ACVRL1 and pulmonary arterial hypertension: There have also been theoretical HHT-specific concerns regarding aberrant hepcidin regulation, but it is intriguing to note that hepcidin perturbations would operate in different directions: Inappropriately high hepcidin concentrations are found in pulmonary arterial hypertension [41] which is usually caused by mutations in BMPR2, but also affects a small subgroup of HHT patients with mutations in ACVRL1/ALK1 [42].