Family study and frequency of blood group with strong B transferase accompanied by decreased A and H antigens

Summary Subgroups of type A blood, named A₁, A₂ and A₁–A₂ intermediate (A_int), are specifically characterized by their peculiar A alleles and have their own A₁-, A₂- or A_int-forms of -N-acetyl-D-galactosaminyltransferase (A-transferase). It is known, however, that certain type A₂B persons exhibit A₁-transferase. The reason may be an unusual -galactosyltransferase (B-transferase). This strong B-transferase competes with A-transferase for the substrate, H antigen, so as to decrease the A and H antigens on the red cells. We studied this blood group over three generations and found that the strong B-transferase is, in fact, inherited with the B gene and is dominant over normal B-transferase. In AB blood groups in Tokyo, the frequency of people with a strong B-transferase is 5% for A₁B and 22% for A₂B. This enzyme does not always cause weak H or A antigens.