In addition, Activin A repressed progesterone synthesis in the reproductive system,157,158 which might explain low progestogen levels in male PAH patients,155 as Activin A plasma levels are increased.89 Similarly, BMP4 and BMP7 also suppressed progesterone synthesis in Granulosa-Lutein cells.159 The crosstalk between progesterone and TGFβ signalling is most likely cell type and context dependent. The gene discussed is TGFB1; the disease is pulmonary arterial hypertension.