PTPN22 and rheumatoid arthritis: In addition to the HLA region, non-HLA gene polymorphisms, including PTPN22 rs2476601 (5, 22), STAT4 rs7574865 (23, 24), TRAF1/C5 rs3761847 (25, 26), CTLA4 rs3087243(27, 28) and PADI4 rs2240340 (6, 29), have also been reported to be strongly associated with RA susceptibility.