Endoglin (ENG), endothelial glycoprotein, also known as CD105, is a coreceptor of the transforming growth factor-β (TGFβ) family signaling complex, which is highly expressed on endothelial cells and plays a key role in angiogenesis. It regulates the responses associated with binding to transforming growth factor β1 egg (Activin-A), bone morphogenetic protein 2 (BMP-2), and bone morphogenetic protein 7 (BMP-7). Endoglin may be involved in autosomal dominant disease, such as hereditary hemorrhagic telangiectasia 1 (HHT1). Circulating soluble ENG is also elevated in pulmonary arterial hypertension(PAH) and is proposed to be a biomarker for the prognosis of group I PAH patients.