PTPN22 and systemic lupus erythematosus: Recently, a variant in the coding region of the PTPN22 gene, which has been found to be associated with a number of autoimmune diseases, including rheumatoid arthritis (RA), type 1 diabetes mellitus (DM), autoimmune thyroid disease (AITD), and systemic lupus erythematosus (SLE) (5), was identified as a second susceptibility locus for JIA (6).