These lesions are a pathological characteristic of inherited hereditary hemorrhagic telangiectasia (HHT), a vascular disorder caused by heterozygous loss-of-function (LOF) mutations in BMP9 and BMP10 signaling pathway genes including those encoding the ligand, BMP9; the type I BMP receptor, ALK1; the auxiliary coreceptor, ENG; and the transcriptional effector, SMAD4 (9–11). Here, SMAD4 is linked to hereditary hemorrhagic telangiectasia.