HLA-DRB1 and rheumatoid arthritis: Linkage studies in RA families and genome wide screening in case control studies have identified over 30 validated additional genetic loci associated with RA such as HLADRB1, PTPN22, TNFAIP3, TRAF1, STAT4, CCR6, PXK, 10p15,12q13 and 22q13 [14,16-23].