Based on the concept that increased local or systemic RANKL/OPG may favour increased osteoclastic bone resorption in different metabolic bone disorders, exogenous injection of recombinant OPG has been efficaciously used in various animal models of bone diseases to modulate bone and mineral abnormalities caused by inadequate osteoclast activity [11]. This evidence concerns the gene TNFRSF11B and metabolic bone disorder.