In T2DM, chronic hyperglycemia enhances oxidative stress involved in the occurrence of complications, consecutive to oxidative lesions appearing in different organs and systems, the result being the increase in free radical production (increasing the oxidant status and the respiratory burst) or a decrease in antioxidant capacity, mediated by superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione (GSH) and PON1. The gene discussed is CAT; the disease is type 2 diabetes mellitus.