Increased serum levels of HIF-1α and VEGF were observed in CTD-PAH patients compared to CTD-non-PAH patients and healthy controls, which, along with their positive correlations with mPAP and BNP levels and negative correlations with the 6MWD, indicate their potential as biomarkers for diagnosing CTD-PAH. This evidence concerns the gene HIF1A and pulmonary arterial hypertension.