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Abstract Introduction Increasing evidence implicates proteostatic dysfunction as an early event in the development of frontotemporal dementia (FTD). This study aimed to explore potential cerebrospinal fluid (CSF) biomarkers associated with the proteolytic systems in genetic FTD caused by CHMP2B mutation. Methods Combining solid‐phase extraction and parallel reaction monitoring mass spectrometry, a panel of 47 peptides derived from 20 proteins was analyzed in CSF from 31 members of the Danish CHMP2B‐FTD family. Results Compared with family controls, mutation carriers had significantly higher levels of complement C9, lysozyme and transcobalamin II, and lower levels of ubiquitin, cathepsin B, and amyloid precursor protein. Discussion Lower CSF ubiquitin concentrations in CHMP2B mutation carriers indicate that ubiquitin levels relate to the specific disease pathology, rather than all‐cause neurodegeneration. Increased lysozyme and complement proteins may indicate innate immune activation. Altered levels of amyloid precursor protein and cathepsins have previously been associated with impaired lysosomal proteolysis in FTD. Highlights CSF markers of proteostasis were explored in CHMP2B‐mediated frontotemporal dementia (FTD). 31 members of the Danish CHMP2B‐FTD family were included. We used solid‐phase extraction and parallel reaction monitoring mass spectrometry. Six protein levels were significantly altered in CHMP2B‐FTD compared with controls. Lower CSF ubiquitin levels in patients suggest association with disease mechanisms.

Abstract Introduction Synaptic dysfunction and degeneration is one of the earliest events in Alzheimer's disease (AD) and the best correlate of cognitive decline. Thus, identification and validation of biomarkers reflecting synaptic degeneration to be used as prognostic biomarkers are greatly needed. Method Solid‐phase extraction and parallel reaction monitoring mass spectrometry were used to quantify 17 synaptic proteins in CSF, in two cross‐sectional studies including AD (n = 52) and controls (n = 37). Results Increased concentrations of beta‐synuclein, gamma‐synuclein, neurogranin, phosphatidylethanolamine‐binding protein 1, and 14‐3‐3 proteins were observed in AD patients compared to controls, while neuronal pentraxin‐2 and neuronal pentraxin receptor were decreased. Discussion We have established a method with a novel panel of synaptic proteins as biomarkers of synaptic dysfunction. The results indicate that several of the proteins included in the panel may serve as synaptic biomarkers for AD.