The ABO histo-blood group system has long been of interest to the biological and medical sciences as these antigens are one of the most important clinical considerations for both transfusion and transplantation.1 and 2 This family of antigens consists of three oligosaccharide epitopes (1–3, Fig. 1), the structures of which were elucidated by Morgan and Watkins in 1957.3 The H(O) antigen was shown to be a disaccharide consisting of l-fucose and d-galactose (3, Fig. 1), while the A and the B antigens (1 and 2) were shown to be trisaccharides containing the disaccharide H antigen with an additional N-acetyl-galactosamine or a galactose residue, respectively. It was later shown by Tuppy and Staudenbauer that individuals who are of the A histo-blood group possess an N-acetyl-galactosaminyl transferase (GTA) capable of adding N-acetyl galactosamine to the 3-OH group of the H antigen galactose moiety. 4 On the other hand, individuals of the B histo-blood group possess a galactosyl transferase (GTB) that adds galactose to this hydroxyl group. The genetic basis of the ABO histo-blood group system was discovered in the 1990s, when the genes responsible for coding GTA and GTB were identified. 5, 6 and 7