An exonic missense mutation c.28G>A is associated with weak B blood group by affecting RNA splicing of the ABO gene

BACKGROUND The amino acid substitutions caused by ABO gene mutations are usually predicted to impact glycosyltransferase's function or its biosynthesis. Here we report an ABO exonic missense mutation that affects B-antigen expression by decreasing the mRNA level of the ABO gene rather than the amino acid change. STUDY DESIGN AND METHODS Serologic studies including plasma total GTB transfer capacity were performed. The exon sequences of the ABO gene were analyzed by Sanger sequencing. B310 cDNA with c.28G>A (p.G10R) mutation was expressed in HeLa cells and total GTB transfer capacity in cell supernatant was measured. Flow cytometry was performed on these HeLa cells after transfection, and agglutination of Hela-Bweak cells was also examined. The mRNA of the ABO gene was analyzed by direct sequencing and real-time reverse transcriptase–polymerase chain reaction. A minigene construct was prepared to evaluate the potential of splicing. RESULTS While plasma total GTB transfer capacity was undetectable in this B3-like individual, the relative percentage of antigen-expressing cells and mean fluorescence index of the Bweak red blood cells (RBCs) were 19 and 14% of normal B RBCs, respectively. There was no significant difference of total GTB transfer capacity in cell supernatant and B-antigen expression on cell surfaces between HeLa cells transfected with B310 cDNA and B cDNA. The mRNA expression level of B310 in peripheral whole blood was significantly reduced. The amount of splicing is significantly lower in c.28G>A construct compared to that in wild-type construct after transfection in K562 cells. CONCLUSION ABO c.28G>A mutation may cause B3-like subgroup by affecting RNA splicing of the ABO gene.