SNCA and Parkinson disease: α-Synuclein overexpression as a model also has limitations, in that the many-fold increase in protein levels31 may induce non-PD-relevant neuronal stress, and it is unclear whether phenotypes observed in transgenic and AAV-based α-synuclein overexpression models are due to overexpression or the formation of disease-relevant pathological α-synuclein assemblies78.