Function
This gene encodes a protein related to the first discovered blood group system, ABO. Which allele is present in an individual determines the blood group. The 'O' blood group is caused by a deletion of guanine-258 in the gene which corresponds to a region near the N-terminus of the protein. This results in a frameshift and translation of an almost entirely different protein. This mutation results in a protein unable to modify oligosaccharides which end in fucose linked to galactose. This sugar combination is termed the H antigen.
The A and B alleles of the ABO gene express enzymes with glycosyltransferase activities that differ, adding either N-acetyl galactosamine or galactose to the H antigen, converting it into the A or B antigen respectively. Individuals who are heterozygous for this gene express both proteins and so make both A and B antigens. Their blood group is AB. Remarkably, the difference between the A and B glycosyltransferase enzymes is only four amino acids. Other minor alleles have been found for this gene.
Read more about this topic: ABO (gene)
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