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Poly-GP in cerebrospinal fluid links C9orf72-associated dipeptide repeat expression to the asymptomatic phase of ALS/FTD

EMBO Mol Med. 2017 Apr 13. pii: e201607486. doi: 10.15252/emmm.201607486. [Epub ahead of print]

Authors/Editors: Lehmer C, Oeckl P, Weishaupt JH, Volk AE, Diehl-Schmid J, Schroeter ML, Lauer M, Kornhuber J, Levin J, Fassbender K, Landwehrmeyer B; German Consortium for Frontotemporal Lobar Degeneration, Schludi MH, Arzberger T, Kremmer E, Flatley A, Feederle R, Steinacker P, Weydt P, Ludolph AC, Edbauer D, Otto M.
Publication Date: 2017

2017_04_Lehmer

Abstract

The C9orf72 GGGGCC repeat expansion is a major cause of amyotrophic lateral sclerosis and frontotemporal dementia (c9ALS/FTD). Non-conventional repeat translation results in five dipeptide repeat proteins (DPRs), but their clinical utility, overall significance, and temporal course in the pathogenesis of c9ALS/FTD are unclear, although animal models support a gain-of-function mechanism. Here, we established a poly-GP immunoassay from cerebrospinal fluid (CSF) to identify and characterize C9orf72 patients. Significant poly-GP levels were already detectable in asymptomatic C9orf72 mutation carriers compared to healthy controls and patients with other neurodegenerative diseases. The poly-GP levels in asymptomatic carriers were similar to symptomatic c9ALS/FTD cases. Poly-GP levels were not correlated with disease onset, clinical scores, and CSF levels of neurofilaments as a marker for axonal damage. Poly-GP determination in CSF revealed a C9orf72 mutation carrier in our cohort and may thus be used as a diagnostic marker in addition to genetic testing to screen patients. Presymptomatic expression of poly-GP and likely other DPR species may contribute to disease onset and thus represents an alluring therapeutic target.

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