• Edwin Jabbari, John Woodside, Tong Guo, Nadia K Magdalinou, Viorica Chelban, Dilan Athauda, Andrew J Lees, Thomas Foltynie, Henry Houlden, Alistair Church, Michele Tm Hu, James B Rowe, Henrik Zetterberg, and Huw R Morris.
• Department of Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, University College London, London, UK e.jabbari@ucl.ac.uk.
• J. Neurol. Neurosurg. Psychiatr. 2019 Jul 1; 90 (7): 768-773.

ObjectiveThe high degree of clinical overlap between atypical parkinsonian syndromes (APS) and Parkinson's disease (PD) makes diagnosis challenging. We aimed to identify novel diagnostic protein biomarkers of APS using multiplex proximity extension assay (PEA) testing.MethodsCerebrospinal fluid (CSF) samples from two independent cohorts, each consisting of APS and PD cases, and controls, were analysed for neurofilament light chain (NF-L) and Olink Neurology and Inflammation PEA biomarker panels. Whole-cohort comparisons of biomarker concentrations were made between APS (n=114), PD (n=37) and control (n=34) groups using logistic regression analyses that included gender, age and disease duration as covariates.ResultsAPS versus controls analyses revealed 11 CSF markers with significantly different levels in cases and controls (p<0.002). Four of these markers also reached significance (p<0.05) in APS versus PD analyses. Disease-specific analyses revealed lower group levels of FGF-5, FGF-19 and SPOCK1 in multiple system atrophy compared with progressive supranuclear palsy and corticobasal syndrome. Receiver operating characteristic curve analyses suggested that the diagnostic accuracy of NF-L was superior to the significant PEA biomarkers in distinguishing APS, PD and controls. The biological processes regulated by the significant proteins include cell differentiation and immune cell migration. Delta and notch-like epidermal growth factor-related receptor (DNER) had the strongest effect size in APS versus controls and APS versus PD analyses. DNER is highly expressed in substantia nigra and is an activator of the NOTCH1 pathway which has been implicated in the aetiology of other neurodegenerative disorders including Alzheimer's disease.ConclusionsPEA testing has identified potential novel diagnostic biomarkers of APS.© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY. Published by BMJ.

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