In recent years, several drugs, such as phosphodiesterase-5 (PDE-5) inhibitors, endothelin receptor antagonists (ERA), and prostanoids approved for the treatment of PAH have been shown to improve the symptoms, exercise tolerance and mortality of patients with PAH (Rubin et al. 2002; Galie et al. 2005; Rubin et al. 2011; Pulido et al. 2013). The gene discussed is PDE5A; the disease is pulmonary arterial hypertension.