SMAD4 and hereditary hemorrhagic telangiectasia: Inhibiting BMP9 and BMP10 induces AVMs in the retina [106], and studies suggest that BMP9 and BMP10 are likely natural ligands for the ENG/ALK1 signaling pathway [107], thereby suggesting that the BMP9/10-ENG-ALK1-SMAD4 pathway plays a role in bAVM formation in HHT patients [108,109].