Autoimmune thyroiditis in IDDM patients

Combined analysis of GAD65 and ICA512(IA-2) autoantibodies in organ and non-organ-specific autoimmune diseases confers high specificity for insulin-dependent diabetes mellitus

There is evidence that insulin-dependent diabetes mellitus (IDDM) may develop in association with other non-beta-cell-specific autoimmune diseases. We aimed to assess whether autoantibodies to the islet cell antigens glutamic acid decarboxylase (Mr 65,000 isoform) (GAD65) and ICA512(IA-2), present alone or in combination, are limited to IDDM or also occur in other organ- or non-organ-specific autoimmune disorders. We determined the frequency of these autoantibodies by radioimmunoassay in 199 sera from patients with autoimmune thyroid diseases (AITD), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and primary biliary cirrhosis (PBC), and compared the results with those from 507 newly diagnosed patients with IDDM and 280 healthy controls. ICA512(IA-2) autoantibodies were detected exclusively in AITD with concurrent IDDM, but not in other autoimmune diseases without IDDM, whereas GAD65 autoantibodies exceeded the limit of normal in 67.7% (21 of 31) of patients with AITD who also had IDDM and in 5.5% (three of 55) of patients with PBC. The frequency of either GAD65 and/or ICA512(IA-2) autoantibodies was significantly higher in patients with AITD who also had IDDM (27 of 31, 87.1%) than in those with AITD alone (one of 53, 1.9%; P<10(-6)), but was not significantly different from those patients with newly diagnosed IDDM (418 of 507, 82.4%). Neither patients with organ- or non-organ-specific autoimmune diseases without IDDM nor healthy controls had autoantibodies against both GAD65 and ICA512(IA-2). Despite the fact that one of the two autoantibodies was occasionally detected in patients with non-beta-cell-specific autoimmune diseases without IDDM, combined determination of GAD65 and ICA512(IA-2) autoantibodies specifically identified IDDM in the majority of patients with AITD. In conclusion, because of the strong association of IDDM with AITD, testing for multiple islet autoanti-bodies could be useful as a predictive marker for risk of progression to IDDM onset amongst patients with autoimmune thyroid disorders.

IDDM and autoimmune thyroid disease in the pediatric age group

Diabetic patients have increased chances of developing autoimmune thyroid disease. Thyroid autoantibodies (Th-AAb) are more frequent in IDDM children than in the general population, ranging between 7 and 40%. As markers of thyroid autoimmunity, we assessed Th-AAb (MsA and TgA) cross-sectionally in 212 children and adolescents (93 girls and 119 boys) aged 1.2-21 years with IDDM from 0-18 years, and longitudinally in 90/212 (43 girls and 47 boys) at diagnosis and during a 3-10 year follow-up. In the cross-sectional study Th-AAb were found in 22/93 girls (23.7%) and 13/119 boys (10.9%). In the longitudinal study Th-AAb were observed at diagnosis in 6 patients, and during the follow-up in 9 girls. In 11/15 Th-AAb positive patients anti-nuclear antibodies were also present. Hormonal assessment revealed hypothyroidism in 3 girls (afterwards on replacement therapy), thyroid ultrasonography showed abnormal patterns in 5 girls, fine needle aspiration biopsy confirmed Hashimoto's thyroiditis in 9 (8 girls and 1 boy), with a higher frequency than that reported among healthy subjects (1-2%). Thyrotoxicosis also occurs with increased frequency in diabetic children than in the general population. We observed Graves' disease in only 1/212 IDDM patients, a 13 year-old boy in whom thyrotoxicosis developed 4 years after diabetes was diagnosed. The high prevalence of thyroid autoimmunity in our patients, particularly in females, suggests that diabetic children and adolescents should be screened for thyroid autoimmunity even if asymptomatic for hypo- or hyperthyroidism. Patients with IDDM and autoimmune thyroid disease should be evaluated for autoantibodies against other organs, such as adrenal glands and gastric mucosa. It is known that patients affected by type 1 (insulin-dependent) diabetes mellitus (IDDM) may have autoantibodies against different organs, such as thyroid, adrenal glands, gastric mucosa, parathyroid, with or without evident dysfunction of the target organ /1-8/. Among organ-specific disorders, autoimmune thyroid disease (ATD) is frequently associated with IDDM and the presence of thyroid autoantibodies (Th-AAb) has been considered a risk factor for the development of hypo- or hyperthyroidism /9/.