Neurofilament Subunit L Levels in the Cerebrospinal Fluid and Serum of Patients with Amyotrophic Lateral Sclerosis

Fluid biomarkers for amyotrophic lateral sclerosis: a review

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the loss of upper and lower motor neurons. Presently, three FDA-approved drugs are available to help slow functional decline for patients with ALS, but no cure yet exists. With an average life expectancy of only two to five years after diagnosis, there is a clear need for biomarkers to improve the care of patients with ALS and to expedite ALS treatment development. Here, we provide a review of the efforts made towards identifying diagnostic, prognostic, susceptibility/risk, and response fluid biomarkers with the intent to facilitate a more rapid and accurate ALS diagnosis, to better predict prognosis, to improve clinical trial design, and to inform interpretation of clinical trial results. Over the course of 20 + years, several promising fluid biomarker candidates for ALS have emerged. These will be discussed, as will the exciting new strategies being explored for ALS biomarker discovery and development.

Serum Ubiquitin C-Terminal Hydrolase-L1, Glial Fibrillary Acidic Protein, and Neurofilament Light Chain Are Good Entry Points and Biomarker Candidates for Neurosyphilis Diagnosis Among Patients Without Human Immunodeficiency Virus to Avoid Lumbar Puncture

BACKGROUND

Laboratory tests to diagnose neurosyphilis using cerebrospinal fluid (CSF) are currently disadvantageous as a lumbar puncture is required, which may result in patients with neurosyphilis missing an opportunity for early diagnosis. Thus, blood biomarker candidates that are more convenient and minimally invasive to collect for diagnosing neurosyphilis is urgently needed.

METHODS

This observational study aimed to analyze serum ubiquitin C-terminal hydrolase-L1 (UCH-L1), glial fibrillary acidic protein (GFAP), and neurofilament light chain (NF-L) levels in 153 patients without human immunodeficiency virus (HIV) and to evaluate their diagnostic performance in neurosyphilis compared with CSF.

RESULTS

Serum UCH-L1, GFAP, and NF-L levels were significantly higher in patients with neurosyphilis compared with patients with uncomplicated syphilis or non-syphilis. For the diagnosis of neurosyphilis, serum UCH-L1, GFAP, and NF-L revealed sensitivities of 90.20%, 80.40%, and 88.24%, and specificities of 92.16%, 78.43%, and 80.39%, respectively, at cutoff levels of 814.50 pg/mL, 442.70 pg/mL, and 45.19 pg/mL, respectively. In patients with syphilis, serum UCH-L1, GFAP, and NF-L levels correlated strongly or moderately with those in the CSF, with similar or better diagnostic performance than those in the CSF. The testing algorithms' sensitivity and specificity increased to 98.04% and 96.08%, respectively, when subjected to parallel and combination testing, respectively.

CONCLUSIONS

To avoid lumbar puncture, each serum UCH-L1, GFAP, and NF-L is a good entry point and biomarker candidate for the diagnosis of neurosyphilis among patients without HIV. These proteins used in concerto can further improve the diagnostic sensitivity and specificity.

Performance of serum neurofilament light chain in a wide spectrum of clinical courses of amyotrophic lateral sclerosis-a cross-sectional multicenter study

BACKGROUND AND PURPOSE

The objective was to assess the performance of serum neurofilament light chain (sNfL) in amyotrophic lateral sclerosis (ALS) in a wide range of disease courses, in terms of progression, duration and tracheostomy invasive ventilation (TIV).

METHODS

A prospective cross-sectional study at 12 ALS centers in Germany was performed. sNfL concentrations were age adjusted using sNfL Z scores expressing the number of standard deviations from the mean of a control reference database and correlated to ALS duration and ALS progression rate (ALS-PR), defined by the decline of the ALS Functional Rating Scale.

RESULTS

In the total ALS cohort (n = 1378) the sNfL Z score was elevated (3.04; 2.46-3.43; 99.88th percentile). There was a strong correlation of sNfL Z score with ALS-PR (p < 0.001). In patients with long (5-10 years, n = 167) or very long ALS duration (>10 years, n = 94) the sNfL Z score was significantly lower compared to the typical ALS duration of <5 years (n = 1059) (p < 0.001). Furthermore, in patients with TIV, decreasing sNfL Z scores were found in correlation with TIV duration and ALS-PR (p = 0.002; p < 0.001).

CONCLUSIONS

The finding of moderate sNfL elevation in patients with long ALS duration underlined the favorable prognosis of low sNfL. The strong correlation of sNfL Z score with ALS-PR strengthened its value as progression marker in clinical management and research. The lowering of sNfL in correlation with long TIV duration could reflect a reduction either in disease activity or in the neuroaxonal substrate of biomarker formation during the protracted course of ALS.

Plasma neurofilament light levels associate with muscle mass and strength in middle-aged and older adults: findings from GenoFit

BACKGROUND

Efforts to enhance diagnostic measures for sarcopenia have led to an increased focus on the screening utility of blood-based biomarkers. In this regard, circulating neurofilament light chain (NfL) levels are a potent indicator of axonal damage and have been linked with several neurological disorders. However, despite the strong neurogenic contribution to skeletal muscle health, no studies have explored the relevance of NfL concentrations to sarcopenia. With that in mind, this study aimed to examine the association between plasma NfL concentration and sarcopenic domains.

METHODS

Three hundred adults aged between 50 and 83 years participated to this study (male participants, n = 150; mean age: 64.2 ± 8.7 years and female participants, n = 150; mean age: 63.9 ± 8.3 years). Body composition was assessed using dual-energy X-ray absorptiometry, and a skeletal muscle index (SMI) was calculated. Muscle strength was assessed with hand dynamometry. Sarcopenia was classified using the European Working Group on Sarcopenia in Older People criteria. Plasma NfL concentration was determined using a highly sensitive, enzyme-linked immunosorbent assay.

RESULTS

Neurofilament light chain levels were associated with grip strength and SMI (P = 0.005 and P = 0.045, respectively) and were significantly elevated in sarcopenic individuals, compared with non-sarcopenic participants (P < 0.001). Individuals with pre-sarcopenia (either low grip strength or low SMI) had significantly higher NfL levels, compared with healthy controls (P = 0.001 and P = 0.006, respectively). Male participants with either low grip strength or low SMI had significantly raised NfL levels (P = 0.006 and P = 0.002, respectively), while in female participants, NfL concentrations were significantly elevated only in those with low grip strength (P = 0.049). NfL concentration displayed acceptable diagnostic accuracy for sarcopenia (area under the curve = 0.726, P < 0.001).

CONCLUSIONS

Our study clearly demonstrates the indicative pertinence of circulating NfL levels to sarcopenic domains, supporting its potential use as a biomarker of sarcopenia. More studies are needed, however, to further illuminate the diagnostic value of circulating NfL. Future research should explore whether NfL levels are more powerfully linked with muscle strength than mass and whether sex mediates the relevance of NfL concentrations to sarcopenic phenotypes.

Cerebrospinal fluid biomarkers of disease activity and progression in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a relentlessly progressive neurodegenerative disease, and only modest disease-modifying strategies have been established to date. Numerous clinical trials have been conducted in the past years, but have been severely hampered by the wide-ranging heterogeneity of both the biological origins and clinical characteristics of the disease. Thus, reliable biomarkers of disease activity are urgently needed to stratify patients into homogenous groups with aligned disease trajectories to allow a more effective design of clinical trial. In this review, the most promising candidate biomarkers in the cerebrospinal fluid (CSF) of patients with ALS will be summarised. Correlations between biomarker levels and clinical outcome parameters are discussed, while highlighting potential pitfalls and intercorrelations of these clinical parameters. Several CSF molecules have shown potential as biomarkers of progression and prognosis, but large, international, multicentric and longitudinal studies are crucial for validation. A more standardised choice of clinical endpoints in these studies, as well as the application of individualised models of clinical progression, would allow the quantification of disease trajectories, thereby allowing a more accurate analysis of the clinical implications of candidate biomarkers. Additionally, a comparative analysis of several biomarkers and ideally the application of a multivariate analysis including comprehensive genotypic, phenotypic and clinical characteristics collectively contributing to biomarker levels in the CSF, could promote their verification. Thus, reliable prognostic markers and markers of disease activity may improve clinical trial design and patient management in the direction of precision medicine.

Plasma Neurofilament Light Is Not Associated with Ongoing Neuroaxonal Injury or Cognitive Decline in Perinatally HIV Infected Adolescents: A Brief Report

Despite combination antiretroviral therapy (cART), adolescents with perinatally acquired human immunodeficiency virus (PHIV) exhibit cerebral injury and cognitive impairment. Plasma neurofilament light (pNfL) is a biomarker identified as a promising marker associated with neuroaxonal injury and cognitive impairment. To investigate whether cerebral injury in cART-treated PHIV adolescents is persistent, we longitudinally measured pNfL. We included 21 PHIV adolescents and 23 controls, matched for age, sex, ethnic origin and socio-economic status. We measured pNfL in both groups and CSF NfL in PHIV adolescents using a highly sensitive Single Molecule Array (Simoa) immunoassay. We compared pNfL between groups over time with a mean follow-up time of 4.6 years and assessed its association with MRI outcomes, cognitive function and HIV-related characteristics using linear mixed models. The median age was 17.5 years (15.5–20.7) and 16.4 years (15.8–19.6) at the second assessment for PHIV adolescents and controls, respectively. We found comparable pNfL (PHIV vs. controls) at the first (2.9 pg/mL (IQR 2.0–3.8) and 3.0 pg/mL (IQR 2.3–3.5), p = 0.499) and second assessment (3.3 pg/mL (IQR 2.5–4.1) and 3.0 pg/mL (IQR 2.5–3.7), p = 0.658) and observed no longitudinal change (coefficient; −0.19, 95% −0.5 to 0.1, p = 0.244). No significant associations were found between pNfL and HIV- or cART-related variables, MRI outcomes or cognitive function. We observed low CSF NfL concentrations at the baseline in PHIV adolescents (100.8 pg/mL, SD = 47.5). Our results suggest that there is no ongoing neuroaxonal injury in cART-treated PHIV adolescents and that the neuroaxonal injury is acquired in the past, emphasizing the importance of early cART to mitigate HIV-related neuroaxonal damage.

Plasma and CSF NfL are differentially associated with biomarker evidence of neurodegeneration in a community-based sample of 70-year-olds

Neurofilament light protein (NfL) in cerebrospinal fluid (CSF) and plasma (P) are suggested to be interchangeable markers of neurodegeneration. However, evidence is scarce from community-based samples. NfL was examined in a small-scale sample of 287 individuals from the Gothenburg H70 Birth cohort 1944 study, using linear models in relation to CSF and magnetic resonance imaging (MRI) biomarker evidence of neurodegeneration. CSF-NfL and P-NfL present distinct associations with biomarker evidence of Alzheimer's disease (AD) pathology and neurodegeneration. P-NfL was associated with several markers that are characteristic of AD, including smaller hippocampal volumes, amyloid beta (Aβ)42, Aβ42/40, and Aβ42/t-tau (total tau). CSF-NfL demonstrated associations with measures of synaptic and neurodegeneration, including t-tau, phosphorylated tau (p-tau), and neurogranin. Our findings suggest that P-NfL and CSF-NfL may exert different effects on markers of neurodegeneration in a small-scale community-based sample of 70-year-olds.

Neurofilament light chain as a biological marker for amyotrophic lateral sclerosis: a meta-analysis study

Aim: The aim of the present metanalysis is to evaluate blood and CSF Neurofilament light chain (NfL) concentrations in ALS patients, compared to healthy controls, ALS mimic disorders (ALSmd) and other neurological diseases (OND), and to evaluate their diagnostic yield against ALSmd. Methods: Search engines were systematically investigated for relevant studies. A random effect model was applied to estimate the pooled standard mean difference in NfL levels between ALS and controls and a bivariate mixed-effects model was applied to estimate their diagnostic accuracy on blood and CSF. Results and conclusions: NfL CSF levels were higher in ALS compared with all other control groups. On blood, NfL levels were significantly higher in ALS patients compared with healthy controls and ALSmd. In a subgroup analysis, the use of SIMOA yielded to a better differentiation between ALS and controls on blood, compared with ELISA. Studies performed on CSF (AUC = 0.90) yielded to better diagnostic performances compared with those conducted on blood (AUC = 0.78). Further prospective investigations are needed to determine a diagnostic cutoff, exploitable in clinical practice.

Neurofilament markers in serum and cerebrospinal fluid of patients with amyotrophic lateral sclerosis

This study aims to determine the serum and cerebrospinal fluid (CSF) levels of neurofilament light chain (NFL) and phosphorylated neurofilament heavy chain (pNFH) in amyotrophic lateral sclerosis (ALS) patients, and to explore their feasibility as valid biomarkers for quantifying disease progression and predicting individual prognosis. 52 patients with ALS and 30 controls with noninflammatory neurological diseases were included. NFL and pNFH levels in serum and CSF were measured by enzyme‐linked immunosorbent assay. Our findings showed that serum and CSF levels of NFL and pNFH in ALS patients were significantly increased. These values were negatively correlated with disease duration (except CSF NFL with disease duration) and ALSFRS‐r score, and positively correlated with disease progression rate (DPR) and upper motor neuron (UMN) score, but did not correlate with bilateral median and ulnar nerve compound muscle action potential (cMAP) amplitudes (except a weak correlation between CSF NFL and cMAP amplitudes). The optimal cut‐off values with high sensitivity and specificity were obtained in ROC curve analysis to discriminate ALS from controls. Kaplan‐Meier survival curves illustrated that survival was significantly shorter for patients with higher neurofilament levels at diagnosis. The Cox proportional hazards regressions confirmed that NFL and pNFH were significant predictors of survival. Overall, NFL and pNFH in serum and CSF can be used as reliable biomarkers in ALS.

Neurofilaments can differentiate ALS subgroups and ALS from common diagnostic mimics

Delayed diagnosis and misdiagnosis are frequent in people with amyotrophic lateral sclerosis (ALS), the most common form of motor neuron disease (MND). Neurofilament light chain (NFL) and phosphorylated neurofilament heavy chain (pNFH) are elevated in ALS patients. We retrospectively quantified cerebrospinal fluid (CSF) NFL, CSF pNFH and plasma NFL in stored samples that were collected at the diagnostic work-up of ALS patients (n = 234), ALS mimics (n = 44) and controls (n = 9). We assessed the diagnostic performance, prognostication value and relationship to the site of onset and genotype. CSF NFL, CSF pNFH and plasma NFL levels were significantly increased in ALS patients compared to patients with neuropathies & myelopathies, patients with myopathies and controls. Furthermore, CSF pNFH and plasma NFL levels were significantly higher in ALS patients than in patients with other MNDs. Bulbar onset ALS patients had significantly higher plasma NFL levels than spinal onset ALS patients. ALS patients with C9orf72HRE mutations had significantly higher plasma NFL levels than patients with SOD1 mutations. Survival was negatively correlated with all three biomarkers. Receiver operating characteristics showed the highest area under the curve for CSF pNFH for differentiating ALS from ALS mimics and for plasma NFL for estimating ALS short and long survival. All three biomarkers have diagnostic value in differentiating ALS from clinically relevant ALS mimics. Plasma NFL levels can be used to differentiate between clinical and genetic ALS subgroups.

Role of Blood Neurofilaments in the Prognosis of Amyotrophic Lateral Sclerosis: A Meta-Analysis

Background: Neurofilaments in cerebrospinal fluid (CSF) and in blood are considered promising biomarkers of amyotrophic lateral sclerosis (ALS) because their levels can be significantly increased in patients with ALS. However, the roles of neurofilaments, especially blood neurofilaments, in the prognosis of ALS are inconsistent. We performed a meta-analysis to explore the prognostic roles of blood neurofilaments in ALS patients.

Methods: We searched all relevant studies on the relationship between blood neurofilament levels and the prognosis of ALS patients in PubMed, Embase, Scopus, and Web of Science before February 2, 2021. The quality of the included articles was assessed using the Quality in Prognosis Studies (QUIPS) scale, and R (version 4.02) was used for statistical analysis.

Results: Fourteen articles were selected, covering 1,619 ALS patients. The results showed that higher blood neurofilament light chain (NfL) levels in ALS patients were associated with a higher risk of death [medium vs. low NfL level: HR = 2.43, 95% CI (1.34–4.39), p < 0.01; high vs. low NfL level: HR = 4.51, 95% CI (2.45–8.32), p < 0.01]. There was a positive correlation between blood phosphorylated neurofilament heavy chain (pNfH) levels and risk of death in ALS patients [HR = 1.87, 95% CI (1.35–2.59), p < 0.01]. The levels of NfL and pNfH in blood positively correlated with disease progression rate (DPR) of ALS patients [NfL: summary r = 0.53, 95% CI (0.45–0.60), p < 0.01; pNfH: summary r = 0.51, 95% CI (0.24–0.71), p < 0.01].

Conclusion: The blood neurofilament levels can predict the prognosis of ALS patients; specifically, higher levels of blood neurofilaments are associated with a greater risk of death.

CSF Diagnostics: A Potentially Valuable Tool in Neurodegenerative and Inflammatory Disorders Involving Motor Neurons: A Review

Cerebrospinal fluid (CSF) diagnostics has emerged as a valid tool for a variety of neurological diseases. However, CSF diagnostics has been playing a subordinate role in the diagnosis of many neurological conditions. Thus, in the multitude of neuromuscular diseases in which motor neurons are affected, a CSF sample is rarely taken routinely. However, CSF diagnostics has the potential to specify the diagnosis and monitor the treatment of neuromuscular disorders. In this review, we therefore focused on a variety of neuromuscular diseases, among them amyotrophic lateral sclerosis (ALS), peripheral neuropathies, and spinal muscular atrophy (SMA), for which CSF diagnostics has emerged as a promising option for determining the disease itself and its progression. We focus on potentially valuable biomarkers among different disorders, such as neurofilaments, cytokines, other proteins, and lipids to determine their suitability, differentiating between different neurological disorders and their potential to determine early disease onset, disease progression, and treatment outcome. We further recommend novel approaches, e.g., the use of mass spectrometry as a promising alternative techniques to standard ELISA assays, potentially enhancing biomarker significance in clinical applications.

Correlation between CSF and blood neurofilament light chain protein: a systematic review and meta-analysis

OBJECTIVE

To assess the overall pooled correlation coefficient estimate between cerebrospinal fluid (CSF) and blood neurofilament light (NfL) protein.

METHODS

We searched Medline, Embase and Web of Science for published articles, from their inception to 9 July 2019, according to Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. Studies reporting the correlation between CSF and blood NfL in humans were included. We conducted a random-effects meta-analysis to calculate the overall pooled correlation coefficient estimate, accounting for correlation technique and assay used. Heterogeneity was assessed using the I2 statistic test. In sensitivity analyses, we calculated the pooled correlation coefficient estimate according to blood NfL assay: single-molecule array digital immunoassay (Simoa), electrochemiluminescence (ECL) assay or ELISA.

RESULTS

Data were extracted from 36 articles, including 3961 paired CSF and blood NfL samples. Overall, 26/36 studies measured blood NfL using Simoa, 8/36 ECL, 1/36 ELISA and 1 study reported all three assay results. The overall meta-analysis demonstrated that the pooled correlation coefficient estimate for CSF and blood NfL was r=0.72. Heterogeneity was significant: I2=83%, p<0.01. In sensitivity analyses, the pooled correlation coefficient was similar for studies measuring blood NfL using Simoa and ECL (r=0.69 and r=0.68, respectively) but weaker for ELISA (r=0.35).

CONCLUSION

Moderate correlations are demonstrated between CSF and blood NfL, especially when blood NfL was measured using Simoa and ECL. Given its high analytical sensitivity, Simoa is the preferred assay for measuring NfL, especially at low or physiological concentrations, and this meta-analysis supports its use as the current most advanced surrogate measure of CSF NfL.

PROSPERO REGISTRATION NUMBER

CRD42019140469.

Cerebrospinal Fluid Neurofilament Light Chain (NfL) Predicts Disease Aggressiveness in Amyotrophic Lateral Sclerosis: An Application of the D50 Disease Progression Model

Amyotrophic lateral sclerosis (ALS) is a relentlessly progressive neurodegenerative disorder. As previous therapeutic trials in ALS have been severely hampered by patients’ heterogeneity, the identification of biomarkers that reliably reflect disease progression represents a priority in ALS research. Here, we used the D50 disease progression model to investigate correlations between cerebrospinal fluid (CSF) neurofilament light chain (NfL) levels and disease aggressiveness. The D50 model quantifies individual disease trajectories for each ALS patient. The value D50 provides a unified measure of a patient’s overall disease aggressiveness (defined as time taken in months to lose 50% of functionality). The relative D50 (rD50) reflects the individual disease covered and can be calculated for any time point in the disease course. We analyzed clinical data from a well-defined cohort of 156 patients with ALS. The concentration of NfL in CSF samples was measured at two different laboratories using the same procedure. Based on patients’ individual D50 values, we defined subgroups with high (<20), intermediate (20–40), or low (>40) disease aggressiveness. NfL levels were compared between these subgroups via analysis of covariance, using an array of confounding factors: age, gender, clinical phenotype, frontotemporal dementia, rD50-derived disease phase, and analyzing laboratory. We found highly significant differences in NfL concentrations between all three D50 subgroups (p < 0.001), representing an increase of NfL levels with increasing disease aggressiveness. The conducted analysis of covariance showed that this correlation was independent of gender, disease phenotype, and phase; however, age, analyzing laboratory, and dementia significantly influenced NfL concentration. We could show that CSF NfL is independent of patients’ disease covered at the time of sampling. The present study provides strong evidence for the potential of NfL to reflect disease aggressiveness in ALS and in addition proofed to remain at stable levels throughout the disease course. Implementation of CSF NfL as a potential read-out for future therapeutic trials in ALS is currently constrained by its demonstrated susceptibility to (pre-)analytical variations. Here we show that the D50 model enables the discovery of correlations between clinical characteristics and CSF analytes and can be recommended for future studies evaluating potential biomarkers.

The role of neurofilament light chain in frontotemporal dementia: a meta-analysis

Frontotemporal dementia (FTD) is the second most frequent dementia, after Alzheimer's, in patients under the age of 65. It encompasses clinical entities characterized by behavioral, language, and executive control dysfunction. Neurofilament light chain (NfL) is a new, non-disease specific, widely studied biomarker indicative of axonal injury and degeneration. Various studies have previously explored the role of NfL in the diagnostic process, monitoring, and prognosis of dementia. The current systematic review and meta-analysis include all the available data concerning the role of NfL in frontotemporal dementia and its use as a potential biomarker in differentiating patients with FTD from (a) healthy individuals, (b) Alzheimer's dementia, (c) Dementia with Lewy bodies, (d) Motor Neuron disease, (e) Parkinsonian syndromes, and (f) psychiatric disorders. We also analyze the utility of NfL in distinguishing specific FTD subgroups. Neurofilament light chain has a potential role in differentiating patients with frontotemporal dementia from healthy controls, patients with Alzheimer's dementia, and psychiatric disorders. Higher NfL levels were also noted in patients with semantic primary progressive aphasia (PPA) when compared with behavioral FTD and non-fluent PPA patients. Further studies exploring the use of NfL in frontotemporal dementia are needed.

Correlational Analysis of ALS Progression and Serum NfL Measured by Simoa Assay in Chinese Patients

Background: Neurofilament light chain (NFL) was believed to be a promising biomarker for the diagnosis of Amyotrophic lateral sclerosis (ALS) and disease burden evaluation.

Objective: To determine the serum NFL level and its clinical relevance, including its association with disease severity [evaluated by the ALS Functional Rating Scale–revised (ALSFRS-r) score and King's College staging system] and progression (evaluated by the disease progression rate (DPR) and diagnostic delay), in ALS patients in China.

Method: Serum NFL levels were detected using the Single Molecule Array (Simoa) technology in 30 ALS patients and 20 healthy controls (HCs).

Results: There were significantly elevated levels of serum NFL in patients with ALS than in the HCs (P < 0.001). The serum NFL levels were significantly higher in rapidly progressive ALS and patients in Stage 3 than in slowly progressive ALS and patients in Stage 2 (P_DPR < 0.001, P_{Diagnosticdelay} = 0.019; P_stage= 0.033). Furthermore, the serum NFL levels negatively correlated with the diagnostic delay (R² = 0.23, P = 0.016), the ALSFRS-r score (R² = 0.15, P = 0.047) and disease duration (R² = 0.15, P = 0.034), and positively correlated with the DPR (R² = 0.42, P < 0.001).

Conclusions: The present study preliminarily investigated the diagnostic value of serum NFL and its clinical relevance in the Chinese ALS population using the ultrasensitive Simoa technology. The results demonstrated that the level of serum NFL may become a potential biomarker for ALS diagnosis and indicate disease severity and progression.

Neurofilaments in motor neuron disorders: towards promising diagnostic and prognostic biomarkers

Motor neuron diseases (MNDs) are etiologically and biologically heterogeneous diseases. The pathobiology of motor neuron degeneration is still largely unknown, and no effective therapy is available. Heterogeneity and lack of specific disease biomarkers have been appointed as leading reasons for past clinical trial failure, and biomarker discovery is pivotal in today's MND research agenda.In the last decade, neurofilaments (NFs) have emerged as promising biomarkers for the clinical assessment of neurodegeneration. NFs are scaffolding proteins with predominant structural functions contributing to the axonal cytoskeleton of myelinated axons. NFs are released in CSF and peripheral blood as a consequence of axonal degeneration, irrespective of the primary causal event. Due to the current availability of highly-sensitive automated technologies capable of precisely quantify proteins in biofluids in the femtomolar range, it is now possible to reliably measure NFs not only in CSF but also in blood.In this review, we will discuss how NFs are impacting research and clinical management in ALS and other MNDs. Besides contributing to the diagnosis at early stages by differentiating between MNDs with different clinical evolution and severity, NFs may provide a useful tool for the early enrolment of patients in clinical trials. Due to their stability across the disease, NFs convey prognostic information and, on a larger scale, help to stratify patients in homogenous groups. Shortcomings of NFs assessment in biofluids will also be discussed according to the available literature in the attempt to predict the most appropriate use of the biomarker in the MND clinic.