Detection of α-synuclein in CSF by RT-QuIC in patients with isolated rapid-eye-movement sleep behaviour disorder: a longitudinal observational study

Summary

Background

Isolated rapid-eye-movement (REM) sleep behaviour disorder (IRBD) can be part of the prodromal stage of the α-synucleinopathies Parkinson's disease and dementia with Lewy bodies. Real-time quaking-induced conversion (RT-QuIC) analysis of CSF has high sensitivity and specificity for the detection of misfolded α-synuclein in patients with Parkinson's disease and dementia with Lewy bodies. We investigated whether RT-QuIC could detect α-synuclein in the CSF of patients with IRBD and be used as a biomarker of prodromal α-synucleinopathy.

Methods

In this longitudinal observational study, CSF samples were obtained by lumbar puncture from patients with video polysomnography-confirmed IRBD recruited at a specialised sleep disorders centre in Barcelona, Spain, and from controls free of neurological disease. CSF samples were stored until analysed using RT-QuIC. After lumbar puncture, participants were assessed clinically for neurological status every 3–12 months. Rates of neurological disease-free survival were estimated using the Kaplan-Meier method. Disease-free survival rates were assessed from the date of lumbar puncture to the date of diagnosis of any neurodegenerative disease, or to the last follow-up visit for censored observations.

Findings

52 patients with IRBD and 40 healthy controls matched for age (p=0·20), sex (p=0·15), and duration of follow-up (p=0·27) underwent lumbar puncture between March 23, 2008, and July 16, 2017. The CSF α-synuclein RT-QuIC assay was positive in 47 (90%) patients with IRBD and in four (10%) controls, resulting in a sensitivity of 90·4% (95% CI 79·4–95·8) and a specificity of 90·0% (95% CI 76·9–96·0). Mean follow-up from lumbar puncture until the end of the study (July 31, 2020) was 7·1 years (SD 2·8) in patients with IRBD and 7·7 years (2·9) in controls. During follow-up, 32 (62%) patients were diagnosed with Parkinson's disease or dementia with Lewy bodies a mean 3·4 years (SD 2·6) after lumbar puncture, of whom 31 (97%) were α-synuclein positive at baseline. Kaplan-Meier analysis showed that patients with IRBD who were α-synuclein negative had lower risk for developing Parkinson's disease or dementia with Lewy bodies at 2, 4, 6, 8, and 10 years of follow-up than patients with IRBD who were α-synuclein positive (log-rank test p=0·028; hazard ratio 0·143, 95% CI 0·019–1·063). During follow-up, none of the controls developed an α-synucleinopathy. Kaplan-Meier analysis showed that participants who were α-synuclein negative (ie, five patients with IRBD plus 36 controls) had lower risk of developing Parkinson's disease or dementia with Lewy bodies at 2, 4, 6, 8 and 10 years after lumbar puncture than participants who were α-synuclein positive (ie, 47 patients with IRBD plus four controls; log-rank test p<0·0001; hazard ratio 0·024, 95% CI 0·003–0·177).

Interpretation

In patients with IRBD, RT-QuIC detects misfolded α-synuclein in the CSF with both sensitivity and specificity of 90%, and α-synuclein positivity was associated with increased risk of subsequent diagnosis of Parkinson's disease or dementia with Lewy bodies. Detection of α-synuclein in the CSF represents a potential prodromal marker of Parkinson's disease and dementia with Lewy bodies. If these findings are replicated in additional cohorts, detection of CSF α-synuclein by RT-QuIC could be used to enrich IRBD cohorts in neuroprotective trials, particularly when assessing interventions that target α-synuclein.

Funding

Department of Health and Social Care Policy Research Programme, the Scottish Government, and the Weston Brain Institute.

Introduction

Parkinson's disease and dementia with Lewy bodies are clinical syndromes featuring neurological symptoms (eg, parkinsonism, cognitive impairment, smell loss, sleep problems) that are associated with deposits of intraneuronal misfolded α-synuclein, which constitute the main component of Lewy bodies and neurites. Rapid-eye-movement (REM) sleep behaviour disorder (RBD) is characterised by dream-enactment behaviours linked to REM sleep without muscle atonia.¹ Most patients with the isolated form of RBD (IRBD) are eventually diagnosed with a clinical form of α-synucleinopathy—namely Parkinson's disease, dementia with Lewy bodies, or, much more rarely, multiple system atrophy.2, 3, 4 The reliable identification of pathological α-synuclein in people with IRBD could represent a valuable biomarker of the prodromal stages of α-synucleinopathies.

Research in context

Evidence before this study

We searched Medline for articles published in any language between Jan 1, 1987, and Nov 7, 2020, with the terms “idiopathic REM sleep behaviour disorder”, “Parkinson disease”, “dementia with Lewy bodies”, “synuclein”, and “RT-QuIC”, and found no previous studies focusing on the detection of misfolded α-synuclein in the CSF of patients with isolated rapid-eye-movement sleep behaviour disorder (IRBD). In one study that assessed the use of real-time quaking-induced conversion (RT-QuIC) for detection of α-synuclein in the CSF of 122 patients with various neurological conditions, α-synuclein was detected in all three patients with IRBD. Another study of 439 CSF samples found that α-synuclein RT-QuIC was positive in 18 of 18 patients with IRBD. Neither of these studies reported detailed baseline and follow-up information for the patients with IRBD who had a positive CSF α-synuclein RT-QuIC response.

Added value of this study

Our findings suggest that in people with IRBD, RT-QuIC is a highly sensitive and specific assay for detecting misfolded α-synuclein in CSF. Detection of α-synuclein in the CSF by RT-QuIC seems to be a biomarker of prodromal Parkinson's disease and dementia with Lewy bodies.

Implications of all the available evidence

RT-QuIC detected misfolded α-synuclein in most of our patients with IRBD. This information could be useful for the design of future neuroprotective trials in IRBD, particularly when investigating agents that interfere with the deposition and propagation of misfolded α-synuclein in the brain.

Biochemical abnormalities in the brain are reflected by changes within the CSF. Real-time quaking-induced conversion (RT-QuIC) is a novel ultrasensitive assay able to detect pathological misfolded proteins.⁵ This technique identifies misfolded α-synuclein in the CSF of patients with manifest Parkinson's disease and dementia with Lewy bodies with a sensitivity of 90–95% and specificity of 80–100%.5, 6, 7, 8, 9, 10, 11, 12 The aim of this study was to assess whether RT-QuIC shows the same high degree of sensitivity and specificity for detecting α-synuclein in the CSF of patients with IRBD as it does in patients with Parkinson's disease and dementia with Lewy bodies, and to determine whether this technique could act as a reliable biomarker of prodromal α-synucleinopathy. Such a finding would provide strong evidence that IRBD is an ongoing α-synucleinopathy detected in the early stages and could contribute to the development of neuroprotective trials in IRBD, focusing on interventions to prevent the deposition and spread of α-synuclein in the brain.¹³