In many pathological processes in which OS has an essential role, increased XO activity is involved: type 1 diabetes mellitus, in which the production of mitochondrial superoxide is not modified, and the generation of ROS thus becomes XO-dependent [29], myocardial ischemia and reperfusion lesions [30], atherosclerosis [25], and neoplastic processes [31]. This evidence concerns the gene XDH and diabetes mellitus.