PTPN22 1858T allele is associated with younger age at onset of type 1 diabetes and is not related to subsequent thyroid autoimmunity.

To evaluate the prevalence of PTPN22 C1858T polymorphism in young type 1 diabetes patients with or without autoimmune thyroiditis. Genotyping was performed in 209 controls and 243 patients diagnosed with diabetes at median age of 8.6 years. Diabetes-related autoimmunity was assessed at diagnosis of the disease, while thyroid-related autoimmunity was determined at diabetes onset and at annual intervals up to 15 years of follow-up. The 1858T allele frequency was 15.2% in patients and 10.5% in controls (odds ratio 1.53, p = 0.037). 1858T positive patients were significantly younger at diagnosis of diabetes than those without this allele (p = 0.003). No association was found between C1858T polymorphism and diabetes-related autoimmunity (p = 0.173) or thyroid autoimmune disease (p = 0.321), respectively. We conclude that PTPN22 1858T allele is an independent risk factor for type 1 diabetes and associated with younger age at the onset of the disease. However, no association with concomitant thyroid autoimmunity was found.