HLA-DRB1 and rheumatoid arthritis: The association of genetic factors including gene polymorphisms with RA susceptibility has been widely described including HLA-DRB1 locus, rs2476601 variant in the protein tyrosine phosphatase gene (PTPN22), in IL2 receptor genes (rs2104286 in IL2RA and rs743777 and IL2RB) and in TNF pathway genes such as tumour necrosis factor (TNF), alpha-induced protein 2 (TNFAIP2) [4], [43]–[46].