ACVRL1 and pulmonary arterial hypertension: Finally, PAH patients with a family history of PAH without identification of either BMPR2 or ACVRL1 mutation (n = 13) were excluded from the analysis in order to limit the risk of misclassification, although their clinical and hemodynamic characteristics were broadly similar to those of BMPR2 mutation carriers (age at PAH diagnosis 38.9 ± 12.5 yrs, mPAP 64 ± 13 mmHg, PVRi 25.9 ± 9.5 mmHg/L/min/m2).