DKK1 and psoriatic arthritis: Overall, immunohistochemical reactivity for TGF-β1 in synovial tissue was elevated in patients with psoriatic arthritis (p = 0.024) and was positively correlated with IL-17A (r = 0.355, p = 0.024) and Dkk1 (r = 0.444, p = 0.004).