In man, the C1858T (R620W) allelic variant of Ptpn22 has been linked to multiple human autoimmune disorders that have a prominent humoral component, including SLE, rheumatoid arthritis, type 1 diabetes, and autoimmune thyroiditis (Begovich et al. 2004; Bottini et al. 2004; Criswell et al. 2005; Gregersen et al. 2006; Kyogoku et al. 2004; Lauwerys and Wakeland 2005; Smyth et al. 2004). Here, PTPN22 is linked to rheumatoid arthritis.