Atypical transmission of ABO blood groups in a French family.

A group AB mother (Mrs P.D.) gave birth to a group O female baby (C.D.). Extensive study of the blood group genetic markers in both the parents and the child, carried out on several occasions, showed nothing unusual outside the ABO system. Mrs P.D. then, gave birth to a second female baby who was also group O. Mrs P.D. had normal amounts of A, B, H and Lewis antigens in her saliva. The H, A and B agglutinability of her red cells was in the range of normal A2B group. This A2B blood group was characterized by very low A gene-specified glycosyltransferase activity in serum. Moreover this activity was undetectable in red blood cell membranes. These results are discussed in the light of various hypotheses in order to explain this unusual transmission of ABO blood group.