PTPN22 and systemic lupus erythematosus: Recently, it was reported the single nucleotide polymorphism (SNP), R620W (rs2476601), in PTPN22 increased susceptibility to several autoimmune diseases including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and insulin dependent diabetes mellitus (IDDM) [11-15].