TGF-β plays a role in the coupling of bone formation to bone resorption [42], thus the severe osteopetrosis phenotype observed in Runx1 CKO mice could be due to loss of TGF-β-mediated coupling of osteoblast-mediated bone formation and osteoclast-mediated bone resorption. The gene discussed is RUNX1; the disease is osteopetrosis.