Nonobese diabetic (NOD) mice with Ptpn22 deficiency show reduced numbers of plasma cells, and B-cell-specific ablation of Ptpn22 decreases the incidence of diabetes in NOD mice, suggesting that Ptpn22 variation may contribute to T1D by modifying B-cell maturation [8, 133]. Here, PTPN22 is linked to type 1 diabetes mellitus.