Statistical analysis revealed that the concentration of HIF-1α in the serum of CTD-PAH patients was significantly greater than that in either the HCs (248.9 ± 18.9 vs. 141 ± 42.9, P < 0.01) or the CTD-non-PAH patients (248.9 ± 18.9 vs. 224.6 ± 12.2, P < 0.01) (Fig. 1A). The gene discussed is HIF1A; the disease is pulmonary arterial hypertension.