Involvement of Gly96 in the formation of the Rh26 epitope

BACKGROUND: The Rh system, a complex blood group system, comprises at least 45 antigens. Red cells expressing c usually express Rh26. Rare cells that are c+ Rh:‐26 give variable reactions with anti‐c and may have weak expression of f (ce). STUDY DESIGN AND METHODS: Serologic and molecular studies were performed with red cells from persons with the c+ Rh:‐26 phenotype occurring in two unrelated Dutch families. Red cells of 11 members of these two families were typed for Rh26, for c (with monoclonal and polyclonal reagents), and for f (ce). The cDNA of three donors was sequenced, while restricted DNA analysis was carried out on material from available members of the two families. RESULTS: Serologic tests showed that the rare c+ Rh:‐26 phenotype was associated with a weak expression of c and a normal expression of f. The cDNA analysis of three members of one family revealed a single‐point mutation (G286A) in exon 2 of the ce allele. Allele‐specific primer amplification, polymerase chain reaction followed by allele‐specific restriction analysis, and single‐strand conformation polymorphism showed the same polymorphism in all other members of both families, whereas it was absent in 80 control donors. CONCLUSION: The c+ Rh:‐26 phenotype, identified in two families, is associated with a single‐ point mutation at nucleotide 286 (G286A) in the ce allele, which predicts a Gly96Ser amino acid substitution. This substitution also affects c, because all anti‐c reagents reacted more weakly. Other polymorphic sites apparently are involved in the formation of the Rh26 epitope as well, because Rh26 is expressed only on the c polypeptide, whereas Gly96 is expressed on all polypeptides.