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

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.

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-B_weak 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.

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 B_weak 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.

ABO c.28G>A mutation may cause B₃ -like subgroup by affecting RNA splicing of the ABO gene.