Diagnostic Value of Cerebrospinal Fluid Neurofilament Light Protein in Neurology: A Systematic Review and Meta-analysis

The path to biomarker-based diagnostic criteria for the spectrum of neurodegenerative diseases

Introduction: The postmortem examination still represents the reference standard for detecting the pathological nature of chronic neurodegenerative diseases (NDD). This approach displays intrinsic conceptual limitations since NDD represent a dynamic spectrum of partially overlapping phenotypes, shared pathomechanistic alterations that often give rise to mixed pathologies.Areas covered: We scrutinized the international clinical diagnostic criteria of NDD and the literature to provide a roadmap toward a biomarker-based classification of the NDD spectrum. A few pathophysiological biomarkers have been established for NDD. These are time-consuming, invasive, and not suitable for preclinical detection. Candidate screening biomarkers are gaining momentum. Blood neurofilament light-chain represents a robust first-line tool to detect neurodegeneration tout court and serum progranulin helps detect genetic frontotemporal dementia. Ultrasensitive assays and retinal scans may identify Aβ pathology early, in blood and the eye, respectively. Ultrasound also represents a minimally invasive option to investigate the substantia nigra. Protein misfolding amplification assays may accurately detect α-synuclein in biofluids.Expert opinion: Data-driven strategies using quantitative rather than categorical variables may be more reliable for quantification of contributions from pathophysiological mechanisms and their spatial-temporal evolution. A systems biology approach is suitable to untangle the dynamics triggering loss of proteostasis, driving neurodegeneration and clinical evolution.

Dynamics of plasma biomarkers in Down syndrome: the relative levels of Aβ42 decrease with age, whereas NT1 tau and NfL increase

Background

Down syndrome (DS) is the most common genetic cause of Alzheimer’s disease (AD), but diagnosis of AD in DS is challenging due to the intellectual disability which accompanies DS. When disease-modifying agents for AD are approved, reliable biomarkers will be required to identify when and how long people with DS should undergo treatment. Three cardinal neuropathological features characterize AD, and AD in DS—Aβ amyloid plaques, tau neurofibrillary tangles, and neuronal loss. Here, we quantified plasma biomarkers of all 3 neuropathological features in a large cohort of people with DS aged from 3 months to 68 years. Our primary aims were (1) to assess changes in the selected plasma biomarkers in DS across age, and (2) to compare biomarkers measured in DS plasma versus age- and sex-matched controls.

Methods

Using ultra-sensitive single molecule array (Simoa) assays, we measured 3 analytes (Aβ42, NfL, and tau) in plasmas of 100 individuals with DS and 100 age- and sex-matched controls. Tau was measured using an assay (NT1) which detects forms of tau containing at least residues 6–198. The stability of the 3 analytes was established using plasma from ten healthy volunteers collected at 6 intervals over a 5-day period.

Results

High Aβ42 and NT1 tau and low NfL were observed in infants. Across all ages, Aβ42 levels were higher in DS than controls. Levels of Aβ42 decreased with age in both DS and controls, but this decrease was greater in DS than controls and became prominent in the third decade of life. NT1 tau fell in adolescents and young adults, but increased in older individuals with DS. NfL levels were low in infants, children, adolescents, and young adults, but thereafter increased in DS compared to controls.

Conclusions

High levels of Aβ42 and tau in both young controls and DS suggest these proteins are produced by normal physiological processes, whereas the changes seen in later life are consistent with emergence of pathological alterations. These plasma biomarker results are in good agreement with prior neuropathology studies and indicate that the third and fourth decades (i.e., 20 to 40 years of age) of life are pivotal periods during which AD processes manifest in DS. Application of the assays used here to longitudinal studies of individuals with DS aged 20 to 50 years of age should further validate the use of these biomarkers, and in time may allow identification and monitoring of people with DS best suited for treatment with AD therapies.

Increased serum neurofilament light chain concentration indicates poor outcome in Guillain-Barré syndrome

Background

Guillain-Barré syndrome (GBS) is an autoimmune disease that results in demyelination and axonal damage. Five percent of patients die and 20% remain significantly disabled on recovery. Recovery is slow in most cases and eventual disability is difficult to predict, especially early in the disease. Blood or cerebrospinal fluid (CSF) biomarkers that could help identify patients at risk of poor outcome are required. We measured serum neurofilament light chain (sNfL) concentrations from blood taken upon admission and investigated a correlation between sNfL and clinical outcome.

Methods

Baseline sNfL levels in 27 GBS patients were compared with a control group of 22 patients with diagnoses not suggestive of any axonal damage. Clinical outcome parameters for GBS patients included (i) the Hughes Functional Score (HFS) at admission, nadir, and discharge; (ii) the number of days hospitalised; and (iii) whether intensive care was necessary.

Results

The median sNfL concentration in our GBS sample on admission was 85.5 pg/ml versus 9.1 pg/ml in controls. A twofold increase in sNfL concentration at baseline was associated with an HFS increase of 0.6 at nadir and reduced the likelihood of discharge with favourable outcome by a factor of almost three. Higher sNfL levels upon admission correlated well with hospitalisation time (r_s = 0.69, p < 0.0001), during which transfer to intensive care occurred more frequently at an odds ratio of 2.4. Patients with baseline sNfL levels below 85.5 pg/ml had a 93% chance of being discharged with an unimpaired walking ability.

Conclusions

sNfL levels measured at hospital admission correlated with clinical outcome in GBS patients. These results represent amounts of acute axonal damage and reflect mechanisms resulting in disability in GBS. Thus, sNfL may serve as a convenient blood-borne biomarker to personalise patient care by identifying those at higher risk of poor outcome.

This was the year that was: brain barriers and brain fluid research in 2019

This editorial highlights advances in brain barrier and brain fluid research published in 2019, as well as addressing current controversies and pressing needs. Topics include recent advances related to: the cerebral endothelium and the neurovascular unit; the choroid plexus, arachnoid membrane; cerebrospinal fluid and the glymphatic hypothesis; the impact of disease states on brain barriers and brain fluids; drug delivery to the brain; and translation of preclinical data to the clinic. This editorial also mourns the loss of two important figures in the field, Malcolm B. Segal and Edward G. Stopa.

Molecular profiling in Parkinsonian syndromes: CSF biomarkers

An accurate and early diagnosis of degenerative parkinsonian syndromes is a major need for their correct and timely therapeutic management. The current diagnostic criteria are mostly based on clinical features and molecular imaging. However, diagnostic doubts often persist especially in the early stages of diseases when signs are slight, ambiguous and overlapping among different syndromes. Molecular imaging may not be altered in the early stages of diseases, also failing to discriminate among different syndromes. Cerebrospinal fluid (CSF) represents an ideal source of biomarkers reflecting different pathways of neuropathological changes taking place in the brain and preceding the clinical onset. The aim of this review is to provide un update on CSF biomarkers in parkinsonian disorders, discussing in detail their association with neuropathological correlates. Their potential contribution in differential diagnosis and prognostic assessment of different parkinsonian syndromes is also discussed. Before entering the clinical use both for diagnostic and prognostic purposes, these CSF biomarkers need to be thoroughly assessed in terms of pre-analytical and analytical variability, as well as to clinical validation in independent cohorts.

Diagnostic value of plasma phosphorylated tau181 in Alzheimer's disease and frontotemporal lobar degeneration

With the potential development of new disease-modifying Alzheimer's disease (AD) therapies, simple, widely available screening tests are needed to identify which individuals, who are experiencing symptoms of cognitive or behavioral decline, should be further evaluated for initiation of treatment. A blood-based test for AD would be a less invasive and less expensive screening tool than the currently approved cerebrospinal fluid or amyloid β positron emission tomography (PET) diagnostic tests. We examined whether plasma tau phosphorylated at residue 181 (pTau181) could differentiate between clinically diagnosed or autopsy-confirmed AD and frontotemporal lobar degeneration. Plasma pTau181 concentrations were increased by 3.5-fold in AD compared to controls and differentiated AD from both clinically diagnosed (receiver operating characteristic area under the curve of 0.894) and autopsy-confirmed frontotemporal lobar degeneration (area under the curve of 0.878). Plasma pTau181 identified individuals who were amyloid β-PET-positive regardless of clinical diagnosis and correlated with cortical tau protein deposition measured by 18F-flortaucipir PET. Plasma pTau181 may be useful to screen for tau pathology associated with AD.

Perspectives in fluid biomarkers in neurodegeneration from the 2019 biomarkers in neurodegenerative diseases course-a joint PhD student course at University College London and University of Gothenburg

Until relatively recently, a diagnosis of probable Alzheimer's disease (AD) and other neurodegenerative disorders was principally based on clinical presentation, with post-mortem examination remaining a gold standard for disease confirmation. This is in sharp contrast to other areas of medicine, where fluid biomarkers, such as troponin levels in myocardial infarction, form an integral part of the diagnostic and treatment criteria. There is a pressing need for such quantifiable and easily accessible tools in neurodegenerative diseases.In this paper, based on lectures given at the 2019 Biomarkers in Neurodegenerative Diseases Course, we provide an overview of a range of cerebrospinal fluid (CSF) and blood biomarkers in neurodegenerative disorders, including the 'core' AD biomarkers amyloid β (Aβ) and tau, as well as other disease-specific and general markers of neuroaxonal injury. We then highlight the main challenges in the field, and how those could be overcome with the aid of new methodological advances, such as assay automation, mass spectrometry and ultrasensitive immunoassays.As we hopefully move towards an era of disease-modifying treatments, reliable biomarkers will be essential to increase diagnostic accuracy, allow for earlier diagnosis, better participant selection and disease activity and treatment effect monitoring.

Evaluation of single molecule array digital immunoassay technology to quantitate neurofilament light chain

Aim: Globally, neurodegeneration accounts for significant morbidity and mortality among the elderly. Millions of people are afflicted with neurodegenerative diseases, with the most notable cases attributed to Alzheimer's, Huntington's, amyotrophic lateral sclerosis and Parkinson's diseases. Sensitive assays that can detect proteopathic anomalies indicative of early neurodegeneration have remained elusive. Therefore, there is an urgent need for sensitive diagnostic and prognostic biomarker assays that can guide the therapeutic regimen in the clinic. Materials & methods: Single molecule array digital immunoassay platform has sensitivity about 1000-fold higher than traditional ligand binding assays. Consequently, we are now beginning to implement ultrasensitive techniques in bioanalysis. Conclusion: In the current study, we evaluated single molecule array technology and report specifications to quantitate neurofilament light chain, a bona-fide biomarker for neurodegeneration. Preliminary neurofilament light screening results from 100 human geriatric cerebrospinal fluid samples displayed huge biological variation and warrants further investigation.

The Challenge of Disease-Modifying Therapies in Parkinson's Disease: Role of CSF Biomarkers

The development of disease modifying strategies in Parkinson's disease (PD) largely depends on the ability to identify suitable populations after accurate diagnostic work-up. Therefore, patient molecular profiling and disease subtyping are mandatory. Thus far, in clinical trials, PD has been considered to be a "single entity". Conversely, in front of the common feature of nigro-striatal degeneration, PD is pathogenically heterogeneous with a series of several biological and molecular pathways that differently contribute to clinical development and progression. Currently available diagnostic criteria for PD mainly rely on clinical features and imaging biomarkers, thus missing to identify the contribution of pathophysiological pathways, also failing to catch abnormalities occurring in the early stages of disease. Cerebrospinal fluid (CSF) is a promising source of biomarkers, with the high potential for reflecting early changes occurring in PD brain. In this review, we provide an overview on CSF biomarkers in PD, discussing their association with different molecular pathways involved either in pathophysiology or progression in detail. Their potential application in the field of disease modifying treatments is also discussed.

Diagnostic Accuracy of Prion Disease Biomarkers in Iatrogenic Creutzfeldt-Jakob Disease

Human prion diseases are classified into sporadic, genetic, and acquired forms. Within this last group, iatrogenic Creutzfeldt-Jakob disease (iCJD) is caused by human-to-human transmission through surgical and medical procedures. After reaching an incidence peak in the 1990s, it is believed that the iCJD historical period is probably coming to an end, thanks to lessons learnt from past infection sources that promoted new prion prevention and decontamination protocols. At this point, we sought to characterise the biomarker profile of iCJD and compare it to that of sporadic CJD (sCJD) for determining the value of available diagnostic tools in promptly recognising iCJD cases. To that end, we collected 23 iCJD samples from seven national CJD surveillance centres and analysed the electroencephalogram and neuroimaging data together with a panel of seven CSF biomarkers: 14-3-3, total tau, phosphorylated/total tau ratio, alpha-synuclein, neurofilament light, YKL-40, and real-time quaking induced conversion of prion protein. Using the cut-off values established for sCJD, we found the sensitivities of these biomarkers for iCJD to be similar to those described for sCJD. Given the limited relevant information on this issue to date, the present study validates the use of current sCJD biomarkers for the diagnosis of future iCJD cases.

Deciphering the factors that influence participation in studies requiring serial lumbar punctures

INTRODUCTION

Cerebrospinal fluid biomarkers increasingly inform the causes of dementia and may provide objective markers of disease progression. There is a need to decipher participant and procedural factors that promote participation in studies incorporating longitudinal biomarker measures.

METHODS

Participant and procedural factors associated with participation in longitudinal biomarker studies were determined in individuals enrolled in studies of memory and aging at the Knight Alzheimer Disease Research Center (Saint Louis, MO, USA).

RESULTS

Complications were encountered following 331 of 1484 lumbar punctures (22.3%; LPs), affecting 280 of 929 participants (30.1%); in >95% complications were minor. Three hundred fifteen of 679 eligible participants (46.4%) completed multiple LPs. Younger age (odds ratio [OR] 2.08 per decade [95% confidence interval (CI) 1.61-2.94]), normal cognition (OR 21.4 [2.85-160.1]), and the absence of heart disease (OR 2.0 [1.01-3.85]) or seizures at study entry identified participants with increased odds of completing three or more LPs.

DISCUSSION

Factors influencing participation may be leveraged to improve recruitment and retention within observational and therapeutic studies requiring serial LPs.

Neurofilaments: The C-Reactive Protein of Neurology

Neurofilaments (NFs) are quickly becoming the biomarkers of choice in the field of neurology, suggesting their use as an unspecific screening marker, much like the use of elevated plasma C-reactive protein (CRP) in other fields. With sensitive techniques being readily available, evidence is growing regarding the diagnostic and prognostic value of NFs in many neurological disorders. Here, we review the latest literature on the structure and function of NFs and report the strengths and pitfalls of NFs as markers of neurodegeneration in the context of neurological diseases of the central and peripheral nervous systems.

Serum Neurofilament Light Predicts Severity and Prognosis in Patients with Ischemic Stroke

Serum neurofilaments are markers of axonal injury. We investigated whether serum neurofilament light (sNfL) is a potential prognostic marker of functional outcome in Chinese patients with acute ischemic stroke (AIS). From May 2015 to December 2018, consecutive patients with AIS from the Department of Neurology of the Second Hospital of Jilin University were included. sNfL concentration was tested at baseline, and stroke severity was analyzed at admission using the NIHSS score. Functional outcome was assessed at discharge by the modified Rankin scale (mRS). The sNfL concentration was tested in 343 patients with a median value of 17.8 (IQR, 13.4-25.2) pg/ml. sNfL concentration paralleled lesion size (P = 0.035). At admission, 174 patients were defined as moderate-to-high stroke (NIHSS ≥ 5); the sNfL concentration in those patients were higher than that observed in patients with minor clinical severity [21.2 (IQR, 15.1-31.7) vs. 14.9 (11.8-19.4) pg/ml, P < 0.001]. For each 1 quartile increase of sNfL concentration, the unadjusted and adjusted risk of moderate-to-high stroke increased by 202% (with the OR of 3.04 (95% CI 2.15-4.32), P < 0.001) and 102% [2.02 (1.10-3.16), P = 0.001), respectively. At discharge, 85 patients (24.8%) had poor functional outcome (mRS, 3-6); the sNfL concentration in those patients were higher than that observed in patients with good outcome [24.1 (IQR, 18.8-33.9) vs. 15.7 (11.9-21.8) pg/ml, P < 0.001]. For each 1 quartile increase of sNfL concentration, the unadjusted and adjusted risk of poor outcome increased by 236% [with the OR of 3.36 (95% CI 2.23-5.06), P < 0.001] and 102% [2.29 (1.37-3.82), P < 0.001], respectively. The results show sNfL is meaningful blood biomarker to monitor stroke severity and functional outcome in ischemic stroke, suggesting that sNfL may play a role in stroke progression.

Detection of Alzheimer Disease Pathology in Patients Using Biochemical Biomarkers: Prospects and Challenges for Use in Clinical Practice

BACKGROUND

Thirty-four years ago, amyloid-β 1-42 peptide was identified in amyloid plaques from brain tissue obtained from patients with Alzheimer disease (AD) and Down syndrome. This finding led to development of immunoassays for this marker of amyloid plaque burden in cerebrospinal fluid (CSF) approximately 10 years later. Subsequently, research immunoassays were developed for total τ protein and τ phosphorylated at the threonine 181 position. Subsequent studies documented the clinical utility of these biomarkers of amyloid plaque burden or τ tangle pathology in cohorts of living patients.

CONTENT

We describe the following: (a) clinical utility of AD biomarkers; (b) measurement challenges, including development of mass spectrometry-based reference methods and automated immunoassays; (c) development of "appropriate use criteria" (AUC) guidelines for safe/appropriate use of CSF testing for diagnosis of AD developed by neurologists, a neuroethicist, and laboratorians; (d) a framework, sponsored by the National Institute of Aging-Alzheimer's Association (NIA-AA), that defines AD on the basis of CSF and imaging methods for detecting amyloid plaque burden, τ tangle pathology, and neurodegeneration. This framework's purpose was investigative but has important implications for future clinical practice; (e) recognition of copathologies in AD patients and challenges for developing methods to detect these in living patients.

SUMMARY

The field can expect availability of validated research tools for detection of AD pathology that support clinical treatment trials of disease-modifying agents and, ultimately, use in clinical practice. Validated methods are becoming available for CSF testing; emergence of validated methods for AD biomarkers in plasma can be expected in the next few years.

Neurofilament Light Predicts Decline in Attention but Not Episodic Memory in Preclinical Alzheimer's Disease

BACKGROUND

Cerebrospinal fluid tau and neurofilament light (NfL) are two biomarkers of neurodegeneration in Alzheimer's disease. Previous reports have shown that the influence of tau on cognitive decline depends on levels of amyloid burden whereas NfL predicts decline independently of amyloid. Most studies use a global cognitive composite as the primary outcome, and it is unknown if critical cognitive domain scores are similarly sensitive to rates of decline due to neurodegeneration.

OBJECTIVE

To examine the unique contribution of amyloid, tau, and NfL to rates of cognitive decline in multiple cognitive composites in a cognitively healthy, middle-aged to older adult cohort.

METHODS

A total of 255 participants (55% female; mean age = 66.2 years, range = 42.5-86.7 years) completed CSF studies and serial cognitive assessments to measure global cognition, episodic memory, and attentional control. Linear mixed effects models were used to examine rates of change on each composite score as a function of baseline biomarker levels.

RESULTS

Total tau predicted decline in attention regardless of amyloid status, but the relationship to global cognition and episodic memory was dependent on amyloid, replicating prior literature. NfL predicted decline in attention and global cognition, but not memory, and this effect was independent of amyloid status.

CONCLUSIONS

These findings suggest that NfL can be used to monitor cognitive decline in aging and Alzheimer's disease and that an attentional control composite may be a better outcome for tracking general neurodegenerative effects on cognition.

"Bridging the Gap" Everything that Could Have Been Avoided If We Had Applied Gender Medicine, Pharmacogenetics and Personalized Medicine in the Gender-Omics and Sex-Omics Era

Gender medicine is the first step of personalized medicine and patient-centred care, an essential development to achieve the standard goal of a holistic approach to patients and diseases. By addressing the interrelation and integration of biological markers (i.e., sex) with indicators of psychological/cultural behaviour (i.e., gender), gender medicine represents the crucial assumption for achieving the personalized health-care required in the third millennium. However, ‘sex’ and ‘gender’ are often misused as synonyms, leading to frequent misunderstandings in those who are not deeply involved in the field. Overall, we have to face the evidence that biological, genetic, epigenetic, psycho-social, cultural, and environmental factors mutually interact in defining sex/gender differences, and at the same time in establishing potential unwanted sex/gender disparities. Prioritizing the role of sex/gender in physiological and pathological processes is crucial in terms of efficient prevention, clinical signs’ identification, prognosis definition, and therapy optimization. In this regard, the omics-approach has become a powerful tool to identify sex/gender-specific disease markers, with potential benefits also in terms of socio-psychological wellbeing for each individual, and cost-effectiveness for National Healthcare systems. “Being a male or being a female” is indeed important from a health point of view and it is no longer possible to avoid “sex and gender lens” when approaching patients. Accordingly, personalized healthcare must be based on evidence from targeted research studies aimed at understanding how sex and gender influence health across the entire life span. The rapid development of genetic tools in the molecular medicine approaches and their impact in healthcare is an example of highly specialized applications that have moved from specialists to primary care providers (e.g., pharmacogenetic and pharmacogenomic applications in routine medical practice). Gender medicine needs to follow the same path and become an established medical approach. To face the genetic, molecular and pharmacological bases of the existing sex/gender gap by means of omics approaches will pave the way to the discovery and identification of novel drug-targets/therapeutic protocols, personalized laboratory tests and diagnostic procedures (sex/gender-omics). In this scenario, the aim of the present review is not to simply resume the state-of-the-art in the field, rather an opportunity to gain insights into gender medicine, spanning from molecular up to social and psychological stances. The description and critical discussion of some key selected multidisciplinary topics considered as paradigmatic of sex/gender differences and sex/gender inequalities will allow to draft and design strategies useful to fill the existing gap and move forward.

Neurofilaments in blood is a new promising preclinical biomarker for the screening of natural scrapie in sheep

Scrapie is a fatal neurodegenerative disease of sheep and goats belonging to the group of Transmissible Spongiform Encephalopathy or prion diseases. The EU has adopted mandatory measures for scrapie surveillance to safeguard public and animal health because it is highly contagious and might decimate all genetic susceptible animals in affected flocks. Definite diagnosis of scrapie relies on the detection of the pathological prion protein in brain tissues and there are still no blood biomarkers available for making diagnosis in living animals that can be used for the screening of sheep in scrapie-affected flocks. Neurofilament light (NfL) protein, a valid biomarker for neuronal and axonal damages, can now be easily measured in blood by the ultra-sensitive single molecule array (Simoa) technology. Recent work reported that serum NfL is increased in neurodegenerative diseases, including human prion diseases, but no data are available for scrapie or other animal prion diseases. Here, we found that the median serum NfL concentration in scrapie animals (56.2, IQR 42.2–84.8, n = 9) was more than 15 times higher (p = 0.00084) than that found in control samples (3.4, IQR 3.0–26.3, n = 11). Moreover, serum NfL concentration in scrapie sheep with clinical signs (n = 2; 75.3, 15.7 pg/ml) did not significantly (p = 0.541; t-test) differ from scrapie animals without clinical signs (n = 7; 61.0, 10.7 pg/ml). The receiver operating characteristic (ROC) curve analysis estimated the cut-off value of 31 pg/ml serum NfL for distinguishing scrapie-infected sheep from controls. The application of this cut-off value gives an accuracy of the test of 95% (percent error of 5.23%). These data indicate that the Simoa test for serum NfL might be a useful screening method for detecting preclinical scrapie in living sheep. Finally, the preliminary data reported here need confirmation in large and more structured studies.

Recent advances in understanding frontotemporal degeneration

Frontotemporal degeneration (FTD) is a heterogeneous spectrum of neurodegenerative disorders characterized by diverse clinical presentations, neuropathological characteristics, and underlying genetic causes. In the last few years, several advances in the knowledge of clinical and biological aspects have been accomplished and three major scenarios have emerged that will represent the core issues in the FTD scene over the next few years. Foremost, the development of cerebrospinal fluid and blood biomarkers as well as neuroimaging techniques will aid the pursuit of new diagnostic and prognostic markers able to identify the ongoing proteinopathy and predict disease progression, which is key in identifying and stratifying patients for enrolment in clinical trials as well as evaluating response to treatment. On the other hand, current research has focused on the first attempts to slow down or revert disease progression, with the identification of disease modulators associated with disease onset and the ongoing development of the first pharmacological treatments for both sporadic and genetic FTD. Future research will certainly improve our knowledge of FTD and possibly open up a new era of disease-modifying therapies for this still-orphan disorder.

An Update on Blood-Based Markers of Alzheimer's Disease Using the SiMoA Platform

The development of blood-based biomarkers of Alzheimer's disease (AD) pathology as tools for screening the general population, and as the first step in a multistep process to determine which non-demented individuals are at greatest risk of developing AD dementia, is essential. Proteins that are reflective of AD pathology, such as amyloid beta 42 (Aβ42), tau proteins [total tau (T-tau) and phosphorylated tau (P-tau)], and neurofilament light chain (NfL), are detectable in the blood. However, a major challenge in measuring these blood-based proteins is that their concentrations are much lower in plasma or serum than in the cerebrospinal fluid. Single molecule array (SiMoA) is an ultrasensitive technology that can detect proteins in blood at sub-femtomolar concentrations (i.e., 10-16 M). In this review, we focus on the utility of SiMoA assays for the measurement of plasma or serum Aβ42, P-tau, T-tau, and NfL levels and discuss future directions.

Multiple system atrophy

Multiple system atrophy (MSA) is a sporadic, adult-onset, relentlessly progressive neurodegenerative disorder, clinically characterized by various combinations of autonomic failure, parkinsonism and ataxia. The neuropathological hallmark of MSA are glial cytoplasmic inclusions consisting of misfolded α-synuclein. Selective atrophy and neuronal loss in striatonigral and olivopontocerebellar systems underlie the division into two main motor phenotypes of MSA-parkinsonian type and MSA-cerebellar type. Isolated autonomic failure and REM sleep behavior disorder are common premotor features of MSA. Beyond the core clinical symptoms, MSA manifests with a number of non-motor and motor features. Red flags highly specific for MSA may provide clues for a correct diagnosis, but in general the diagnostic accuracy of the second consensus criteria is suboptimal, particularly in early disease stages. In this chapter, the authors discuss the historical milestones, etiopathogenesis, neuropathological findings, clinical features, red flags, differential diagnosis, diagnostic criteria, imaging and other biomarkers, current treatment, unmet needs and future treatments for MSA.

Progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a neurodegenerative disease characterized pathologically by 4 repeat tau deposition in various cell types and anatomical regions. Richardson's syndrome (RS) is the initially described and one of the clinical phenotypes associated with PSP pathology, characterized by vertical supranuclear gaze paly in particular downwards, postural instability with early falls and subcortical frontal dementia. PSP can manifest as several other clinical phenotypes, including PSP-parkinsonism, -pure akinesia with gait freezing, -frontotemporal dementia, - corticobasal syndrome, - speech/language impairment. RS can also have a pathologic diagnosis other than PSP, including corticobasal degeneration, FTD-TDP-43 and others. New clinical diagnostic criteria take into account this phenotypic variability in an attempt to diagnose the disease earlier, given the current lack of a validated biomarker. At present, therapeutic options for PSP are symptomatic and insufficient. Recent large neuroprotective trials have failed to provide a positive clinical outcome, however, have led to the design of better studies that are ongoing and hold promise for a neuroprotective treatment for PSP.

CSF or serum neurofilament light added to α-Synuclein panel discriminates Parkinson's from controls

BACKGROUND

Neurofilament light chain is a marker of axonal damage and is of interest as a biofluid biomarker for PD. The objective of this study was to investigate whether CSF or serum neurofilament contributes to a combination of CSF biomarkers in defining the optimal biomarker panel for discriminating PD patients from healthy controls. In addition, we aimed to assess whether CSF and/or serum neurofilament levels are associated with clinical measures of disease severity.

METHODS

We measured neurofilament light chain levels in CSF and/or serum of 139 PD patients and 52 age-matched healthy controls. We used stepwise logistic regression analyses to test whether neurofilament contributes to a biomarker CSF panel including total, oligomeric, and phosphorylated α-synuclein and Alzheimer's disease biomarkers. Measures of disease severity included disease duration, UPDRS-III, Hoehn & Yahr stage, and MMSE.

RESULTS

After correcting for age, CSF neurofilament levels were 42% higher in PD patients compared with controls (P < 0.01), whereas serum neurofilament levels were 37% higher (P = 0.08). Combining CSF neurofilament, phosphorylated-/total α-synuclein, and oligomeric-/total α-synuclein yielded the best-fitting model for discriminating PD patients from controls (area under the curve 0.92). The discriminatory potential of serum neurofilament in the CSF biomarker panel was similar (area under the curve 0.90). Higher serum neurofilament was associated with a lower MMSE score. There were no other associations between CSF and/or serum neurofilament levels and clinical disease severity.

CONCLUSIONS

CSF neurofilament contributes to a panel of CSF α-synuclein species in differentiating PD patients from healthy controls. Serum neurofilament may have added value to a biofluid biomarker panel for differentiating PD patients from controls. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Targeted Multiple Reaction Monitoring Analysis of CSF Identifies UCHL1 and GPNMB as Candidate Biomarkers for ALS

The neurodegenerative diseases amyotrophic lateral sclerosis (ALS) and Parkinson’s disease (PD) share some common molecular deficits including disruption of protein homeostasis leading to disease-specific protein aggregation. While insoluble protein aggregates are the defining pathological confirmation of diagnosis, patient stratification based on early molecular etiologies may identify distinct subgroups within a clinical diagnosis that would respond differently in therapeutic development programs. We are developing targeted multiple reaction monitoring (MRM) mass spectrometry methods to rigorously quantify CSF proteins from known disease genes involved in lysosomal, ubiquitin-proteasomal, and autophagy pathways. Analysis of CSF from 21 PD, 21 ALS, and 25 control patients, rigorously matched for gender, age, and age of sample, revealed significant changes in peptide levels between PD, ALS, and control. In patients with PD, levels of two peptides for chromogranin B (CHGB, secretogranin 1) were significantly reduced. In CSF of patients with ALS, levels of two peptides from ubiquitin carboxy-terminal hydrolase like protein 1 (UCHL1) and one peptide each for glycoprotein non-metastatic melanoma protein B (GPNMB) and cathepsin D (CTSD) were all increased. Analysis of patients with ALS separated into two groups based on length of survival after CSF sampling revealed that the increases in GPNMB and UCHL1 were specific for short-lived ALS patients. While analysis of additional cohorts is required to validate these candidate biomarkers, this study suggests methods for stratification of ALS patients for clinical trials and identifies targets for drug efficacy measurements during therapeutic development.

Neurofilament light chain is a promising serum biomarker in spinocerebellar ataxia type 3

BACKGROUND

Spinocerebellar ataxia type 3 (SCA3) is the most common subtype of autosomal dominantly inherited spinocerebellar ataxias (SCAs). No validated blood biomarker is available to assess either disease progression or therapeutic response. Neurofilament light chain (NfL) was recently proposed as a serum biomarker for many neurodegenerative disorders. The present study investigated whether NfL was a promising serum biomarker for SCA3.

METHODS

Seventeen SCA3 patients and 9 controls were enrolled in cohort A, and 116 SCA3 individuals (preclinical and patients) and 91 controls were recruited as cohort B. We assessed whether serum NfL correlated with cerebrospinal fluid (CSF) NfL in cohort A and correlations between serum NfL levels and clinical features and brain volumes were determined in cohort B. The single-molecule array method was used to measure serum NfL levels. Disease severity was determined using the scale for the assessment and rating of ataxia (SARA) and the international cooperative ataxia rating scale (ICARS). Cerebellar and brainstem volumes were assessed using MRI neuroimaging measurements.

RESULTS

Serum/CSF NfL levels in cohort A were elevated in SCA3 patients, and serum and CSF NfL exhibited a significant positive correlation (r = 0.9179, p < 0.0001). Levels of serum NfL in cohort B were significantly higher in preclinical SCA3 (15.03 ± 7.49 vs 6.88 ± 2.72 pg/ mL, p < 0.0001) and manifest SCA3 subjects (37.56 ± 13.47 vs 9.07 ± 6.02 pg/ mL, p < 0.0001) compared to those in controls. Serum NfL concentrations increased from early disease stage to the next stage. Levels of serum NfL in ATXN3 mutation carriers were positively associated with SARA (r = 0.5458, p < 0.0001) and ICARS scores (r = 0.5522, p < 0.0001). Significant negative associations with cerebellar volumes (r = - 0.4217, p = 0.0003) and brainstem volumes (r = - 0.4263, p = 0.0003) were observed. All changes remained significant after adjustment for age and CAG repeat.

CONCLUSIONS

Levels of serum NfL were significantly elevated in SCA3 individuals and correlated with disease severity. Serum NfL is a promising serum biomarker of disease onset and progression, and a potential candidate biomarker of treatment response in SCA3.

Comparison of variables associated with cerebrospinal fluid neurofilament, total-tau, and neurogranin

INTRODUCTION

Three cerebrospinal fluid (CSF) markers of neurodegeneration (N) (neurofilament light [NfL], total-tau [T-tau], and neurogranin [Ng]) have been proposed under the AT(N) scheme of the National Institute on Aging-Alzheimer's Association Research Framework.

METHODS

We examined, in a community-based population (N = 777, aged 50-95) (1) what variables were associated with each of the CSF (N) markers, and (2) whether the variables associated with each marker differed by increased brain amyloid. CSF T-tau was measured with an automated electrochemiluminescence Elecsys immunoassay; NfL and Ng were measured with in-house enzyme-linked immunosorbent assays.

RESULTS

Multiple variables were differentially associated with CSF NfL and T-tau levels, but not Ng. Most associations were attenuated after adjustment for age and sex. T-tau had the strongest association with cognition in the presence of amyloidosis, followed by Ng. Variables associations with NfL did not differ by amyloid status.

DISCUSSION

Understanding factors that influence CSF (N) markers will assist in the interpretation and utility of these markers in clinical practice.

Iron is increased in the brains of ageing mice lacking the neurofilament light gene

There has been strong interest in the role of metals in neurodegeneration, and how ageing may predispose the brain to related diseases such as Alzheimer’s disease. Recent work has also highlighted a potential interaction between different metal species and various components of the cytoskeletal network in the brain, which themselves have a reported role in age-related degenerative disease and other neurological disorders. Neurofilaments are one such class of intermediate filament protein that have a demonstrated capacity to bind and utilise cation species. In this study, we investigated the consequences of altering the neurofilamentous network on metal ion homeostasis by examining neurofilament light (NFL) gene knockout mice, relative to wildtype control animals, at adulthood (5 months of age) and advanced age (22 months). Inductively coupled plasma mass spectroscopy demonstrated that the concentrations of iron (Fe), copper (Cu) and zinc (Zn) varied across brain regions and peripheral nerve samples. Zn and Fe showed statistically significant interactions between genotype and age, as well as between genotype and region, and Cu demonstrated a genotype and region interaction. The most substantial difference between genotypes was found in Fe in the older animals, where, across many regions examined, there was elevated Fe in the NFL knockout mice. This data indicates a potential relationship between the neurofilamentous cytoskeleton and the processing and/or storage of Fe through ageing.

Alzheimer Disease: An Update on Pathobiology and Treatment Strategies

Alzheimer disease (AD) is a heterogeneous disease with a complex pathobiology. The presence of extracellular β-amyloid deposition as neuritic plaques and intracellular accumulation of hyperphosphorylated tau as neurofibrillary tangles remains the primary neuropathologic criteria for AD diagnosis. However, a number of recent fundamental discoveries highlight important pathological roles for other critical cellular and molecular processes. Despite this, no disease-modifying treatment currently exists, and numerous phase 3 clinical trials have failed to demonstrate benefits. Here, we review recent advances in our understanding of AD pathobiology and discuss current treatment strategies, highlighting recent clinical trials and opportunities for developing future disease-modifying therapies.

A case series on the value of tau and neurofilament protein levels to predict and detect delirium in cardiac surgery patients

BACKGROUND

Delirium following cardiac surgery is a relevant complication in the majority of elderly patients but its prediction is challenging. Cardiopulmonary bypass, essential for many interventions in cardiac surgery, is responsible for a severe inflammatory response leading to neuroinflammation and subsequent delirium. Neurofilament light protein (NfL) and tau protein (tau) are specific biomarkers to detect neuroaxonal injury as well as glial fibrillary acidic protein (GFAP), a marker of astrocytic activation.

METHODS

We thought to examine the perioperative course of these markers in a case series of each three cardiac surgery patients under off-pump cardiac arterial bypass without evolving delirium (OPCAB-NDEL), patients with a procedure under cardio-pulmonary bypass (CPB) without delirium (CPB-NDEL) and delirium after a CPB procedure (CPB-DEL). Delirium was diagnosed by the Confusion Assessment Method for the ICU and chart reviews.

RESULTS

We observed increased preoperative levels of tau in patients with later delirium, whereas values of NfL and GFAP did not differ. In the postoperative course, all biomarkers increased multi-fold. NfL levels sharply increased in patients with CPB reaching the highest levels in the CPB-DEL group.

CONCLUSION

Tau and NfL might be of benefit to identify patients in cardiac surgery at risk for delirium and to detect patients with the postoperative emergence of delirium.

Intrathecal immunoglobulins and neurofilament light after autologous haematopoietic stem cell transplantation for multiple sclerosis

BACKGROUND

Oligoclonal bands (OCB) are widely believed to be stable over time and rarely affected by disease-modifying treatment in MS. It is presently unknown how intrathecal immunoglobulin production and other cerebrospinal fluid (CSF) biomarkers are impacted by a highly efficacious procedure such as autologous haematopoietic stem cell transplantation (aHSCT).

OBJECTIVE

To describe the evolution of intrathecal immunoglobulin and neurofilament light (NFL) over time in MS patients treated with aHSCT.

METHODS

In this retrospective study, available data from previously made CSF investigations in 46 patients treated with aHSCT were analysed.

RESULTS

After a median follow-up time of 745 days, immunoglobulin G (IgG) OCB remained detectable in 74% of patients, the proportion of patients with a pathological IgG index went down from 70% to 46%, and the proportion of patients with a pathological NFL went down from 72% to 24%. In patients with follow-up time >1500 days, IgG OCB were detectable in 50% of patients, 14% had a pathological IgG index and none a pathological NFL.

CONCLUSIONS

Intrathecal immunoglobulin production and NFL were lower after treatment with aHSCT, decreased over time and were normalised in a significant portion of patients. This challenges the notion that OCB are unaffected by therapeutic intervention in MS.