CSF proteome profiling identifies novel biomarkers for Frontotemporal Dementia and its pathological subtypes

BackgroundFrontotemporal dementia (FTD) is caused by frontotemporal lobar degeneration (FTLD) and the most common forms are characterized by either tau (FTLD-Tau) or TDP43 (FTLD-TDP) brain aggregates. However, FTD-specific fluid biomarkers are lacking. Furthermore, the pathological subtypes are not distinct in their presentation, hampering accurate subtyping at clinical diagnosis. Therefore, there is a strong need to identify fluid biomarkers that could aid in FTD diagnosis and to discriminate the pathological subtypes.MethodWe employed an antibody-based proteomic technology to analyze >600 proteins in a large multicenter cohort including cerebrospinal fluid (CSF) samples from FTD (n = 189), AD (n = 235) and cognitively unimpaired individuals (n = 196). For a subset of cases the underlying neuropathology was known or could be predicted (FTLD-Tau = 85 and FTLD-TDP = 57). Differences in protein expression profiles were analyzed by nested linear models. Penalized generalized linear modeling was used to identify classification protein panels. Protein panels were then validated in independent clinical cohorts (cohort 1: n = 157; cohort 2: n = 165) and a neuropathology cohort (n = 100) using customized assays.ResultWe observed 65 differentially regulated proteins in FTD versus controls and AD patients, associated with axonogenesis, synapse assembly, or locomotory behavior pathways. We identified panels of 14 and 13 proteins that could discriminate FTD from controls (AUC = 0.96, 95%CI:0.91-0.99) and AD patients (AUC = 0.91, 95%CI:0.85-0.96), respectively. Most of these proteins (21 out of 27) were translated into customized panels, which discriminated between groups with high accuracy for all three cohorts (FTDvsCon: AUCs > 0.96, FTDvsAD: AUCs > 0.88). When comparing the FTLD-Tau and FTLD-TDP subtypes, we observed that 86 proteins were increased in FTLD-Tau, and associated with developmental and cellular processes and locomotion pathways. A panel of 8 proteins could discri