TFL is a selective cyclic guanosine monophosphate (cGMP) specific phosphodiesterase 5 (PDE5) inhibitor used in the treatment of first-line erectile dysfunction (ED), benign prostatic hyperplasia (BPH) and pulmonary hypertension (Choi et al., 2019; Yang et al., 2019). The gene discussed is PDE5A; the disease is pulmonary arterial hypertension.