The changes caused by hypothyroidism in the testicle are also associated with oxidative stress (OS), caused by the high production of reactive oxygen species (ROS), such as superoxide (O2−), hydroxyl (OH+), peroxyl (RO2−), hydroperoxyl (HO2−) and hydrogen peroxide (H2O2) [13,14], or the low production of antioxidant factors such as the enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) [13]. This evidence concerns the gene CAT and hypothyroidism.