PTPN22 and type 1 diabetes mellitus: The major histocompatibility complex (MHC) class II, the cytotoxic T-lymphocyte–associated antigen 4 (CTLA4) and the protein tyrosine phosphatase non-receptor type 22 (PTPN22) loci have all been proven important in the pathogenesis of autoimmunity globally, whereas insulin (INS) gene is a disease-specific T1DM susceptibility locus (6).