The heightened Smad/ID signalling to BMP6/TNFα is unlikely to promote dPASMC proliferation since Smad/ID signalling inhibits PASMC proliferation28, 29 and reduced pulmonary vascular Smad/ID signalling is consistently reported in PAH in humans and animal models5, 39, 40. This evidence concerns the gene TNF and pulmonary arterial hypertension.