The human Rhesus (Rh) blood group is determined by 2 highly homologous
RH genes,
RHD and
RHCE. These genes are located on chromosome 1p36.1, a genomic region representing copy number variation. In Rh-positive individuals, both
RHD and
RHCE genes are present, while in most Rh-negative individuals
RHD genes are missing and are homozygous for a single
RHCE gene. Some individuals with a serologically Rh-negative phenotype were diagnosed to be
RHD-gene positive by a locus-specific DNA assay using polymerase chain reactions with sequence-specific primers (PCR-SSP). Therefore, the current PCR-based assay, examining the presence or absence of partial sequences of
RHD genes, does not necessarily produce correct typing results. Alterations in the genomic structure of
RHD that cause negative gene expressions are difficult to detect by the PCR-based assay because of highly homologous sequences of the 2
RH genes. In the present study, we examined, by extended chromatin fiber fluorescence
in situ hybridization (fiber-FISH) with 2 DNA probes for introns 3 and 7 of the
RH genes, the genomic structure of the
RH gene region in 6 Rh-negative Japanese donors whose genotype was diagnosed as
RHD-gene positive by the PCR-SSP assay. We demonstrated that varied sizes of deletion and/or insertion in the
RH loci caused the Rh-negative phenotype.
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