Several studies supporting this hypothesis showed that the CAT enzyme is a major protein target of the lipid peroxidation product 4‐HNE in autoimmune diseases such as the SLE.18 In order to verify our hypothesis, we evaluate in a comparative way the reactivity of plasmas of patients with GD and healthy controls toward the native CAT and toward the MDA‐ and H2O2‐modified enzyme. The gene discussed is CAT; the disease is autoimmune disease.