RANKL signaling is impeded by the binding of the soluble decoy receptor osteoprotegerin (OPG)9,16,17, which negatively regulates osteoclast differentiation; thus, the RANKL–OPG balance is related to osseous diseases, including rheumatoid arthritis, osteoporosis, and periodontal disease. The gene discussed is TNFSF11; the disease is periodontal disorder.