ACVRL1 and pulmonary arterial hypertension: They might be explained by unproven porto-pulmonary hypertension [30], or could represent a subset of patients with ACVRL-1 mutations that develop hepatic arteriovenous malformations, leading to high CO and group 2 PH, and have a simultaneous proliferative vasculopathy in the lung, leading to Group 1 PAH, or could be a consequence of the high CO.