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

To evaluate whether the presence of diabetes-specific autoantibodies may predict the development of autoimmune thyroiditis (AIT) in children with type 1 diabetes (T1D).

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), T(3) and T(4) 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.

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).

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.