Gene organization and rearrangements at the human Rhesus blood group locusrevealed by fiber-FISH analysis

The human Rhesus (Rh) blood group locus is composed of two highly homologou s genes, the RHD and RI-ICE genes on chromosome I, encoding the D, C/c, and E/e antigens in common Rh-positive phenotypes. In general, the RND gene is either absent or grossly deleted in Rh-negative individuals. In this study , gene organization at the RH locus of Japanese donors with different serol ogical phenotypes was directly analyzed by two-color fluorescence in situ h ybridization on DNA fibers released from their lymphocytes (fiber-FISH) and by using DNA probes of introns 3 and 7 of the RHCE and RHD genes. Six Rh-p ositive samples (two with the D+C-c+E+e-, two with the D+C+c-E-e+, and two with the D+C+c+E+e+ phenotype) showed the presence of two REI genes within a region of less than 200 kb on chromosome 1p36.1. Of great interest was th e finding that the genes were arranged in the antidromic order of the telom ere - RHCE (5'-->3') - RHD (3'-->5') - centromere. On the other hand, two t ypical Rh-negative samples (D-C-c+E+e+) showed the presence of only one RHC E gene, as expected. Moreover, further analysis combined with a locus-speci fic assay of three Rh-negative samples (D-C+c+E+e+, D-C+c+E-e+, and D-C+c-E -e+) showed the possible presence of the RND gene(s) and complex rearrangem ents, including partial deletion, duplication, and recombination, in this r egion; these could be responsible for the Rh-negative phenotype.