However, when the level of ROS exceeds the defense mechanisms, these enzymes may be itself oxidatively damaged.12 Indeed, anti‐CAT autoantibodies' production was described in human autoimmune pathologies such as systemic lupus erythematosus (SLE) and arthritis rheumatoid (AR).13 However, there is no report about the oxidative effects of ROS on CAT enzyme in thyroid disorders. Here, CAT is linked to rheumatoid arthritis.