Of the T1D loci reported to date, we focused on PTPN22 because GWAS data identify it as a key shared risk gene between CD and T1D.2, 3, 4PTPN22 encodes the phosphatase PEP, which inhibits TCR signaling by dephosphorylating Src family kinases.26 This evidence concerns the gene PTPN22 and type 1 diabetes mellitus.