Consistent with a role of LYP in preventing autoimmunity, a SNP in PTPN22 human gene, which results in the LYP mutant R620W, confers increased risk to several autoimmune disorders, including RA, SLE, and Type 1 diabetes (T1D) (55, 64–67). The gene discussed is PTPN22; the disease is type 1 diabetes mellitus.