While testing these PAH variants in an in vitro signaling assay could clarify if they retain signaling activities, our ability to carry out these experiments is limited as BMP9/BMP10 signal strongly in most standard cell lines, including HepG2, A204, and HEK293 cells (28, 47, 48, 49). The gene discussed is GDF2; the disease is pulmonary arterial hypertension.