PTPN22 and systemic lupus erythematosus: The first described example concerns a nonsynonymous variant (R602W, rs2476601) in PTPN22 (a tyrosine phosphatase expressed in T cells): the 602W allele protects from CD but predisposes to RA, SLE (systemic lupus erythematosus), T1D (reviewed in [5]), and vitiligo [6].