Nonetheless, the contribution of other genetic polymorphisms on RA susceptibility has been also investigated: among these, SNPs in signal transducer and activator of transcription 4 (STAT4), Fc gamma receptor (FCGR), protein tyrosine phosphatase nonreceptor type 22 (PTPN22), PADI-4, tumor necrosis factor (TNF), and interleukin 6 (IL6) genes have been associated with disease development in several case-control studies [27]. Here, IL6 is linked to rheumatoid arthritis.