Thyroid profiles such as thyroxine (T4), free thyroxine (fT4), and thyroid-stimulating hormone (TSH) and biomarkers of oxidative stress, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-px), and malondialdehyde (MDA), were assessed on day 0 in all dogs and on days 14 and 45 post-levothyroxine sodium treatment in dogs with hypothyroidism. This evidence concerns the gene SOD1 and hypothyroidism.