Nikolic et al. studied BMP9 plasma levels in patients with PAH of groups 1, 2 and 3, focusing particularly PoPH, and found markedly lower BMP9 levels in PoPH patients vs. healthy controls, vs. PAH of other etiologies, and vs. group 2 and 3 PH (213). The gene discussed is GDF2; the disease is Pulmonary arterial hypertension associated with portal hypertension.