SPP1 and heritable pulmonary arterial hypertension: Higher expression of latent transforming growth factor beta binding protein 2 (LTBP2) and periostin (POSTN) was found in all PAH patients (Fig. 7A, B), whereas lower expression of secreted phosphoprotein 1 (SPP1) and limbic system associated membrane protein (LSAMP) was found in most of the PAH patients except the HPAH patients (Fig. 7C, D).