ALAS2 and pulmonary arterial hypertension: One factor affecting mitochondrial respiration in the PBMC of PAH patients may be the disturbance in iron metabolism and mitochondrial proteins containing iron–sulfur clusters [12,13], as we found the mRNA regulation of ALAS2, the key enzyme in the heme synthesis of erythroid progenitor cells, the regulation of various Hbs, and the regulation of the mitochondrially localized iron-sequestering protein FTMT.