The frequency of variants in the growth differentiation factor 2 gene (GDF2), which encodes the ligand of BMPR2/ACVRL1 (BMP9), was reported to be approximately 1% in the PAH cases in European cohorts, but was higher in Chinese patients (approximately 6.7%) [60,62,70]. Here, ACVRL1 is linked to pulmonary arterial hypertension.