The inherited vascular condition hereditary haemorrhagic telangiectasia (HHT) [9] is of significant relevance to TGF-β signalling because the genes for endoglin, ALK-1 and SMAD4 (a co-Smad and downstream effector of the TGF-β signalling pathway), are mutated in different HHT families [10-12]. The gene discussed is SMAD4; the disease is hereditary hemorrhagic telangiectasia.