member, it is appropriate
to look only for this specific variant in cascade testing of subsequent family members,
using Sanger sequencing or a non-sequencing approach, unless there is reason to suspect
additional genetic contributors.
Predictive (or cascade) testing refers to testing of individuals with or without a
phenotype, often unaffected relatives of an affected proband, with the aim of targeting
clinical surveillance to individuals with the genetic predisposition. Sanger sequencing
to detect the known familial variant is often used here.
WES and WGS also enable opportunistic screening. The American College of Medical Genetics
& Genomics (ACMG) recommend that a pre-specified panel of well-characterized disease-associated
genes be interrogated whenever clinical exome or genome sequencing is undertaken,
irrespective of the primary indication for genomic analysis.
49
This panel currently includes 73 genes (‘ACMG SF v3.0’), many of which are ICC genes
(Supplementary material online,
Table S1
).
50
The costs and benefits of actively seeking secondary findings remain under evaluation,
and these recommendations have not been widely adopted outside the USA. Several companies
also offer direct-to-consumer sequencing that includes analysis of ICC genes for individuals
without symptoms or signs of disease. The costs and benefits of actively seeking secondary
findings remain under evaluation, and a consensus has not been reached about these
recommendations.
Genome-wide association study and polygenic risk scores
Genome-wide association study is used to test associations between genetic variants
and human traits or disease phenotypes (Figure 2A).
51
Typically, in a GWAS, each study individual is genotyped by means of a DNA SNP (SNV)
array for 200 000 to 1 000 000 known SNVs, although, increasingly, whole-genome sequence
data may be used. Array-based genotyping is almost invariably followed by imputation,
a process of using the known linkage disequilibrium (correlation) between SNVs in
order to predict (impute) unobserved genotypes that are not directly assayed on the
array. This permits examination of a greater number of variants (up to 10s of millions).
Each variant is then tested for association with the trait or phenotype of interest.
Since the positions of the SNVs are known in the genome, the results of a GWAS in
one study may be combined with others in a meta-analysis to improve statistical power.
Variants with an association P-value <5 × 10−8 are generally considered statistically
significant, based on multiple testing correction for the roughly 1 000 000 independent
common variant tests (haplotype blocks) in the human genome.
52
Figure 2
Genome-wide association studies (GWAS) test the association of common genetic variants
with traits or diseases. Results are shown as a Manhattan plot (A) where the P-value
(y-axis) is plotted against the genomic position (x-axis) for millions of common variants
across the genome (blue markers). Polygenic risk scores (B) are generally derived
from GWAS and calculated for an individual i (PRSi
) as the sum of the products of allelic dosage (dosageij
) by the regression coefficient/weight (bj) for all M genetic variants (j). Created
with Biorender.com.
Similar analytic methods can be used to examine WGS and WES data. Since 2006, the
GWAS approach has been successfully implemented across a broad range of phenotypes
in cardiovascular genetics. It has been widely applied to identify common variants
that modulate interindividual variability of quantitative cardiophysiologic traits,
such as electrocardiogram (ECG) parameters,
53
cardiovascular magnetic resonance (CMR) parameters
54
and blood pressure,
55
with the premise that the genetic variants that impinge on such traits also contribute
to disease. Genome-wide association study has also been widely applied for identification
of susceptibility variants for common multifactorial disorders such as coronary artery
disease,
56
heart failure,
57
and AFib.
58
An analytic technique referred to as Mendelian randomization uses genetic information
as an instrumental variable to assess for the causal relations between risk factors
and diseases. For example, using this approach, GWAS studies of SCD have suggested
a genetic correlation between SCD and coronary disease, traditional coronary artery
disease risk factors, and electrical instability traits (QT and AFib).
59
Genome-wide association studies are increasingly being used to identify common variants
that contribute to susceptibility to rare/less common cardiovascular disorders such
as BrS,
60
LQTS,
28
DCM,
61
and HCM.
29,
30
Notably, GWAS enable the identification of many genetic variants associated with a
given trait or disease, which can be used to ‘score’ a specific individual for their
aggregate genetic predisposition to that specific trait or disease. Such scores are
referred to as polygenic risk scores (PRS) or genomic risk scores. Polygenic risk
scores result in numeric estimates that represent the cumulative burden of genetic
predisposition to a specific phenotype. The phenotype can be a disease such as DCM,
or a trait such as left ventricular (LV) systolic dysfunction. The scores are typically
calculated by combining the effects of many genetic variants in a mathematical framework
to derive a single numeric value for an individual. The number of variants included
in a PRS may range from a few to several million. The genetic variants chosen for
inclusion in a PRS, and the importance or weight given to each variant, are typically
derived from large-scale genetic association studies (i.e. GWAS) with the disease
or trait of interest.
Since genotypes vary at each genomic position across individuals, PRS follow a distribution
in the population (Figure 2B). Typically, individuals in the lower tails of a polygenic
risk score have a lower risk of developing the disease or trait of interest, whereas
those in the upper tails have a higher risk. Polygenic risk scores have been calculated
for many conditions including cardiovascular diseases.
62
Both the number of conditions for which they have been calculated and the mathematical
methods for selecting and weighing variants are rapidly evolving. Polygenic risk scores
have been largely utilized for research purposes to date, but scores are increasingly
being applied to clinical trial settings
63–65
indicating the potential clinical utility of using these risk markers in the management
and prevention of common diseases. The potential utility of PRS in less common conditions
such as inherited arrhythmias and cardiomyopathies is also being explored.
28–30,
66–68
In the coming years, we anticipate that PRS are likely to enter the clinical practice
landscape and become more widely utilized. At present, it seems too early, however.
Eventually, PRS may hopefully be able to provide information not only on disease risk
but also disease mechanism and therapeutic efficacy.
Recommendation
Consensus statement instruction
Ref.
Genetic testing in patients with a potential cardiogenetic condition is performed
only with appropriate genetic counselling.
Expert opinion
In patients with a clear specific phenotype, it is appropriate to perform genetic
testing analysing genes with definite or strong evidence supporting disease causation.
10,
17,
20,
21,
69
In patients with a clear specific phenotype, it may be appropriate to analyse genes
with moderate evidence supporting disease causation.
10,
17,
20,
21,
69
In selected cases with a definite phenotype and no genetic diagnosis after testing
of the genes with definite or strong evidence supporting disease causation, broader
genetic testing may be considered. Such selected cases may include familial cases,
those with atypical features, such as extracardiac manifestations and those with unusual
early disease onset.
17
Variant interpretation in the clinical setting is greatly enhanced by the use of disease-specific,
multi-disciplinary teams that could include clinical disease experts, clinical geneticists,
or genetic counsellors and molecular geneticists.
10,
70–75
Variant interpretation is best performed using standard guidelines for interpretation
and can be enhanced by gene-specific rule specifications tailored for the gene and
disease under consideration.
17,
76,
77
Reported Variants of Uncertain Clinical Significance (VUS) may be reclassified, i.e.
‘upgraded’ [Likely Pathogenic/Pathogenic (LP/P)] or ‘downgraded’ (Likely Benign/Benign),
in multi-disciplinary clinics with access to molecular genetics laboratories, according
to robustness of clinical phenotype and/or familial segregation evidence.
10,
70–75,
78
Genetic testing for genes with (i) limited, (ii) disputed, or (iii) refuted evidence
should not be performed in patients with a weak (non-definite) phenotype in the clinical
setting.
10,
17,
20,
21,
69
In families where a LP/P variant has been identified, detailed genetic counselling
and guidance regarding inheritance patterns, variant penetrance, and risk should be
offered, and cascade testing facilitated.
Expert opinion
In patients with a high probability of a specific inherited cardiac disease and a
molecular screening performed in a pre-NGS era or with an incomplete NGS panel, repetition
of the testing should be considered.
Expert opinion
Choice of genetic tests and interpretation of variants
Background
A basic tenet of clinical genetic testing is that the genes evaluated should have
strong scientific evidence supporting their disease association.
69
Given the challenge of variant interpretation,
79
there is risk of inaccurate information being provided to patients and families when
genes with limited evidence for disease causality are tested. In the context of life-changing
diagnoses which may provoke significant anxiety or aggressive treatment interventions,
optimizing methods for best practice of genetic variant interpretation is essential.
Recent collaborative projects involving clinical disease experts, genetic counsellors,
and clinical/molecular geneticists have provided detailed evidence-based gene classifications
for Mendelian arrhythmia and cardiomyopathy disorders, highlighting genes with moderate,
strong or definitive evidence for disease causation, and others with limited or disputed
evidence
12–15,
17,
22
(for definitions of these classifications see page 7 in: https://clinicalgenome.org/site/assets/files/5391/gene_curation_sop_pdf-1.pdf).
In 2015, the ACMG provided a standard, criteria-based approach for the interpretation
of genetic variants in clinical testing.
69
Criteria include the frequency of the allele in people with and without disease, the
degree of familial segregation with other affected family members, topological location
within relevant functional domains of the protein, and functional analysis of the
variant. Importantly, no single criterion alone, including abnormal functional assay,
is sufficient to conclude the pathogenicity of a genetic variant. A summation of the
evidence leads to a provisional classification of the variant along a probabilistic
range of categories: Pathogenic (P), Likely Pathogenic (LP), Variant of Uncertain
Clinical Significance (VUS), Likely Benign (LB), Benign (B). Although challenging
to quantify, according to ACMG guidelines the terms LP and LB suggest a >90% certainty
of a variant being disease-causing or benign, highlighting the significant range of
probability for variants classified as VUS.
The VUS classification represents the ‘Achilles Heel’ of genetic variant interpretation
in the clinical arena. At times, high-volume, multi-disciplinary clinics may have
sufficient clinical expertise or evidence that may allow for an upgrading or downgrading
of the variant to pathogenic or benign, respectively.
74,
77,
78
In contrast, the absence of segregation of a VUS interpreted variant with a robust
familial phenotype may lead to re-classifying to likely benign. These examples highlight
that most laboratory-based variant interpretation is done in the absence of detailed
clinical phenotyping knowledge available in a multidisciplinary clinic. To minimize
the burden of VUS classifications, collaborative expert teams have proposed ACMG-modified,
gene-specific rules which take in to account the specific knowledge accumulated for
certain genes in specific conditions.
76,
80
Where possible, this approach may enhance variant interpretation classification.
77
Genes that do not have sufficient evidence to date as single-gene causes for disease
should not receive variant interpretations. Clinical testing laboratories that continue
to offer these genes on their panels should clearly label their limited evidence,
but may consider providing unclassified, identified variants to clinics in support
of ongoing research on candidate genes.
Use of the obtained genetic knowledge
After genetic testing, a clinically actionable result (LP/P) can provide diagnostic
clarification in the proband (Table 5
). It also provides information relevant to prognosis and relevant to therapeutic
choices in many but not all disease entities (Table 5
). In addition, it offers the potential for cascade (predictive) testing of at-risk
family members.
81–85
Cascade testing involves targeted testing of first-degree relatives for the LP/P variant
found in the proband (‘appropriate relatives’). When cascade testing is performed
in an at-risk relative, those who are found not to carry the disease-causing gene
variant can be released from further clinical surveillance in the vast majority of
conditions. Some exceptions exist and are discussed at the individual disease level.
In general, cascade screening is recommended when results will affect clinical management.
When the results are ‘only’ useful for family planning, cascade screening may be considered.
Recommendations for cascade screening and the age at which this should be performed
are disease- and sometimes gene-specific. Those who are found to carry the disease-causing
gene variant should undergo clinical screening at regular intervals. Family members
of a patient where genetic testing is not done or is negative (no likely-pathogenic
or pathogenic variant is identified) also require clinical screening at regular intervals
because there is considerable phenotypic heterogeneity in age of onset and disease
progression within members of the same family. That being said, in some diseases,
there is emerging evidence that a negative genetic test in the proband or the affected
individual may indicate lower probability of monogenic disease.
Table 5
Impact of genetic testing for the proband
Disease
Diagnostic
Prognostic
Therapeutic
Arrhythmia syndromes
Long QT syndrome
+++
+++
+++
CPVT
+++
+
+
Brugada syndrome
+
+
+
Progressive cardiac conduction disease
+
+
+
Short QT syndrome
+
+
+
Sinus node disease
–
+
–
Atrial fibrillation
–
+
–
Early repolarization syndrome
–
–
–
Cardiomyopathies
Hypertrophic cardiomyopathy
+++
++
++
Dilated cardiomyopathy
++
+++
++
Arrhythmogenic cardiomyopathy
+++
++
++
Left ventricular non-compaction
+
+
–
Restrictive cardiomyopathy
+
+
+
Congenital heart disease
Syndromic CHD
+++
+
–
Non-syndromic CHD
+
–
–
Familial CHD
++
–
–
+++
: is recommended/is indicated or useful.
++
: can be recommended/can be useful.
+
: may be considered/may be useful.
–
: is not recommended/is not indicated nor useful.
In the event that a VUS is reported, a disease-specific multidisciplinary team can
help to further classify the variant as LP or LB, based on the criteria outlined in
detail above. A VUS that has not been upgraded to LP should not be used to facilitate
cascade screening; rather, clinical screening is required. When multiple family members
exhibit a characteristic phenotype, robust co-segregation of the variant with the
affected family members can contribute to classification of the variant as LP or even
P.
A pathogenic variant can also be identified at postmortem testing (i.e. after the
usually SCD of a family member) using blood or tissue collected at autopsy. Postmortem
testing is especially useful in instances where the family variant is unknown and
no other affected family members are still living.
86–88
Access to a molecular autopsy as well as considerations related to costs and insurance
coverage for this testing can vary between countries and jurisdictions. Nevertheless,
identification of a LP/P variant may confirm or establish a familial diagnosis and
allow cascade genetic testing of other at-risk relatives as outlined previously.
In addition, detailed genetic counselling and guidance is recommended and should start
before a genetic test is performed. Families should be informed of the mode of inheritance
of disease, most commonly AD inheritance whereby there is a 50% chance the variant
will be passed on to offspring, regardless of sex. Families should be informed that
carrying the LP/P variant does not necessarily mean development of clinical disease,
reflecting variable penetrance, e.g. some gene variant carriers may never develop
clinical disease (genotype positive, phenotype negative) or may only develop very
mild disease and therefore be at low risk of disease complications. In all families
and couples (with most conditions) where pregnancy is being planned, the above factors
need to be discussed, as well as reproduction options such as prenatal genetic testing
and preimplantation genetic diagnosis.
State of genetic testing for inherited arrhythmia syndromes
Long QT syndrome
Impact of genetic testing for the index case
Disease
Diagnostic
Prognostic
Therapeutic
LQTS
+++
+++
+++
Recommendations
Consensus statement instruction
Ref.
Molecular genetic testing for definitive disease associated genes (currently KCNQ1,
KCNH2, SCN5A, CALM1, CALM2, and CALM3) should be offered to all index patients with
a high probability diagnosis of LQTS, based on examination of the patient’s clinical
history, family history, and ECG characteristics obtained at baseline, during ECG
Holter recording and exercise stress test (Schwartz Score ≥ 3.5, Supplementary
Table S2
).
a
20
Analysis of specific genes should be offered to patients with a specific diagnosis
as follows: KCNQ1 and KCNE1 in patients with Jervell and Lange-Nielsen syndrome, CACNA1C
in Timothy syndrome, KCNJ2 in Andersen–Tawil syndrome, and TRDN in patients suspected
to have triadin knockout syndrome.
20,
89–93
An analysis of CACNA1C and KCNE1 may be performed in all index patients in whom a
cardiologist has established a diagnosis of LQTS with a high probability, based on
examination of the patient’s clinical history, family history, and ECG characteristics
obtained at baseline, during ECG Holter recording and exercise stress test (Schwartz
Score ≥ 3.5).
a
20
Variant-specific genetic testing is recommended for family members and appropriate
relatives following the identification of the disease-causing variant.
Expert opinion
Predictive genetic testing in related children is recommended from birth onward (any
age).
Expert opinion
a
The Schwartz score can be found in Supplementary material online,
Table S2
.
Background
The congenital LQTS is a genetically transmitted channelopathy, characterized by prolongation
of the QT interval on the baseline ECG, usually associated with T-wave abnormalities
(i.e. notched T waves, biphasic T waves).
15
To make a diagnosis of congenital LQTS it is essential to exclude secondary causes,
i.e. QT-prolonging drugs or electrolyte imbalances.
94
Prolongation of action potential duration favours early afterdepolarizations and torsades
de pointes (TdP) is the typical arrhythmia in this disease.
95–98
Torsades de pointes, frequently triggered by pauses and/or adrenergic stimulation,
98
can cause self-terminating dizziness or syncopal events or can degenerate into ventricular
fibrillation (VF) and SCD. Electrocardiogram characteristics associated with high
risk of life-threatening arrhythmias, include T wave alternans and functional 2:1
atrioventricular block, which are frequently present in patients who present perinatally.
To make a diagnosis of LQTS, it may be important to evaluate not only basal ECG but
also the behaviour of QTc during exercise stress test and 24-h, preferably 12-lead,
Holter recording.
99,
100
Diagnostic criteria have been developed to support the diagnosis of the disease, i.e.
the ‘Schwartz score’.
101
Long QT syndrome has a prevalence of at least 1:2500 people
102
and clinical manifestations tend to occur during childhood or teenage years. Among
symptomatic index cases, the untreated 10-year mortality is ∼50%.
103,
104
Summary of the major long QT syndrome genes
Table 6
(and Supplementary material online,
Table S3
) summarize all genes associated with LQTS and their ClinGen classification.
20
Long QT syndrome genes can be divided in three main groups: those genes in which pathogenic
variants reduce potassium outward currents, those in which pathogenic variants increase
sodium inward current, and those in which pathogenic variants increase calcium inward
current.
Table 6
Genes implicated in long QT syndrome (LQTS)
Gene
Locus
Phenotype—syndrome
Protein (functional effect)
Frequency
ClinGen classification
KCNQ1
11p15.5
LQTS, JLNS
Loss-of-I
Ks channel function
40–55%
Definitive
KCNH2
7q35-36
LQTS
Loss-of-I
Kr channel function
30–45%
Definitive
SCN5A
3p21-p24
LQTS
Increase in I
Na1.5 channel function
5–10%
Definitive
CALM1
14q32.11
LQTS
L-type calcium channel (↑)
<1%
Definitive
CALM2
2p21
LQTS
L-type calcium channel (↑)
<1%
Definitive
CALM3
19q13.32
LQTS
L-type calcium channel (↑)
<1%
Definitive
TRDN
6q22.31
Recessive LQTS
L-type calcium channel (↑)
<1%
Strong
KCNE1
21q22.1
LQTS, JLNS, a-LQTS
Loss-of-I
K channel function
<1%
Strong in aLQTS, definitive in JLNS
KCNE2
21q22.1
a-LQTS
Loss-of-I
K channel function
<1%
Strong in aLQTS
KCNJ2
17q23
ATS
Loss-of-I
K1 channel function
<1%
Definitive in ATS
CACNA1C
12p13.3
TS, LQTS
L-type calcium channel (↑)
<1%
Definitive in TS, moderate in LQTS
Functional effect: (↓) loss-of-function or (↑) gain-of-function at the cellular in
vitro level.
a-LQTS, acquired-long QT syndrome; ATS, Andersen–Tawil syndrome; JLNS, Jervell and
Lange-Nielsen syndrome; RWS, Romano–Ward syndrome; TS, Timothy syndrome.
Potassium channel-related LQTS:
95,
96
pathogenic variants in potassium channels genes are responsible for the vast majority
of LQTS cases and KCNQ1 and KCNH2, encoding for the alpha subunit of potassium channels
conducting the I
Ks and I
Kr currents, respectively, account for 80% of all genetically explained LQTS cases.
95,
96
Homozygous or compound heterozygous pathogenic variants in KCNQ1 and KCNE1 cause the
recessive Jervell and Lange-Nielsen syndrome (JLNS), in which the cardiac phenotype
is combined with congenital deafness.
105
KCNE1 is strongly associated with acquired-LQTS (aLQTS),
94
as is KCNE2, and it also causes an uncommon subtype usually associated with low penetrance
and with a mild phenotype.
106
Finally, in this subgroup, the Andersen–Tawil syndrome (ATS), caused by pathogenic
variants in the KCNJ2 gene, is generally included,
95,
96,
107
although it should be questioned whether ATS is actually a subform of LQTS.
74,
107
Patients with ATS frequently also present with extra cardiac features, including skeletal
myopathy (periodic muscular weakness) and several skeletal and facial dysmorphic features.
95,
96
Sodium channel-related LQTS: pathogenic variants in SCN5A, causing an increase of
sodium inward current, are the third most frequent cause of LQTS and have a predominant
role in forms with malignant perinatal presentation.
108,
109
Overlapping phenotypes (LQTS, BrS, and cardiac conduction defects) are described.
110
Other components of the Na channel complex have been proposed as candidate genes for
LQTS, but there is insufficient evidence to confirm an association.
20
Calcium channel-related LQTS: pathogenic variants causing an increase of calcium inward
current are associated with rare but malignant forms of LQTS, some with associated
syndromic features. Specifically, Timothy syndrome, caused by the pathogenic G406R
variant in CACNA1C
89
is characterized by a perinatal presentation of life-threatening arrhythmias frequently
associated with syndactyly, CHDs, cognitive abnormalities, and autism. Long QT syndrome
caused by any of the three CALM genes
90,
111
represents another malignant form of the disease and data from the International Calmodulinopathy
Registry show life-threatening arrhythmias in 78% of the cases, mean QTc of almost
600 ms and a perinatal presentation in 58%.
91
Some of these cases show neurological features unrelated to cardiac arrest, and cardiac
structural abnormalities.
91
The triadin knockout syndrome (TKOS)
92,
93
is a recessive syndrome caused by pathogenic variants in TRDN; data from the International
Registry show that cardiac arrest is the first clinical manifestation in 71% of patients,
and transient QT prolongation, sometimes with T-wave inversion in V1–V3/V5 is frequently
observed.
93
Patients in this category also frequent present with neuromuscular involvement. All
these forms, which cause QT prolongation secondary to abnormal calcium handling, have
in common an early malignant presentation and a poor response to conventional medical
therapies.
Index cases (proband)
In LQTS patients with a high probability of LQTS, based on examination of the patient’s
clinical history, family history, and ECG characteristics obtained both in baseline,
during ECG, Holter recording and exercise stress test (Schwartz Score ≥ 3.5), molecular
testing is recommended with a different level of strength depending of the type of
gene. In genes with definitive evidence, currently KCNQ1, KCNH2, SCN5A, CALM1, CALM2,
and CALM3, the testing is strongly recommended in all probands
20
(Figure 3
), including an analysis of CNV, and a disease-causing variant is identified in around
70–85% of cases.
95,
112
A possible exception is an active athlete with a prolonged QTc. Indeed, not rarely
athletes develop significant QT prolongation which is fully reversible on detraining.
113
In such cases the diagnosis of LQTS should not be made.
113
Another strong recommendation is provided in the context of specific syndromes for
causative genes, i.e. KCNE1 in patients with JLNS,
105
CACNA1C in patients with Timothy syndrome,
89
KCNJ2 in patients with ATS,
95
and TRDN in patients with Triadin Knock-out syndrome
92,
93
(Figure 3
). CACNA1C and KCNE1 that have a moderate evidence in the context of LQTS, the testing
may be considered in patients with a high probability of diagnosis. Only in this subgroup
of patients with high probability of LQTS may a broader genetic testing be considered
if no disease-causing variant is identified in established genes, and only in experienced
centres and with a careful interpretation of the variant identified. However, in these
cases a negative genetic test does not exclude the disease, already established clinically.
In patients with an intermediate probability of LQTS (e.g. prolonged QTc with a Schwartz
score 1.5–3.0), testing of genes with limited, disputed and refuted evidence should
not be performed, while testing of the established genes may be considered, mostly
to help rule out the diagnosis after extensive phenotypic investigation.
Figure 3
Clinical algorithm for genetic testing and family screening in long-QT syndrome.
Family screening
Cascade screening in family members is indicated whenever a disease-causing variant
is identified in the index case. Indeed, low penetrance and variable expressivity,
do not allow one to exclude the diagnosis only on the basis of a normal baseline ECG.
114,
115
Early identification of affected family members is important to establish preventive
measures, as the risk of life-threatening arrhythmias is not negligible even among
those with a normal baseline QTc.
116
Prognostic and therapeutic implications of long QT syndrome genetic testing
In LQTS, the identification of a disease-causing variant contributes to risk stratification.
Indeed, the identification of a pathogenic variant in KCNQ1, KCNH2, or SCN5A has a
role together with the length of the QTc in identifying the risk of life-threatening
arrhythmias in asymptomatic subjects.
117
Also, the location of the variant across the protein is important. In fact, location
in the pore region of KCNH2,
118
the transmembrane location,
118
the S6 segment specifically,
119
and dominant-negative effect for KCNQ1, are independent risk factors for cardiac events.
120
Furthermore, some specific pathogenic variants are associated with unusually high
clinical severity (high penetrance, long QTc, high incidence of SCD), such as the
KCNQ1-A341V
121
or the SCN5A-G1631D.
108
Others, such as SCN5A-D1790G and the E1784K, that not only causes LQTS, but it is
also associated with BrS and sinus node dysfunction (SND)
110
are relatively benign.
122
Thus, when managing families with the latter pathogenic variant, the possibility of
an overlap syndrome should be considered. In the recessive JLNS, it matters whether
there are two pathogenic variants in KCNE1 or in KCNQ1, with the former presenting
with a more benign disease course in terms of risk of life-threatening arrhythmias.
105
Finally, there are some specific genetic subtypes that are at particular high risk
of SCD in paediatric age, as patients carrying a pathogenic variant in one of the
CALM genes
90,
91
and despite no systematic studies, the available data suggest that whenever the variants
affect the calcium current, the phenotype tends to be more complex and severe.
89–93,
111
The role of SNVs as genetic modifier has also been documented, but its evaluation
has not yet entered clinical practice in a standardized manner.
2,
123
The amazing progress in understanding the genotype-phenotype correlation has allowed
LQTS to become the first disease for which initial steps for gene-specific management
have become possible and are already usefully implemented. Patients with a pathogenic
variant in KCNQ1 are at higher risk during sympathetic activation (e.g. during exercise,
swimming and emotional stress), and antiadrenergic intervention such as beta-blockers
124,
125
and left cardiac sympathetic denervation (LCSD)
126,
127
are particularly effective. An implantable cardioverter-defibrillator (ICD) is rarely
needed and certainly not for primary prevention, in contrast to the other subtypes
where the predicted risk in patients with very long QTc may lead to an earlier primary
ICD implantation.
116
In KCNH2-LQTS patients, it is essential to preserve adequate potassium levels, and
oral potassium may help.
128
Also, these patients are at higher risk when aroused from sleep or rest by a sudden
noise
129,
130
and in the post-partum phase.
131
Removal of telephones and alarm clocks from their bedrooms is recommended. The realization
that SCN5A variants producing LQTS have a ‘gain-of-function’ support the use of late
sodium current blockers, in particular mexiletine, in those patients with a QTc >500 ms,
if their QTc shortens by more than 40 ms after oral loading test.
132–134
Recently, mexiletine was shown to shorten QTc also in a significant percentage of
KCNH2 patients
135
opening the possibility of its clinical use also in this genetic subgroup. Finally,
very preliminary data, showed that a drug combining lumacaftor and ivacaftor, already
in clinical use for cystic fibrosis, could have a role in patients carrying KCNH2
variants causing a trafficking defect, but data on more patients are still needed.
136,
137
All LQTS patients should avoid QT-prolonging drugs (see www.crediblemeds.org).
Acquired long QT syndrome
Recommendations
Consensus statement instruction
Ref.
Molecular genetic testing for definitive disease associated genes (currently KCNQ1,
KCNH2, SCN5A, KCNE1, and KCNE2) should be offered to all patients with acquired LQTS
who experienced drug-induced TdP, are aged below 40 years and have a QTc >440 ms (males)
and >450 ms (females) in the absence of culprit drug
20,
94
Cascade family screening for the presence of pertinent variants should be considered
when QT prolonging drugs are or could be prescribed
Expert opinion
The acquired LQTS, is a clinical condition characterized by QT prolongation (usually
defined as >500 ms or >60–70 ms drug-induced change from baseline) sometimes associated
with TdP, which is induced by QT-prolonging drugs and more rarely hypokalaemia or
bradycardia.
94
The probability of developing an acquired LQTS depends on two major factors: (i) the
intrinsic risk conferred by a given drug, which is provided by CredibleMeds website
(https://crediblemeds.org); (ii) the repolarization reserve of a subject in which
genetic factors play a role.
2
The genetic predisposition to acquired LQTS includes both ultra-rare,
138
rare,
139
and common genetic variants.
140
The role of molecular testing in the isolated setting of drug-induced LQTS requires
individualized consideration. In the study by Itoh et al.,
94
the probability of identifying a LP/P variant in patients with acquired LQTS was mainly
dependent on three variables, i.e. age below 40 years, QTc (at baseline) >440 ms and
presence of TdP/symptom. When all three variables were present, a LP/P variant was
identified in more than 60% of the patients.
94
Molecular genetic screening in older individuals has a much lower yield and can therefore
not be recommended on a standard basis.
94
Variants which are unequivocally associated with drug-induced LQTS (e.g. D85N in KCNE1)
should be reported as a relevant result.
73
Active family screening for the presence of these variants should be considered when
QT prolonging drugs are or could be prescribed (expert opinion).
Catecholaminergic polymorphic ventricular tachycardia
Impact of genetic testing for the index case
Disease
Diagnostic
Prognostic
Therapeutic
CPVT
+++
+
+
Recommendation
Consensus statement instruction
Ref.
In any patient satisfying the diagnostic criteria for CPVT (such as Class 1 clinical
diagnosis
a
or CPVT diagnostic score >3.5
b
), molecular genetic testing is recommended for the currently established definite/strong
evidence CPVT-susceptibility genes: RYR2, CASQ2, CALM1-3, TRDN, and TECRL.
91,
141–145
In phenotype-positive CPVT patients (definition: see rec. 1) who are negative for
those established CPVT-susceptibility genes, genetic testing may be considered for
CPVT phenocopies resulting from pathogenic variants in the KCNJ2, SCN5A, and PKP2
genes.
17,
146–148
In patients with a modest phenotype for CPVT (i.e. CPVT diagnostic score ≥ 2 but <
3.5
b
), genetic testing may be considered for the established definite/strong evidence
CPVT-susceptibility genes: RYR2, CASQ2, CALM1-3, TRDN, and TECRL.
17,
91,
141–145
Variant-specific genetic testing is recommended for family members and appropriate
relatives following the identification of the disease-causative variant.
149,
150
Predictive genetic testing in related children at risk of inheriting a P/LP variant
is recommended from birth onward (any age).
Expert opinion
a
Adapted from HRS/EHRA/APHRS Expert consensus recommendations on diagnosis of CPVT.
15
b
Adapted from Giudicessi et al.,
151
see Supplementary material online,
Table S4
.
Background
Catecholaminergic polymorphic ventricular tachycardia (VT) is an uncommon inherited
arrhythmia syndrome with an unknown prevalence [estimated to be in the 1:20 000 range
(personal guess, AW)]. It is characterized by polymorphic (rarely documented but typically
bidirectional) ventricular arrhythmias in young individuals with structurally normal
hearts. Catecholaminergic polymorphic ventricular tachycardia-associated arrhythmias
are mediated adrenergically (i.e. occur during exercise or emotional stress), are
often asymptomatic but may also cause syncope, syncope followed by generalized seizures,
sudden cardiac arrest, and SCD.
17,
152,
153
Importantly, the occurrence of exercise-induced arrhythmias may be variable, so with
a strong clinical suspicion more than one exercise test is warranted. CPVT is less
common than other conditions causing SCD, yet disproportionately accounts for a high
percentage (10–15%) of SCD cases in the young,
154–156
in ±6% of those labelled as idiopathic ventricular fibrillation (IVF)
157
and in ±1% of sudden infant death syndrome,
158
although the latter association is hard to confirm.
Diagnostic implications of catecholaminergic polymorphic ventricular tachycardia genetic
testing
Catecholaminergic polymorphic ventricular tachycardia usually segregates as an AD
trait but AR segregation is also possible (Table 7
). Compared to LQTS, there is also a higher frequency of sporadic de novo variants,
particularly with the most common CPVT-causative gene, RYR2.
159,
160
This gene encodes the cardiac ryanodine receptor (RyR2), also called the calcium release
channel and is responsible for release of calcium from the sarcoplasmic reticulum
into the cytosol. Catecholaminergic polymorphic ventricular tachycardia 1-associated
gain-of-function pathogenic variants in RYR2 lead to a leaky RyR2 protein by various
mechanisms. This in turn leads to increased diastolic cytosolic calcium levels with
arrhythmic consequences, in particular under adrenergic circumstances. RyR2 variants
associated with a loss-of-function cellular phenotype are associated with the calcium
release deficiency syndrome (CRDS), a newly described disease entity with specific
electrophysiological characteristics distinguishable from CPVT.
161,
162
Table 7
Genes implicated in catecholamine polymorphic ventricular tachycardia (CPVT)
Gene
Locus
Phenotype—syndrome
Protein (functional effect)
Frequency
ClinGen classification
RyR2
1q43
CPVT/AD
RyR2 (↑); inappropriate Ca2+ release from the SR
60–70%
Definite
CASQ2
1p13.1
CPVT/AR
Inappropriate Ca2+ release from the SR
±5%
Definite
CASQ2
1p13.1
CPVT/AD
Inappropriate Ca2+ release from the SR
±5%
Moderate
CALM 1–3
14q32.112p2119q13.32
CPVT/AD
↑ RyR2 binding affinity resulting in inappropriate Ca2+ release from the SR
<1%
Strong
TECRL
a
4q13.1
CPVT/AR
Altered Ca2+ homeostasis, possibly linked to fatty acid/lipid metabolism
<1%
Definite
TRDN
a
6q22.31
CPVT/AR
↓ expression leading to remodelling of the cardiac dyad/calcium release unit
<1%
Definite
KCNJ2
17q24.3
ATS/AD
Loss-of-I
K1 channel function
<1%
Definite
AD, autosomal dominant; AR, autosomal recessive.
a
TECRL and TRDN may result in a CPVT-LQTS overlap phenotype consisting of modest QTc-prolongation
and adrenergically triggered ventricular arrhythmia.
Other genes with an AD inheritance pattern are the 3 CALM genes, which also associate
with other phenotypes, e.g. LQTS and IVF.
91
Those with a CPVT phenotype present at early age.
91
Genes with a predominant AR trait are CASQ2, TRDN, and TECRL.
93,
141–144
As expected, recessive CPVT is more severe than dominant CPVT.
A phenotype closely resembling CPVT is ATS, caused by functional loss-of-function
variants in the gene KCNJ2 encoding for the Kir2.1 inwardly rectifying potassium channel
(I
K1).
163
Also the SCN5A associated phenotype Multifocal Purkinje-related Premature Contractions
(MEPPC) can mimic CPVT although usually the ectopy burden is, as in ATS, also high
in the resting state.
146,
147
Finally, the PKP2 gene, may in an earlier stage manifest as a disease without structural
alterations but with adrenergically-mediated arrhythmias.
148
These genes might be tested in those patients with a CPVT-like phenotype, who are
genotype negative for the strong CPVT genes (Supplementary material online,
Table S5
).
Index cases
The yield of genetic testing in CPVT is highest (60%) in patients with a strong phenotype,
i.e. a typical exercise test (occasionally including bi-directional VT).
145,
151,
164
In patients with a less typical clinical presentation [adrenergically induced syncope,
IVF or isolated extrasystoles during the exercise test) the yield is much lower (15–20%)].
145,
164
This is not trivial because the ‘background noise’ in the RYR2 gene, i.e. the presence
of benign variants, is a little over 3%. This raises the likelihood of a false-positive
result in patients with a non-typical phenotype to 1 in 6 (compared to 1:20 in cases
with a strong phenotype).
164
The latter findings have actually been used to propose a phenotype enhanced variant
readjudication approach.
151
This approach significantly reduced the number of VUS by either promoting or demoting
specific variants.
151
Specifically, akin to the ‘Schwartz score’ for LQTS, Wilde and Ackerman introduced
the analogous CPVT diagnostic score to improve the clinical veracity of the diagnosis
of CPVT.
151
In patients with a CPVT diagnostic score of > 3.5 (without the genetic test result),
the likelihood of CPVT1 (i.e. RYR2-mediated CPVT) is at least 60%. Furthermore, given
that genetic test companies currently designate almost every novel missense variant
in RYR2 as a VUS because of the in silico challenges of assessing the pathogenicity
of variants in the 4967 amino acid-containing protein, incorporation of this clinical
score can assist physicians with decoding the genetic test result more accurately.
For example, in a patient with a robust clinical score for CPVT but a VUS test result
in RYR2, the genetic test ordering physician (the phenotyper) can upgrade that test
with result to at least a ‘likely pathogenic variant’ designation with 95% confidence.
151
Family screening
An active family screening approach is important in all CPVT families. Family-specific,
cascade genetic testing for the identified CPVT-causative, pathogenic variant should
be pursued regardless of symptom status and stress test expressivity. Even asymptomatic,
normal stress test individuals who are genotype positive (i.e. genotype positive/phenotype
negative) may require active therapy.
149,
150
For many cases of CPVT2 stemming from homozygous variants in CASQ2, consanguinity
is present. An alternative explanation is compound heterozygosity which is often the
case for TRDN-mediated CPVT. The latter is part of the phenotypic spectrum of TKOS.
93
Heterozygous carriers of the relevant variants in TRDN and TECRL normally have no
phenotype and do not need active treatment. This may not be true for family members
heterozygous for a variant in CASQ2-encoded calsequestrin, which seems to suggest
AD segregation.
165
In a more recent study, one-third of the heterozygous patients fulfil the diagnostic
criteria for CPVT and some of them even presented with a cardiac arrest or exercise-related
syncope.
166
These data were not considered sufficient to upscale the monoallelic gene status beyond
the moderate level.
17
Yet, exercise-test-guided treatment is probably warranted in these patients.
Prognostic and therapeutic implications of catecholaminergic polymorphic ventricular
tachycardia genetic testing
While there is strong and obvious impact diagnostically with respect to CPVT genetic
testing, the prognostic impact is less and the therapeutic impact is negligible currently.
Prognostically, there are data to suggest that specific locations within the RyR2
(i.e. the C-terminal channel forming domain) may confer increased susceptibility to
CPVT-triggered arrhythmias.
167
More importantly, patients with CALM-mediated CPVT are at increased risk,
91
and AR disease presents more often at earlier age and with more malignant arrhythmias.
Therapeutically, in all CPVT genotypes, ß-adrenoceptor blockade (preferably with the
non-selective beta blockers nadolol or propranolol) is the cornerstone of therapy,
with upscaling therapy dependent on the (persistent) presence of symptoms and/or of
ventricular arrhythmias during an exercise test, available in the form of combination
drug therapy with the addition of Flecainide,
168
and LCSD.
169
Implantable cardioverter-defibrillator therapy should whenever possible be avoided
in CPVT patients.
170
Patients satisfying a clinical diagnosis of CPVT but who are negative for both the
established CPVT-causative genes and the genes underlying the CPVT phenocopies (i.e.
genotype negative/phenotype positive) should also be treated similarly.
149,
167
Brugada syndrome
Impact of genetic testing for the index case
Disease
Diagnostic
Prognostic
Therapeutic
Brugada syndrome
+
+
+
Recommendation
Consensus statement instruction
Ref.
Genetic testing with sequencing of SCN5A is recommended for an index case diagnosed
with BrS with a type I ECG in standard or high precordial leads occurring either (i)
spontaneously, or (ii) induced by sodium-channel blockade in presence of supporting
clinical features or family history.
21,
171
Rare variants in genes with a disputed or refuted gene-disease clinical validity should
not be reported routinely
a
for BrS genetic testing in a diagnostic setting.
21
Targeted sequencing of variant(s) of unknown significance in SCN5A with a population
allele frequency <1 × 10−5 identified in an index case can be considered concurrently
with phenotyping for family members, following genetic counselling, to assess variant
pathogenicity through co-segregation analysis.
172
Variant-specific genetic testing is recommended for family members and appropriate
relatives following the identification of the disease-causative variant.
Expert opinion
Predictive genetic testing (of pathogenic SCN5A variants) in related children is recommended
from birth onward (any age).
Expert opinion
a
Unless in a research setting.
Background
Brugada syndrome is an inherited arrhythmogenic disorder characterized by ST-segment
elevation in the right precordial leads and malignant ventricular arrhythmias, sometimes
associated with conduction disease and atrial arrhythmias. The prevalence of BrS is
estimated to be 1 in 2000 worldwide, with higher prevalence in Asia.
173
Symptomatic patients are typically males presenting in their fourth decade of life.
174,
175
Brugada syndrome may be involved in ∼18–28% of unexplained sudden deaths/arrests.
176,
177
According to the 2013 HRS/EHRA/APHRS expert consensus statement,
15
BrS is diagnosed in patients with ST-segment elevation with type I morphology ≥2 mm
in ≥1 lead among the right precordial leads V1, V2 positioned in the 4th intercostal
space (standard ECG) or the 2nd and 3rd intercostal spaces (high parasternal leads),
178
observed either spontaneously or after provocative drug testing with a class I antiarrhythmic
drug. In light of data highlighting the limited specificity of provocative testing,
179
the Shanghai scoring system was proposed whereby the diagnosis of definite BrS in
presence of type I ECG that is only manifested with provocative testing also requires
supporting clinical features (Supplementary material online,
Table S6
).
180
Brugada syndrome phenocopies such as myocardial ischaemia, electrolyte disturbances
and drug intoxications should be excluded before a diagnosis of BrS can be made.
181
Drug-induced and fever-induced Brugada ECG pattern is not considered a BrS phenocopy
and in both conditions genetic testing with sequencing of SCN5A may be considered.
Risk stratification in BrS relies primarily on symptoms and the ECG. Patients with
suspected arrhythmic syncope with a spontaneous type I ECG are at high risk of malignant
arrhythmic events (∼2.3%/year
182
) and should consider ICD implantation.
15
Asymptomatic patients with drug-induced type I ECG are at low risk (≤0.4%/year
183
) and should be managed conservatively. All BrS patients should be counselled to (i)
avoid drugs that impair cardiac sodium channels (brugadadrugs.org
184
), (ii) avoid alcohol intoxication, (iii) immediately treat fever with antipyretic
drugs, and (iv) seek urgent medical attention following a syncope. The role of invasive
electrophysiological testing for risk stratification remains controversial.
Diagnostic implications of Brugada syndrome genetic testing
Disease-causing rare genetic variants in SCN5A that result in loss of function of
the cardiac sodium channel are identified in ∼20% of cases (Table 8
). In families with pathogenic SCN5A variants, penetrance is incomplete and non-carriers
of the SCN5A variant may show a positive provocative drug challenge,
185
in line with the complex heritability of BrS. Case–control GWAS in BrS identified
several genetic loci harbouring common variants associated with the disease.
60
Polygenic scores derived from GWAS (PRSBrS) could underlie variable disease expressivity
in carriers of SCN5A pathogenic variants.
67
Brugada syndrome in the absence of rare SCN5A variants is largely polygenic. PRSBrS
are strongly associated with response to provocative drug testing.
66
For instance, a PRSBrS comprised of three common variants (rs11708996, rs10428132,
and rs9388451) below the 10th percentile provides a sensitivity of 99% and a negative
predictive value of 93% for drug-induced type I ECG, based on a population of 1368
patients that underwent ajmaline testing for suspected BrS.
66
Assessment of PRSBrS that include more genetic variation associated with BrS is ongoing.
Table 8
Gene implicated in Brugada syndrome
Gene
Locus
Phenotype—syndrome
Protein (functional effect)
Frequency
ClinGen classification
SCN5A
3p22.2
BrS/AD
Loss of I
Na1.5 channel function
15–30%
Definite
Other genes have been implicated in BrS (Supplementary material online,
Table S7
). However, the gene-disease validity of most of those genes (other than SCN5A) has
been disputed following rigorous assessment of available data using the ClinGen framework.
21
Although a disputed ClinGen status does not challenge a role of the gene product in
BrS pathophysiology, it strongly argues against reporting those genes in the diagnostic
setting. An algorithm for genetic testing of index cases with BrS and family members
is shown in Figure 4
.
Figure 4
Clinical algorithm for genetic testing and family screening in Brugada syndrome.
Index cases
The presence of a LP/P SCN5A variant confirms the diagnosis of BrS in probands with
a type I ECG, but the absence of such variant does not exclude the diagnosis. In drug-induced
type I BrS pattern in the absence of supporting clinical context and family history,
it can be considered to perform SCN5A testing for the purpose of risk prediction,
management and family screening. Interestingly, according to the Shanghai score, adding
an SCN5A P/LP variant to a patient with ‘isolated’ drug-induced type 1 would increase
his score from 2.0 to 2.5 which remains insufficient for ‘probable/definite BrS’.
169
Family screening
Genetic testing should be offered to family members regardless of age
186
when a LP/P SCN5A variant is identified in a relative with BrS. Carriers of such variants
should be instructed to take the same precautions as those with BrS (see above). Asymptomatic
relatives who do not carry the SCN5A variant and have a completely normal resting
ECG (also in the higher placed leads) can be discharged. Although phenotype positive-genotype
negative family members have been described in genotype positive families,
173
standard provocative testing in these individuals is not supported by current data.
Screening of relatives of SCN5A negative BrS probands should be done clinically using
an ECG (also with high parasternal leads). Provocative testing can be considered based
on patient’s symptoms, resting ECG and personal preference, for the sake of prevention
(treatment of fever, avoidance of drugs (brugadadrugs.org), and avoidance of alcohol
intoxication). It should be noted and discussed with the patient prior to provocative
testing that a positive provocative test in the absence of symptoms and SCN5A (P/LP)
variant is diagnostic for BrS but is associated with a very low arrhythmic event rate,
and should therefore be managed conservatively. In a large study from a single centre
66
which included relatives of SCN5A negative BrS probands, PRSBrS was significantly
associated with drug-induced BrS, highlighting its potential in clinical practice.
Yet, further studies in other cohorts are needed before widespread use of polygenic
scores in BrS.
Of note, several pathogenic SCN5A variants are associated with a phenotype with both
right precordial ST-segment elevation as well as QTc prolongation.
187
Clearly, in the family screening process the QTc should also carefully be evaluated
and affected individuals should also avoid drugs from the www.crediblemeds.org list.
Prognostic and therapeutic implications of Brugada syndrome genetic testing
Brugada syndrome patients with pathogenic SCN5A variants exhibit more conduction abnormalities,
188,
189
and have worse arrhythmic outcomes.
171,
189,
190
The presence of SCN5A pathogenic variants does not, by itself, justify prophylactic
ICD implantation, but should trigger an aggressive management in presence of clinical
risk markers such as (arrhythmic) syncope. Because of the risk of conduction disturbance,
the presence and type of SCN5A pathogenic variants should also be considered when
selecting an implantable device, in addition to the baseline ECG and arrhythmia documentation.
(Progressive) cardiac conduction disease
Impact of genetic testing for the index case
Disease
Diagnostic
Prognostic
Therapeutic
Cardiac conduction disease
+
+
+
Recommendation
Consensus statement instruction
Ref.
Targeted genetic testing is recommended as part of the diagnostic evaluation for index
patients with isolated cardiac conduction disease (CCD/PCCD) or with concomitant structural
heart disease or extracardiac disease, when there is early age of diagnosis or a suspicion
of laminopathy, especially when there is documentation of a positive family history
of CCD/PCCD.
Expert opinion
Targeted genetic testing may be considered as part of the diagnostic evaluation for
index patients with isolated cardiac conduction disease (CCD/PCCD) or with concomitant
structural heart disease or extracardiac disease, especially in the setting of a positive
family history.
Expert opinion
Variant-specific genetic testing is recommended for family members and appropriate
relatives following the identification of the disease-causative variant.
Expert opinion
Predictive genetic testing in related children may be considered from birth onward
(any age) in specific settings.
Expert opinion
Background
Cardiac conduction disease (CCD) is a heterogeneous and often age-dependent, progressive
cardiac conduction disease (PCCD) disorder characterized by a disturbed electrical
impulse propagation in the atrioventricular (AV) node and His-Purkinje system. On
the surface ECG, prolonged P-wave duration, AV block, and different degrees of bundle
branch block (manifested as QRS fragmentation or QRS widening with normal or abnormal
axis deviation) are typical features. Syncope or even cardiac arrest can occur from
severe sinus node disease (manifested with sinus bradycardia or significant sinus
pauses) of from complete AV block.
191,
192
Fibrotic degeneration, ischaemia, infiltrative processes, valve calcifications, tumours,
or thyroid dysfunction may lead to acquired dysfunction and CCD. However, in idiopathic
or familial forms heritable factors significantly contribute to CCD/PCCD (Lenègre’s
disease). Isolated forms (‘primary electrical heart diseases’) can be distinguished
from CCD/PCCD in the setting of cardiomyopathies (typically DCM) or of syndromic disorders,
e.g. with CHD or neurological phenotypes (Table 9
). Clinical disease expression may vary between pathogenic variant carriers within
the family, but also between different families and often has an age-dependent course.
Table 9
Genes implicated in CCD/PCCD
Gene
Locus
Phenotype—syndrome
Protein (functional effect)
Frequency
ClinGen classification
Genes for isolated SND
SCN5A
3p22.2
BrS1, SND, ASS, (LQT3)
194–196,
203,
204
Cardiac Na channel α subunit (Nav1.5)
Loss-of-function, I
Na ↓
>10%
NA/major gene; definite for LQTS, BrS1
TRPM4
19q13.33
205,
206
Transient receptor potential melastatin 4 channel
Gain-of-function
1–10%
NA/major gene
Genes for syndromal disorders with CCD/PCCD
LMNA
1q22
DCM (CMD1A), AFib, SND (Emery-Dreifuss muscular dystrophy 2/3, congenital muscular
dystrophy, limb-girdle myopathy, familial lipodystrophy type 2, Hutchinson-Gilford
progeria, and various other disorders)
197,
199,
200
Lamin A/C
>10%
NA/major gene; definite for DCM
DES
2q35
DCM (CMD1I), ACM, Myofibrillar myopathy (MFM1)
Desmin
()
NA/rare gene;
Definite for DCM, moderate for ACM
DMD
Xp21.2-p21.1
DCM (CMD3B), muscular dystrophy (Becker or Duchenne type)
207
Dystrophin
()
NA/rare gene
DMPK
19q13.32
DCM, myotonic dystrophy (DM1)
208
Myotonic dystrophy protein kinase
()
NA/rare gene
EMD
Xq28
DCM, LVNC, SND, Emery-Dreifuss muscular dystrophy (EMD)
209,
210
Emerin
()
NA/rare gene
LAMP2
Xq24
HCM, DCM, LVNCDanon disease (glycogen storage disease), skeletal muscle involvement,
mental retardation
211
Lysosomal-associated membrane protein 2
()
NA/rare gene;
Definite for HCM
ZNF9
3q21.3
DCM, myotonic dystrophy (DM2)
212
Zink finger protein 9 (CZNP)
()
NA/rare gene
GLA
Xq22.1
Fabry disease (HCM, RCM, acral paresthaesia, PNP, kidney insufficiency, angio-keratoma,
anhydrosis, cornea verticillata, etc.)
Galactosidase α
()
NA/rare gene; definite for HCM
PRKAG2
7q36.1
Cardiac preexcitation (WPW), LVH/HCM,
213
AMP-activated protein kinase γ2-subunit
()
NA/rare gene; definite for HCM
TNNI3K
1p31.1
DCM, AFIB
214
Troponin I-interacting MAP kinase
()
NA/rare gene
NKX2-5
5q35.1
ASD7, (VSD7, TOF)
Transcription factor Nkx2.5
()
NA/rare gene
GJC1
17q21.31
Bone malformations (brachyfacial pattern, finger deformity, and dental dysplasia)
215
Connexin 45
()
NA/rare gene
TBX5
12q24.21
Holt-Oram syndrome (HOS) (hand-heart syndrome): ASD, hand and limb malformation (e.g.,
triphalangeal thumb), other CHD
Transcription factor TBX5
()
NA/rare gene
MYL4
17q21.32
AFib/conduction disease
atrial-specific myosin light chain
()
NA, rare gene
mtDNA
Mitochondrial DNA
Kearns-Sayre syndrome (KSS): Ptosis, progressive external ophthalmoplegia, ataxia,
retinitis pigmentosa; Chronic progressive external ophthalmoplegia (CPEO), ptosis
216
(37 mitochondrial genes)
()
NA/rare gene
Frequency: refers to mutation detection rate;
25
core genes: major (>10%) or minor (1–10%); rare gene (<1%); (): mutation rate unknown
and/or single reports.
Other phenotypes: […], phenotype associated with gene, but unlinked with CCD/PCCD.
ClinGen: Clinical Genome Resource of NCBI; https://clinicalgenome.org, NA: not available
= not yet curated.
ACM, arrhythmogenic cardiomyopathy; AFib, atrial fibrillation; ASD, atrial septal
defect; ASS, atrial stand still; BrS, Brugada syndrome, CHD, congenital heart disease,
DCM, dilated cardiomyopathy; HCM, hypertrophic cardiomyopathy; LQT, long-QT syndrome
subtype; LVH, left ventricular hypertrophy; LVNC, left ventricular non-compaction
cardiomyopathy; PNP, polyneuropathy; WPW, Wolff–Parkinson–White syndrome; RCM, restrictive
cardiomyopathy; SND, sinus node dysfunction; TOF, Tetralogy of Fallot; VSD, ventricular
septal defect; X-chr., X-chromosomal.
Diagnostic implications of genetic testing in cardiac conduction disease/progressive
cardiac conduction disease
Cardiac conduction disease/PCCD is genetically heterogeneous;
193
in the majority of CCD families an AD mode of inheritance is pertinent, whereas CCD/PCCD
in the setting of some neuromuscular disorders is X-chromosomal linked and severely
affects male patients. A de novo or recessive occurrence is rare.
194,
195
Most pathogenic variants are non-synonymous or truncating pathogenic variants; so
far, the frequency of small indels and CNV has not been addressed systematically.
Susceptible genes for each CCD subgroup are listed below (Table 9
, Supplementary material online,
Table S8
). The overall and gene-specific mutation yield (sensitivity) is unknown and also
for each gene; however, recent studies using targeted or WES suggested a pathogenic
variant detection rate of >50% in index cases, with SCN5A and LMNA as core genes,
196,
197
accounting for ∼20% each (TRPM4: 5–10%). This also implies that in a measurable fraction
of cases, including family clusterings of diseases, investigations of associated known
heart disease genes are still insufficient to reveal the underlying substrate, suggesting
that new causal genes have yet to be discovered.
Index case
Upon the ECG diagnosis of CCD/PCCD and without evidence for acquired causes, an inherited
form appears likely. However, cardiac sarcoidosis is a relatively common diagnosis
in isolated AV block and should be systematically excluded before a genetic diagnosis
is considered in sporadic isolated AV block. Screening for cardiac sarcoidosis (using
CMR or positron emission tomography–fluorodeoxyglucose) in patients younger than 60 years
with unexplained second-degree (Mobitz II) or third-degree AV block can be useful.
198
Further routine work-up includes exercise ECG, Holter ECG and echocardiography to
address presence of a cardiomyopathy or CHD. Cardiac magnetic resonance imaging (MRI)
(with gadolinium enhancement) may be considered, in particular for LMNA pathogenic
variant carriers.
193,
199,
200
Early-onset or idiopathic forms of CCD/PCCD should prompt consideration of genetic
testing, especially if the family history is indicative (CCD/PCCD, pacemaker implants,
cardiomyopathy, etc.).
For the major genes associated with CCD, specialized cardiogenetic services have established
targeted gene panels for CCD/PCCD testing. Four genes (SCN5A, LMNA, GLA, and PRKAG2;
Table 9
) are therefore recommended to be investigated.
50
The identification of a pathogenic variant in a disease-validated gene confirms not
only the suspected diagnosis of CCD/PCCD, but also allows its classification as a
genetic (and potentially heritable) disorder with or without additional clinical features.
Family investigation
A careful clinical and, if suitable [i.e. with knowledge of the pathogenic (ACMG class
4/5 i.e. LP/P) variant in a validated CCD/PCCD gene], genetic investigation is recommended
and therefore indicated in family members as a part of a directed ‘family cascade
screening’. This includes a comprehensive assessment of the family pedigree. In relatives
testing negative for this pathogenic variant, monitoring for CCD/PCCD or its development
and downstream investigations in the family branch are not further needed. In contrast,
pathogenic variant-positive family members should be evaluated carefully for the presence
of isolated or syndromic forms of CCD/PCCD with regard to typical phenotypic features
of the underlying gene (Table 9
). In addition, genotype-dependant recommendations will be similar to those for the
index case. Asymptomatic children in the first decade of life do not strictly needed
to be investigated for their genetic status, although in specific settings an earlier
evaluation may be pertinent.
Prognostic and therapeutic implications of genetic testing
Genotype may not clearly stratify risk of CCD progression, but different underlying
inherited aetiologies for CCD do give prognostic information, e.g. LMNA for SCD risk.
In addition, pathogenic variants in distinct genes (e.g. LMNA, TNNI3K) may be associated
with development of heart failure, whereas other genes may exhibit extracardiac features,
such as myopathy, which require additional, specialized treatment. Patients with LMNA
pathogenic variants may develop atrial and ventricular arrhythmias as well as progressive
(end-stage) heart failure and the potential need for ICD or cardiac resynchronization
therapy defibrillator therapy (upon the development of phenotypic expression) or heart
transplantation.
200–202
A risk stratification scheme has recently been proposed.
200
Patients with SCN5A pathogenic variants may also develop BrS, so avoidance of particular
drugs and fever is recommended to reduce ventricular arrhythmias.
Short QT syndrome
Impact of genetic testing for the index case
Disease
Diagnostic
Prognostic
Therapeutic
SQTS
+
+
+
Recommendation
Consensus statement instruction
Ref.
In any patient satisfying the diagnostic criteria for SQTS (such as Class 1 clinical
diagnosis
a
or SQTS diagnostic score >4
b
), molecular genetic testing is recommended for the definitive disease associated
genes (currently KCNH2, KCNQ1).
17
Testing of KCNJ2 and SLC4A3 may be performed in all index patients in whom a cardiologist
has established with a high probability a diagnosis of SQTS, based on examination
of the patient’s clinical history, family history, and ECG characteristics obtained
at baseline or during ECG Holter recording and exercise stress test (SQTS diagnostic
score ≥4).
17,
217,
218
Variant-specific genetic testing is recommended for family members and appropriate
relatives following the identification of the disease-causative variant.
Expert opinion
Predictive genetic testing in related children may be considered in specific settings.
Expert opinion
a
Adapted from HRS/EHRA/APHRS Expert consensus recommendations on diagnosis of SQTS.
15
b
Adapted from Gollob et al.,
219
see Supplementary material online,
Table S9
.
Background
Short QT syndrome is a very rare channelopathy, characterized by a short QT interval
on the basal ECG and by an increased risk of both atrial and ventricular arrhythmias.
15,
96
The QT evaluation should be performed not only in basal condition but also during
ECG Holter recording and exercise stress test, as typical of this disease is the reduced
rate-adaptation of QT during exercise
220
and the evidence of a short QTc at different heart rates and not only during bradycardia.
96
The cut-off value of ‘short’ QT interval for defining SQTS remains a matter of debate
as there is an overlap between healthy subjects and patients with SQTS. Short QT syndrome
is usually diagnosed in the presence of a QTc consistently below 330–340 ms; while
between 340 and 360 ms additional criteria are needed and specifically, the presence
of a pathogenic variant, family history of SQTS, family history of SCD below age 40
or survival after an episode of VT/VF in the absence of heart disease.
15,
96
No specific triggers for life-threatening arrhythmias have been recognized and age
at presentation is quite variable.
Diagnostic implications of short QT syndrome genetic testing
Short QT syndrome is a genetically heterogeneous AD disease. Four SQTS-susceptibility
potassium channel genes, KCNH2,
221
KCNQ1,
222
KCNJ2,
217
and SLC4A3
223
have been identified (Table 10
). Only the first two genes have a definite or strong disease association.
17
Pathogenic variants in the first three genes yield a gain-of-function to their encoded
potassium channel. A missense mutation in SLC4A3
223
encoding the anion exchange protein 3 (AE3) has been identified in two large families
with SQTS by WES. Although the functional change of the mutation supports a contribution
to the accelerated repolarization, further study will be necessary. Loss of function
type mutations in L-type calcium channel related genes, CACNA1C, CACNA2b,
224
and CACNA2D1
218
have been linked to SQTS
17
(Supplementary material online,
Table S10
), frequently showing overlapping BrS features.
224
However, the evidence of these genes is limited at most.
Table 10
Genes implicated in short QT syndrome (SQTS)
Gene
Locus
Phenotype—syndrome
Protein (functional effect)
Frequency
ClinGen classification
KCNH2
7q35-36
SQTS/AD
Increase in I
Kr channel function
<10%
Definite
KCNQ1
11p15.5
SQTS/AD
Increase in I
Ks channel function
5%
Strong
KCNJ2
17q23
SQTS/AD
Increase in I
K1 channel function
±1%
Moderate
SLC4A3
2q35
SQTS/AD
pH (↑) and Cl− (↓)
<1%
a
Strong–moderate
b
Functional effect: (↓) loss-of-function or (↑) gain-of-function at the cellular in
vitro level.
a
Might be significantly higher (personal communication AAMW and MG).
b
Classification discussed between members of the Clin Gen curation panel. Maybe become
strong based on new data (personal communication AAMW and MG).
BrS, Brugada syndrome; SQTS, short QT syndrome.
Index cases
Short QT syndrome is diagnosed clinically in index patients
13,
15,
219
and the presence of a disease-causing variant is a key finding to support the diagnosis
above all in cases in which the QTc is short, but not below 330–340 ms.
13,
15,
219
Genetic screening for two potassium channel genes (KCNQ1 and KCNH2) is recommended
and for two other genes (KCNJ2 and SLC4A3) may be considered for index cases
17
(Figure 5
). Compared to loss-of function mutations identified in LQTS, the reported number
of mutations in SQTS is very small.
225
All other genes should be screened in patients with a high probability of the disease
and only in experienced centres as variant interpretation may be critical. If a SQTS
patient shows an overlapping phenotype with BrS, mutations in L-type calcium channel
related genes may be involved.
Figure 5
Clinical algorithm for genetic testing and family screening in short-QT syndrome.
aAdapted from HRS/EHRA/APHRS Expert consensus recommendations on diagnosis of SQTS.
15
bAdapted from Gollob et al.,
219
see Supplementary material online,
Table S9
.
A short QTc is also found in patients with the AR primary systemic carnitine deficiency
syndrome, which is characterized by hypoketotic hypoglycaemia, hyperammonaemia, liver
dysfunction, hypotonia, and cardiomyopathy and caused by variants in SLC22A5.
226
Indeed, homozygote or compound heterozygote variants have been identified in unexplained
SCD or resuscitated cardiac arrest cases without overt extra-cardiac manifestations.
227,
228
The QT interval in these patients is responsive to carnitine supplementation treatment.
227,
228
Family screening
Cascade screening in family members is indicated whenever a definite disease-causing
variant is identified in the index case. However, results should be managed carefully.
Prognostic and therapeutic implications of short QT syndrome genetic testing
Implantation of an ICD with/without hydroquinidine is recommended for high-risk patients
independent of genetic status. In the long-term follow-up of SQTS patients, hydroquinidine
prevented events, and the QT prolongation effect was more relevant in KCNH2-based
patients.
229
In asymptomatic patients and family members with pathogenic variants, hydroquinidine
prolonged QT intervals, though its efficacy for preventing life-threatening arrhythmias
still needs to be proved.
230,
231
There are some phenotypic differences among different genotypes. The onset of arrhythmias
in KCNH2-based patients seems to occur later in life than in other subtypes,
232
while the occurrence of AFib is more frequent in this subtype.
233
However, life-threatening arrhythmias are equally frequent among different genotypes.
232
Atrial fibrillation
Impact of genetic testing for the index case
Disease
Diagnostic
Prognostic
Therapeutic
Atrial fibrillation
–
+
–
Recommendation
Consensus statement instruction
Ref.
An analysis of SCN5A, KCNQ1, MYL4 and truncating TTN variants may be performed in
all index patients in whom the diagnosis of familial (young = age < 60) AF, is established,
based on examination of the patient’s clinical history, family history, and ECG characteristics.
234–243
Expert opinion
Variant-specific genetic testing may be recommended for family members and appropriate
relatives following the identification of the disease-causative variant.
Expert opinion
Predictive genetic testing in related children may be considered in specific settings.
Expert opinion
Background
Atrial fibrillation is the most common cardiac arrhythmia worldwide, and it may be
associated with an unfavourable prognosis, depending on the clinical profile and access
to treatment. Atrial fibrillation is characterized by uncoordinated electrical activity
in the atria. This causes a rapid and irregular heartbeat and increases the risk of
stroke and sudden death. Its prevalence is around 0.4% in the general population and
increases to approximately 6% in those over 65 years of age. The incidence of the
familial form of AFib is unknown. The incidence of AFib increases together with the
numbers of affected individuals with early onset AFib in the family.
244
Today, familial AFib is more commonly diagnosed. In a cohort study of 914 patients
with AF, 36% had lone AFib. A positive family history for AFib was present in 15%
of those lone AFib patients (5% of all AFib patients).
245
Atrial fibrillation is also commonly related to dilated or hypertrophic cardiomyopathies,
246
LQTS,
247
or SQTS,
230,
248
BrS,
234
CPVT,
249,
250
familial amyloidosis,
251
congenital cardiac abnormalities,
252
and pre-excitation syndromes.
213,
253
The prognosis for AFib patients is determined by assessing associated cardiovascular
disease and identifying patients with genetic predisposition to AFib may have important
clinical implications. Furthermore, testing to identify genes that play a role in
the initiation of AFib may provide new understanding and new therapeutic options.
Also, early recognition of AFib patients at risk may reduce morbidity and mortality.
254
Genetic forms of atrial fibrillation
There has not yet been a consensus curation for isolated familial AFib (despite the
fact that AFib is a well-established feature of many inherited cardiac syndromes,
and the existence of some monogenic forms of isolated AFib). Table 11
summarizes the existing evidence for genes implicated in AF. Evidence supporting AFib
as a single-gene disease has emerged over the last decade. Genetic forms of AFib may
be observed in association with other phenotypes (Brugada, conduction disease, cardiomyopathy),
or may be isolated, probably particularly in young individuals.
242,
243
Genes involved include those encoding both ion channels and sarcomere-related proteins.
Table 11
Genes implicated in atrial fibrillation
Gene
Locus
Phenotype—syndrome
Protein (functional effect)
Frequency
ClinGen classification
SCN5A
3p22.2
AFib/conduct.
Decrease in I
Na1.5 channel function
()
NA, major gene
KCNQ1
11p15.5
AFib/SQTS
Increase in I
Ks channel function
()
NA, rare gene
KCNH2
7q35-36
AFib/SQTS
Increase in I
Kr channel function
()
NA, rare gene
TBX5
12q24.21
AFib/Holt Oram syndr.
T-Box transcription factor 5
()
NA, rare gene
GJA5
1q21.1
AFib/atrial standstill
Decrease in Connexin 40 function
()
NA, rare gene
MYL4
17q21.32
AFib/conduction disease
atrial-specific myosin light chain
()
NA, rare gene
TTN
2q31.2
AFib/DCM
Titin
()
NA, rare gene
KCN5A
12p13.32
AFib
Decrease in Ultrarapid component of the atrial-specific delayed rectifier potassium
current (I
kur)
()
NA, rare gene
GJC1
17q21.31
AFib
decrease in Connexin 45 function
()
NA, rare gene
NPPA
1p36.22
AFib
Atrial naturetic protein (ANP), loss of interaction with the ANP receptor
()
NA, rare gene
LMNA
1q22
AFib/conduction disease DCM (CMD1A), (Emery-Dreifuss muscular dystrophy 2/3, congenital
muscular dystrophy, limb-girdle myopathy, familial lipodystrophy type 2, Hutchinson-Gilford
progeria, and various other disorders)
197,
199,
200
Lamin A/C
()
NA/rare gene ‘Definitive’ for DCM
(): mutation rate unknown and/or single reports.
From a purely electrical or ion channel perspective, loss-of-function genetic variants
in the SCN5A gene may provoke an AFib phenotype, commonly in patients who also manifest
BrS and/or conduction system disease.
234–236
Additionally, gain-of-function mutations in SCN5A may cause AFib in isolation.
237
In a large Chinese family with AFib segregating as an AD trait, a gain-of-function
variant in KCNQ1 (S140G) was identified.
238
Similarly, a loss-of-function variant in the KCN5A gene encoding the ultrarapid component
of the atrial-specific delayed rectifier potassium current (Ikur) has been described
in a large pedigree with familial AFib.
255
Two additional potassium channels, KCNJ2 and KCNH2, have been reported to cause AFib
in patients with associated SQTS.
256,
257
Lastly, genetic defects effecting gap junction function (GJA5, GJC1) may also provoke
AFib.
258
The association of AFib with variants in other genes like KCNE2, RYR2, and SCN1B are
not yet strong enough to warrant routine genetic screening outside a research setting.
Genes encoding sarcomeric proteins may also provoke AFib in the absence of ventricular
involvement. The MYL4 gene, encoding the atrial-specific myosin light chain, has been
described as a cause of early-onset AFib and conduction system disease.
239
Similarly, mutations in LMNA and TTN (in particular A-band localizing variants) commonly
provoke atrial arrhythmias.
240,
241,
243
Finally, a more rare and unique form of familial AFib has been reported secondary
to a genetic defect in the NPPA gene, which encodes the atrial naturetic peptide,
implicating neurohormonal dysregulation in provoking AFib.
259
Sinus node disease
Impact of genetic testing for the index case
Disease
Diagnostic
Prognostic
Therapeutic
Sinus node disease
–
+
–
Recommendations
Consensus statement instruction
Ref.
(Targeted) Genetic testing may be considered as part of the diagnostic evaluation
for index patients with familial or isolated, but otherwise unexplained sinus node
dysfunction (SND) or with SND and concomitant atrial fibrillation, cardiac conduction
disease (CCD), structural heart disease or with SND and extracardiac disease (syndromal
forms), especially in the setting of a positive family history.
Expert opinion
Interrogation for a putative family history and family cascade screening including
clinical screening and variant-specific genetic testing, are recommended for appropriate
relatives.
Expert opinion
Background
Sinus node dysfunction (for diagnostic criteria, see ref.
260
) is an aetiologically and thereby clinically heterogeneous, often age-dependent disorder.
Sinus node dysfunction is commonly acquired; inherited (‘idiopathic’ or familial)
forms are less common, in particular in elder patients where ischaemia or age-related
degeneration of the sinoatrial (SA) node occur. Infiltrative disorders (e.g. sarcoidosis,
amyloidosis, hemochromatosis, collagen vascular disease or metastatic cancer), cardiac
procedures, infections (e.g. bacterial endocarditis and Chagas disease), and obstructive
sleep apnoea commonly result in SND. External causes are abnormally increased vagal
tone, autonomic dysfunction, hypothyroidism, hyperkalaemia, hypokalaemia, hypocalcaemia,
hypoxia and hypothermia, cardiac surgery, as well as increased intracranial pressure
or medications.
Isolated (i.e. otherwise unexplained) or familial forms (‘primary electrical heart
diseases’) can be distinguished from syndromal forms (heritability of SND and heart
rate is meanwhile noted from several large studies).
261–264
In the surface ECG, sinus bradycardia (<50 b.p.m.) is a typical feature; significant
bradycardia or pauses may result in dizziness, syncope or rarely cardiac arrest.
192,
265
Other ECG signs are chronotropic incompetence, sinus pause (>3 s) or sinus arrest,
various degrees of SA exit block, atrial fibrillation, and AV node blockade.
Diagnostic implications of genetic testing in sinus node dysfunction
Sinus node dysfunction is genetically heterogeneous. There has not yet been a consensus
curation for sinus node disease. The overall variant detection rate (sensitivity)
for ‘idiopathic’ or familial forms is unknown, but currently estimated <25%. The majority
of SND patients have an AD mode of inheritance; de novo occurrence and other modes
(X-chromosomal, recessive occurrence, digenic traits, or CNVs) are rare. Susceptible
genes for each SND subgroup are listed below (Table 12
and Supplementary material online,
Table S11
). Core genes for SND include SCN5A, HCN4, and LMNA.
Table 12
Genes implicated in sinus node disease (SND)
Gene
Locus
Phenotype/syndrome
Protein (functional effect)
Frequency
ClinGen classification
Genes for isolated SND
SCN5A
3p22.2
BrS1, SND, ASS, LQT3
195,
266,
267
Cardiac Na+ channel α subunit (Nav1.5) (loss-of-function, I
Na↓)
1–10%
NA/major gene ‘Definitive’ for LQTS, BrS
HCN4
15q24.1
Familial SND, ST, left ventricular non-compaction.
268,
269
Hyperpolarization-activated cyclic nucleotide-gated K+ channel 4 (loss-of-function,
I
f ↓)
1–10%
NA/major gene
GNB2
7q22.1
Familial SND
270
G-protein β subunit 2 (gain-of-function, I
K, ACh↑)
<1%
NA/rare gene
KCNQ1
11p15.4
SQTS, [LQT1], AFib, SND
271,
272
K+ voltage-gated channel (subfamily Q, 1) (Kv7.1) (Gain-of-function, IKs↑)
<1%
NA/rare gene. ‘Definitive’ for LQTS
KCNJ5
11q24.3
Familial SND
273,
274
G-protein gated inwardly rectifying K+ (GIRK) channel 5 (Kv3.4) (Gain-of-function,
I
K, ACh↑)
<1%
NA/rare gene
RYR2
1q43
CPVT, SND
249,
275
Ryanodine receptor 2 (gain-of-function)
<1%
NA/rare gene ‘Definitive’ for CPVT
Genes for syndromal disorders with SND
LMNA
1q22
DCM (CMD1A), Afib (Emery-Dreifuss muscular dystrophy 2/3, congenital muscular dystrophy,
limb-girdle myopathy, familial lipodystrophy type 2, Hutchinson-Gilford progeria,
and various other disorders)
197,
199,
200
Lamin A/C
1–10%
NA/rare gene ‘Definitive’ for DCM
CACNA1D
3p21.1
+ Inner ear deafness
276,
277
(neurodevelopmental disorders, autisms spectrum disorder with epilepsy; primary aldosteronism)
L-type calcium voltage-gated channel subunit alpha 1-D (Cav1.3)
()
NA/rare gene
GNB5
15q21.2
+ Developmental delay, speech defects, severe hypotonia, pathological gastro-oesophageal
reflux, retinal disease
278
G-protein β subunit 5, (inhibitory G-protein signaling)
()
NA/rare gene
SGOL1
3p24.3
CAID syndrome; cohesinopathy with chronic atrial and intestinal dysrhythmia
279
Nuclear protein for chromosome segregation
()
NA/rare gene
EMD
Xq28
DCM, LVNC, AFib, Emery-Dreifuss muscular dystrophy (EMD)
209,
280
Emerin
()
NA/rare gene
Frequency: refers to mutation detection rate
29
; core genes: major (>10%) or minor (1–10%); rare gene (<1%); (): mutation rate unknown
and/or single reports.
Other Phenotypes: […], phenotype associated with gene, but unlinked with SND.
ClinGen: Clinical Genome Resource of NCBI; https://clinicalgenome.org.
ASS, atrial stand still; AFib, atrial fibrillation; ASD, atrial septal defect; BrS,
Brugada syndrome, CPVT, catecholaminergic polymorphic ventricular tachycardia; DCM,
dilated cardiomyopathy; LQT, long-QT syndrome type; LVNC, left ventricular non-compaction
cardiomyopathy; SND, sinus node dysfunction; ST, sinus tachycardia; X-chr., X-chromosomal.
Index case with sinus node dysfunction
Upon the ECG diagnosis of SND and without evidence for acquired causes, an inherited
form appears likely, particularly when it is found in younger individuals (<age 60).
Routine work-up includes exercise ECG, Holter ECG, and echocardiography to address
presence of a cardiomyopathy or CHD. Cardiac MRI (with gadolinium application) may
be considered, in particular for LMNA pathogenic variant carriers.
193,
199,
200
For the major genes associated with SND (Table 12
), specialized cardiogenetic services have established targeted gene panels for SND
and/or CCD/PCCD testing. Two genes (SCN5A and LMNA) are part of the medically actionable
gene list (currently 73 genes) of the ACMG and are therefore recommended to be investigated.
49
The identification of a pathogenic variant in a disease-validated gene confirms not
only the (suspected) diagnosis of SND, but also allows its classification as a genetic
(and potentially heritable) disorder with or without additional clinical features.
Family investigation
A careful clinical and, if suitable [i.e. with knowledge of the pathogenic (ACMG class
4/5) variant in a validated SND], genetic investigation (testing for the relevant
variant) is recommended and therefore indicated in family members as a part of a directed
‘family cascade screening’. This includes a comprehensive assessment of the family
pedigree.
In relatives without this pathogenic variant, monitoring for SND or its development
and downstream investigations in the family branch are not further needed. In contrast,
pathogenic variant-positive family members shall be carefully evaluated for presence
of isolated or syndromal forms of SND with regard to typical phenotypic features of
the underlying gene (Table 12
). In addition, genotype-depending recommendations will be similar as for the index
case. Asymptomatic children in the first decade of life are not strictly needed to
be investigated for their genetic status (in the presence of normal findings during
routine cardiological investigation).
Prognostic and therapeutic implications of genetic testing
There is no genotype-based risk stratification for patients with SND. However, mutations
in distinct genes (e.g. LMNA, SCN5A, KCNQ1) may be associated with other overlapping
phenotypes (e.g. BrS, SQTS) or with the development of heart failure and arrhythmias
(i.e. LMNA), whereas other genes may exhibit particular extracardiac features. This
has impact for the mode of monitoring during follow-up (which should include regular
imaging studies in families with f.e. LMNA and SCN5A variants).
Patients with LMNA variants may develop atrial and ventricular arrhythmias as well
as progressive (end-stage) heart failure and the potential need for ICD therapy or
heart transplantation. A risk stratification scheme has recently been proposed.
200
Patients with SCN5A pathogenic variants may also develop BrS; avoidance of particular
drugs and fever are recommended to reduce ventricular arrhythmias.
Early repolarization syndrome
Impact of genetic testing for the index case
Disease
Diagnostic
Prognostic
Therapeutic
Early repolarization syndrome
–
–
–
Recommendation
Consensus statement instruction
Ref.
In unexplained cardiac arrest survivors diagnosed clinically with ERS, molecular genetic
testing may be appropriate.
Expert opinion
In asymptomatic individuals with only an ECG-based early repolarization pattern, genetic
testing should not be performed.
Expert opinion
Background
The presence of a J wave, a positive deflection immediately following the QRS complex,
in f.e. the inferolateral ECG leads is known as early repolarization pattern (ERP).
Early repolarization pattern is a common ECG finding (estimated incidence 1–13%),
usually considered innocent amongst healthy asymptomatic young individuals and athletes.
281
Case–control and epidemiological studies have, however, described an association between
J waves and unexplained cardiac arrest (UCA).
282–284
Haïssaguerre et al. found that ERP was present in 31% of 206 case subjects with IVF
cases and 5% of 412 matched subjects without heart disease.
284
The link between ERP and malignant arrhythmias is also supported by the accentuation
of the J wave before the onset of VF, an association with VF storms and the observation
of triggering PVCs coincident with the J wave.
284–286
The term early repolarization syndrome (ERS) has since been used to identify UCA survivors
with an ECG with a suggestive/suspicious ERP.
15
According to animal models and an early ECG imaging study, an imbalance in myocyte
currents in favour of enhanced outward currents (I
to and I
KATP) during phase 2 of the action potential causes premature myocardial repolarization
and variable loss of the action potential dome, which is most marked in the epicardial
myocardium. In turn, epicardial heterogeneity in repolarization duration and transmural
heterogeneity is most marked in the inferior LV wall resulting in localized steep
gradients of repolarization and inferior J point elevation.
287,
288
Increasing evidence supports an alternative hypothesis, according to which the J point
elevation typical of ERP could be an expression of delayed depolarization.
289–291
Early repolarization pattern shows at least moderate heritability in nuclear families
292
and across general population studies.
293
It is over-represented in families of UCA survivors
294
and autopsy negative SCD families.
295,
296
There has not yet been a consensus curation for ERS. SCN5A variants with loss-of-function
(determined by patch clamping expression studies) have been identified in 2–10% of
patients with ERS, the patients showed signs of conduction slowing, supporting a depolarization
phenotype.
297–299
Two paediatric ERS cases have been identified with a duplication and a de novo missense
variant in KCND3 responsible for I
TO.
300,
301
Furthermore, a recent general population GWAS has associated ERP with a genome-wide
significant SNP tagging the KCND3 locus (encoding the I
To current alpha subunit), suggesting the possibility of polygenic heritability.
302
There is, however, absence of other highly penetrant, reproducible and truly rare
single gene causes of ERS. For example, the p.S422L variant in KCNJ8 responsible for
I
KATP, has been implicated frequently in ERS but has too high a population frequency
to cause a rare monogenic disorder.
303,
304
Supplementary material online,
Table S12
summarizes all genes which have been associated with ERS.
Wolff–Parkinson–White syndrome
Background
WPW is a condition where an extraconnection in the heart, called an accessory pathway
(AP), is present, resulting in a pattern of pre-excitation during sinus rhythm. The
most common arrhythmia associated with WPW is a paroxysmal supraventricular tachycardia,
where the impulse uses the AP either from atrium to ventricle (antidromic circus movement
tachycardia) or, more common, vice versa (orthodromic circus movement tachycardia).
Resulting symptoms include dizziness, a sensation of fluttering or pounding in the
chest (palpitations), shortness of breath, pre-syncope and syncope. In rare cases,
arrhythmias associated with WPW can lead to cardiac arrest and sudden death.
Wolff–Parkinson–White affects 1 to 3 in 1000 people worldwide and is the second most
common cause of paroxysmal supraventricular tachycardia in most parts of the world.
Complications of WPW can occur at any age, although many individuals born with an
AP in the heart never experience any health problems associated with the condition.
Genetics of Wolff–Parkinson–White
Non-syndromic cases
Most cases of WPW occur in people with no apparent family history of the condition.
These cases are described as sporadic and are usually not inherited. Familial WPW
accounts for only a small percentage of all cases of this condition.
305
The familial form of the disorder typically has an AD pattern of inheritance. No specific
genes have been identified for non-syndromic pre-excitation to date.
Syndromic cases
Wolff–Parkinson–White often occurs with other structural abnormalities of the heart
or underlying heart disease. The most common heart defect associated with the condition
is Ebstein’s anomaly, which affects the tricuspid valve and right ventricle. In at
least 10% of patients with Ebstein’s anomaly, one or more APs are present.
306
Other genetic syndromes associated with APs include hypokalaemic periodic paralysis
(a condition that causes episodes of extreme muscle weakness), Pompe disease (a disorder
characterized by the storage of excess glycogen), Danon disease (a condition that
weakens the heart and skeletal muscles and causes intellectual disability), and tuberous
sclerosis complex (a condition that results in the growth of non-cancerous tumours
in many parts of the body).
An important subset of syndromic WPW associates with HCM. The locus for this (combined)
condition, consisting of pre-excitation, HCM and (progressive) conduction abnormalities,
was first identified in 1995
307
and the gene, PRKAG2, encoding for the enzyme AMP-activated protein kinase (AMPK),
was identified in 2001, resulting in glycogen storage abnormalities in the heart.
308
In a recent relatively large series one-third of individuals carrying a pathogenic
PRKAG2 variant had evidence of pre-excitation and approximately two-thirds had an
increased wall thickness.
309
In conclusion, only in the presence of the combination of pre-excitation and HCM and/or
progressive CCD is genetic testing pertinent (see above and State of genetic testing
for cardiomyopathies section). The vast majority of WPW cases, however, will be isolated
and not based on a genetic cause.
State of genetic testing for cardiomyopathies
Hypertrophic cardiomyopathy
Impact of genetic testing for the index case
Disease
Diagnostic
Prognostic
Therapeutic
HCM
+++
++
++
Recommendation
Consensus statement instruction
Ref.
For genetic testing in a proband with HCM (including those cases diagnosed post-mortem),
the initial tier of genes tested should include genes with definitive or strong evidence
of pathogenicity (currently MYH7, MYBPC3, TNNI3, TPM1, MYL2, MYL3, ACTC1, and TNNT2).
10
For genetic testing in a proband with HCM, the initial tier of genes tested may include
genes with moderate evidence of pathogenicity (CSRP3, TNNC1, JPH2).
10,
310–314
In patients with HCM, genetic testing is recommended for identification of family
members at risk of developing HCM.
315–318
In patients with atypical clinical presentation of HCM, or when another genetic condition
associated with unexplained hypertrophy is suspected (e.g. HCM phenocopy) genetic
testing is recommended.
10,
253,
308,
319–324
Predictive genetic testing in related children is recommended in those aged >10–12 years.
82,
85,
318
In patients with HCM who harbour a variant of uncertain significance, the usefulness
of genetic testing of phenotype-negative relatives for the purpose of variant reclassification
is uncertain.
10,
315,
325
Predictive genetic testing in related children aged below 10–12 years may be considered,
especially where there is a family history of early-onset disease.
82
85
In patients with HCM who harbour a variant of uncertain significance, testing of affected
family members for the purpose of variant classification may be considered.
Expert opinion
For patients with HCM in whom genetic testing found no LP/P variants, cascade genetic
testing of family relatives is not recommended.
10,
315–317,
325
Ongoing clinical screening is not recommended in genotype-negative relatives in most
families with genotype-positive HCM
10,
315,
316,
325
Background
Hypertrophic cardiomyopathy is a relative common inherited cardiac condition characterized
by hypertrophy of the LV wall, not explained by other conditions (i.e. hypertension
or valvular heart disease). Typically, the hypertrophy is asymmetric and confined
to the intraventricular septum. Clinical sequalae of HCM include diastolic dysfunction,
heart failure, atrial arrhythmias (with associated thrombogenic events), and malignant
ventricular arrhythmias. Genetic testing provides an opportunity to improve care of
patients with HCM and their family members. Offspring of carriers have a 50% chance
of inheriting the same disease-causing genetic variant.
16,
81,
326
It is essential to take a multigenerational family history of HCM including those
suspected of dying suddenly. Engaging patients and family members means discussing
the role of genetic testing including appropriate pre- and post-test genetic counselling,
and its impact on psychological, social, legal, ethical, and professional implications
of a positive test. Genetic assessment should ideally be performed in a specialized
multidisciplinary HCM centre.
16,
326
Next-generation sequencing led to an expansion in the number of genes included in
diagnostic gene panel. However, inclusion of genes with limited gene-disease association,
diminish the efficacy of genetic counselling by adding uncertainty and misinterpretation,
among others leading to false positive results.
10,
82,
315–317,
327–329
Recommendation for genes with a definite, strong or moderate evidence of pathogenicity
of HCM and phenocopies are depicted in Table 13
.
Table 13
Genes implicated in hypertrophic cardiomyopathy
Gene
Locus
Syndrome
Protein (functional effect)
Frequency
ClinGen classification
MYBPC3
11p11.2
Familial HCM
↓contractility due to ↓Ca2+ sensitivity
40–45%
Definite
MYH7
14q11.2-q12
Familial HCM
↓contractility due to ↓Ca2+ sensitivity
15–25%
Definite
TNNI3
19q13.4
Familial HCM
Loss of function (inhibitory)
1–7%
Definite
TNNT2
1q32.1
Familial HCM
Increase oxygen consumption
1–7%
Definite
TPM1
15q22.2
Familial HCM
Loss-of-function of the thin filament
1–2%
Definite
ACTC1
15q.14
Familial HCM
Gain-of-function causing high contractile phenotype
1–2%
Definite
MYL2
12q24.11
Familial HCM
Loss-of-function
1–2%
Definite
MYL3
3p21.31
Familial HCM
Loss-of-function
1–2%
Definite
Intrinsic cardiomyopathy genes
ACTN2
1q43
LVH, LVNC, DCM, and idiopathic VF
Loss-of-function
<1%
Moderate
PLN
6q22.31
HCM, DCM, and ARVC
Loss-of-function of SERCA (Ca2+ overload) mitochondrial disease
<1%
Definite
JPH2
20q13.12
Familial HCM/DCM
Unknown
<1%
Moderate
FHOD3
18q12.2
Familial HCM/DCM
Actin filament polymerization disruption
0.5–2%
Not curated by ClinGen
CSRP3
11p15.1
Late onset familial HCM, DCM
Unknown (non-sarcomeric gene)
<1%
Moderate
TNNC1
3p21.1
Familial HCM
Disruption of Ca2+ handling
<1%
Moderate
Syndromic genes, where isolated LVH may be seen
CACNA1C
12p13.33
Timothy syndrome, BrS, LQTS
Intracellular Ca (2+) overload
<1%
Definite
DES
2q35
Desminopathy (DCM), myofibrillar myopathy
Dysfunction through Z-disk and myofibril disintegration, followed by abnormal accumulation
of intracellular proteins
<1%
Definite
FHL1
Xq26.3
Emery-Dreifuss MD, cardiac conduction abnormalities, arrhythmias, HCM
Dysfunction through Z-disk and myofibril disintegration, followed by abnormal accumulation
of intracellular proteins
<1%
Definite
FLNC
7q32.1
Myofibrillar myopathy, HCM, RCM, distal myopathy
Dysfunction through Z-disk and myofibril disintegration, followed by abnormal accumulation
of intracellular proteins
<1%
Not curated by ClinGen
GLA
Xq22.1
Fabry disease
Loss-of-function
<1%
Definite
LAMP2
Xq24
Danon disease
Loss-of-function
<1%
Definite
PRKAG2
7q36.1
PRKAG2 cardiomyopathy
Dysfunction of AMPK
1–2%
Definite
PTPN11
12q24.13
Noonan syndrome
RASopathy
<1%
Definite
RAF1
3p25.2
Noonan syndrome
RASopathy
<1%
Definite
RIT1
1q22
Noonan syndrome
RASopathy
<1%
Definite
TTR
18q12.1
Transthyretin amyloidosis
Loss-of-function causing amyloid deposition in peripheral nerves and heart
1–2%
Definite
ALPK3
15q25.3
Infant-onset HCM/DCM
Biallelic loss-of-function
<1%
Strong
Syndromic genes, where LVH is occurs together with other syndromic features
ABCC9
12p12.1
Cantu syndrome
Reduce ATP-mediated potassium channel inhibition (gain-of-function)
<1%
Definite
BAG3
10q26.11
Myofibrillar myopathy
Dysfunction through Z-disk and myofibril disintegration, followed by abnormal accumulation
of intracellular proteins
<1%
Definite
CAV3
3p25.3
Caveolinopathy
Disruption of caveolae formation
<1%
Definite
COX15
10q24.2
Leigh syndrome
Loss-of-function of SERCA (Ca2+ overload) mitochondrial disease
<1%
Strong
CRYAB
15
Alpha-B crystallinopathy
Dysfunction through Z-disk and myofibril disintegration, followed by abnormal accumulation
of intracellular proteins
<1%
Definite
FXN
9q21.11
Friedreich ataxia
Loss-of-function of mitochondrial protein
<1%
Definite
GAA
17q25.3
Pompe disease
Loss-of-function
<1%
Definite
LDB3/ZASP
10q23.2
Myofibrillar myopathy
Dysfunction through Z-disk and myofibril disintegration, followed by abnormal accumulation
of intracellular proteins
<1%
Moderate
MYO6
6q14.1
Bilateral hearing loss
Disruption of the structural integrity of inner ear hair cells
<1%
Definite
SLC25A4
4q35.1
Mitochondrial disease
RASopathy
<1%
Definite
ACM, arrhythmogenic cardiomyopathy; BrS, Brugada syndrome; DCM, dilated cardiomyopathy;
HCM, hypertrophic cardiomyopathy; LQTS, long QT syndrome.
Diagnostic implications of genetic testing
Index case
Hypertrophic cardiomyopathy is predominantly a disease of the sarcomere. First-line
genetic testing primarily includes panel testing for genes with strong evidence for
being disease-causing in HCM.
10
Gene panels generally (and are recommended to) include 8 sarcomere genes, including
MYH7, MYBPC3, TNNI3, TNNT2, TPM1, MYL2, MYL3, and ACTC1, and typically identify a
disease-causing variant in approximately 30% of sporadic and 60% of familial cases.
10,
315,
316,
328–330
Variants in TNNC1 (troponin C1) have moderate evidence of pathogenicity
310,
331
(Table 13
). A number of non-sarcomeric pathogenic variants with moderate to strong evidence
of pathogenicity may be included in the initial tier of genes tested, including CSRP3,
JPH2, ALPK3, and FHOD3.
311–314
Expanding to larger panels, including the genes summarized in Supplementary material
online,
Table S13
, usually does not add diagnostic value.
69,
315
Initial genetic testing is usually performed in the index case (proband).
315
In up to 40% of patients with HCM, no sarcomere variant is identified, and there is
no family history of disease.
332
Genes associated with HCM phenocopies may be included in first-tier genetic testing
if there is clinical suspicion based on phenotype evaluation of a syndromic disorder,
including PRKAG2 (glycogen storage disease),
253,
308,
319
LAMP2 (Danon disease),
320
GLA (Fabry disease),
321
and relevant genes for transthyretin amyloid cardiomyopathy,
322
and Pompe disease.
333–335
In some circumstances, the genetic test result may alter the management of the index
case, such as enzyme replacement therapy in patients with Fabry disease or more aggressive
clinical management of patients with Danon disease, or increased awareness for sinus
bradycardia and AV block in PRKAG2.
323,
324
Postmortem testing for HCM-associated variants using blood or tissue collected at
autopsy has been reported, particularly in instances where the family variant is unknown
and no other affected family members are still living.
86–88
Access to a molecular autopsy as well as considerations related to costs and insurance
coverage for this testing can vary between jurisdictions. Nevertheless, identification
of a LP/P variant not only confirms the diagnosis of HCM but allows cascade genetic
testing of other at-risk relatives as outlined previously.
Family screening
After genetic testing, a clinically actionable result (likely-pathogenic or pathogenic)
can provide diagnostic clarification in the proband and offers the potential for cascade
(predictive) testing of at-risk family members.
81–85
Cascade testing involves targeted testing of first-degree relatives for the LP/P variant
found in the proband. When cascade testing is performed in an at-risk relative, those
who are found not to carry the disease-causing gene variant can be released from further
clinical surveillance. Those who are found to carry the disease-causing gene variant
should undergo clinical screening at regular intervals. Family members of a patient
where genetic testing is not done or is negative (no likely-pathogenic or pathogenic
variant is identified) also require clinical screening at regular intervals because
there is considerable phenotypic heterogeneity in age of onset and disease progression
within members of the same family.
Prognostic and therapeutic implications of genetic testing
Although there is some evidence that individuals who carry >1 LP/P variant may have
more severe disease, including SCD, the role of the genetic test result in the determination
of risk in SCD remains uncertain and is therefore not clinically useful. Similarly,
a genetic result per se does not influence decisions related to implanting an ICD
in patients with HCM. Several studies have reported that patients with HCM who carry
LP/P sarcomere variants have a worse prognosis compared to sarcomere variant negative
patients. This includes earlier onset of disease, higher incidence of SCD, higher
incidence of AFib and ventricular arrhythmias, HF, and overall mortality.
83,
329,
336–338
However, there remains considerable intra- and inter-familial heterogeneity with variants
in the same gene that currently limits the application of genetic information for
clinical decision-making, including risk stratification for SCD in the proband.
318,
339
Early data on polygenic risk scores suggests they may correlate with disease severity.
29,
30
Discovery of an HCM phenocopy may modify therapeutic options, such as enzyme replacement
therapy in Fabry patients.
Dilated cardiomyopathy
Impact of genetic testing for the index case
Disease
Diagnostic
Prognostic
Therapeutic
DCM
++
+++
++
Recommendation
Consensus statement instruction
Ref.
Genetic testing is recommended for probands with DCM and family history of DCM, and
the initial tier of genes tested should include genes with definitive or strong evidence
of pathogenicity (currently BAG3, DES, FLNC, LMNA, MYH7, PLN, RBM20, SCN5A, TNNC1,
TNNT2, TTN, DSP).
19,
340
For genetic testing in a proband with DCM, the initial tier of genes tested may include
genes with moderate evidence of pathogenicity (ACTC1, ACTN2, JPH2, NEXN, TNNI3, TPM1,
VCL).
19
Genetic testing is recommended for patients with DCM and family history of premature
unexpected sudden death or in a DCM patient with clinical features suggestive of a
particular/rare genetic disease (such as atrioventricular block or sinus dysfunction
or creatine phosphokinase elevation).
340
Genetic testing can be useful for patients with apparently sporadic DCM, particularly
in the presence of either severe systolic dysfunction (left ventricular ejection fraction < 35%),
or a malignant arrhythmia phenotype (e.g. sustained ventricular tachycardia/fibrillation),
or particularly at a younger age.
340
Genetic testing may be considered for patients with DCM related to an acquired or
environmental cause that may overlap with a genetic cause (such as peripartum or alcoholic
cardiomyopathy).
341,
342
Genetic testing is useful for patients with DCM to improve risk stratification and
guide therapy.
201,
343–348
Variant-specific genetic testing is recommended for family members and appropriate
relatives following the identification of the disease-causative variant.
16,
340,
349
Predictive genetic testing in related children is recommended in those aged >10–12 years.
16,
350
Predictive genetic testing in related children aged below 10–12 years may be considered,
especially where there is a family history of early-onset disease.
16,
350
Background
Dilated cardiomyopathy is defined by the presence of LV or biventricular dilatation
and systolic dysfunction in the absence of abnormal loading conditions (hypertension,
valve disease) or coronary artery disease sufficient to cause global systolic impairment.
351
A new category of hypokinetic non-dilated cardiomyopathy was also proposed
352
to characterize patients with systolic dysfunction but without LV dilatation. Dilated
cardiomyopathy encompasses a broad range of genetic or acquired disorders and careful
diagnostic work-up should be performed to identify the underlying cause and then consider
an aetiology-oriented approach to therapy.
352
In the pre-molecular era, systematic cardiac screening of the relatives of patients
with DCM identified probable familial disease in about 20–35% of cases.
353–355
Subsequently, identification of DCM-related genes and development of high-throughput
sequencing technologies led to the identification of pathogenic variants in up to
50% of DCM patients
340,
355
including a non-marginal yield in sporadic DCM.
356
Moreover, there are more and more situations in which genetic predisposition interacts
with extrinsic or environmental factors resulting in mixed genetic/environmental causes,
such as myocarditis, as well as peripartum, alcoholic, or chemotherapy-related cardiomyopathies.
341,
342,
357,
358
Summary of the common dilated cardiomyopathy genes
About 100 genes have been reported to be possibly related to DCM (main genes in Table 14
). The disease-specific metrics designed by the Clinical Genome Resource (ClinGen),
reclassified many of these genes to limited or disputed evidence
19
(Supplementary material online,
Table S14
). Truncating variants in titin gene (TTN) are the most frequent in DCM, accounting
for up to 20% of cases.
24
A case–control study demonstrated that variants in TTN, DSP, MYH7, LMNA, BAG3, TNNT2,
TNNC1, PLN, ACTC1, NEXN, TPM1, and VCL are significantly enriched in DCM cases.
359
Mutated genes are most often related to sarcomeric genes, z-disc/cytoskeleton, intercalated
disc, and ion flux in large series with large panels indicating partial overlap with
other cardiomyopathy subtypes [such as ACM (arrhythmogenic right ventricular cardiomyopathy,
ARVC)] as well as with channelopathies.
340
Table 14
Genes implicated in dilated cardiomyopathy
Gene
Locus
Phenotype–syndrome
Protein (functional effect)
Frequency
ClinGen classification
TTN
2q31.2
DCM
Titin
∼15–25%
Definitive
LMNA
1q22
DCM, ACM
Lamin A/C
∼4–7%
Definitive
MYH7
14q11.2
HCM
Bêta Myosin heavy chain
∼3–5%
Definitive
TNNT2
1q32.1
HCM, DCM
Troponin T
∼2%
Definitive
RBM20
10q25.2
DCM
RNA-binding motif protein 20
∼2%
Definitive
PLN
6q22.31
DCM, ACM
Phospholamban
∼1% (more in Netherlands)
Definitive
FLNC
7q32.1
DCM≫BiVACM
Filamin-C
∼3%
Definitive
BAG3
10q26.11
DCM, myopathy
BAG family molecular chaperone regulator 3
∼2%
Definitive
DSP
6p24.3
ARVC, DCM
Desmoplakin
1–3%
Strong
TPM1
15q22.1
HCM, DCM
alpha-tropomyosin
∼1–2%
Moderate
ACTC1
15q11q14
HCM, DCM
Cardiac alpha-actin
<1%
Moderate
ACTN2
1q43
HCM, DCM, LVNC
Alpha-actinin-2
<1%
Moderate
DES
2q35
DCM, Myopathy, ACM
Desmin
<1%
Definitive
JPH2
20q13.12
DCM, HCM
Junctophilin 2
<1%
Moderate
NEXN
1p31.1
DCM, HCM
Nexilin
<1%
Moderate
SCN5A
3p22.2
LQTS, Brugada, DCM, ACM
Sodium channel protein type 5 subunit alpha
<1%
Definitive
TNNC1
3p21.1
DCM, HCM
Cardiac Troponin C
<1%
Definitive
TNNI3
19q13.4
HCM, DCM
Cardiac troponin I
<1%
Moderate
VCL
10q22.2
DCM
Metavinculin
<1%
Moderate
ACM, arrhythmogenic cardiomyopathy; DCM, dilated cardiomyopathy; HCM, hypertrophic
cardiomyopathy.
Series also suggest that the single-variant Mendelian disease model is insufficient
to explain some DCM cases, since multiple variants (mainly compound heterozygous may
be observed in up to 38% in DCM patients).
340
Preliminary data suggest a complex polygenic architecture for some DCM patients with
a combination of rare and frequent variants and interactions with environmental factors.
29,
30,
360,
361
Diagnostic implications of dilated cardiomyopathy genetic testing
Index cases
The yield of genetic study in DCM is variable and depends on familial context (familial
vs. sporadic DCM, history of SCD), presence of particular associated cardiac or extra-cardiac
signs, type of genetic testing selection, and stringency of variant interpretation.
It can be grossly estimated to be 20–50% and is the highest in DCM with familial forms
or with particular associated cardiac or extra-cardiac signs.
340,
349,
356
As in other conditions genetic testing in an index patient, and identification of
a pathogenic variant, may have several impacts since the information is able to confirm
the genetic origin and mode of inheritance, can distinguish DCM from other cardiomyopathies
such as ACM and is useful for appropriate aetiology-management of patients. Genetic
testing is therefore useful in all DCM patients, is recommended in DCM patients with
the highest yield of pathogenic variant screening and should be considered even in
the absence of familial context or associated clinical features (<60 years of age).
High-throughput sequencing with targeted sequencing panels of genes is the most cost-effective
approach and recommended technique.
362
Panels should include validated genes in DCM (see Table 14
), with most prevalent genes such as TTN as well as genes with prognostic or therapeutic
implications, such as LMNA or FLNC. Genetic testing/panel can be oriented by the presence
of a particular extra-cardiac phenotype such as neuromuscular diseases, mitochondrial
diseases, congenital syndromes.
363
Family screening
Most genetic DCM inheritance follows an AD pattern, although X-linked, recessive,
and mitochondrial patterns of inheritance occur (see genetic influences on disease
and modes of inheritance section).
360,
364
Penetrance in AD DCM is age-dependent. Therefore, an individual who carries a disease-causing
variant is more likely to show a disease phenotype with increasing age, and a normal
phenotypic assessment by echocardiogram and ECG does not exclude the possibility of
later onset disease. The identification of a LP/P in the index case allows specific
cascade genetic screening to identify gene carriers among relatives.
16,
350,
365
Relatives who do not carry the pathogenic variant are reassured and cardiac follow-up
is no longer required. Relatives who carry the pathogenic variant must be periodically
investigated for early detection of the phenotype, to allow optimal management and
prevention of the complications. A genetic diagnosis can be useful for reproductive
counselling and planning, including options for prenatal or pre-implantation genetic
testing to prevent the transmission of DCM.
366
Prognostic and therapeutic implications of dilated cardiomyopathy genetic testing
The identification of a specific genetic substrate can help to manage the patients
and guide clinical decisions. Patients with pathogenic LMNA variants have consistently
been associated with a poor prognosis, especially with a high risk of SCD related
either to conduction defect or ventricular arrhythmia.
201,
343,
344
There are, however, exceptions for particular founder pathogenic variants.
367
Preventive pacemaker (PM) or ICD therapy should be considered early in LMNA carriers,
and algorithms for ICD implantation include the pathogenic variant mechanism (truncating
vs. missense variant) as associated with higher SCD risk.
201,
343,
344
Higher risk of SCD is also associated with pathogenic variants, especially truncated
variants, in FLNC, DES, RBM20, and PLN genes,
345–348,
368
so that preventive ICD implantation may also be considered in these patients. Desmosomal
pathogenic variants in patients with DCM or biventricular cardiomyopathy are also
associated with a greater risk of life-threatening ventricular arrhythmias/SCD.
369
Patients with DCM are also at greater risk for heart failure and heart transplantation
when they are carriers of pathogenic variants in LMNA, RBM20, and DSP genes.
345,
369
Preventive PM implantation related to conduction defect should also be considered
in patients with DCM and muscular dystrophy related to dystrophin, DES and EMD genes.
345,
348
Arrhythmogenic cardiomyopathy
Disease
Diagnostic
Prognostic
Therapeutic
ACM
+++
++
++
Recommendations
Consensus statement instruction
Ref.
Comprehensive genetic testing is recommended for all patients with consistent phenotypic
features of ACM, including those cases diagnosed post-mortem, whatever familial context.
370
Genetic testing of first tier definitive disease-associated genes (currently PKP2,
DSP, DSG2, DSC2, JUP, TMEM43, PLN, FLNC, DES, LMNA) is recommended.
370,
371
Owing to the possibility of complex genotypes, in families with multiple affected
members, the case with the more severe and/or earlier phenotype may be considered
the ‘genetic proband’ and be tested first.
362
In patients with a borderline ACM phenotype, comprehensive genetic testing may be
considered. The identification of a LP/P genetic variant would be useful to confirm
the diagnosis.
372
Variant-specific genetic testing is recommended for family members and appropriate
relatives following the identification of the disease-causative variant.
370,
373
Predictive genetic testing in related children is recommended in those aged >10–12 years.
370,
374
Predictive genetic testing in related children aged below 10–12 years may be considered,
especially where there is a family history of early-onset disease.
Expert opinion
Background
Arrhythmogenic cardiomyopathy is mainly characterized by fibro or fibrofatty myocardial
replacement which can cause progressive global/regional ventricular dysfunction, and
high burden of ventricular arrhythmias.
375
Structural alterations can affect left, right, or both ventricles which lead to three
recognized phenotypic variants: the dominant-right (‘the classic arrhythmogenic right
ventricular cardiomyopathy’—ARVC) variant, the biventricular variant (Biv ACM), and
the dominant-left variant (also known as ‘arrhythmogenic left ventricular cardiomyopathy’—ALVC).
The identification of a LP/P genetic variant is a major diagnostic criterion in all
types and can be a necessary requirement for the ALVC variant.
372
The most common pattern of inheritance in monogenic ACM is AD. However, Naxos disease
and Carvajal syndrome, which lead to the identification of the desmosomal cause of
the disease are both recessive conditions.
373
Diagnostic implications of arrhythmogenic cardiomyopathy genetic testing
Arrhythmogenic right ventricular cardiomyopathy is predominantly associated with variants
in desmosomal genes. Haploinsufficiency is a well-recognized molecular mechanism in
these genes, and loss-of-function variants (nonsense, frameshift and splicing site)
have the strongest evidence for pathogenicity.
374
The interpretation of missense or in-frame insertion/deletion variants is generally
challenging and segregation with the phenotype in the families is usually mandatory
for establishing their causality. Nearly 50% of patients with ARVC have one or more
desmosomal pathogenic variants, with PKP2 the most common mutated gene.
371,
376
The number of variants that could be considered pathogenic in JUP is anecdotally besides
Naxos disease. Non-desmosomal gene variants represent a minority of ARVC causes, and
have been reported in a limited number of cases. Familial segregation studies are
limited in some of the new proposed genes and the evidence supporting their causality
is limited.
Biventricular ACM is also frequently associated with desmosomal genetic variants.
Specific variants in PLN (p.Arg14del) and TMEM43 (p.Ser358Leu) are highly relevant
in some countries where a founder effect has been demonstrated.
377,
378
The identification of other pathogenic variants in these two genes associated with
ACM is quite rare. Initial investigations postulated RYR2 gene as part of the genetic
substrate of ARVC.
379
However, after decades of their initial descriptions, and after investigation of thousands
of patients, evidence no longer supports these associations.
Desmoplakin (DSP) is by far the most commonly mutated desmosomal gene in patients
with ALVC. DSG2 and DSC2 genes variants have also been described in ALVC patients
but represent a significantly lower number of cases.
369
Non-desmosomal genes can be more relevant in the left-dominant variant of the disease.
Truncations in FLNC, RBM20, and some DES variants were consistently associated with
this phenotype often without overt skeletal myopathy, which is traditionally related
to these genes.
346,
380,
381
The yield of genetic study in ACM is highly variable and depends on several factors
(type of ventricle affected, familial clustering, ethnicity of the cohort and selection
criteria, type of genetic testing selection, and the stringency of variant interpretation)
but can be grossly estimated in the 50–60% range.
Index cases
Genetic testing is indicated in a proband with consistent phenotypic features of ACM,
including those cases diagnosed post-mortem.
370,
375,
382
The identification of a LP/P genetic variant would also be useful to confirm the diagnosis
in patients with a borderline phenotype. In those cases with isolated LV compromise,
the demonstration of a pathogenic genetic variant could be necessary to link the electrical
and/or structural manifestations with the diagnosis of ACM.
372
In families with multiple affected members, the case with the more severe and/or earlier
phenotype must be considered the ‘genetic proband’ and be tested first to enhance
the detection of complex genotypes causing the disease (homozygous or compound/double
heterozygous situations).
372
Nowadays, the recommended genetic test for ACM must include a minimal number of genes
that have clinically demonstrated their association with the disease (see Table 15
). Genes with limited or disputed evidence are summarized in Supplementary material
online,
Table S15
. High-throughput sequencing has demonstrated a high level of accuracy and is the
recommended technique. Targeted sequencing panels of genes is the most cost-effective
approach.
362
Copy number variation’s analysis should be included, since this type of variant can
be found in 1–4% of negative studies.
371
Whole-exome/genome sequencing must assure adequate coverage in causative genes, and
its application without filtering against genes of interest should be considered only
in research contexts. Owing to the limited yield of genetic testing in ACM, a negative
result does not rule out the diagnosis. The high genetic noise based on the prevalence
of rare variants in ACM genes (especially missense changes in desmosomal genes) in
the general population strengthens the importance of interpretation of the results
by experts in cardiovascular molecular genetics.
374
Table 15
Genes implicated in arrhythmogenic cardiomyopathy
Gene
Locus
Phenotype/syndrome
Protein (Cellular complex)
Frequency
ClinGen classification
PKP2
12p11.21
Classic ARVC. BiVACM and ALVC in a minority of cases.
Plakophilin 2 (desmosome)
20–45%
Definite
DSP
6p24.3
Frequent BiVACM and ALVC. Occasional hair and skin features. Rare homozygous variants—Carvajal
Syndrome.
Desmoplakin (desmosome)
2–15%
Definite
DSG2
18q12.1
Frequent BiVACM and ALVC.
Desmoglein 2 (desmosome)
4–15%
Definite
DSC2
18q12.1
ARVC. Less frequent BiVACM and ALVC.
Desmocollin 2 (desmosome)
2–7%
Definite
FLNC
7q32.1
ALVC. Right ventricular involvement is rare
Filamin-C (cytoskeleton)
3%
Definite
a
JUP
17q21.2
Naxos disease (cardioectodermal)
Plakoglobin (desmosome)
<1% (higher in Naxos, Greece)
Definite
TMEM43
3p25.1
ARVC and BiVACM
Transmembrane protein 43 (nuclear envelope)
<1% (higher in Newfoundland)
Definite
PLN
6q22.31
Frequent ALVC/DCM
Phospholamban (sarcoplasmic reticulum; calcium handling)
1% (10–15% in Netherlands)
Definite
a
DES
2q35
Frequent ALVC. Right ventricular involvement is also possible.
Conduction system abnormalities common. Skeletal myopathy possible.
Desmin (cytoskeleton)
1–2%
Moderate
ALVC, arrhythmogenic left ventricular cardiomyopathy; ARVC, arrhythmogenic right ventricular
cardiomyopathy; BiVACM, bi-ventricular arrhythmogenic cardiomyopathy; DCM, dilated
cardiomyopathy.
a
Genes with a clear association with ALVC and included also in the ClinGen classification
for DCM.
Family screening
The identification of a LP/P variant in the index case allows specific cascade genetic
screening to identify gene carriers among relatives.
370,
373
Incomplete penetrance and highly variable clinical expression associated with most
ACM-related genes must be considered in the interpretation of the results, genetic
counselling and clinical management.
383,
384
Clinical and genetic evaluations of older generations in the family is also recommended
and could be valuable for phenotype delineation associated with a particular genotype.
The identification of relatives without the family pathogenic variant allows psychological
relief and optimizes the clinical resources. On the other hand, variant-carrier relatives
must be investigated periodically should be advised of the benefit of life-style modifications.
Prognostic and therapeutic implications of arrhythmogenic cardiomyopathy genetic testing
Arrhythmogenic cardiomyopathy is characterized by highly variable intra/interfamilial
phenotype severity and the influence of environmental factors is probably more determinant
than in other cardiomyopathies.
385
Some investigations have suggested that ACM patients with an identifiable causative
genetic variant do not have significant differences in disease course and prognosis
from gene elusive patients.
383
Nevertheless, identification of the specific genetic substrate can guide the clinical
decisions in some scenarios. Preventive (early) ICD implantation may be considered
in ACM patients with truncations in FLNC, DSP, LMNA, DES and PLN pathogenic variants,
who present with reduced LV systolic function.
370,
380,
381
Arrhythmogenic cardiomyopathy patients with cadherin-2 (CDH2) pathogenic variants
have a higher incidence of ventricular arrhythmias, while development of heart failure
is rare.
386
Since the ClinGen curation of genes for ACM, new evidence supports CDH2 as a disease
gene in a small subset of ACM patients.
387
Indeed, in ACM severe ventricular arrhythmias may present before ventricular dysfunction
or structural manifestations are evident, that is why the detection of P/LP variant
in an index case will allow through familial cascade screening early detection and
prompt stratification of arrhythmic risk of those mutation carriers.
For LMNA, PLN and ACM caused by desmosome gene variants (mainly PKP2) specific calculators
have been developed.
344,
388,
389
Those patients initially diagnosed with DCM where a pathogenic desmosomal variant
is identified could have a greater risk of life-threatening ventricular arrhythmias
and sudden death, regardless of the LV ejection fraction.
369
Patients with complex genotypes (homozygous and compound/double heterozygous) carrying
clearly disease-causing variants, have a worse prognosis (considering ventricular
arrhythmias and ventricular dysfunction) compared with single pathogenic variant carriers.
376,
390,
391
Competitive or high-level leisure sport has been demonstrated to increase penetrance,
incidence of ventricular arrhythmias and progression to ventricular dysfunction in
carriers of pathogenic desmosomal variants.
392,
393
Left ventricular non-compaction cardiomyopathy
Disease
Diagnostic
Prognostic
Therapeutic
LVNC
+
+
–
Recommendation
Consensus statement instruction
Ref.
LVNC cardiomyopathy genetic testing may be useful for patients in whom a cardiologist
has established a clinical diagnosis of LVNC based on examination of the patient’s
clinical history, family history, and electrocardiographic/echocardiographic/MRI phenotype.
387,
394–396
Genetic testing may be useful for patients with a clinical diagnosis of LVNC cardiomyopathy
associated with other cardiac or non-cardiac syndromic features.
397–399
Genetic testing should not be performed in isolated (incidental) LVNC with normal
LV function, no associated syndromic features and no family history.
387,
394,
400
Variant specific genetic testing may be considered for family members and appropriate
relatives following the identification of the disease-causative variant.
Expert opinion
Background
Left ventricular non-compaction (LVNC) is a phenotype that can present as a cardiomyopathy
characterized by prominent LV trabeculations with deep intertrabecular recesses and
thinning of the compact epicardium.
394
In children, LVNC can present with severe heart failure and life threatening arrhythmias.
In adults, the clinical presentation and significance is less clear, particularly
when the diagnosis is made outside the context of an affected family. Patients with
LVNC can present with isolated LV trabeculations with no LV dysfunction, LVNC associated
with other cardiomyopathies such as HCM or DCM, or can present with LVNC associated
with other cardiac (e.g. conduction disease) or non-cardiac systemic features (e.g.
skeletal abnormalities in Holt-Oram syndrome).
387,
394–396,
400,
401
Major adverse events in adults include life-threatening arrhythmias, thromboembolism,
and heart failure. Genetic testing in LVNC, therefore, is strongly guided by a comprehensive
clinical evaluation of the patient and their family. Isolated LVNC, with no LV dysfunction
and detected incidentally on MRI will have a very low genetic testing yield compared
to LVNC associated with other cardiomyopathies and LV dysfunction, syndromic features,
and/or a strong family history where the genetic testing yield will be significantly
higher.
394,
396–399,
401,
402
Left ventricular non-compaction is most commonly inherited as an AD trait in families,
although AR, X-linked, and mitochondrial inheritance is also seen, often in children.
Studies of the genetic causes of LVNC have primarily identified variants in cardiomyopathy
genes and specifically sarcomere genes, including MYH7, MYBPC3, and TTN with reported
genetic testing yields between 17% and 41% (Table 16
).
394
Other genetic diseases where LVNC is part of a clinical syndrome are also important
to consider, such as LDB3 (LIM-domain binding protein 3) with DCM and myopathy, TBX5
in Holt–Oram syndrome, NKX2-5 with conduction disease, and TAZ (taffazin) associated
with Barth syndrome in males
387,
394–399
(Table 16
). The choice of which genes to test in LVNC is strongly guided by the clinical phenotype,
including presentation (symptomatic vs. incidental finding on cardiac MRI), association
with other cardiomyopathies, other systemic cardiac or non-cardiac features, and presence
of a family history of LVNC or other inherited cardiomyopathies.
402
There are not many known ‘LVNC only’ genes, so genetic testing is guided by the other
cardiomyopathies such as HCM or DCM (see Table 16
). Most commonly a broad cardiomyopathy panel will represent the first step of genetic
testing, with additional selection of genes guided by the phenotype. Left ventricular
non-compaction in the setting of physiological changes such as during pregnancy or
in athletes, as well as LVNC diagnosed incidentally on imaging studies, has a high
prevalence in normal adult populations leading to overdiagnosis of LVNC as a pathogenic
entity.
403
Therefore, genetic testing should rarely be considered in these settings and may lead
to more harm than benefit related to uncertain genetic findings including variants
of uncertain significance.
Table 16
Genes implicated in left ventricular noncompaction in adults
Gene
Locus
Syndrome
Protein (functional effect)
Frequency
ClinGen classification
MHY7
14q11.2
LVNC, DCM or HCM
Beta myosin heavy chain
10–15%
NA/major gene
MYBPC3
11p11.2
LVNC, DCM or HCM
Myosin binding protein C
5–15%
NA/major gene
TTN
2q31.2
LVNC, DCM
Titin
5–10%
NA/major gene
ACTC1
15q11.14
LVNC, DCM or HCM
Cardiac alpha-actin
1–5%
NA/rare gene
RYR2
1q43
LVNC, DCM
Ryanodine receptor type 2
1–2%
NA/rare gene
PRDM16
1p36
LVNC
PR domain zinc finger protein 16
1–2%
NA/rare gene
LBD3
11p15.1
LVNC, DCM
LIM domain binding 3
1–2%
NA/rare gene
TBX5
12q24.1
LVNC, Holt-Oram syndrome
T-box transcription factor 5
1–2%
NA/rare gene
NKX2-5
5q35.1
LVNC, DCM, conduction disease
Homeobox protein Nkx2-5
1–2%
NA/rare gene
HCN4
15q24.1
LVNC, conduction disease
Hyperpolarization-activated cyclic nucleotide-gated K+ channel 4
1–2%
NA/rare gene
TAZ
Xp28
LVNC, Barth syndrome
Tafazzin
1–2%
NA/rare gene
DCM, dilated cardiomyopathy; HCM, hypertrophic cardiomyopathy; LVNC, left ventricular
noncompaction.
Diagnostic implications of left ventricular non-compaction genetic testing
The main benefit of genetic testing in LVNC is for diagnosis in the index cases and
to then use this genetic diagnosis for cascade testing in family members.
394
The identification of a genetic cause may also be useful in guiding reproductive decisions
such as pre-implantation genetic diagnosis.
Prognostic and therapeutic implications
Currently, no significant genotype-phenotype correlations have been associated with
LVNC alone and therefore, little prognostic information is available based on the
genetic findings. There are some emerging data suggesting that specific genotypes
such as MYH7 pathogenic variants or multiple pathogenic variants in patients with
LVNC and LV dysfunction may be associated with worse clinical outcomes compared to
sporadic cases.
394
Restrictive cardiomyopathy
Disease
Diagnostic
Prognostic
Therapeutic
RCM
+
+
+
Recommendation
Consensus statement instruction
Ref
RCM genetic testing may be considered for patients in whom a cardiologist has established
a clinical diagnosis of RCM based on examination of the patient’s clinical history,
family history, and electrocardiographic/echocardiographic phenotype.
402,
404–406
Genetic testing specifically for TTR pathogenic variants is recommended for patients
with RCM and a clinical diagnosis of cardiac TTR amyloidosis.
407,
408
Variant-specific genetic testing may be considered for family members and appropriate
relatives following the identification of the disease-causative variant.
Expert opinion
Background
Restrictive cardiomyopathy (RCM), defined by the presence of impaired LV filling and
diminished diastolic volume with normal or near-normal LV wall thickness and ejection
fraction, is a relatively rare cardiomyopathy which can have both genetic and non-genetic
causes. These causes generally relate to infiltrative (e.g. amyloidosis), non-infiltrative
(e.g. myofibrillar myopathies), storage diseases (e.g. Fabry disease), and endomyocardial
aetiologies such as carcinoid heart disease.
404
In children, RCM often presents with severe heart failure, and carries a poor prognosis
with heart transplant being the only viable long-term treatment option. In adults,
there is significant overlap with HCM and DCM, and patients often present with heart
failure and life-threatening arrhythmias. While the genetic basis of RCM is still
emerging, there are significant commonalities with the genetic causes of HCM and DCM
mainly relating to sarcomere and cytoskeletal disease genes.
402,
405,
406
The inheritance pattern of RCM spans AD, AR, X-linked, and mitochondrial forms of
transmission. Detailed family history and comprehensive clinical evaluation are essential
to establish both cardiac features, as well as potential syndromic manifestations
seen in RCM such as skeletal myopathies. Our knowledge of the specific genetic causes
of RCM is rapidly growing. Currently, sarcomere and cytoskeletal disease genes include
MYH7, TNNI3, TNNT2, ACTC1, FLNC, and TTN, reflecting the common genetic aetiologies
of HCM and DCM
402,
405,
406
(Table 17
). In practical terms, genetic testing for RCM incorporates gene panels used for HCM
and DCM, and relevant phenocopies such as GLA gene in suspected Fabry disease (Table 17
). The yield of genetic testing in familial RCM is difficult to estimate due to the
range of aetiologies and the rare prevalence of disease, but may be up to 60%.
402,
405
Inherited infiltrative diseases can lead to RCM, with amyloidosis being the most common,
caused by pathogenic variants in the TTR gene which encodes transthyretin.
407,
408
Pathological deposition of mis-folded amyloid can occur in many organs such as the
liver, kidney, eyes, as well as the heart, so-called cardiac amyloidosis.
407
Table 17
Genes implicated in restrictive cardiomyopathy
Gene
Locus
Syndrome
Protein (functional effect)
Frequency
ClinGen classification
MHY7
14q11.2
RCM
Beta myosin heavy chain
10–15%
NA/major gene
TTN
2q31.2
RCM
Titin
5–10%
NA/major gene
ACTC1
15q11.14
RCM
Cardiac alpha-actin
5–10%
NA/major gene
TNNI3
19q13.4
RCM
Cardiac troponin I
5–10%
NA/major gene
TTR
18q12.1
RCM, amyloidosis
Transthyretin
1–5%
NA/major gene
FLNC
7Q32.1
RCM
Filamin-C
1–5%
NA/major gene
TNNT2
1q32.1
RCM
Cardiac troponin T
1–2%
NA/rare gene
RCM, restrictive cardiomyopathy.
Diagnostic implications of restrictive cardiomyopathy genetic testing
The main benefit of genetic testing in familial RCM is for diagnosis in the index
cases and to then use this genetic diagnosis for cascade testing in at-risk family
members. The identification of a genetic cause may also be useful in guiding reproductive
decisions such as pre-implantation genetic diagnosis.
Prognostic and therapeutic implications
The genetic diagnosis may guide clinical management strategies. For example, a genetic
diagnosis of Fabry disease may lead to the introduction of enzyme replacement therapy
for the deficiency in alpha-galactosidase enzyme.
409
Similarly, a genetic diagnosis of TTR cardiac amyloidosis may be amenable to newer
targeted treatments that inhibit hepatic synthesis of the TTR protein, stabilize the
tetramer, or disrupt fibrils, such as tafamidis.
407,
410,
411
As the genetic architecture of RCM is further elucidated and underlying disease mechanisms
identified, the impact of the genetic diagnosis in terms of guiding clinical management
and informing prognosis will become more prominent.
State of genetic testing for sudden cardiac death or survivors of unexplained cardiac
arrest
Recommendations
Consensus statement instruction
Ref.
Unexpected sudden deaths should be investigated with a general autopsy, toxicology,
and cardiac pathology (where possible).
6,
412
If a sudden death is likely to be due to a cardiac genetic cause, or remains unexplained
after pathological evaluation, EDTA blood, and/or fresh tissue (e.g. liver or spleen)
should be retained for potential genetic analysis. Other sources of DNA such as blood
spots and tissue stored in suitable media at room temperature may suffice.
15,
413–416
When a SCD could be attributable to a likely genetic cause, post-mortem genetic testing
in the deceased individual targeted to the likely cause should be performed.
414
, expert opinion
When a SCD remains unexplained despite an autopsy and toxicology, post-mortem genetic
testing in the deceased individual targeted to channelopathy genes should be performed when
the circumstances and/or family history support a primary electrical disease.
15,
415,
416
When a SCD <50 years old remains unexplained despite an autopsy, toxicology and channelopathy gene
panel testing, post-mortem genetic testing in the deceased individual may be extended to
a wider panel including cardiomyopathy genes.
15,
415,
416
In a decedent with unexplained SCD or an UCA survivor, hypothesis-free (post-mortem)
genetic testing using exome or genome sequencing should not be performed.
Expert opinion
In selected UCA survivors with idiopathic VF, genetic testing for founder variants,
a
where relevant, should be considered.
417
In UCA survivors, genetic testing of channelopathy and cardiomyopathy genes may be
considered.
418–421
In relatives of UCA survivors or SCD decedents in whom a pathogenic variant has been
identified, predictive genetic testing should be performed.
413,
422
In relatives of UCA survivors or SCD decedents, clinical evaluation of 1st degree
family members should be performed, and targeted to the index case’s phenotype if
present.
422–427
In decedents with SCD or survivors with cardiac arrest in whom a non-genetic cause
has been identified, genetic testing of the index case and clinical evaluation of
relatives should not be performed.
Expert opinion
a
In this setting, a founder variant is a pathogenic variant that has a relatively high
prevalence in the population in a particular geographic region due to the presence
of the variant in a single ancestor or small number of ancestors.
Background
Sudden cardiac death is the most common mode of death due to cardiac disease. Approximately
1–3 per 100 000 individuals under 35 years old die suddenly and unexpectedly every
year within this age group.
6,
412
A significant minority of decedents will have signs of cardiomyopathy on autopsy that
may then receive a molecular diagnosis after post-mortem genetic testing.
413
However, 30–40% of cases of SCD in the young remain unexplained despite toxicological
assessment and evaluation by an expert cardiac pathologist.
15,
414,
415
Many have had an underlying heritable cardiac channelopathy such as CPVT, LQTS, or
BrS.
6,
15
Early studies of diagnostic utility of post-mortem genetic testing, the ‘molecular
autopsy’, in series of sudden arrhythmic death syndrome/sudden unexplained death decedents
provided a pathogenic variant yield of 24% in the major channelopathy genes [CPVT1
(RyR2); LQT1-3 (KCNQ1, KCNH2, SCN5A) and BrS1 (SCN5A)].
415
A population-based NGS study then proposed a 27% burden of ‘clinically relevant’ pathogenic
variants by including cardiomyopathy genes and rare subsequently disputed channelopathy
genes in the panel.
416
Most recently, a large molecular autopsy series in an extended panel of 77 cardiac
genes detected a lower yield (13%) of LP/P variants according to the more stringent
ACMG criteria.
417
These variants were immediately useful in guiding family evaluation and they increased
the diagnostic yield by 50% when undertaken in families who were also undergoing clinical
testing. Furthermore, a proportion of these variants were present in cardiomyopathy
genes, indicating a concealed structural cause of SCD.
417,
418
If focus is placed on younger cases, exertional circumstances of death and the use
of exome sequencing in parent and child trios, then yields can increase substantially.
419,
420
When individuals survive a cardiac arrest (i.e. non-fatal cardiac arrest), they may
present with a range of aetiologies including genetic disorders for which genetic
testing is already described in this document. Detailed clinical screening is warranted
with emphasis of finding evidence for these aetiologies.
5
If no cause is detectable, the subject is described as UCA, or IVF. Idiopathic ventricular
fibrillation is defined as a resuscitated cardiac arrest victim with a normal ECG,
preferably with documentation of VF, in whom known cardiac, respiratory, metabolic,
and toxicological causes have been excluded through clinical evaluation.
6,
15
It is estimated to account for ∼5–7% of all out-of-hospital cardiac arrests.
422,
423
Genetic investigation of case series of UCA survivors have employed a mixture of cardiac
panels and exome sequencing, identifying a yield of channelopathy- and cardiomyopathy-associated
putative pathogenic variants ranging from 3% to 27%.
424–426
This heterogeneity likely reflects differences in genes studied, adjudication of variant
pathogenicity, patient sub-phenotypes and variability in diagnostic conclusions. Importantly,
pathogenic variants in cardiomyopathy genes, especially ACM, in UCA survivors without
a cardiomyopathic phenotype suggest an underlying concealed structural substrate.
Phenotypes may, however, evolve over time in some cases.
427
The most robust genetic finding has been a Dutch founder haplotype at the DPP6 gene
associated with short-coupled-VF. No other genetic defects in or around the DPP6 gene
have been reported in other UCA populations.
428
In other patients with short-coupled-VF RyR2 variants have been identified and it
appears that these variants are characterized by a loss of function phenotype.
161,
162,
429,
430
A term CRDS has been coined for this condition.
161
The role of genetic testing after a sudden unexpected death or cardiac arrest is visualized
in Figure 6
. Recently, WES with virtual panel analysis performed systematically in 228 survivors
of cardiac arrest of uncertain aetiology was shown to identify a pathogenic variant
in 10% of cases.
421
Figure 6
Flowchart of the work up of a sudden cardiac death or non-fatal cardiac arrest.
Recommendations
Consensus statement instruction
Ref
Genetic testing for patients with congenital heart disease (CHD) should prioritize
the personal goals and preferences of the patient, parents or guardian, require pre-test
genetic counseling and should be coordinated by multidisciplinary teams with expertise
in genetics of CHD.
Antenatal testing
When foetal congenital heart disease (CHD) is identified on antenatal ultrasound examinations,
a chromosomal microarray (CMA) or CNV sequencing (CNV seq) of foetal tissue [amniocentesis
or chorionic villous sample (CVS)] should be offered.
431–433
Trio WES on amniocentesis or CVS samples may be performed in prenatal cases with syndromic
and/or complex CHD.
431–433
Neonates and infants requiring investigation or procedures for complex CHD
CMA or CNV seq is indicated in infants with CHD to identify pathogenic CNVs.
434
, Expert opinion
Standard karyotype analysis may be performed in infants with CHD (or in parents of
children with pathogenic CNVs) to identify balanced translocations.
Expert opinion
Trio WES or WGS may be performed in infants with complex CHD to identify pathogenic
variants/indels, contributing to prognostication for extracardiac outcome and for
cardiac outcome.
435
, expert opinion
Targeted CHD gene panels to identify variants in a set of CHD-related genes may be
performed in infants with complex CHD.
436
, Expert opinion
Patients with CHD and extracardiac anomalies
CMA or CNV seq is indicated in patients with CHD and extracardiac anomalies to identify
pathogenic CNVs.
437
Trio testing for de novo or inherited (autosomal or X-linked recessive) pathogenic
variants with either WES or WGS should be performed in patients with CHD and extracardiac
anomalies.
438–440
Familial forms of CHD
WES/WGS of the affected family members should be performed in families with at least
two first degree relatives with heterotaxy or CHD.
441–444
Targeted analysis of a specific gene may be performed if the CHD type is highly suggestive
of a specific gene.
442
, Expert opinion
Sporadic non-syndromic CHD (excl. neonates or infants)
CMA or CNV seq for pathogenic CNVs may be performed in older individuals with sporadic
non-syndromic CHD.
434,
445
Trio testing for de novo or inherited (autosomal or X-linked recessive) pathogenic
variants with either WES or WGS in older patients with sporadic non-syndromic CHD
has a low diagnostic yield and limited utility, and should not be performed routinely.
440
, Expert opinion
Heterotaxy
WES/WGS of the affected family members should be performed in families with at least
two first degree relatives with CHD.
446,
447
Trio testing for de novo or inherited (autosomal or X-linked recessive) pathogenic
variants with either WES or WGS should be performed in patients with syndromic heterotaxy
(e.g. primary ciliary dyskinesia).
446,
448
Routine trio testing for de novo or inherited (autosomal or X-linked recessive) pathogenic
variants with either WES or WGS should not be performed in patients with sporadic
non-syndromic heterotaxy.
446
; expert opinion
State of genetic testing for congenital heart disease
Background
Genetic testing in patients with CHD (Table 18
) is moving rapidly, with recent definition of patient subgroups most likely to achieve
a genetic diagnosis, beyond well-known causes such as Down syndrome and velocardiofacial
syndrome (Figure 7
).
Figure 7
Genetic causes of congenital heart defects. Non-syndromic (lower panel) and syndromic
(upper panel) cohorts. The diagram in the left panel displays the relative prevalence
of the three broad CHD subgroups, namely syndromic CHD, sporadic non-syndromic CHD,
and familial non-syndromic CHD. The diagrams in the central panel display the current
yield of standard karyotyping, CMA and WES/WGS in the non-syndromic (lower panel)
and syndromic (upper panel) cohorts, respectively, illustrating the low diagnostic
yield in sporadic non-syndromic CHD, compared to the syndromic cohort. The pie diagrams
at the right display the most common causes of aneuploidies and of CNVs, and the inheritance
pattern of single gene defects. The percentages displayed in the diagrams are based
on.
440,
441,
445,
463,
464
CHD, congenital heart defect; CNV, copy number variant; T13, trisomy 13; T18, Trisomy
18; T21, trisomy 21; WBS, Williams–Beuren syndrome.
Table 18
Categories of CHD
Category
Definition
Primary type/s of causative genetic variants
Diagnostic yielda
CMA
WES
WGS
b
Syndromic (CHD+ECA)
CHD seen in conjunction with extracardiac anomalies including (but not limited to)
neurological, cranio-facial, limb, growth, skeletal, and genitourinary differences
de novo
c
or inherited CNVs and SNVs
∼3–25%
∼25%
∼41%
Non-syndromic, inherited
CHD seen without features suggestive of a genetic syndrome, often affecting multiple
family members
Inherited SNVs
Unknown
∼31–46%
∼36%
Sporadic
CHD without a suspected hereditary component and without being associated with a known
syndrome
Multiple variants contributing synergistically
∼3–10%
∼2–10%
d
∼10%
a
Based on literature with clinically applicable results, i.e. studies conducting clinical
evaluations of variants according to ACMG guidelines.
69
b
Based on our clinical experience in conjunction with Alankarage et al., 2019.
441
c
De novo, not inherited from either parent.
d
Based on large cohort-based studies without clinical evaluation of variants. Information
presented is collated from research reported in refs
439–442,
444,
454–457
and modified from ref.
458
CHD, congenital heart disease; CMA, chromosome microarray; CNV, copy number variant;
ECA, extracardiac anomaly; SNV, single-nucleotide variant; WES, whole-exome sequencing;
WGS, whole-genome sequencing.
A genetic diagnosis usually has little impact on treatment of the CHD itself but may
assist in risk stratification
449
and influence priorities during follow-up, such as surveillance for AV block in patients
with pathogenic variants in NKX2.5
450
or TBX5, or screening for extracardiac features, such as immune dysfunction in 22q11
deletion syndrome or platelet dysfunction in Noonan syndrome.
451
Some forms of inherited cardiovascular disease, such as the arrhythmia syndromes,
involve a relatively small number of genes, with tight genotype-phenotype relationships,
supportive functional data and well-established prognostic implications. In contrast,
CHD has a large number of genes that are implicated in the development of CHD, with
at least 130 genes identified as having a role in causation of human CHD, presenting
either in isolation or in association with extra-cardiac features (see http://chdgene.victorchang.edu.au/).
This includes genes associated with heterotaxy syndromes, which are sometimes present
in patients with single ventricles and other rare CHD subtypes. Of note, no ClinGen
curation yet exists for CHD genes, and for some putative CHD genes, further genomic
and functional studies are required to confirm their role in CHD. Even for established
CHD genes, variant interpretation is frequently complicated by the fact that CHD often
affects singletons, precluding segregation analysis, and when it aggregates in families,
is associated with reduced penetrance and variable expressivity. Nevertheless, a molecular
diagnosis may be relevant in pre-conception counselling and carries numerous psychological
benefits as well.
452
Indications for genetic testing vary according to age and mode of presentation, such
as the severity of a CHD, the type of CHD, the presence of extracardiac features and
the presence of non-genetic factors predisposing to CHD. The diagnosis of a monogenic
cause of CHD is less likely when environmental factors occur, such as twin-to-twin
transfusion, prematurity-associated patent ductus arterious, or maternal risk factors.
453
Extracardiac features, such as developmental delay, growth delay or facial dysmorphic
features, are not apparent in foetuses or infants. Early genetic diagnosis can help
to differentiate between syndromic and non-syndromic CHD, contributing to prognostication
for cardiac and extracardiac outcome in these patients.
Antenatal testing
When fetal cardiac anomalies are identified on ultrasound assessments and fetal aneuploidies
are excluded, chromosomal microarray (MCA) or copy number sequencing (CNV seq) on
DNA derived from amniocentesis specimens or chorionic villous samples (CVS) detect
pathogenic chromosomal abnormalities in about 10–15% of fetuses with CHD.
465,
466
In those with normal CMA or CNVseq, a genetic diagnosis is made by subsequent prenatal
trio whole exome sequencing (WES) in 5–12%.
441
The yield of prenatal CMA or WES varies according to presence of extracardiac anomalies
and type of CHD.
465,
466
Some CHD types have a low positive predictive value for being associated with chromosomal
anomalies, while other CHD types have a higher likelihood of being caused by a pathogenic
variant in a specific gene for syndromic or isolated CHD.
465
When offering prenatal genetic testing for CHD, expert advice should be sought to
counsel on expected yield and on potential risks of amniocentesis or CVS, and personal
goals and preferences of the parents should be prioritized.
467
When these conditions are met, prenatal CMA or CNVseq can be offered for fetal CHD.
439–441
Trio whole exome sequencing (WES) on amniocentesis or CVS can be considered in prenatal
cases with syndromic and/or complex CHD where the anticipated post-natal course carries
a high risk of morbidity or mortality.
439–441
Antenatal screening
Routine antenatal testing on amniocentesis or CVS is focused on the identification
of major chromosomal abnormalities including Trisomy 13, 18, 21 and 22q11 deletion,
responsible for velocardiofacial syndrome, and should be offered to any patient pursuing
invasive prenatal diagnosis without prior knowledge of cardiac or other malformations.
459
Cell-free DNA testing on a maternal blood sample is emerging as a non-invasive means
of aneuploidy screening for foetuses with no apparent structural abnormalities although
this approach currently lacks resolution in definition of sub-microscopic chromosomal
anomalies.
460–462
Neonates and infants requiring investigation or procedures for congenital heart disease
Testing for pathogenic chromosomal CNVs by CMA or CNV seq should be performed.
434
These techniques have essentially replaced standard karyotype analysis as first line
testing, although conventional karyotyping may be performed particularly in assessment
of balanced translocations. Testing for SNVs or small insertion/deletions can be considered,
although yield in sporadic cases is low.
435
For these variants, WES or WGS are replacing ‘CHD’ ‘panels’ (usually comprising 10–40
genes
436
) considering the low diagnostic yield of CHD gene panels and the ability to re-interrogate
WES/WGS results taking into consideration future findings.
Patients with congenital heart disease and extracardiac anomalies
Patients with CHD and extracardiac anomalies, including additional major congenital
anomalies (with functional consequences and/or requiring treatment), dysmorphism (association
of at least three dysmorphic features), abnormal growth, and neurodevelopmental abnormalities,
are regarded as syndromal forms of CHD, and collectivel account for around 20% of
the total CHD cohort. Patients with syndromic CHD should undergo CMA or CNV seq,
437
followed by trio testing for de novo or inherited (primarily autosomal or X-linked
recessive) pathogenic SNVs with either WES or WGS if CMA is not diagnostic, because
of the substantial rate of achieving a genetic diagnosis in ∼25–40%.
438
Given its potential to detect both CNVs and SNVs, WGS has shown promise in becoming
a first tier analysis in syndromic CHD. De novo variants account for ∼90% of these
genetic causes.
439,
440
Familial forms of congenital heart disease
In patients with familial forms of CHD (one or more affected first degree relative),
inherited single-gene defects may be identified by WES. The diagnostic yield with
two affected family members is conventionally thought to be around 10% with a substantially
higher yield when three or more are affected.
441
Families with at least two first degree relatives with CHD may benefit from WES/WGS
of the affected family members.
441–444
In some families, the CHD type is highly suggestive of a specific gene (e.g. ELN pathogenic
variants in supravalvar aortic stenosis without Williams–Beuren syndrome) (see Table 19
). In such families targeted analysis of this specific gene can be considered, followed
by WES if this initial investigation is negative.
442
Table 19
Non-exhaustive list of high confident genes for non-syndromic human CHD
Familial non-syndromic CHD
Gene
Inheritance
Atrial septal defect
GATA4
AD
Atrial septal defect (with or without atrioventricular conduction block)
NKX2.5
AD
TBX5
AD
*
Atrioventricular septal defect
CRELD1
AD
NR2F2
AD
Supravalvar aortic stenosis
ELN
AD
Aortic valve stenosis
NOTCH1
AD
TAB2
AD
**
Tetralogy of Fallot
NOTCH1
AD
FLT4
AD
Patent ductus arteriosus
TFAP2B
AD
***
Heterotaxy
ACVR2B
AD
CFC1
AD
NODAL
AD
CCDC11
AR
CFAP53
AR
PKD1L1
AR
ZIC3
XL
Pathogenic variants in TBX5, TAB2, and TFAP2B can cause non-syndromic CHD, or may
be associated with *hand anomalies, **connective tissue disorder, or ***facial dysmorphism.
Sporadic non-syndromic congenital heart disease
Congenital heart disease with no syndromal or familial pattern should be considered
as being of ‘undetermined cause’ because only a small proportion of these patients
will have single-gene variants that may be identified with WGS or WES (<5%).
434,
440,
445
Routine testing of such patients remains in the realm of research and is not currently
justified in clinical practice. Some apparently non-syndromic infants will later present
with syndromic associations including developmental delay, and would be considered
for genetic testing, highlighting the difficulty in defining access to testing on
the basis of categorization early in life.
Heterotaxy
Diagnostic genetic testing strategy for patients with heterotaxy, defined as left-right
patterning anomalies of the thoracic and/or abdominal organs, is in line with that
proposed for CHD: WES or WGS should be offered to familial heterotaxy and to syndromic
patients (e.g. primary ciliary dyskinesia), but is a lower priority for heterotaxy
patients with no syndromic appearance or familial occurrence.
446–448
We summarize recommendations for genetic testing in the different categories in the
table of recommendations. These recommendations should be applied (1) in consideration
of technology availability, access and health insurance issues and sociocultural differences,
(2) in the light of shared decision making between a trained healthcare professional
and the patient, parents or guardian, and (3) only if adequate pre- and post-test
counseling can be guaranteed. Genetic testing in the pediatric domain should be coordinated
between cardiology and clinical genetics specialists, with support by genetic counselors
and ideally a multidisciplinary clinic for return of results and liaison with genetic
pathologists and developmental biologists. Thus, identification of congenital heart
disease should prompt a referral to a center specializing in pediatric cardiovascular
genetics.
State of genetic testing for coronary artery disease and heart failure
Some inherited conditions may lead to coronary artery disease. For example, monogenic
predisposition to familial hypercholesterolaemia is a powerful predictor of premature
coronary artery disease.
468
The major genes are APOB, LDLR, PCSK9. Over the past two decades, a widespread contribution
of polygenic risk to coronary artery disease susceptibility has been demonstrated.
469,
470
Novel genetic susceptibility mechanisms including clonal haematopoiesis of indeterminate
potential, a somatic rather than germline genetic process, have also been shown to
play a role in coronary artery disease susceptibility recently.
471
Genetic evaluation in clinical practice is currently directed at identifying individuals
with an inherited predisposition to coronary artery disease that may enable a mechanistic
understanding of the disease, and inform carrier testing. Although research indicates
that genetic predisposition may be useful for risk prediction both in primary and
secondary prevention settings,
4,
63,
64,
472
the predictive utility of polygenic risk scores for coronary artery disease are debated
473,
474
and such scores are not routinely used in clinical practice. Data have also emerged
to indicate that risk reduction after treatment with statins
475
or proprotein convertase subtulisin/kexin type 9 (PCSK9) inhibitors
63,
64
may be greatest for individuals with the highest inherited burden of polygenic predisposition
to coronary artery disease. Despite rapid innovations in the understanding of both
inherited and somatic genetic variation that may underlie coronary artery disease,
and despite increasing development of comprehensive polygenic risk assays for coronary
artery disease and component clinical risk factors, clinical genetic testing is largely
focused on addressing low-density lipoprotein, an underlying treatable clinical risk
factor for coronary artery disease.
Genetic testing for heart failure is in some sense a superset of the earlier sections
on genetic testing for cardiomyopathy. In patients with ischaemic cardiomyopathy,
testing should be considered according to the recommendations in the paragraph above
for coronary artery disease; there is currently no further indication for testing
with respect to the presentation of heart failure as a result of coronary artery disease.
In cases where patients present with heart failure with preserved or reduced ejection
fraction with an apparent explanatory cause such as uncontrolled hypertension or valve
disease there is also currently no indication for genetic testing. Heart failure that
is unexplained should always lead to a detailed family history and if a Mendelian
pattern of inheritance is suggested, then panel testing for cardiomyopathy should
proceed as described earlier in this document. In (young) cases of heart failure with
no apparent cause and no family history, or in cases where alcohol or pregnancy appear
to be co-factors, many would consider Mendelian panel testing, particularly because
of the demonstrated contribution from modifying effects of titin loss-of-function
variants. While genome wide association studies for heart failure and for LV remodelling
are now published, and while this polygenic tail would be expected to modify Mendelian
causes of heart failure, such tools have yet to be translated into predictive scores
that would provide utility in a clinical setting.
Conclusion and future directions
In the past decade, we have seen significant progress in genetic testing of the inherited
cardiovascular diseases. Understanding of the genetic basis of disease has improved
both in terms of new disease genes, as well as new genetic mechanisms such as oligogenic
disease and the emergence of polygenic risk scores. At the present time, cardiovascular
genetic testing already offers numerous benefits in terms of more diagnostic precision,
influencing therapeutic options, and informing prognosis. Indeed ‘genetic cardiology’
is recognized as a new field, with such sub-specialty experts needed to facilitate
the translation of genetic findings into improved clinical care. While great progress
has been made, new challenges and gaps in our knowledge remain, including the accurate
classification and interpretation of variants, robust curation of potentially new
disease genes, and understanding variable phenotype penetrance both within and between
families. Furthermore, understanding the genetic landscape of cardiovascular diseases
in other ethnic populations with different genetic backgrounds will be important to
ensure the benefits of genetic testing are realized on a truly global scale.
Looking to the future, with the advances being made in the field of gene therapy,
the identification of the patient’s fundamental disease-causative substrate may enable
not only genotype-guided therapies but also gene-specific, even pathogenic variant-specific
therapies.
23,
476
For AR disorders like TKOS, a molecular diagnosis could permit ‘gene replacement’
therapies. However, most genetic heart conditions are AD conditions resulting in either
haploinsufficiency or a dominant negative state. For some, allele-specific oligonucleotide/short
interfering RNA (siRNA) therapies to knock down the mutant allele may be sufficient.
477,
478
This gene therapy strategy requires a novel therapeutic for each pathogenic variant
however. Similarly, gene-editing with CRISPR/Cas9-based strategies requires a unique
effort for each pathogenic variant.
479
For those genetic heart diseases with hundreds of unique disease-causative variants
within each disease-susceptibility gene, a gene-editing solution may not be feasible.
Most recently, proof-of-principle for a gene-specific gene therapy solution has been
provided. This therapy, called Suppression-Replacement (SupRep) gene therapy envisions
the AAV9 delivery (or some future iteration) of the therapeutic cargo containing a
single, gene-specific siRNA to knockdown both the mutant allele and the wild type
allele, followed by a bio-engineered complementary DNA (cDNA) of the gene of interest
that is immune to siRNA-mediated knockdown.
480
Regardless of the underlying gene therapy strategy being explored, numerous obstacles
will need to be overcome before these promising in vitro data will be translated into
available therapies in humans.
Funding
J.B. is supported by a senior clinical investigator fellowship by the FWO – Flanders.
Supplementary Material
euac030_Supplementary_Data
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