A NOVEL SINGLE MISSENSE MUTATION IDENTIFIED ALONG THE RH50 GENE IN A COMPOSITE HETEROZYGOUS RH-NULL BLOOD-DONOR OF THE REGULATOR TYPE

Rare individuals who lack all of the Rh blood group antigens are calle d Rh-null and may be classified as ''regulator'' or ''amorph'' types. The suppression of Rh antigen expression for regulator types may be at tributed to mutations of the RH50 gene, which is independent of the RH locus. The RH50 gene encodes a glycoprotein that interacts with the R h proteins to form a functional complex within the red blood cell memb rane. This report describes an RH50 gene mutation for a previously unc lassified Rh-null donor. Sequencing cDNA clones from Rh50 mRNA reveale d a single base change (G836A) yielding a missense and nonconservative mutation (Gly279Glu) within a predicted hydrophobic domain for this m embrane protein. Genomic DNA studies using polymerase chain reaction ( PCR) restriction analysis and sequencing showed that the Rh-null propo situs was a composite heterozygote for this mutation, carrying two all eles with the A and G at nucleotide 836, respectively. In contrast, cD NA 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) wa s inherited maternally, whereas the silent RH50 allele (836G) was from paternal transmission. These findings provide further evidence that r are but diverse genetic alterations may occur along the RH50 gene wher e the Rh-null syndrome of the regulator type occurs. The single amino acid change (Gly to Glu) provides insight into the critical value of t hese residues for assembly of the Rh antigen complex within the membra ne. (C) 1998 by The American Society of Hematology.