PTPRN and type 1 diabetes mellitus: Before anti-ZnT8 were available, initial positivity for anti-GAD was considered to be a risk factor for a development of an autoimmune diabetes, as shown in a cohort of over 6000 pediatric patients (TEDDY study, 36): anti-GAD, anti-IA-2 and anti-insulin were analyzed from 3 months onwards up to 15 years of age quarterly in pediatric patients with a genetic risk for T1DM.