PDE5A and pulmonary arterial hypertension: In addition, a fair number of genes with historical relevance to pulmonary hypertension (Figure 1B), such as associated with vascular tone, phospho diesterase enzyme 5 (PDE5a), a target of current therapies is increased; guanylate cyclase 1B3 (GUCY1B3), a receptor for nitric oxide is decreased; the inducible form of prostaglandin-endoperoxide synthase 2 (PTGS2) is decreased, among others related to prostaglandin and nitric oxide synthesis and response.