ACVRL1 and pulmonary arterial hypertension: Interestingly, through deeper investigations, we could identify at least one gene, i.e. LFNG, whose regulation by BMP9 was weakly impaired in newborn heterozygous ALK1-mutated ECs, but more intensely suppressed in ALK1 or BMPR2-mutated HMVECs from PAH patients.