Are zinc transporter type 8 antibodies a marker of autoimmune thyroiditis in non-obese adults with new-onset diabetes?

Objective: The diagnosis of autoimmune diabetes in non-obese adults is based on the detection of glutamic acid decarboxylase autoantibodies (GADA), islet cell antibodies (ICA) and antibodies to tyrosine phosphatase (IA-2A). Zinc transporter 8 (ZnT8) has been identified as a new autoantigen in patients with type 1 diabetes mellitus. The coincidence of autoimmune thyroiditis (AITD) with diabetes is common; therefore, screening of TSH and thyroid peroxidase antibodies (ATPO) is recommended during the diagnosis of diabetes. In this study, we determined whether the occurrence of islet autoantibodies is associated with a positive titre of ATPO in newly diagnosed adult-onset autoimmune diabetic patients.

Design And Methods: THE STUDY INVOLVED 80 NON-OBESE ADULTS AGED 44 (INTERQUARTILE RANGE (IQR): 37-51) years with a BMI of 24.0 (IQR: 22.2-26.0) kg/m(2) and new-onset diabetes. The markers of autoimmune diabetes (GADA, ICA, IA-2A and ZnT8A), TSH and thyroid peroxidase antibodies (ATPO) were evaluated.

Results: IN THE STUDY POPULATION, 70% (N=56) OF THE SUBJECTS WERE POSITIVE FOR AT LEAST ONE OF THE FOUR ASSESSED MARKERS OF AUTOIMMUNE DIABETES (83.9% GADA, 62.5% ICA, 42.8% IA-2A AND 33% ZNT8A) AND 37.5% OF THE SUBJECTS WERE POSITIVE FOR ATPO. THE ZNT8A-POSITIVE SUBJECTS HAD HIGHER ATPO TITRES THAN THE ZNT8A-NEGATIVE SUBJECTS (172.7 (IQR: 0.36-410.4) vs 92.4 (IQR: 0-23.7) IU/ml, P=0.001). Based on the assessed islet autoantibodies, the occurrence of positive ZnT8A and GADA was found to be related to a positive titre of ATPO using logistic regression (OR=5.48, 95% CI: 1.65-18.14, P=0.006 and OR=3.42, 95% CI: 1.09-10.71, P=0.03 respectively).

Conclusions: In non-obese adults with new-onset diabetes, the presence of GADA and especially ZnT8 autoantibodies increases the risk of AITD.