The association between autoimmune thyroiditis, autoimmune gastritis and type 1 diabetes.

Type 1 diabetes mellitus (DM1), autoimmune thyroid disease (ATD) and autoimmune gastritis often occur together forming the so-called autoimmune polyendocrine syndrome (APS) type 3. Thyroid autoimmunity is evident in up to one third and gastric autoimmunity in up to a quarter of patients with DM1. Also relatives of DM1 patients, particularly mothers, have higher frequencies of these autoimmune conditions. Vice versa, gastric autoimmunity is present in one third of ATD patients and islet autoimmunity in one out ten. The BB-DP rat, the NOD mouse, the OS chicken and the neonatal thymectomy mouse model are animal models of APS type 3. In these models the autoimmune destruction of the various target tissues has been shown to be a multi-step process in which several genetic polymorphisms need to converge to induce both local anomalies in the target gland and anomalies in the immune system. With regard to environmental factors, excess iodine is well known to elicit/aggravate thyroid autoimmunity in these animal models. Screening DM1 patients and their relatives (particularly females) for thyroid autoimmunity is recommended. If positive, excess iodine should be avoided and thyroxin treatment considered. Whether autoimmune thyroiditis and autoimmune gastritis patients should be screened for islet Ab is not clarified.