Furthermore, mice with a disrupted Rankl gene (Rankl−/−) also show severe osteopetrosis and a defect in tooth eruption and completely lack osteoclasts.76 However, deletion of the Opg gene in mice (Opg−/−) caused severe osteoporosis with decreased BMD and high bone turnover rate, disorganized matrix, and increased mortality compared with their control littermates.87,88. The gene discussed is TNFSF11; the disease is osteoporosis.