Therefore, we hypothesize the synovial expression of TGF-β1 is a differentiating factor for the development of erosive peripheral disease in psoriatic arthritis (TGF-β1 can prime IL-17 A), and synovial expression of Dkk1 may be related to peripheral joint destruction as in rheumatoid arthritis. The gene discussed is TGFB1; the disease is psoriatic arthritis.