GDF2 and idiopathic pulmonary arterial hypertension: The UK NIHR BioResource–Rare Diseases PAH Study, utilizing ~ 1000 PAH cases of primarily adult-onset IPAH, identified an ATPase gene (ATP13A3), growth differentiation factor 2 (GDF2; also known as BMP9), and SOX17 as risk genes contributing to 0.8–1.1% of cases [23].