– Endoglin is a single-pass type I membrane protein which restricted to endothelial cells in all tissues except bone marrow. Endoglin as major glycoprotein of vascular endothelium, it has been found on endothelial cells, activated macrophages, fibroblasts, and smooth muscle cells. Furthermore, Homodimer forms a heteromeric complex with the signaling receptors for transforming growth factor-beta: TGFBR1 and/or TGFBR2. It may have an important role in the binding of endothelial cells to integrins and/or other RGD receptors. Defects in ENG are the cause of hereditary hemorrhagic telangiectasia type 1 (HHT1), which is an autosomal dominant multisystemic vascular dysplasia, characterized by recurrent epistaxis, muco-cutaneous telangiectases, gastro-intestinal hemorrhage, and pulmonary (PAVM), cerebral (CAVM) and hepatic arteriovenous malformations.