COL18A1 and pulmonary arterial hypertension: Increased serum levels of endostatin (ES), a potent angiostatic factor, were found in CTD-PAH patients vs. those in IPAH patients; ES was also significantly higher in CTD-PAH than it was in porto-pulmonary hypertension and appeared to correlate with 6MWD, BNP levels, WHO-FC, PVR and mixed venous oxygen saturation.