A novel single missense mutation identified along the RH50 gene in a composite heterozygous Rhnull blood donor of the regulator type

Abstract

Rare individuals who lack all of the Rh blood group antigens are called Rh null and may be classified as ''regulator'' or ''amorph'' types. The suppression of Rh antigen expression for regulator types may be attributed to mutations of the RH50 gene, which is independent of the RH locus. The RH50 gene encodes a glycoprotein that interacts with the Rh proteins to form a functional complex within the red blood cell membrane. This report describes an RH50 gene mutation for a previously unclassified Rh null donor. Sequencing cDNA clones from Rh50 mRNA revealed a single base change (G836A) yielding a missense and nonconservative mutation (Gly279Glu) within a predicted hydrophobic domain for this membrane protein. Genomic DNA studies using polymerase chain reaction (PCR) restriction analysis and sequencing showed that the Rh null propositus was a composite heterozygote for this mutation, carrying two alleles with the A and G at nucleotide 836, respectively. In contrast, cDNA studies showed that only the A836 sequence was present, suggesting that the second allele with G836 was apparently silent (no transcript detected). Family studies showed that the mutant RH50 allele (836A) was inherited maternally, whereas the silent RH50 allele (836G) was from paternal transmission. These findings provide further evidence that rare but diverse genetic alterations may occur along the RH50 gene where the Rh null syndrome of the regulator type occurs. The single amino acid change (Gly to Glu) provides insight into the critical value of these residues for assembly of the Rh antigen complex within the membrane.