Tumor necrosis factor-α (TNF-α) has also been reported to promote differentiation of osteoclasts from osteoclast precursors derived from bone marrow cells in vitro.5, 6, 7 TNF-α-induced osteoclast formation can be central to osteoerosive disorders such as rheumatoid arthritis, postmenopausal osteoporosis, periprosthetic bone loss, and periodontal disease.8, 9, 10, 11. The gene discussed is TNF; the disease is rheumatoid arthritis.