We read with great interest the review by Scholzel et al. [1], about chronic thromboembolic pulmonary hypertension (CTEPH), and especially, the sections on pathophysiology, risk factors and diagnostic work-up. However, we would like a further comment about congenital abnormalities causing hypercoagulability in these subjects. In fact, in our experience [2, 3], we have observed CTEPH patients with methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism or combined deficiency of proteins C and S. Can we consider these abnormalities as predisposing factors for CTEPH? Should thrombophilia screening be performed in subjects with suspect PAH? Could these abnormalities play a role in recurrent pulmonary hypertension after pulmonary endarterectomy?