[9] The O allele lacks both enzymatic activities because of the frameshift caused by a deletion of guanine-258 in the gene which corresponds to a region near the N-terminus of the protein.

[15][16] Furthermore, the expression of ABO blood group antigens in normal human tissues is dependent upon the type of differentiation of the epithelium.

[17] Several studies have observed that a relative down-regulation of GTA and GTB occurs in oral carcinomas in association with tumor development.

[19][20] A multi-locus genetic risk score study based on a combination of 27 loci, including the ABO gene, identified individuals at increased risk for both incident and recurrent coronary artery disease events, as well as an enhanced clinical benefit from statin therapy.

[8] This article incorporates text from the United States National Library of Medicine, which is in the public domain.