Genotype analysis to clarify RhD variants in discrepant samples of Chilean population

The Rh blood group system is one of the most polymorphic and immunogenic systems known in humans. In the past decade, intense investigation has yielded considerable knowledge of the molecular background of this system. The genes encoding 2 distinct Rh proteins that carry C or c together with either E or e antigens, and the D antigen, have been cloned, and the molecular bases of many of the antigens and of the phenotypes have been determined. A related protein, the Rh glycoprotein is essential for assembly of the Rh protein complex in the erythrocyte membrane and for expression of Rh antigens. The purpose of this review is to provide an overview of several aspects of the Rh blood group system, including the confusing terminology, progress in molecular understanding, and how this developing knowledge can be used in the clinical setting. Extensive documentation is provided to enable the interested reader to obtain further information. (Blood. 2000;95:375-387) Show more

The Rh blood group antigens derive from 2 genes, RHD and RHCE, that are located at chromosomal position 1p34.1-1p36 (chromosome 1, short arm, region 3, band 4, subband 1, through band 6). In whites, a cde haplotype with a deletion of the whole RHD gene occurs with a frequency of approximately 40%. The relative position of the 2 RH genes and the location of the RHD deletion was previously unknown. A model has been developed for the RH locus using RHD- and RHCE-related nucleotide sequences deposited in nucleotide sequence databases along with polymerase chain reaction (PCR) and nucleotide sequencing. The open reading frames of both RH genes had opposite orientations. The 3' ends of the genes faced each other and were separated by about 30 000 base pair (bp) that contained the SMP1 gene. The RHD gene was flanked by 2 DNA segments, dubbed Rhesus boxes, with a length of approximately 9000 bp, 98.6% homology, and identical orientation. The Rhesus box contained the RHD deletion occurring within a stretch of 1463 bp of identity. PCR with sequence-specific priming (PCR-SSP) and PCR with restriction fragment length polymorphism (PCR-RFLP) were used for specific detection of the RHD deletion. The molecular structure of the RH gene locus explains the mechanisms for generating RHD/RHCE hybrid alleles and the RHD deletion. Specific detection of the RHD(-) genotype is now possible. (Blood. 2000;95:3662-3668) Show more

Antigens of the Rh blood group system are encoded by 2 homologous genes, RHD and RHCE, that produce 2 red cell membrane proteins. The D-negative phenotype is considered to result, almost invariably, from homozygosity for a complete deletion of RHD. The basis of all PCR tests for predicting fetal D phenotype from DNA obtained from amniocytes or maternal plasma is detection of the presence of RHD. These tests are used in order to ascertain the risk of hemolytic disease of the newborn. We have identified an RHD pseudogene (RHD psi) in Rh D-negative Africans. RHDpsi contains a 37 base pair (bp) insert in exon 4, which may introduce a stop codon at position 210. The insert is a sequence duplication across the boundary of intron 3 and exon 4. RHDpsi contains another stop codon in exon 6. The frequency of RHDpsi in black South Africans is approximately 0.0714. Of 82 D-negative black Africans, 66% had RHDpsi, 15% had the RHD-CE-D hybrid gene associated with the VS+ V- phenotype, and only 18% completely lacked RHD. RHDpsi is present in about 24% of D-negative African Americans and 17% of D-negative South Africans of mixed race. No RHD transcript could be detected in D-negative individuals with RHDpsi, probably as a result of nonsense-mediated mRNA decay. Existing PCR-based methods for predicting D phenotype from DNA are not suitable for testing Africans or any population containing a substantial proportion of people with African ethnicity. Consequently, we have developed a new test that detects the 37 bp insert in exon 4 of RHDpsi. (Blood. 2000; 95:12-18) Show more