A novel blood group B subgroup: serological and genetic studies

A discrepancy in the ABO blood groups between a newborn child and her parents was identified. Serological and DNA investigative techniques were performed. A weak variant of B (B-w) was detected on the erythrocytes of the child, her grandmother and great-uncle. Adsorption-elution studies showed that their erythrocytes adsorb and yield anti-B on elution. The B-w antigenic strength of the A(1)B(w) cells of her mother and maternal aunt was reduced when compared to that of the A(2)B(w) from another family member. Only one of 15 different anti-B sera agglutinated the A(1)B(w) erythrocytes. Agglutinin anti-B that reacted strongly with normal B erythrocytes and did not agglutinate the B-w cells, was found in the sera of the A(1)B(w) individuals. The B-w serum glycosyltransferase could not convert O cells into B cells and no B substance was found in saliva. All family members with the B-w/AB(w) phenotypes were heterozygous for a B allele and DNA sequencing revealed a novel missense mutation in exon 7 of the B allele (556A > G), resulting in M186V. This substitution changes a highly conserved region of the enzyme, proposed to be a disordered loop near the enzyme cleft, and is expected to diminish the enzyme's activity, leading to this B-w phenotype.