The Nature of Some Subtypes of A

The subtype A_xB has been encountered and described, along with two new examples of the subtype A_x. Anti-A and anti-A,B that has been absorbed by and eluted from erythrocytes of subtype A_x are sensitive to at least partial inhibition by the salivary secretions of the A_x person, thereby implying that A determinants are expressed in the salivary secretions as well as on the erythrocytes. Saliva of the A_xB person did not possess such inhibitory activity. However, family study disclosed that this person was likely to possess an unusual A²B genotype in which the B gene suppresses, at the phenotypic level, the expression of paired A. Furthermore, an underlying disease, myeloid metaplasia, may have further suppressed the expression of A determinants on both erythrocytes and in salivary secretions. Three other pedigrees revealed suppression of A by paired B, and in one instance, the genotype A¹B was found to give rise to the phenotype A₂B. Some population studies fail to demonstrate satisfactory Hardy-Weinberg equilibrium when tested in accordance with the usual four allele theory of inheritance for the A₁A₂BO phenotypes. An additional allele, suppressor B (B^[unknown]) was assumed for five such studies, and a more satisfactory fit between expected and observed values was obtained.