The serum VEGF concentration in the CTD-PAH group was significantly greater than that in the HC group (251.1 ± 48.4 vs. 143.5 ± 33.8, P < 0.0001) and the CTD-non-PAH group (251.1 ± 48.4 vs. 222.1 ± 18.6, P = 0.0026) (Fig. 1B). This evidence concerns the gene VEGFA and pulmonary arterial hypertension.