SFRP1 and bone Paget disease: RANKL - receptor activator of nuclear factor kappa-Β ligand, DKK-1 - Dickkopf-related protein-1, sFRP-1 - soluble frizzled-related protein 1, PDB - Paget’s disease of bone, OPG - osteoprotegerin, BAP - bone-specific alkaline phosphatase