Although a significant reduction of OPG levels upon infusion of this biologic agent was recently reported in long-standing RA patients with severe disease undergoing anti-TNF-α therapy [120], a single administration of anti-TNF-α infliximab did not lead to any significant reduction of OPG levels in our series of AS patients [121]. The gene discussed is TNFRSF11B; the disease is rheumatoid arthritis.