Synaptic Loss in Primary Tauopathies Revealed by [11C]UCB‐J Positron Emission Tomography

Background Synaptic loss is a prominent and early feature of many neurodegenerative diseases. Objectives We tested the hypothesis that synaptic density is reduced in the primary tauopathies of progressive supranuclear palsy (PSP) (Richardson’s syndrome) and amyloid‐negative corticobasal syndrome (CBS). Methods Forty‐four participants (15 CBS, 14 PSP, and 15 age‐/sex‐/education‐matched controls) underwent PET with the radioligand [11C]UCB‐J, which binds to synaptic vesicle glycoprotein 2A, a marker of synaptic density; participants also had 3 Tesla MRI and clinical and neuropsychological assessment. Results Nine CBS patients had negative amyloid biomarkers determined by [11C]PiB PET and hence were deemed likely to have corticobasal degeneration (CBD). Patients with PSP‐Richardson’s syndrome and amyloid‐negative CBS were impaired in executive, memory, and visuospatial tasks. [11C]UCB‐J binding was reduced across frontal, temporal, parietal, and occipital lobes, cingulate, hippocampus, insula, amygdala, and subcortical structures in both PSP and CBD patients compared to controls (P