Detection of A1A2 and A2AAm1 heterozygotes among human A blood group phenotypes.

From the variations of alpha-N-acetylgalactosaminyltransferases activities with the pH, evidence was obtained for the recognition of A1A2 heterozygotes in normal A blood group sera. Besides, unusual transferase properties associated with two A2 sera from individuals out of AAm1 siblings, lead to the identification of the very infrequent A2AAm1 genotypes. These results strongly support the simultaneous coexistence of both A1 and A2 transferases in heterozygotes' sera, and bring some new information on the genetical background of the Am phenotype. The meaning of transferase properties directly determined on whole sera is briefly discussed.