It is accepted that RANKL, RANK, and osteoprotegerin are essential for controlling the oesteoclast development and functions in bone remodeling, and inhibition of RANKL activity by osteoprotegerin injection results in significantly reduced bone loss in arthritis (Kong et al., 1999) and osteoporosis (Mizuno et al., 1998). This evidence concerns the gene TNFRSF11A and osteoporosis.