The role of sclerostin in bone metabolism is emerging. Sclerostin is the secreted expression of the SOST gene. In adult human bone, sclerostin is expressed only by osteocytes and inhibits bone formation by osteoblasts. It has been proposed that sclerostin expression by newly embedded osteocytes at the onset of osteoid mineralization may serve as a negative feedback signal on osteoblasts to prevent overfilling of the basic multicellular unit.