SPP1 and bone Paget disease: Methods: Serum levels of osteopontin, sclerostin, receptor activator of nuclear factor kappa-Β ligand (RANKL), osteoprotegerin, Dickkopf-related protein 1 (DKK-1), and soluble frizzled-related protein 1 (sFRP-1) were measured in 57 patients with Paget’s disease of bone and 24 controls with primary osteoarthritis.