"Unclassifiable" weak A blood group and deficient H phenotype (Hm) in one pedigree. Variants of A and H types in a family.

A new variant of blood group A [A(WAS)] was expressed in three generations of a Caucasian family: Phenotype included weak mixed field hemagglutination by anti-A reagents, secretion of H substance, and presence of anti-A1 in serum. The A(WAS) variant was inherited in a Mendelian fashion, dominant to O. A-transferase activity was absent from cells and saliva but was 0.2% of normal A1 transferase activity in serum, with a pH optimum of 6.0. Family members expressing A(WAS) also demonstrated partly deficient H type on cells (Hm). H-transferase activity in serum was normal for a weak A subgroup and showed typical Km and acceptor specificities. Linkage of H-modifier and ABO loci cannot be excluded.