Autoimmune thyroiditis in children and adolescents with type 1 diabetes mellitus is associated with elevated IgG4 but not with low vitamin D

Objective: To assess levels of vitamin D and of immunoglobulin G subclasses in children and adolescents with type 1 Diabetes Mellitus with or without autoimmune thyroiditis. Design: Among 213 patients with type 1 diabetes, the cases with thyroid-specific autoantibodies formed Group 1 [n=19, M/F: 7/12, median age 13 years (10.1-14.7)]. Nineteen age-, gender-, and diabetes duration-matched cases with type 1 diabetes without any other systemic disease were designated as controls [Group 2, M/F: 7/12, median age 12.9 years (10.5-14.9)]. Results: Levels of thyroid hormones, vitamin D, total IgG and IgG subclasses, as well as IgG subclasses/total IgG ratios were similar between the groups. Five cases (26%) in Group 1 had IgG4 levels > + 2 SDS, whereas there were no such cases in Group 2 (p=0.046). These five patients had similar clinical features but higher median IgG4 levels and IgG4/Total IgG ratios compared to the subjects with IgG4 levels < + 2 SDS in Group 1 and Group 2. Conclusions: There was no difference of vitamin D levels between the groups. Only a small percentage of patients with type 1 diabetes also having autoimmune thyroiditis had elevated serum IgG4 levels, revealing the heterogeneity of autoimmune thyroiditis and existence of IgG4 thyroiditis in the pediatric age group. Total IgG, the other IgG subclasses, and vitamin D levels did not differ in patients with autoimmune thyroiditis and type 1 diabetes compared to those suffering only from type 1 diabetes.