PTPN22 and type 1 diabetes mellitus: Complete loss of function or partial defects in TCR signaling result in immunodeficiency, but autoimmune reactions have also been described16 as genetic alterations of TCR signaling genes like ZAP70, SH2D1A, LAT, and PTPN22 are associated with arthritis, multiple sclerosis, T1D and thyroiditis17–21.