Xanthine oxidase (XO) is involved in the oxidation of hypoxanthine to xanthine and of xanthine to uric acid in the presence of xanthine oxidase (XO), resulting in the endothelial generation of both O2•− and H2O2; its expression is increased in patients with coronary artery disease and its inhibition has been reported to alleviate the arterial endothelial dysfunction (recently reviewed in ref. [75]). This evidence concerns the gene XDH and coronary artery disorder.