ACVRL1 and hereditary hemorrhagic telangiectasia: To evaluate whether losing the remaining functional Eng or Acvrl1 allele in postnatal life leads to a better mouse model of HHT pathology, genetic tools such as Cre-lox technology have been used to deplete (or “knock out”) the target genes (Eng or Acvrl1) at a time of choice (Figure 2).