Establishing Alpha-synuclein RT-QuIC Assay as a Diagnostic Technique in REM Sleep Behaviour Disorder

Establishing Alpha-synuclein Real Time - Quaking Induced Conversion (RT-QuIC) Assay as a Diagnostic Technique in Rapid Eye Movement (REM) Sleep Behaviour Disorder (RBD)

We hypothesise that a real-time quaking induced conversion assay for the detection of pathological alpha-synuclein (α -syn RTQuIC) can be used to differentiate between cases of idiopathic REM-sleep behaviour disorder (RBD) and RBD that is symptomatic of prodromal α-synucleinopathies.

This study will be the largest analysis of cerebrospinal fluid (CSF) α-synuclein in Rapid Eye Movement Behaviour Disorder (RBD) patients to date. In line with the The National CJD Research & Surveillance Unit (NCJDRSU)'s recent inclusion of a positive RT-QuIC for pathological prion protein in the diagnostic criteria for Creutzfeldt-Jakob Disease (CJD) [1], we aim to deploy this novel method to establish it as an accurate research and diagnostic resource in the assessment and prognosis of RBD. This research is transformative and has the potential to change practice.

Currently, there is no simple method with high sensitivity and specificity available which can identify patients who will go on to develop an α - synucleinopathy. Clinical assessment of a panel of markers (e.g. Postuma et al. 2015) are time-consuming and impractical in normal clinical settings, with the majority of patients presenting to sleep physicians, geriatricians, and non-specialised neurology clinics, both publicly and privately. This has a major impact on counselling strategies for RBD patients, appropriate follow-up, trials of novel neuro-protective agents in alpha-synucleinopathies before full-blown phenotype is manifest and enhancing understanding of pathways involved in RBD out-with the dopaminergic system.

RBD is a common, sometimes fatal disease (through injury to self/others) and treatments are indiscriminate regarding aetiology with limited evidence-base. A simple test using CSF (analogous to measuring CSF-orexin levels to diagnose narcolepsy+cataplexy) with high sensitivity and specificity is ideal. Thus, we believe that the central thesis of our work will not only inform subsequent behavioural, genetic and neuroimaging characterisation of our established RBD cohort, but will also translate the α-syn RT-QuIC concept into evidence-based and effective clinical practice.

Inclusion Criteria:

• Patients diagnosed with Rapid Eye Movement Behaviour Disorder (RBD) using the International Classification of Sleep Disorders version 3 (ICSD-3) criteria [18] - Patients aged 18 years and over - Patient able to give written informed consent

Exclusion Criteria:

• RBD secondary to medication or withdrawal state. - <18 years old - Inability to give written informed consent - Contraindication to lumbar puncture procedure (e.g. patients taking Warfarin)