A modulated XO activity has also been related with pulmonary hypertension [99], and the signaling pathway of the transcription factor early growth response-1 (Egr-1) has targets implicated in proliferation, inflammation and fibrosis; and it is known to be involved in pulmonary vascular remodelling that leads to pulmonary hypertension [100]. This evidence concerns the gene XDH and pulmonary arterial hypertension.