DKK1 and osteosclerosis: 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.