Associations between blood type and disease have been studied since the early 
1900s when researchers determined that antibodies and antigens are inherited. In 
the 1950s, the chemical identification of the carbohydrate structure of surface 
antigens led to the understanding of biosynthetic pathways. The blood type is 
defined by oligosaccharide structures, which are specific to the antigens, thus, 
blood group antigens are secondary gene products, while the primary gene 
products are various glycosyltransferase enzymes that attach the sugar molecules 
to the oligosaccharide chain. Blood group antigens are found on red blood cells, 
platelets, leukocytes, plasma proteins, certain tissues, and various cell 
surface enzymes, and also exist in soluble form in body secretions such as 
breast milk, seminal fluid, saliva, sweat, gastric secretions, urine, and 
amniotic fluid. Recent advances in technology, biochemistry, and genetics have 
clarified the functional classifications of human blood group antigens, the 
structure of the A, B, H, and Lewis determinants and the enzymes that produce 
them, and the association of blood group antigens with disease risks. Further 
research to identify differences in the biochemical composition of blood group 
antigens, and the relationship to risks for disease, can be important for the 
identification of targets for the development of nutritional intervention 
strategies, or the identification of druggable targets. WIREs Syst Biol Med 
2016, 8:517-535. doi: 10.1002/wsbm.1355 For further resources related to this 
article, please visit the WIREs website.