The pathogenesis of PHT in SCD is likely multifactorial, including hemolysis, impaired nitric oxide bioavailability, chronic hypoxemia, and increased endothelin-1, a potent pulmonary vasoconstrictor, mediated via hypoxia and via the erythropoietic cell-derived placenta growth factor, chronic thromboembolic disease, and asplenia [516]. The gene discussed is EDN1; the disease is pulmonary hypertension, primary, 1.