Overview of the selection of the study population. CHD-APAH, pulmonary arterial hypertension (PAH) associated with congential heart disease; CTD-APAH, PAH associated with connective tissue disease without interstitial lung disease; FPAH, familial PAH; IPAH, idiopathic PAH; PH, pulmonary hypertension; PVOD, pulmonary veno-occlusive disease; RHC, right heart catheterization; SSc-APAH, PAH associated with systemic sclerosis without interstitial lung disease.