In addition to HLA, non-HLA genes such as peptidyl arginine deiminase 4 (PADI4), protein tyrosine phosphatase, non-receptor type 22 (PTPN22), and signal transducer and activator of transcription 4 (STAT4) have also been implicated in RA pathogenesis, further underscoring the genetic complexity of the disease. The gene discussed is PTPN22; the disease is rheumatoid arthritis.