Synaptic loss in behavioural variant frontotemporal dementia revealed by [11C]UCB-J PET
Synaptic loss is an early feature of neurodegenerative disease models, and is often severe in post mortem clinical studies, including frontotemporal dementia. Positron emission tomography (PET) imaging with radiotracers that bind to synaptic vesicle glycoprotein 2A enables quantification of synapses in vivo . This study used [ 11 C]UCB-J PET in people with behavioural variant frontotemporal dementia (bvFTD), testing the hypothesis that synaptic loss is severe and related to clinical severity. We performed a cross-sectional observational study of bvFTD, versus healthy controls, in which participants underwent neurological examination, neuropsychological assessment, magnetic resonance imaging (MRI) and [ 11 C]UCB-J PET. Patients were recruited from the Cambridge Centre for Frontotemporal Dementia at the University of Cambridge, and healthy volunteers from the UK National Institute for Health Research Join Dementia Research register. Eleven people with a clinical diagnosis of probable bvFTD and 25 age- and sex-matched healthy controls were included. All participants underwent dynamic [ 11 C]UCB-J PET imaging, structural MRI and a neuropsychological battery, including the Addenbrooke’s cognitive examination (ACE-R), and INECO frontal screening (IFS). General linear models were used to compare [ 11 C]UCB-J binding potential maps between groups, and correlate synaptic density with cognitive performance and clinical features in patients. Group-comparison and correlation analyses were also performed using partial-volume corrected [ 11 C]UCB-J binding potential from regions of interest (ROIs). Patients with bvFTD showed severe synaptic loss compared to controls. In particular, [ 11 C]UCB-J binding was significantly reduced bilaterally in medial and dorsolateral frontal regions, inferior frontal gyri, anterior and posterior cingulate gyrus, insular cortex and medial temporal lobe. Synaptic loss in the left frontal and cingulate regions correlated significantly with cognitive impairments as assessed with ACE-R and IFS. Results from ROI-based analyses mirrored the voxel-wise results. In keeping with preclinical models, and human post mortem data, there is widespread frontotemporal loss of synapses in symptomatic bvFTD, in proportion to disease severity. [ 11 C]UCB-J PET could support translational studies and experimental medicines strategies for new disease-modifying treatments for neurodegeneration.