Non-O blood groups have been associated with a variety of diseases and phenotypes, including arterial and venous thrombosis.1,20,23,30,32,33 The ABO blood groups are determined by the ABO gene, and the A and B allele encodes glycosyltransferase A and B, respectively, whereas the O allele encodes a nonactive enzyme. The gene discussed is ABO; the disease is Venous thrombosis.