USAG1 (uterine sensitization associated gene 1), also known asSOSTDC1 (sclerostin domain–containing 1), Ectodin, is a secreted protein with a glycosylated N-terminus that contains a C-terminal cysteine knot domain. This C-terminal cysteine knot domain is present in numerous growth factors, including TGFβ, NGF, PDGF, vWF, NDP, and mucin-2, and involved in dimerization, receptor binding, and signal transduction. SOSTDC1 negatively regulates BMP signaling during cellular proliferation, differentiation, and apoptosis in several biological processes (such as dentary morphogenesis, embryo implantation in the endo-metrium, and healing of bone fractures) [8]. In addition, SOSTDC1 might also involve cancer development processes through the regulation of the Wnt pathway.