IRF5 and rheumatoid arthritis: It has been observed that the S2 and S3P groups are predominantly linked to an increased susceptibility to seropositive RA, while the following single nucleotide polymorphisms (SNPs) are the most significant non-HLA gene variants related to RA: phosphatase non-receptor type 22 (PTPN22), interleukin-23 receptor (IL23R), TNF receptor-associated factor 1 (TRAF1), cytotoxic T-lymphocyte-associated protein 4 (CTLA4), interferon regulatory factor 5 (IRF5), signal transducer and activator of transcription 4 (STAT4), chemokine receptor 6 (CCR6), and protein-arginine deiminase type-4 (PADI4).