Global Alk1 deletion is lethal at mid-gestation with impaired vascular development and vessel dilation (Oh et al., 2000), and homozygous endothelial cell deletion of Alk1 is lethal within several days of excision in neonates due to AVMs and pulmonary hemorrhage (Tual-Chalot et al., 2014; Park et al., 2008b). This evidence concerns the gene ACVRL1 and Pulmonary hemorrhage.