We centre our review on two vascular diseases that are caused by perturbation in TGF-β family signalling, i.e. hereditary haemorrhagic telangiectasia (HHT) and pulmonary arterial hypertension (PAH), two haploinsufficiency diseases of which patients can have inactivating mutations in one allele of a TGF-β family (co)receptor. The gene discussed is TGFB1; the disease is hereditary hemorrhagic telangiectasia.