NAGAT（ABO) is a member of the glycosyltransferase 6 family. The ABO protein is the basis of the ABO blood group system and related to the first discovered blood group system， ABO. The allele that is present in an individual determines the blood group. The histo-blood group ABO is comprised of 3 carbohydrate antigens: A， B， and H. A， B， and AB individuals express a glycosyltransferase activity which converts the H antigen to the A antigen（by addition of UDP-GalNAc) or to the B antigen（by addition of UDP-Gal)， whereas O individuals are deficient of such activity.
