16Cys encoded by the RHce gene is associated with altered expression of the e antigen and is frequent in the R-0 haplotype

Serological observations have suggested that numerous D, many e (especially in Blades), several E, and rare c variants exist within the Rh blood group system. The molecular basis for expression of many of these variants has b een elucidated. This study describes five unrelated Caucasians whose red bl ood cells reacted with polyclonal anti-e but did not react with some monocl onal anti-e, which suggested that they carried a variant e antigen. Molecul ar investigation revealed the presence of a 48G -->C change (encoding cyste ine instead of tryptophan at amino acid 16) in their RHce gene. No other di fferences were found, which suggests that amino acid residues located in th e first transmembrane region can affect expression of the e antigen, whose critical residues are on the predicted fourth external loop of the protein, This polymorphism has not previously been observed because polyclonal anti -e does not distinguish this variant from wild type. This position is polym orphic in RHce alleles and the presence of the 48C nucleotide is often foun d in the R-0(Dce) haplotype.