In patients with AS, serum levels of IL-34 and RANKL adjusted for age and weight were significantly correlated with enthesitis (0.798, P < 0.01; 0.347, P < 0.05, respectively) and bone erosion (0.822, P < 0.01; 0.368, P < 0.05, respectively). The gene discussed is IL34; the disease is enthesitis.