Frequency and characterization of known and novel RHD variant alleles in 37 782 Dutch D-negative pregnant women.

To guide anti-D prophylaxis, Dutch D- pregnant women are offered a quantitative fetal-RHD-genotyping assay to determine the RHD status of their fetus. This allowed us to determine the frequency of different maternal RHD variants in 37 782 serologically D- pregnant women. A variant allele is present in at least 0·96% of Dutch D- pregnant women The D- serology could be confirmed after further serological testing in only 54% of these women, which emphasizes the potential relevance of genotyping of blood donors. 43 different RHD variant alleles were detected, including 15 novel alleles (11 null-, 2 partial D- and 2 DEL-alleles). Of those novel null alleles, one allele contained a single missense mutation (RHD*443C>G) and one allele had a single amino acid deletion (RHD*424_426del). The D- phenotype was confirmed by transduction of human D- erythroblasts, consolidating that, for the first time, a single amino acid change or deletion causes the D- phenotype. Transduction also confirmed the phenotypes for the two new variant DEL-alleles (RHD*721A>C and RHD*884T>C) and the novel partial RHD*492C>A allele. Notably, in three additional cases the DEL phenotype was observed but sequencing of the coding sequence, flanking introns and promoter region revealed an apparently wild-type RHD allele without mutations.

RHD and RHCE variant and zygosity genotyping via multiplex ligation-dependent probe amplification.

BACKGROUND: The presence of a D variant may hamper correct serologic D typing, which may result in D immunization. D variants can be determined via RHD genotyping. However, a convenient single assay to identify D variants is still lacking. We developed and evaluated a multiplex ligation-dependent probe amplification (MLPA) assay to determine clinically relevant RHD and RHCE variant alleles and RHD zygosity. STUDY DESIGN AND METHODS: We analyzed 236 cases (73 normal and 163 selected samples) with the RH-MLPA assay, which is able to determine 79 RHD and 17 RHCE variant alleles and RHD zygosity. To confirm the results, mutations were verified by RHD and/or RHCE exon-specific sequencing and RHD zygosity was verified by quantitative real-time polymerase chain reaction (PCR) for 18 cases. RESULTS: In 99% of the cases, the RH-MLPA assay correctly determined whether a person carried only wild-type RHD and RHCE alleles (n = 69) or (a) variant RHD allele(s) and/or (a) variant RHCE allele(s) (n = 164). In only three cases, including two new RHD variant alleles, the variant allele was not identified, due to lack of detecting probes. These were RHD*DCS2, a new partial RHD allele, RHD*525T (Phe175Leu), and a new D- null allele, RHD*443G (Thr148Arg). All RHD (n = 175) and RHCE variant alleles (n = 79) indicated by the RH-MLPA assay were confirmed by sequencing. RHD zygosity was confirmed by quantitative PCR. Two hematopoietic chimeras were recognized. CONCLUSION: The RH-MLPA genotyping assay is a fast, easy, and reliable method to determine almost all clinically relevant RHD and RHCE variant alleles, RHD zygosity, and RHD+/RHD- chimeras in blood donors, blood recipients, and pregnant women.