TNFSF11 and osteoporosis: OPG deficient mice (OPG−/−) and RANKL overexpressing transgenic mice (RANKL-Tg) both exhibited an osteoporosis phenotype due to enhanced osteoclastogenesis, but OPG−/− mice have enhanced bone resorption as compared to RANKL–Tg due to a higher RANKL/OPG ratio in OPG−/− mice [51,52].