Also known as OPG, TR1 and OCIF, this gene encodes Osteoprotegerin, a heparin-binding secretory glycoprotein that belongs to the TNF-receptor superfamily. The TNFR superfamily consists primarily of transmembrane proteins that elicit signal transduction in a variety of cells and are known to mediate diverse biological responses, including cytotoxicity and apoptosis, Osteoprotegerin (OPG) was isolated independently by two laboratories in 1997 [1,2].