Genetic basis of the RhD-positive and RhD-negative blood group polymorphism as determined by Southern analysis

Several lines of evidence have previously indicated that the RhD, c, and E blood group antigens are most likely carried by three distinct but homologous red blood cell membrane proteins. To determine whether these polypeptides are encoded by one or several related genes, we have performed Southern blot analysis of genomic DNA prepared from donors of different Rh phenotypes. Using an entire Rh cDNA probe and several exon- specific probes covering the cloned gene from its 5′ to 3′ ends, we have shown that the Rh locus carried by the genome of RhD-positive individuals is composed of two different but strongly related genes of identical general organization whether they expressed the C or c and E or e antigens, and, surprisingly, even when they do not express these epitopes, as in the D-- phenotype. The only antigenic variation found to be associated with a consistent genomic polymorphism corresponded to the RhD-positive/RhD-negative phenotypes. Indeed, one of the two Rh genes was completely lacking when the genomes of several unrelated RhD- negative donors were analyzed. From the present study we conclude that one of the two genes of the Rh locus encodes the RhC/c and RhE/e polypeptides while the other encodes the RhD protein. The absence of any D gene and of its postulated allelic form d in the RhD-negative genome explains finally why no Rhd antigen has ever been shown.