Taken together, these observations support a unifying pathobiological framework in which PAH is driven not only by vasoconstriction but by a profound imbalance within the TGF-β superfamily, characterised by reduced antiproliferative BMP/BMPR2 signalling and excessive activin- and TGF-β-mediated pro-proliferative activity. This evidence concerns the gene TGFB1 and pulmonary arterial hypertension.