More than 80% of patients have mutations in one of the following genes (1): Endoglin (ENG) gene, which encodes a receptor for transforming growth factor beta-1 (TGF-β1) and transforming growth factor beta-3 Activin A receptor-like type 1 (ACVRL1) gene, which encodes the activin receptor-like kinase (ALK1) SMADH4 (MADH4) gene, which encodes SMAD4, a protein active in the TGF beta signalling pathway General reference 1.