Background and Objectives The low prevalence antigen, Be a , is produced by a complex that also produces weak c, e and f (ce). We report here the molecular basis associated with Be a antigen expression.
Materials and MethodsPeripheral blood samples from four Be(a+) probands were tested. Haemagglutination, gDNA extraction, PCR-based assays, reticulocyte RNA isolation, Rh-cDNA analyses, and sequencing were performed by standard procedures.Results RBCs from Probands 1 and 3 were D)C)E)c+e+, and from Probands 2 and 4 were D+C+E)c+ W e+. In proband 1, cDNA sequencing of RHCE revealed heterozygosity of nucleotide (nt) 662C ⁄ G in exon 5 of RHCE*ce. No other nucleotide changes were observed. As the 662C>G nucleotide change ablates a MscI restriction enzyme cleavage site, PCR-RFLP analysis was performed and the RHCE*ce nt 662C ⁄ G heterozygosity was detected on gDNA from the four probands and two children from both Proband 3 and Proband 4.
ConclusionThe low prevalence Rh antigen, Be a , is associated with a single nucleotide change in exon 5 of RHCE*ce; that of 662C>G and this change is predicted to alter proline at amino acid position 221 of Rhce to arginine. The fundamental differences in the properties of these two amino acids may impose a steric and ⁄ or charge-related effect on the protein, and thereby provide an explanation for the weakened expression of c, e and f (ce) antigens in the Be a phenotype.
This is the first example of a MAR-like antibody made by a DCWe/DCWe woman. The specificity cannot be called anti-MAR, because some MAR-negative samples react, albeit weakly. The original anti-MAR, made by a DCWe/DCXe woman, did not react with DCWe/DCWe, DCWe/DCXe, or DCXe/DCXe RBCs. It is apparent that the specificity of "anti-MAR" differs slightly, depending on the CW/CX status of the antibody maker.
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