Introduction:The pathophysiological processes of neurodegenerative diseases begin years before diagnosis. However, pre-diagnostic changes in cognition and physical function are poorly understood, especially in sporadic neurodegenerative disease. Methods: UK Biobank data were extracted. Cognitive and functional measures in individuals who subsequently developed Alzheimer's disease (AD), Parkinson disease, frontotemporal dementia, progressive supranuclear palsy, dementia with Lewy bodies, or multiple system atrophy were compared against individuals without neurodegenerative diagnoses. The same measures were regressed against time to diagnosis, after adjusting for the effects of age. Results: There was evidence for pre-diagnostic cognitive impairment and decline with time, particularly in AD. Pre-diagnostic functional impairment and decline were observed in multiple diseases. Discussion: The scale and longitudinal follow-up of UK Biobank participants provides evidence for cognitive and functional decline years before symptoms become obvious in multiple neurodegenerative diseases. Identifying pre-diagnostic functional and cognitive changes could improve selection for preventive and early disease-modifying treatment trials.

Introduction: Prediagnostic features of Parkinson's Disease are well described but prediagnostic Progressive Supranuclear Palsy (PSP) is less understood. The diagnosis of PSP is delayed by an average of three years after symptom onset. Understanding the changes that occur in the prediagnostic period will aid earlier diagnosis, clarify the natural history, and may aid the design of early disease-modifying therapy trials. We set out to identify motor and cognitive markers of prediagnostic PSP, with Parkinson's disease as a comparator condition, in a large prospective cohort. Methods: Baseline UK Biobank data from 502,504 individuals were collected between 2006 and 2010. Subsequent PSP and Parkinson's disease cases were identified from primary and secondary care electronic health records' diagnostic coding data and death registry, with 5404 matched controls. Results: 176 PSP cases (time to diagnosis 7.8 ± 2.8 years) and 2526 Parkinson's disease cases (time to diagnosis 7.8 ± 2.9 years) were identified. At baseline, those later diagnosed with PSP had slower reaction times, weaker hand grip, lower fluid intelligence, prospective memory, self-rated health scores and digit recall than controls. Reaction times were correlated with time to diagnosis. The PSP group had higher mortality than both Parkinson's disease and control groups. Conclusions: Motor slowing, cognitive dysfunction, and postural instability are clinical diagnostic features of PSP that are typically symptomatic three years before diagnosis. Objective markers of these features were evident on average 7.8 years before diagnosis. Our findings suggest the existence of a long prediagnostic phase in PSP, with subtle changes in motor and cognitive function.

Objective: Synaptic loss is an early feature of neurodegenerative disease models, and is severe in post mortem clinical studies, including frontotemporal dementia. Positron emission tomography (PET) with radiotracers that bind to synaptic vesicle glycoprotein 2A enables quantification of synaptic density in vivo. This study used [ 11 C]UCB-J PET in participants with behavioral variant frontotemporal dementia (bvFTD), testing the hypothesis that synaptic loss is severe and related to clinical severity. Methods: Eleven participants with clinically probable bvFTD and 25 age-and sex-matched healthy controls were included. Participants underwent dynamic [ 11 C]UCB-J PET, structural magnetic resonance imaging, and a neuropsychological battery, including the revised Addenbrooke Cognitive Examination, and INECO frontal screening. General linear models compared [ 11 C]UCB-J binding potential maps and gray matter volume between groups, and assessed associations between synaptic density and clinical severity in patients. Analyses were also performed using partial volume corrected [ 11 C]UCB-J binding potential from regions of interest (ROIs). Results: Patients with bvFTD showed severe synaptic loss compared to controls. [ 11 C]UCB-J binding was 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 frontal and cingulate regions correlated significantly with cognitive impairments. Synaptic loss was more severe than atrophy. Results from ROI-based analyses mirrored the voxelwise results. Interpretation: In accordance with preclinical models, and human postmortem evidence, there is widespread frontotemporal loss of synapses in symptomatic bvFTD, in proportion to severity. [ 11 C]UCB-J PET could support translational studies and experimental medicine strategies for new disease-modifying treatments for neurodegeneration.