STAT4 and rheumatoid arthritis: Other genes implicated in RA predisposition include PTPN22 (protein tyrosine phosphatase non-receptor type 22), STAT4 (signal transducer and activator of transcription-4), and TRAF1-C5 (tumor necrosis factor receptor-associated factor 1), although their exact roles in autoimmunity remain incompletely understood.