Disruption of the BMP9/BMP10—ALK1/BMPR‐II signaling axis seems to underlie many cases of human PAH (Atkinson et al., 2002; Hodgson et al., 2019; Morrell et al., 2019) and is implicated in the pathogenesis of HHT caused by germ‐line ACVRL1 and ENG mutations (Kritharis et al., 2018). The gene discussed is ACVRL1; the disease is hereditary hemorrhagic telangiectasia.