GAD2 and major depressive disorder: High titers of the GAD65 autoantibody linked to cerebellar ataxia, stiff-person syndrome, and chronic epilepsy, as well as type 1 diabetes, were strongly associated with poor results in the attention module and the presence of depression, whereas higher titers of the myositis Ab PM/Scl-75 correlated with low attention scores and elevated psychiatric and sleep disturbances, among other significant findings (Fig. 3A).