Mutations in these genes involved in TGF-β family signaling are causally related to hereditary hemorrhagic telangiectasia, and mutations in BMPR2 and Smad4 cause pulmonary arterial pulmonary hypertension, indicating that the TGF-β/BMP signaling plays an important role in maintaining vascular function. Here, TGFB1 is linked to hereditary hemorrhagic telangiectasia.