Another example of the rare Ay phenotype

The red cells of a patient typed as group O, but her serum lacked anti-A. Upon further testing, it appeared that the ABO phenotype was Am. Saliva studies demonstrated a normal amount of H substance but reduced A substance. Family studies established the ABO genotype of the proposita as A1O. The results suggest that modification of the cellular and salivary expression of the A antigen in this patient was the result of a double dose of the modifier gene y, and that the ABO phenotype, while having characteristics similar to that of an Am, was actually Ay.