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

Abstract

ObjectiveThe 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 methodsThe 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/m2and new-onset diabetes. The markers of autoimmune diabetes (GADA, ICA, IA-2A and ZnT8A), TSH and thyroid peroxidase antibodies (ATPO) were evaluated.ResultsIn 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).ConclusionsIn non-obese adults with new-onset diabetes, the presence of GADA and especially ZnT8 autoantibodies increases the risk of AITD.