We used quantitative real-time PCR to confirm the changes in expression of three genes that have been implicated in the pathogenesis of PAH: Has2, Hapln3 and Retnla. The first two genes relate directly to hyaluronic acid, a component of the extracellular matrix that has been implicated in PAH [18]. The gene discussed is HAPLN3; the disease is pulmonary arterial hypertension.