RHD gene polymorphisms among RhD-Negative Chinese in Taiwan

Background and Objective: The rare occurrence of anti-D-associated hemolytic disease of the newborn among Chinese is attributable in part to the existence of the weak D phenotype D(el) among apparently RhD-negative individuals. While exciting advances in the molecular genetics of the Rh blood group have been noted in recent years, the genomic structure of the D(el) phenotype has seldom been studied in the literature. We try to explore the genomic structure of the RhD gene among apparently Rh-negative Chinese in Taiwan in this study. Methods: Genomic DNA from 230 samples of apparently RhD-negative Chinese was studied using four polymerase chain reaction (PCR-based RhD typing methods. These PCR methods amplified RHD and RHCE genes at exons 4, 5, 7 and 10. All nucleotides responsible for exofacial amino acid differences between RhD and RhCeEe peptides, including amino acids 169, 170, 172, 223, 226, 233, 238, 350, 353, and 354, were contained in these amplified DNA segments. Southern blot analysis using RHD cDNA fragments as probes was performed. Results: According to the serological study, 155 samples (67.4%) were genuinely RhD-negative and 75 samples (32.6%) were of the D(el) phenotype. Successful amplifications for RHD sequences were possible in all 75 D(el) samples using four PCR methods. Apparently, all D(el) individuals carried an intact RHD gene. While 145 individuals of 155 genuinely Rh-negative (63.0% of apparently RhD-negative individuals) had total deletion of their RHD genes, 10 individuals (4.3% of apparently RhD-negative individuals) were shown to have a preserved 3' noncoding region of the RHD exon 10 and a gross deletion of RHD exons 4-10. Conclusions: Three classes of RhD-negative polymorphisms among Chinese in Taiwan were observed. These included D(el) with grossly intact RHD and weak RhD expression, genuinely RhD-negative with partial preservation of the RHD gene, and genuinely RhD-negative with total deletion of the RHD gene. A molecular study is warranted to clarify the mechanism responsible for the weak RHD gene expression in D(el) individuals.