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The worldwide prevalence of Parkinson’s disease (PD) has been constantly increasing in the last decades. With rising life expectancy, a longer disease duration in PD patients is observed, further increasing the need and socioeconomic importance of adequate PD treatment. Today, PD is exclusively treated symptomatically, mainly by dopaminergic stimulation, while efforts to modify disease progression could not yet be translated to the clinics. New formulations of approved drugs and treatment options of motor fluctuations in advanced stages accompanied by telehealth monitoring have improved PD patients care. In addition, continuous improvement in the understanding of PD disease mechanisms resulted in the identification of new pharmacological targets. Applying novel trial designs, targeting of pre-symptomatic disease stages, and the acknowledgment of PD heterogeneity raise hopes to overcome past failures in the development of drugs for disease modification. In this review, we address these recent developments and venture a glimpse into the future of PD therapy in the years to come.

TDP-43 is the primary or secondary pathological hallmark of neurodegenerative diseases, such as amyotrophic lateral sclerosis, half of frontotemporal dementia cases, and limbic age-related TDP-43 encephalopathy, which clinically resembles Alzheimer’s dementia. In such diseases, a biomarker that can detect TDP-43 proteinopathy in life would help to stratify patients according to their definite diagnosis of pathology, rather than in clinical subgroups of uncertain pathology. For therapies developed to target pathological proteins that cause the disease a biomarker to detect and track the underlying pathology would greatly enhance such undertakings. This article reviews the latest developments and outlooks of deriving TDP-43-specific biomarkers from the pathophysiological processes involved in the development of TDP-43 proteinopathy and studies using biosamples from clinical entities associated with TDP-43 pathology to investigate biomarker candidates.

Objective: Levels of chitotriosidase (CHIT1) are increased in the cerebrospinal fluid (CSF) of amyotrophic lateral sclerosis (ALS) patients reflecting microglial activation. Here, we determine the diagnostic and prognostic potential of CHIT1 for early symptomatic ALS. Methods: Overall, 275 patients from 8 European neurological centers were examined. We included ALS with 6 months from symptom onset, other motoneuron diseases (oMND), ALS mimics (DCon) and non-neurodegenerative controls (Con). CSF CHIT1 levels were analyzed for diagnostic power and association with progression and survival in comparison to the benchmark neurofilament. The 24-bp duplication polymorphism of CHIT1 was analyzed in a subset of patients (N=65). Results: Homozygous CHIT1 duplication mutation carriers (9%) invariably had undetectable CSF CHIT1 levels, while heterozygous carriers had similar levels as patients with wildtype CHIT1 (p=0.414). In both early and late symptomatic ALS CHIT1 levels was increased, did not correlate with patients’ progression rates, and was higher in patients diagnosed with higher diagnostic certainty. Neurofilament levels correlated with CHIT1 levels and prevailed over CHIT1 regarding diagnostic performance. Both CHIT1 and neurofilaments were identified as independent predictors of survival in late but not early symptomatic ALS. Evidence is provided that CHIT1 predicts progression in El Escorial diagnostic category in the group of ALS cases with a short duration. Conclusions: CSF CHIT1 level may have additional value in the prognostication of ALS patients with a short history of symptoms classified in diagnostic categories of lower clinical certainty. To fully interpret apparently low CHIT1 levels knowledge of CHIT1 genotype is needed.

ZusammenfassungDie Alzheimer-Krankheit ist pathologisch durch die Aggregation und Akkumulation von Amyloid-β und Protein Tau gekennzeichnet. Bisher war das Ziel der meisten Interventionsstudien die toxischen Proteinprodukte zum Beispiel durch die Immunisierung mit Antikörpern gegen Tau und Amyloid-β zu reduzieren. In den letzten Jahren sind jedoch Möglichkeiten entstanden, direkt auf die Entstehung dieser Proteinprodukte einzuwirken. Dabei werden Antisense-Oligonukleotide (ASO) eingesetzt, die die Proteintranslation pathologischer Alzheimer-Gene hemmen und damit frühzeitig auf die Krankheitsentwicklung Einfluss nehmen. Unser Beitrag fasst den aktuellen Stand der Entwicklung ASO-basierter Therapiestrategien bei der Alzheimer-Krankheit zusammen.

The routine clinical integration of individualized objective markers of disease activity in those diagnosed with the neurodegenerative disorder amyotrophic lateral sclerosis is a key requirement for therapeutic development. A large, multicentre, clinic-based, longitudinal cohort was used to systematically appraise the leading candidate biofluid biomarkers in the stratification and potential therapeutic assessment of those with amyotrophic lateral sclerosis. Incident patients diagnosed with amyotrophic lateral sclerosis (n = 258), other neurological diseases (n = 80) and healthy control participants (n = 101), were recruited and followed at intervals of 3–6 months for up to 30 months. Cerebrospinal fluid neurofilament light chain and chitotriosidase 1 and blood neurofilament light chain, creatine kinase, ferritin, complement C3 and C4 and C-reactive protein were measured. Blood neurofilament light chain, creatine kinase, serum ferritin, C3 and cerebrospinal fluid neurofilament light chain and chitotriosidase 1 were all significantly elevated in amyotrophic lateral sclerosis patients. First-visit plasma neurofilament light chain level was additionally strongly associated with survival (hazard ratio for one standard deviation increase in log10 plasma neurofilament light chain 2.99, 95% confidence interval 1.65–5.41, P = 0.016) and rate of disability progression, independent of other prognostic factors. A small increase in level was noted within the first 12 months after reported symptom onset (slope 0.031 log10 units per month, 95% confidence interval 0.012–0.049, P = 0.006). Modelling the inclusion of plasma neurofilament light chain as a therapeutic trial outcome measure demonstrated that a significant reduction in sample size and earlier detection of disease-slowing is possible, compared with using the revised Amyotrophic Lateral Sclerosis Functional Rating Scale. This study provides strong evidence that blood neurofilament light chain levels outperform conventional measures of disease activity at the group level. The application of blood neurofilament light chain has the potential to radically reduce the duration and cost of therapeutic trials. It might also offer a first step towards the goal of more personalized objective disease activity monitoring for those living with amyotrophic lateral sclerosis.

We describe an autosomal dominant, multi-generational, amyotrophic lateral sclerosis (ALS) pedigree in which disease co-segregates with a heterozygous p.Y374X nonsense mutation within TDP-43. Mislocalization of TDP-43 and formation of insoluble TDP-43-positive neuronal cytoplasmic inclusions is the hallmark pathology in95% of ALS patients. Neuropathological examination of the single case for which CNS tissue was available indicated typical TDP-43 pathology within lower motor neurons, but classical TDP-43-positive inclusions were absent from motor cortex. The mutated allele is transcribed and translated in patient fibroblasts and motor cortex tissue, but overall TDP-43 protein expression is reduced compared to wild-type controls. Despite absence of TDP-43-positive inclusions we confirmed deficient TDP-43 splicing function within motor cortex tissue. Furthermore, urea fractionation and mass spectrometry of motor cortex tissue carrying the mutation revealed atypical TDP-43 protein species but not typical C-terminal fragments. We conclude that the p.Y374X mutation underpins a monogenic, fully penetrant form of ALS. Reduced expression of TDP-43 combined with atypical TDP-43 protein species and absent C-terminal fragments extends the molecular phenotypes associated with TDP-43 mutations and with ALS more broadly. Future work will need to include the findings from this pedigree in dissecting the mechanisms of TDP-43-mediated toxicity.

The pathological hallmark of amyotrophic lateral sclerosis (ALS) is the presence of cytoplasmic inclusions, containing C‐terminal fragments of the protein TDP‐43. Here, we tested the hypothesis that highly sensitive mass spectrometry with parallel reaction monitoring (MS‐PRM) can generate a high‐resolution map of pathological TDP‐43 peptide ratios to form the basis for quantitation of abnormal C‐terminal TDP‐43 fragment enrichment. Human cortex and spinal cord, microscopically staged for the presence of p‐TDP‐43, p‐tau, alpha‐synuclein, and beta‐amyloid pathology, were biochemically fractionated and analyzed by immunoblot and MS for the detection of full‐length and truncated (disease‐specific) TDP‐43 peptides. This informed the synthesis of heavy isotope‐labeled peptides for absolute quantification of TDP‐43 by MS‐PRM across 16 ALS, 8 Parkinson’s, 8 Alzheimer’s disease, and 8 aged control cases. We confirmed by immunoblot the previously described enrichment of pathological C‐terminal fragments in ALS‐TDP urea fractions. Subsequent MS analysis resolved specific TDP‐43 N‐ and C‐terminal peptides, including a novel N‐terminal truncation site‐specific peptide. Absolute quantification of peptides by MS‐PRM showed an increased C:N‐terminal TDP‐43 peptide ratio in ALS‐TDP brain compared to normal and disease controls. A C:N‐terminal ratio >1.5 discriminated ALS from controls with a sensitivity of 100% (CI 79.6–100) and specificity of 100% (CI 68–100), and from Parkinson’s and Alzheimer’s disease with a sensitivity of 93% (CI 70–100) and specificity of 100% (CI 68–100). N‐terminal truncation site‐specific peptides were increased in ALS in line with C‐terminal fragment enrichment, but were also found in a proportion of Alzheimer cases with normal C:N‐terminal ratio but coexistent limbic TDP‐43 neuropathological changes. In conclusion this is a novel, sensitive, and specific method to quantify the enrichment of pathological TDP‐43 fragments in human brain, which could form the basis for an antibody‐free assay. Our methodology has the potential to help clarify if specific pathological TDP‐43 peptide signatures are associated with primary or secondary TDP‐43 proteinopathies., The pathological hallmark of amyotrophic lateral sclerosis (ALS) is the presence of cytoplasmic inclusions, containing C‐terminal fragments of the protein TDP‐43. Here, we used a high‐resolution map of TDP‐43 peptides to form the basis for absolute quantitation of abnormal C‐terminal TDP‐43 fragment enrichment. The C:N‐terminal peptide ratio is increased in ALS brains and N‐terminal truncation‐specific peptides confirm the pathological cleavage of TDP‐43 in ALS and surprisingly AD.

ZusammenfassungDie behaviorale frontotemporale Demenz (bvFTD) ist bei Patienten vor dem 65. Lebensjahr die zweithäufigste Demenzerkrankung nach der Alzheimer-Erkrankung. Die frontotemporalen Atrophien können sich in Form zweier klinischer Subtypen manifestieren. Entweder stehen bei der behavioralen FTD klinisch Verhaltens-, und Persönlichkeitsveränderungen im Vordergrund oder bei der primär progredienten Aphasie eine Störung von Sprachverständnis und -produktion. Eine sichere Diagnose kann bisher nur post mortem mit Hilfe der Neuropathologie oder durch den Nachweis einer genetischen Mutation erfolgen. Zur Diagnosestellung werden neben der klinischen Einteilung derzeit Bildgebungsverfahren (MRT und FDG-PET) zur Beurteilung des Frontal-, und Temporallappens ergänzt. Die Untersuchung von Tau, Amyloid-ß und der Neurofilamente kann zur Abgrenzung einer Alzheimer-Erkrankung erfolgen.

TDP-43 accumulates in nerve cells of nearly all cases of amyotrophic lateral sclerosis (ALS; the commonest form of motor neuron disease) and in the majority of Tau-negative frontotemporal lobar degeneration (FTLD). There is currently no biochemical test or marker of disease activity for ALS or FTLD, and the clinical diagnosis depends on the opinion of an experienced neurologist. TDP-43 has a key role in the pathogenesis of ALS/FTLD. Measuring TDP-43 in easily accessible biofluids, such as blood or cerebrospinal fluid, might reduce diagnostic delay and offer a readout for use in future drug trials. However, attempts at measuring disease-specific forms of TDP-43 in peripheral biofluids of ALS and FTLD patients have not yielded consistent results, and only some of the pathological biochemical features of TDP-43 found in human brain tissue have been detected in clinical biofluids to date. Reflecting on the molecular pathology of TDP-43, this review provides a critical overview on biofluid studies and future directions to develop a TDP-43-based clinical biomarker for ALS and FTLD.

TDP-43 pathology is a key feature of amyotrophic lateral sclerosis (ALS), but the mechanisms linking TDP-43 to altered cellular function and neurodegeneration remain unclear. We have recently described a mouse model in which human wild-type or mutant TDP-43 are expressed at low levels and where altered stress granule formation is a robust phenotype of TDP-43M337V/− expressing cells. In the present study we use this model to investigate the functional connectivity of human TDP-43 in primary motor neurons under resting conditions and in response to oxidative stress. The interactome of human TDP-43WT or TDP-43M337V was compared by mass spectrometry, and gene ontology enrichment analysis identified pathways dysregulated by the M337V mutation. We found that under normal conditions the interactome of human TDP-43WT was enriched for proteins involved in transcription, translation and poly(A)-RNA binding. In response to oxidative stress, TDP-43WT recruits proteins of the endoplasmic reticulum and endosomal-extracellular transport pathways, interactions which are reduced in the presence of the M337V mutation. Specifically, TDP-43M337V impaired protein-protein interactions involved in stress granule formation including reduced binding to the translation initiation factors Poly(A)-binding protein and Eif4a1 and the endoplasmic reticulum chaperone Grp78. The M337V mutation also affected interactions involved in endosomal-extracellular transport and this this was associated with reduced extracellular vesicle secretion in primary motor neurons from TDP-43M337V/− mice and in human iPSCs-derived motor neurons. Taken together, our analysis highlights a TDP-43 interaction network in motor neurons and demonstrates that an ALS associated mutation may alter the interactome to drive aberrant pathways involved in the pathogenesis of ALS.

Background The identification of blood-based biomarkers specific to the diagnosis of amyotrophic lateral sclerosis (ALS) is an active field of academic and clinical research. While inheritance studies have advanced the field, a majority of patients do not have a known genetic link to the disease, making direct sequence-based genetic testing for ALS difficult. The ability to detect biofluid-based epigenetic changes in ALS would expand the relevance of using genomic information for disease diagnosis. Methods Assessing differences in chromosomal conformations (i.e. how they are positioned in 3-dimensions) represents one approach for assessing epigenetic changes. In this study, we used an industrial platform, EpiSwitch™, to compare the genomic architecture of healthy and diseased patient samples (blood and tissue) to discover a chromosomal conformation signature (CCS) with diagnostic potential in ALS. A three-step biomarker selection process yielded a distinct CCS for ALS, comprised of conformation changes in eight genomic loci and detectable in blood. Findings We applied the ALS CCS to determine a diagnosis for 74 unblinded patient samples and subsequently conducted a blinded diagnostic study of 16 samples. Sensitivity and specificity for ALS detection in the 74 unblinded patient samples were 83∙33% (CI 51∙59 to 97∙91%) and 76∙92% (46∙19 to 94∙96%), respectively. In the blinded cohort, sensitivity reached 87∙50% (CI 47∙35 to 99∙68%) and specificity was 75∙0% (34∙91 to 96∙81%). Interpretations The sensitivity and specificity values achieved using the ALS CCS identified and validated in this study provide an indication that the detection of chromosome conformation signatures is a promising approach to disease diagnosis and can potentially augment current strategies for diagnosing ALS. Fund This research was funded by Oxford BioDynamics and Innovate UK. Work in the Oxford MND Care and Research Centre is supported by grants from the Motor Neurone Disease Association and the Medical Research Council. Additional support was provided by the Northeast ALS Consortium (NEALS).

ObjectiveTo determine the diagnostic and prognostic performance of serum neurofilament light chain (NFL) in amyotrophic lateral sclerosis (ALS).MethodsThis single-centre, prospective, longitudinal study included the following patients: 124 patients with ALS; 50 patients without neurodegenerative diseases; 44 patients with conditions included in the differential diagnosis of ALS (disease controls); 65 patients with other neurodegenerative diseases (20 with frontotemporal dementia, 20 with Alzheimer’s disease, 19 with Parkinson’s disease, 6 with Creutzfeldt-Jakob disease (CJD)). Serum NFL levels were measured using the ultrasensitive single molecule array (Simoa) technology.ResultsSerum NFL levels were higher in ALS in comparison to all other categories except for CJD. A cut-off level of 62 pg/mL discriminated between ALS and all other conditions with 85.5% sensitivity (95% CI 78% to 91.2%) and 81.8% specificity (95% CI 74.9% to 87.4%). Among patients with ALS, serum NFL correlated positively with disease progression rate (rs=0.336, 95% CI 0.14 to 0.506, p=0.0008), and higher levels were associated with shorter survival (p=0.0054). Serum NFL did not differ among patients in different ALS pathological stages as evaluated by diffusion-tensor imaging, and in single patients NFL levels were stable over time.ConclusionsSerum NFL is increased in ALS in comparison to other conditions and can serve as diagnostic and prognostic biomarker. We established a cut-off level for the diagnosis of ALS.

Die frontotemporale Demenz wird im Vergleich zur „Alzheimer-Erkrankung“ in der Bevolkerung kaum wahrgenommen. Sie macht jedoch immerhin etwa 20 % der Demenzen bei Patienten unter 65 Jahren aus und ist auf diesem Gebiet die zweithaufigste Diagnose [1].

ObjectiveTo examine neurofilament (Nf) concentrations according to symptom onset and clinical diagnostic certainty categories of amyotrophic lateral sclerosis (ALS).MethodsWe measured Nf light chain (NfL) and phosphorylated Nf heavy chain (pNfH) CSF and NfL serum levels in patients with ALS with first symptom onset ≤6 months (n = 54) or >6 months (n = 135) from sampling, and patients with other neurologic diseases, differential diagnoses of a motor neuron disease (MND mimics), and other MND variants to determine the diagnostic accuracy in patients with ALS with early symptom onset. Samples were received multicentric and analyzed by ELISA and Simoa platform and related to other clinical measures.ResultsNfL and pNfH in CSF and NfL in serum were increased in early and later symptomatic phase ALS (p < 0.0001). CSF and serum NfL and CSF pNfH discriminated patients with ALS with early symptom onset from those with other neurologic diseases and MND mimics with high sensitivity (94%, 88%, 98%, and 89%, 100%, 78%) and specificity (86%, 92%, 91%, and 94%, 90%, 98%) and did not vary between clinical diagnostic categories of ALS in the early symptomatic phase group. Baseline NfL and pNfH levels were not significantly different in patients with ALS with clinical progression to definite or probable ALS at follow-up.ConclusionThe measurement of Nf has potential to enhance diagnostic accuracy of ALS in those presenting soon after symptom onset, and is measurable across multiple centers.Classification of evidenceThis study provides Class II evidence that CSF and serum Nf concentrations discriminate ALS with early symptom onset from other neurologic diseases.

Frontotemporal lobar degeneration (FTLD) is a heterogeneous group of syndromes with different symptoms. Frontotemporal lobar degeneration is mostly used as a clinical umbrella term for different diseases. In some clinical subtypes of the FTLD spectrum, a close correlation with underlying pathology can be found. Neuroimaging techniques, such as magnetic resonance imaging and position emission tomography help to detect neuroanatomical lesions and therefore obtain relevance for in vivo prediction of neurodegeneration. However, there is still a lack of neurochemical biomarkers helping to differentiate between underlying histopathologies. The following review gives an overview about present neurochemical biomarker studies and perspective approaches in the diagnosis of FTLD.

TAR DNA-binding protein 43 (TDP-43) is one of the neuropathological hallmarks in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). It is present in patients' blood and cerebrospinal fluid (CSF); however, the source and clinical relevance of TDP-43 measurements in body fluids is uncertain. We investigated paired CSF and serum samples, blood lymphocytes, brain urea fractions and purified exosomes from CSF for TDP-43 by one- (1D), and two-dimensional (2D) Western immunoblotting (WB) and quantitative mass spectrometry (MRM) in patients with ALS, FTLD and non-neurodegenerative diseases. By means of 2D-WB we were able to demonstrate a similar isoform pattern of TDP-43 in lymphocytes, serum and CSF in contrast to that of brain urea fractions with TDP-43 pathology. We found that the TDP-43 CSF to blood concentration ratio is about 1:200. As a possible brain specific fraction we found TDP-43 in exosome preparations from CSF by immunoblot and MRM. We conclude that TDP-43 in CSF originates mainly from blood. Measurements of TDP-43 in CSF and blood are of minor importance as a diagnostic tool, but may be important for monitoring therapy effects of TDP-43 modifying drugs.

Die Amyotrophe Lateralsklerose (ALS) und die Gruppe der Frontotemporalen Lobardegenera­tionen (FTLD) sind progredient neurodegenera­tive Erkrankungen, die bei der ALS zu einer schweren kontinuierlich fortscheitenden Lahmung der Muskulatur und schlieslich respiratorischer Insuffizienz und bei der FTLD zu einer zunehmenden Storung des Verhaltens, der Sprache und in manchen Fallen der Motorik fuhrt. In den letzten Jahren ruckte die klinische Uberlappung der beiden Krankheitsbilder wieder in den Vordergrund, nachdem man aggregiertes TDP-43 im Zytoplasma von Nervenzellen als gemeinsame histopathologische Veranderung gefunden hat. Es wurde die Hypothese formuliert, dass es sich bei beiden Krankheitsbildern um die Pole eines sowohl klinischen als auch pathophysiologischen Kontinuums handelt. Zunachst konnten als moglicher molekularer Mechanismus Mutationen im TDP-43-Gen nachgewiesen werden. Weiterhin wurde eine pathologische Repeat-Expansion auf Chromosom 9 – C9orf72 – beschrieben, die in Europa mit etwa 25 bis 30% aller genetisch bedingten ALS-Erkrankungen und etwa 11% aller genetisch bedingten FTLD-Erkrankungen assoziiert ist. Interessant ist, dass auch bis zu 20% der zunachst sporadisch Erkrankten eine C9orf72 Expansion aufweisen. Bei asymptomatischen Gentragern und bei sporadischen Formen der Erkrankung bereitet vor allem im Fruhstadium der Erkrankungen das rechtzeitige Erkennen und richtige Einordnen der Symptome von ALS und FTLD Schwierigkeiten. Zur besseren differen­zialdiagnostischen und prognostischen Einschatzung sind daher zuverlassige Biomarker notig.

Increased serum neurofilament is associated with CNS axonal loss from a range of causes. We assessed its potential as a minimally-invasive indicator of active CNS pathology in those with neurological symptoms.GP referrals to the Neurology Rapid Access Clinic (RAC) at the John Radcliffe Hospital, Oxford were approached to take part. Informed consent was taken under a local Research Ethics Committee-approved protocol. Serum was taken prior to clinical assessment and tested for phosphorylated neurofilament heavy chain (pNFH) using a commercial ELISA (Euroimmun, Germany). Participants were followed up for final diagnosis.The 62 participants had a range of symptoms, with final diagnoses including migraine, functional, neurodegenerative and inflammatory conditions. Receiver Operating Curve analysis defined cut-off levels based on serum pNfH levels in healthy controls and patients with motor neurone disease measured as part of an independent local biomarker study. pNFH levels in the ‘pathological’ range were associated with serious underlying pathology in several RAC referrals. Ongoing analysis of the cohort will be presented.Alongside clinical reasoning, serum pNFH may have significant value for the improved triage of those presenting to primary care with neurological symptoms. Further study in larger populations, including healthy individuals, is now warranted.

Frontotemporal lobar degeneration (FTLD) is a spectrum of rare neurodegenerative diseases with overlapping symptoms and neuropathology. It includes the behavioral variant of frontotemporal dementia (bvFTD), the semantic and non-fluent variant of primary progressive aphasia (svPPA and nfvPPA), FTD with motor neuron disease (FTD-MND), progressive supranuclear palsy, and corticobasal syndrome. The diagnosis of the FTLD spectrum of diseases is based on clinical symptoms which hampers the differentiation of the diseases among each other and with other disorders that show a similar clinical appearance resulting in a high rate of misdiagnoses. This highlights the need for objective and selective measures in the diagnostic criteria and there is extensive research on neurochemical biomarkers in FTLD as one option to address this unmet clinical need. Here, we review the advances in CSF biomarker research in FTLD in the last 2 years with regard to the validation of previously suggested and identification of new biomarker candidates for the differential diagnosis of FTLD. New biomarkers for frontotemporal lobar degeneration (FTLD) are urgently needed to support differential diagnosis within the disease spectrum and with related neurodegenerative diseases such as Alzheimer disease (AD). Here, we review the advances in cerebrospinal fluid biomarker research in FTLD and provide a list of promising candidate markers.

Frontotemporal lobar degeneration (FTLD) comprises a spectrum of rare neurodegenerative diseases with an estimated prevalence of 15-22 cases per 100,000 persons including the behavioral variant of frontotemporal dementia (bvFTD), progressive non-fluent aphasia (PNFA), semantic dementia (SD), FTD with motor neuron disease (FTD-MND), progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS). The pathogenesis of the diseases is still unclear and clinical diagnosis of FTLD is hampered by overlapping symptoms within the FTLD subtypes and with other neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). Intracellular protein aggregates in the brain are a major hallmark of FTLD and implicate alterations in protein metabolism or function in the disease's pathogenesis. Cerebrospinal fluid (CSF) which surrounds the brain can be used to study changes in neurodegenerative diseases and to identify disease-related mechanisms or neurochemical biomarkers for diagnosis. In the present review, we will give an overview of the current literature on proteomic studies in CSF of FTLD patients. Reports of targeted and unbiased proteomic approaches are included and the results are discussed in regard of their informative value about disease pathology and the suitability to be used as diagnostic biomarkers. Finally, we will give some future perspectives on CSF proteomics and a list of candidate biomarkers which might be interesting for validation in further studies. This article is part of a Special Issue entitled: Neuroproteomics: Applications in neuroscience and neurology.

The impairment of the ubiquitin-proteasome system (UPS) is thought to be an early event in neurodegeneration, and monitoring UPS alterations might serve as a disease biomarker. Our aim was to establish an alternate method to antibody-based assays for the selective measurement of free monoubiquitin in cerebrospinal fluid (CSF). Free monoubiquitin was measured with liquid chromatography-multiple reaction monitoring mass spectrometry (LC-MS/MS) in CSF of patients with Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), behavioral variant of frontotemporal dementia (bvFTD), Creutzfeldt-Jakob disease (CJD), Parkinson's disease (PD), primary progressive aphasia (PPA), and progressive supranuclear palsy (PSP). The LC-MS/MS method showed excellent intra- and interassay precision (4.4-7.4% and 4.9-10.3%) and accuracy (100-107% and 100-106%). CSF ubiquitin concentration was increased compared with that of controls (33.0 ± 9.7 ng/mL) in AD (47.5 ± 13.1 ng/mL, p0.05) and CJD patients (171.5 ± 103.5 ng/mL, p0.001) but not in other neurodegenerative diseases. Receiver operating characteristic curve (ROC) analysis of AD vs control patients revealed an area under the curve (AUC) of 0.832, and the specificity and sensitivity were 75 and 75%, respectively. ROC analysis of AD and FTLD patients yielded an AUC of 0.776, and the specificity and sensitivity were 53 and 100%, respectively. In conclusion, our LC-MS/MS method may facilitate ubiquitin determination to a broader community and might help to discriminate AD, CJD, and FTLD patients.

Objectives S100B was proposed to be a CSF and blood biomarker in a number of neurological diseases. The route of S100B to the CSF and the blood in neurodegenerative diseases is unclear. To assess the impact of the physiological or impaired blood-CSF-barrier (BCSFB) function on S100B concentrations in CSF and serum, we analysed S100B in correlation of the albumin quotient. Materials and methods S100Bserum and S100BCSF were quantified in samples from patients with a variety of neurological diseases using an immunoluminometric assay (Sangtec LIA-mat). Measures were analysed for a potential relation to the CSF/serum-albumin quotient (Qalb), which indicates the BCSFB functionality. Results We reasserted increased S100B concentrations in CSF and serum of CJD patients. Elevated S100Bserum correlated with elevated S100BCSF in all diagnoses but with exceptions. Neither S100BCSF nor S100Bserum did correlate with Qalb, even when the BCSFB function was progressively impaired as demonstrated by increased Qalb. Conclusions The lack of correlation between Qalb and S100BCSF is typically seen for proteins which are brain derived. Therefore, we propose that S100B enters the blood with the bulk flow via Pacchioni's granules and along the spinal nerve sheaths.

Glial fibrillary acidic protein (GFAP) is an established indicator of astrogliosis. Therefore, variable cerebrospinal fluid (CSF) concentrations of this protein might reflect disease-specific pathologic profiles. In patients with narcolepsy, a loss of hypocretin-1 (hcrt-1) neurons in the brain and low concentrations of hcrt-1 in CSF have been reported. We performed a commercially available enzyme-linked immunosorbent assay to investigate if GFAP also is altered in the CSF of these patients. Here we detected significantly higher CSF levels of GFAP in patients with low hcrt-1 levels, of which the majority had a diagnosis of narcolepsy and cataplexy (NC); however, this finding was not observed in patients with hcrt-1 levels that were within reference range. In conclusion, GFAP may be useful as an additional disease biomarker in patients with narcolepsy, and this hypothesis should be investigated in larger studies.