Similarly, SOST is also an inhibitor of the Wnt pathway.[21] SOST knockout mice exhibit osteosclerosis and noticeable increased bone mass.[22] In humans, SOST levels are age-dependent, tending to increase with age, and postmenopausal women have noticeable elevated SOST levels compared with women before menopause.[23,24] As both DKK1 and SOST are Wnt pathway inhibitors and secretory proteins, serum concentration of these proteins is often measured to assess their degree of expression in the bone microenvironment. Here, SOST is linked to osteosclerosis.