Some reports observed an increase of pyruvate kinase muscle 2 (PKM2) in PAECs and blood outgrowth ECs (BOECs) of PAH patients and in the Sugen/ hypoxia model, while the PKM1 did not have its activity altered, inferring that polypyrimidine tract binding protein 1 (PTBP1) could be responsible for the selective splicing of PKM2/PKM1 isoform [26,27]. The gene discussed is PKM; the disease is pulmonary arterial hypertension.