Matuskey D, Tinaz S, Wilcox KC, et al. - Researchers conducted the study for analyzing synaptic loss in people with mild bilateral Parkinson disease in vivo with highresolution PET imaging of synaptic vesicle glycoprotein 2A (SV2A) and postmortem in more advanced individuals with autoradiography. For this investigation, they measured the density of all synapses with SV2A in Parkinson disease patients with mild bilateral disease (N = 12) and matched normal controls (N = 12) utilizing in vivo high-resolution PET imaging as well as post mortem autoradiography in an independent sample with Parkinson disease (N = 15) and normal controls (N = 13) in the substantia nigra and putamen. According to post hoc analyses, Parkinson disease group showed lower SV2A in the substantia nigra, red nucleus and locus coeruleus. In addition, exploratory analyses exhibited lower SV2A binding in clinically relevant cortical areas. This research presents the first proof of synaptic loss in brainstem nuclei involved in Parkinson disease pathogenesis in living individuals. SV2A imaging holds promise to understand synaptic changes that are central to the disease.