PTPN22 and rheumatoid arthritis: The present study focuses on five confirmed RA susceptibility genes/loci - HLA-DRB1 (6p21), PTPN22 (1p13), OLIG3/TNFAIP3 (6q23), STAT4 (2q32) and TRAF1/C5 (9q33) - that are associated with RA with low-to-moderate risk in UK patients [6-8].