Our observation of increased TSP-1 in the plasma of scleroderma patients following the development of PAH corroborates prior studies reporting greater TSP-1 protein levels in the lung tissue and pulmonary vasculature, specifically of patients with different forms of PAH, including scleroderma-associated disease17, 18, 57, and the recent report of higher plasma levels of TSP-1 in patients with more severe PH and decreased survival38. This evidence concerns the gene THBS1 and pulmonary arterial hypertension.