It is interesting that there is a report of PAH patients with FOXF1 mutations that do not have alveolar capillary dysplasia (ACD) with misalignment of pulmonary veins (MPV) suggesting a variable incompletely penetrant phenotype66, and a recent report describing a family member with PAH without ACD and two siblings with ACD67. The gene discussed is FOXF1; the disease is alveolar capillary dysplasia with misalignment of pulmonary veins.