Diagnosis: Given the presence of fasting hyperglycemia (129 mg/dL), the positivity for a pancreatic autoantibody (anti-IA2), and a HLA trait with increased risk for development of autoimmune diabetes (HLA DR3/DR4), a diagnosis of type 1 diabetes mellitus (T1DM) was made and treatment with insulin at 0.3 U/kg/day was started. Here, PTPRN is linked to type 1 diabetes mellitus.