GDF2 and pulmonary arterial hypertension: Rare heterozygous variants in the BMP9 (GDF2) gene are significantly enriched in adult-onset disease, based on exome-wide gene burden testing, and represent between 0.8% and 6.6% of all PAH cases with over 60 pathogenic variants reported to date 14, 15••, 16, 17•, 18.