SPP1 and pulmonary arterial hypertension: Osteopontin, which our LC–MS/MS analysis identified at higher levels in CDH, is highly expressed by pulmonary artery smooth muscle cells and adventitial fibroblasts from patients with pulmonary hypertension30,31 and osteopontin levels in serum correlate with pulmonary hypertension severity32,33, prompting us to select it for further evaluation.