TPO and major depressive disorder: For instance, thyroperoxidase antibodies are significantly more common in patients with MDD and BD even after accounting for lithium exposure,89, 90 a finding that may be related to a shared genetic vulnerability to BD and autoimmune thyroiditis.84 In another one of many examples, Ching et al.91 reported that 2 out of 20 patients with a diagnosis of MDD had raised levels of autoantibodies to glutamic acid decarboxylase 65 (GAD65) and Ro52 in both the serum and cerebrospinal fluid, with one of the patients meeting criteria for stiff-person syndrome.