ALK and pulmonary arterial hypertension: The previous determination of responsible gene mutations, concerning bone morphogenetic protein receptor II (BMPRII) [2], activin receptor-like kinase-1 (ALK-1) [3] and recent discovery of dysregulated genes encoding for hypoxia inducible factor 3-alpha (HIF-3 alpha), mitochondrial cytochrome-c oxidase, and superoxide dismutase-2 in human and experimental PAH [4] provide a new understanding of genetic predisposition to PAH.