In group 1 PAH patients alone, there was a direct correlation between CHI3L1 levels and mPAP (R2 = 0.11, P = 0.025) (Figure 1E) and pulmonary vascular resistance (R2 = 0.09, P = 0.06) (Figure 1F). This evidence concerns the gene CHI3L1 and pulmonary arterial hypertension.