PTPN22 and type 1 diabetes mellitus: More than 60 genes outside the HLA loci region such as CTLA4, PTPN22, KIR, VNTR, IL2RA, INS, etc. also contribute to T1D.137,139 Environmental triggers, daily dietary habits, and related enterovirus infection are associated with the development of T1D.140 Susceptibility factors such as obesity, vitamin D levels, virus infection, and human microbiota are similar to other autoimmune diseases.