GADA positivity at onset of type 1 diabetes is a risk factor for the development of autoimmune thyroiditis

Kordonouri O, Charpentier N, Hartmann R. GADA positivity at onset of type 1 diabetes is a risk factor for the development of autoimmune thyroiditis. Aim: To evaluate whether the presence of diabetes‐specific autoantibodies may predict the development of autoimmune thyroiditis (AIT) in children with type 1 diabetes (T1D). Methods: Glutamic acid decarboxylase antibodies (GADA), tyrosine phosphatase IA2 antibodies (IA2A), and insulin autoantibodies (IAA) were determined at T1D onset in 341 children and adolescents. Thyroid antibodies (anti‐TG, anti‐TPO), thyroid stimulating hormone (TSH), T₃ and T₄ were measured in 335 patients at T1D onset and thereafter annually with a follow‐up time of 1–15 yr. In case of thyroid antibody positivity and/or TSH elevation, thyroid gland sonography was performed. Treatment with l ‐thyroxine was started if persistent elevation of TSH and/or thyroid volume was present. Results: The majority of patients (92.1%) had at least one T1D antibody (71.6% GADA, 73.0% IA2A, and 44.9% IAA). GADA positive patients were older than those without GADA (p < 0.001). Thyroid autoimmunity was found in 15 of 335 patients (4.5%) at T1D onset with female preponderance (p = 0.013). At the end of follow‐up, 70 patients (20.9%) had developed thyroid autoantibodies [cumulative incidence (CI) 0.36 ± 0.06 at 10 yr of T1D]. In 30 patients (9.0%), AIT was diagnosed up to 9.4 yr after T1D onset (CI 0.24 ± 0.06 at 10 yr). AIT incidence was not influenced by IAA or IA2A positivity. In multivariate analysis, GADA positive patients were estimated to have a 3.5‐fold increased risk of AIT (CI 0.31 ± 0.11 at 10 yr) compared to those without GADA (p = 0.024). Conclusion: Based on the present results, a special focus should be given to GADA positive patients concerning screening for AIT as they are at increased risk to develop autoimmune thyroiditis.