Pulmonary Hypertension in Patients With Neurofibromatosis Type I

Abstract

Neurofibromatosis type I (NF1) is a rare genetic disease caused by mutations in the NF1 gene, which codes for tumor suppressor neurofibromin. NF1 is transmitted as an autosomal dominant and fully penetrant trait with no sex predominance. Precapillary pulmonary hypertension (PH) is a severe complication of NF1, initially described in patients with advanced parenchymal lung disease, which may complicate the course of NF1. We conducted this study to describe clinical, functional, radiologic, and hemodynamic characteristics and outcome of patients with NF1-associated PH. We identified 8 new cases of NF1-associated PH in patients carrying a NF1 gene mutation. No bone morphogenic protein receptor 2 (BMPR2) point mutation or large size rearrangements were identified. Seven female patients and 1 male patient were reported, suggesting a possible female predominance. PH occurred late in the course of the disease (median age, 62 yr; range, 53-68 yr). Dyspnea and signs of right heart failure were the major symptoms leading to the diagnosis of PH. At diagnosis, patients had severe hemodynamic impairment with low cardiac index (median, 2.3 L/min per m2; range, 1.9-4.7) and elevated indexed pulmonary vascular resistance (median, 15.1 mm Hg/L/min per m2; range, 4.5-25.9). All patients were in New York Heart Association functional class III with severe exercise limitation (median 6-min walk distance, 180 m; range, 60-375 m). Most patients had associated parenchymal lung disease, but some had no or mild lung involvement with disproportionate pulmonary vascular disease. Overall, the impact of PH therapy was limited and outcomes were poor. In conclusion, PH represents a rare but severe complication of NF1, characterized by female predominance, late onset in the course of NF1, and severe functional and hemodynamic impairment. Because of poor outcome and limited impact of specific PH therapy, eligible patients require early referral for lung transplantation. Further studies are needed to better understand the pathophysiology and the role, if any, of neurofibromin in NF1-associated PH. Abbreviations: 6MWD = 6-minute walk distance, ACVRL1 = activin A receptor type II-like kinase-1, BMPR2 = bone morphogenic protein receptor 2, CI = cardiac index, CT = computed tomography, DLCO = diffusion capacity of carbon monoxide, FEV1 = forced expiratory volume in one second, FVC = forced vital capacity, GAP = GTPase-activating protein, GTP =guanosine triphosphate, GTPase = guanosine triphosphotase, HIV = human immunodeficiency virus, HRCT = high-resolution computed tomography, mPAP = mean pulmonary arterial pressure, mTOR = mammalian target of rapamycin, NF1 = neurofibromatosis type I, NIH = National Institutes of Health, NYHA: New York Heart Association, PAH = pulmonary arterial hypertension, PCWP = pulmonary capillary wedge pressure, PFT = pulmonary function test, PH = pulmonary hypertension, PVRi = indexed pulmonary vascular resistance, RAP = right atrial pressure, SpO2 = pulse arterial oxygen saturation, TLC = total lung capacity, TPRi = indexed total pulmonary resistance, VEGF = vascular endothelial growth factor, VSMC = vascular smooth muscle cells.