Mutations in other BMPR2-related genes have been linked to PAH albeit at lowerfrequencies, including type I receptors (ACVRL1, ENG), SMADfamily members (SMAD4, SMAD9), and BMPR2 ligands (GDF2which encodes BMP9) [29, 30, 31, 32, 33]. This evidence concerns the gene GDF2 and pulmonary arterial hypertension.