In this study, we investigated the effects of GV‐971 on α‐syn aggregation at three levels, that is, in vitro using a protein aggregation assay and a dopaminergic neuronal cell line, ex vivo using PD and DLB brain slices, and in vivo using a commonly used PD mouse model, Prnp‐SNCAA53T. The gene discussed is PRNP; the disease is Parkinson disease.