One might interpret such controversial findings as BMP9 exerts different roles at different stages of PAH; a beneficial role during the initial stage of PAH (where genetic studies are very powerful in identifying the underlying cause of the disease) and a more complicated role during the late stage of the disease which can often be demonstrated in cells isolated from patients who are at advanced stages of PAH. The gene discussed is GDF2; the disease is pulmonary arterial hypertension.