In the patients with DM and SIgAD we observed a significantly higher rate of autoimmune thyroiditis compared to the patients with DM and normal or elevated IgA levels (42.9% versus 3.5%; OR = 20.6; 95% CI: 3.94 to 107.92; p = 0.0003). This evidence concerns the gene CD79A and selective IgA deficiency disease.