[Molecular approaches to the Rh blood group system]

The Rh system clinically is one of the important blood groups. The major Rh antigens are RhD, RhC/c, and RhE/e, which are carried by two integral membrane polypeptides consisted of 416 amino acids. These polypeptides are encoded by two closely related genes, RHD and RHCE. Both RH genes are composed of ten exons. It is thought that multiple recombinations, nucleotide substitutions, large nucleotide gaps (due to Alu sequence), and high level of the homology between the RHD and RHCE genes are the important factors in the formation and evolution of these genes. The RHD gene is deleted in most white individuals who lack the RhD antigen, while 12% of Japanese individuals have an RHD gene. Molecular analyses have elucidated the background of various Rh-related variants; D--, partial D, weak D, and Rhnull. The Rhnull phenotype is divided into the most common type by the Rhnull regulator gene and second type by the amorph gene that arose by homozygosity of a silent allele at the RH locus. The RhAG glycoprotein has been regarded as a most critical Rhnull gene of the reglurator type and a critical co-expressing factor of the Rh polypetides on red blood cells. Studies on the autoantibodies against red blood cells in aoutoimmune hemolytic anemia have suggested that the public epitopes of autoantigens exist on the Rh polypeptides.