The STR polymorphisms in intron 8 may provide information about the molecular evolution of RH haplotypes

We identified simple-sequence repeat polymorphisms in intron 8 of the RHD and RHCE genes, both of which contained the 5-bp repeat unit (AAAAT)n. We analyzed the polymorphisms of this short tandem repeat (STR) in 104 Japanese RhD-positive and 124 RhD-negative (87 RHD gene negative and 37 nonfunctional RHD gene positive) donors by the polymerase chain reaction (PCR) and subsequent typing by electrophoresis and silver staining. We found five alleles (10, 11, 12, 13, and 14 repeats) in the RHD gene and four (7, 8, 9, and 10 repeats) in the RHCE gene. The Rh phenotypes were closely associated with polymorphisms of the STR. The Ce allele had 12 repeats in the RHD gene and 9 repeats in the RHCE gene at high frequency. The cE allele frequently had 10-12 repeats in the RHD gene and 10 repeats in the RHCE gene. The 10 repeats in the RHCE gene were identified exclusively in the 87 RHD gene-negative donors and 9 repeats were identified only in those with the RhC antigen. These results indicate that both haplotypes of dce and dcE arose from single RHD gene deletion and recombination events, respectively. In the 37 RhD-negative donors with a nonfunctional RHD gene, 12 repeats in the RHD gene and 9 repeats in the RHCE gene were frequently observed. Thus, the RhD-negative with a nonfunctional RHD gene combination might have arisen from the DCe haplotype via a mutation that abolished RHD gene expression. These findings suggest that the STR polymorphisms might shed light upon the molecular evolution of RH haplotypes.