BackgroundBi-allelic mutations of the EIF2AK4 gene cause heritable pulmonary veno-occlusive disease and/or pulmonary capillary haemangiomatosis (PVOD/PCH). We aimed to assess the eff ect of EIF2AK4 mutations on the clinical phenotypes and outcomes of PVOD/PCH.Methods We did a population-based study using clinical, functional, and haemodynamic data from the registry of the French Pulmonary Hypertension Network. We reviewed the clinical data and outcomes from all patients referred to the French Referral Centre (Pulmonary Department, Hospital Kremlin-Bicêtre, University Paris-Sud) with either confi rmed or highly probable PVOD/PCH with DNA available for mutation screening (excluding patients with other risk factors of pulmonary hypertension, such as chronic respiratory diseases). We sequenced the coding sequence and intronic junctions of the EIF2AK4 gene, and compared clinical characteristics and outcomes between EIF2AK4 mutation carriers and non-carriers. Medical therapies approved for pulmonary arterial hypertension (prostacyclin derivatives, endothelin receptor antagonists and phosphodiesterase type-5 inhibitors) were given to patients according to the clinical judgment and discretion of treating physicians. The primary outcome was the event-free survival (death or transplantation). Secondary outcomes included response to therapies for pulmonary arterial hypertension and survival after lung transplantation. A satisfactory clinical response to specifi c therapy for pulmonary arterial hypertension was defi ned by achieving New York Heart Association functional class I or II, a 6-min walk distance of more than 440 m, and a cardiac index greater than 2·5 L/min per m² at the fi rst reassessment after initiation of specifi c therapy for pulmonary arterial hypertension.Findings We obtained data from Jan 1, 2003, to June 1, 2016, and identifi ed 94 patients with sporadic or heritable PVOD/PCH (confi rmed or highly probable). 27 (29%) of these patients had bi-allelic EIF2AK4 mutations. PVOD/ PCH due to EIF2AK4 mutations occurred from birth to age 50 years, and these patients were younger at presentation than non-carriers (median 26·0 years [range 0–50.3] vs 60·0 years [6·7–81·4] years; p