In line with these studies, mice heterozygous for mutations in Eng or Acvrl1 (Eng+/– or Alk1+/–) display reduced expression levels of the affected gene and develop some HHT-like lesions at the adult stage, albeit with a low penetrance, including telangiectases, nosebleeds, and dilated vessels with reduced vascular smooth muscle cell (VSMC) coverage (40–42). Here, ACVRL1 is linked to hereditary hemorrhagic telangiectasia.