GDF-15 (mean minimum detectable dose: 2 pg/ml) was detectable in all patients and turned out to be increased in both IPAH and CTEPH as compared to control (IPAH vs CTRL vs CTEPH: median = 1798 pg/ml (IQR: 857–3,430) vs 497 pg/ml (IQR: 384–883) vs 1,355 pg/ml (IQR: 600–2,474); IPAH vs CTRL p < 0.0001, CTEPH vs CTRL p < 0.001, Figure 1C), with no significant differences between CTEPH and IPAH. The gene discussed is GDF15; the disease is idiopathic pulmonary arterial hypertension.