C9orf72 hexanucleotide repeat expansions as the causative mutation for chromosome 9p21-linked amyotrophic lateral sclerosis and frontotemporal dementia.

To further assess the presence of a large hexanucleotide repeat expansion in the first intron of the C9orf72 gene identified as the genetic cause of chromosome 9p21-linked amyotrophic lateral sclerosis and frontotemporal dementia (c9ALS/FTD) in 4 unrelated families with a conclusive linkage to c9ALS/FTD. A repeat-primed polymerase chain reaction assay. Academic research. Affected and unaffected individuals from 4 ALS/FTD families. The amplified C9orf72 repeat expansion. We show that the repeat is expanded in and segregated perfectly with the disease in these 4 pedigrees. Our findings further confirm the C9orf72 hexanucleotide repeat expansion as the causative mutation for c9ALS/FTD and strengthen the hypothesis that ALS and FTD belong to the same disease spectrum.