Although, the number of SV2A proteins per vesicle is considered to be relatively consistent across vesicles, all studies have been conducted in healthy rodent models.41-44 Vesicular dysfunction is a well-known pathology in people with PD and thus, we cannot assume that vesicular number or SV2A expression remains consistent compared with healthy aging.7,8,45 It could be more appropriate to characterize the observed differences in SV2A as reflecting synaptic changes or dysfunction, rather than density. Here, SV2A is linked to Parkinson disease.