Evaluation of mutant huntingtin and neurofilament proteins as potential markers in Huntington's disease

Neurochemical changes in the progression of Huntington's disease: A meta-analysis of in vivo1H-MRS studies

Proton magnetic resonance spectroscopy (1H-MRS) allows measuring specific brain metabolic alterations in Huntington's disease (HD), and these metabolite profiles may serve as non-invasive biomarkers associated with disease progression. Despite this potential, previous findings are inconsistent. Accordingly, we performed a meta-analysis on available in vivo1H-MRS studies in premanifest (Pre-HD) and symptomatic HD stages (Symp-HD), and quantified neurometabolic changes relative to controls in 9 Pre-HD studies (227 controls and 188 mutation carriers) and 14 Symp-HD studies (326 controls and 306 patients). Our results indicated decreased N-acetylaspartate and creatine in the basal ganglia in both Pre-HD and Symp-HD. The overall level of myo-inositol was decreased in Pre-HD while increased in Symp-HD. Besides, Symp-HD patients showed more severe metabolism disruption than Pre-HD patients. Taken together, 1H-MRS is important for elucidating progressive metabolite changes from Pre-HD to clinical conversion; N-acetylaspartate and creatine in the basal ganglia are already sensitive at the preclinical stage and are promising biomarkers for tracking disease progression; overall myo-inositol is a possible characteristic metabolite for distinguishing HD stages.

Neurofilaments in neurologic disease

Neurofilaments (NFs), major cytoskeletal constituents of neurons, have emerged as universal biomarkers of neuronal injury. Neuroaxonal damage underlies permanent disability in various neurological conditions. It is crucial to accurately quantify and longitudinally monitor this damage to evaluate disease progression, evaluate treatment effectiveness, contribute to novel treatment development, and offer prognostic insights. Neurofilaments show promise for this purpose, as their levels increase with neuroaxonal damage in both cerebrospinal fluid and blood, independent of specific causal pathways. New assays with high sensitivity allow reliable measurement of neurofilaments in body fluids and open avenues to investigate their role in neurological disorders. This book chapter will delve into the evolving landscape of neurofilaments, starting with their structure and cellular functions within neurons. It will then provide a comprehensive overview of their broad clinical value as biomarkers in diseases affecting the central or peripheral nervous system.

NfL concentration in CSF is a quantitative marker of the rate of neurodegeneration in aging and Huntington's disease: a semi-mechanistic model-based analysis

The concentrations of neurofilament light chain (NfL) in cerebrospinal fluid (CSF) and plasma have become key biomarkers of many neurodegenerative diseases, including Huntington's Disease (HD). However, the relationship between the dynamics of NfL concentrations in CSF and the time-course of neurodegeneration (whole brain atrophy) has not yet been described in a quantitative and mechanistic manner. Here, we present a novel semi-mechanistic model, which postulates that the amount of NfL entering the CSF corresponds to the amount of NfL released from damaged neurons, whose degeneration results in a decrease in brain volume. In mathematical terms, the model expresses the NfL concentration in CSF in terms of the NfL concentration in brain tissue, the rate of change of whole brain volume and the CSF flow rate. To test our model, we used a non-linear mixed effects approach to analyze NfL and brain volume data from the HD-CSF study, a 24-month prospective study of individuals with premanifest HD, manifest HD and healthy controls. The time-course of whole brain volume, obtained from MRI, was represented empirically by a 2nd order polynomial, from which its rate of change was computed. CSF flow rates in healthy and HD populations were taken from recent literature data. By estimating the NfL concentration in brain tissue, the model successfully described the time-course of the NfL concentration in CSF in both HD subjects and healthy controls. Furthermore, the model-derived estimate of NfL concentration in brain agreed well with recent direct experimental measurements. The consistency of our model with the NfL and brain volume data suggests that the NfL concentration in CSF reflects the rate, rather than the extent, of neurodegeneration and that the increase in NfL concentration over time is a measure of the accelerating rate of neurodegeneration associated with aging and HD. For HD subjects, the degree of acceleration was found to increase markedly with the number of CAG repeats on their HTT gene. The application of our semi-mechanistic NfL model to other neurodegenerative diseases is discussed.

Genetic Interventions for Spinocerebellar Ataxia and Huntington's Disease: A Qualitative Study of the Patient Perspective

Background

For various genetic disorders characterized by expanded cytosine-adenine-guanine (CAG) repeats, such as spinocerebellar ataxia (SCA) subtypes and Huntington's disease (HD), genetic interventions are currently being tested in different clinical trial phases. The patient's perspective on such interventions should be included in the further development and implementation of these new treatments.

Objective

To obtain insight into the thoughts and perspectives of individuals with SCA and HD on genetic interventions.

Methods

In this qualitative study, participants were interviewed using semi-structured interview techniques. Topics discussed were possible risks and benefits, and logistic factors such as timing, location and expertise. Data were analyzed using a generic thematic analysis. Responses were coded into superordinate themes.

Results

Ten participants (five with SCA and five with HD) were interviewed. In general, participants seemed to be willing to undergo genetic interventions. Important motives were the lack of alternative disease-modifying treatment options, the hope for slowing down disease progression, and preservation of current quality of life. Before undergoing genetic interventions, participants wished to be further informed. Logistic factors such as mode and frequency of administration, expertise of the healthcare provider, and timing of treatment are of influence in the decision-making process.

Conclusions

This study identified assumptions, motives, and topics that require further attention before these new therapies, if proven effective, can be implemented in clinical practice. The results may help in the design of care pathways for genetic interventions for these and other rare genetic movement disorders.

Mapping neurodegeneration across the Huntington's disease spectrum: a five-year longitudinal analysis of plasma neurofilament light

BACKGROUND

Neurofilament light (NfL) has previously been highlighted as a potential biomarker for Huntington's Disease (HD) using cross-sectional analyses. Our study aim was to investigate how longitudinal trajectories of plasma NfL relate to HD disease stage.

METHODS

108 participants [78 individuals with the HD mutation, and 30 healthy controls (HC)] were included in this study. Individuals with the HD mutation were categorised separately by both HD-Integrated Staging System (HD-ISS) (Study 1) and PIN score-Approximated Staging System (PASS) (Study 2) criteria. Plasma NfL trajectories were examined using Mixed Linear Modeling (MLM); associations with symptom presentation were assessed using Spearman's rho correlations.

FINDINGS

The MLM coefficients for disease stage (HD-ISS β = 32.73, p < 0.0001; PASS β = 33.00, p < 0.0001) and disease stage∗time (HD-ISS β = 7.85, p = 0.004; PASS β = 6.58, p = 0.0047) suggest these are significant contributors to plasma NfL levels. In addition, the plasma NfL rate of change varied significantly across time (HD-ISS β = 3.14, p = 0.04; PASS β = 2.94, p = 0.050). The annualised rate of change was 8.32% for HC; 10.55%, 12.75% and 15.62% for HD-ISS Stage ≤1, Stage 2, and Stage 3, respectively; and 12.13%, 10.46%, 10.33%, 17.52%, for PASS Stage 0, Stage 1, Stage 2, and Stage 3, respectively. Plasma NfL levels correlated with the Symbol Digit Modalities Test (SDMT) in HD-ISS Stage ≤1, and both SDMT and Total Motor Score in Stage 3 (ps < 0.01).

INTERPRETATION

Our findings suggest that plasma NfL levels increase linearly across earlier disease stages, correlating with the cognitive SDMT measure. Thereafter, an increase or surge in plasma NfL levels, paired with correlations with both cognitive and motor measures, suggest a late acceleration in clinical and pathological progression.

FUNDING

NIH (NS111655); the UCSD HDSA CoE; the UCSD ADRC (NIH-NIA P30 AG062429).

Neurofilaments as biomarkers in neurological disorders - towards clinical application

Neurofilament proteins have been validated as specific body fluid biomarkers of neuro-axonal injury. The advent of highly sensitive analytical platforms that enable reliable quantification of neurofilaments in blood samples and simplify longitudinal follow-up has paved the way for the development of neurofilaments as a biomarker in clinical practice. Potential applications include assessment of disease activity, monitoring of treatment responses, and determining prognosis in many acute and chronic neurological disorders as well as their use as an outcome measure in trials of novel therapies. Progress has now moved the measurement of neurofilaments to the doorstep of routine clinical practice for the evaluation of individuals. In this Review, we first outline current knowledge on the structure and function of neurofilaments. We then discuss analytical and statistical approaches and challenges in determining neurofilament levels in different clinical contexts and assess the implications of neurofilament light chain (NfL) levels in normal ageing and the confounding factors that need to be considered when interpreting NfL measures. In addition, we summarize the current value and potential clinical applications of neurofilaments as a biomarker of neuro-axonal damage in a range of neurological disorders, including multiple sclerosis, Alzheimer disease, frontotemporal dementia, amyotrophic lateral sclerosis, stroke and cerebrovascular disease, traumatic brain injury, and Parkinson disease. We also consider the steps needed to complete the translation of neurofilaments from the laboratory to the management of neurological diseases in clinical practice.

CSF neurofilament light chain profiling and quantitation in neurological diseases

Neurofilament light chain is an established marker of neuroaxonal injury that is elevated in CSF and blood across various neurological diseases. It is increasingly used in clinical practice to aid diagnosis and monitor progression and as an outcome measure to assess safety and efficacy of disease-modifying therapies across the clinical translational neuroscience field. Quantitative methods for neurofilament light chain in human biofluids have relied on immunoassays, which have limited capacity to describe the structure of the protein in CSF and how this might vary in different neurodegenerative diseases. In this study, we characterized and quantified neurofilament light chain species in CSF across neurodegenerative and neuroinflammatory diseases and healthy controls using targeted mass spectrometry. We show that the quantitative immunoprecipitation-tandem mass spectrometry method developed in this study strongly correlates to single-molecule array measurements in CSF across the broad spectrum of neurodegenerative diseases and was replicable across mass spectrometry methods and centres. In summary, we have created an accurate and cost-effective assay for measuring a key biomarker in translational neuroscience research and clinical practice, which can be easily multiplexed and translated into clinical laboratories for the screening and monitoring of neurodegenerative disease or acute brain injury.

Diffusion MRI marks progressive alterations in fiber integrity in the zQ175DN mouse model of Huntington's disease

Huntington's disease (HD) is a progressive neurodegenerative disease affecting motor and cognitive abilities. Multiple studies have found white matter anomalies in HD-affected humans and animal models of HD. The identification of sensitive white-matter-based biomarkers in HD animal models will be important in understanding disease mechanisms and testing the efficacy of therapeutic interventions. Here we investigated the progression of white matter deficits in the knock-in zQ175DN heterozygous (HET) mouse model of HD at 3, 6 and 11 months of age (M), reflecting different states of phenotypic progression. We compared findings from traditional diffusion tensor imaging (DTI) and advanced fixel-based analysis (FBA) diffusion metrics for their sensitivity in detecting white matter anomalies in the striatum, motor cortex, and segments of the corpus callosum. FBA metrics revealed progressive and widespread reductions of fiber cross-section and fiber density in myelinated bundles of HET mice. The corpus callosum genu was the most affected structure in HET mice at 6 and 11 M based on the DTI and FBA metrics, while the striatum showed the earliest progressive differences starting at 3 M based on the FBA metrics. Overall, FBA metrics detected earlier and more prominent alterations in myelinated fiber bundles compared to the DTI metrics. Luxol fast blue staining showed no loss in myelin density, indicating that diffusion anomalies could not be explained by myelin reduction but diffusion anomalies in HET mice were accompanied by increased levels of neurofilament light chain protein at 11 M. Altogether, our findings reveal progressive alterations in myelinated fiber bundles that can be measured using diffusion MRI, representing a candidate noninvasive imaging biomarker to study phenotype progression and the efficacy of therapeutic interventions in zQ175DN mice. Moreover, our study exposed higher sensitivity of FBA than DTI metrics, suggesting a potential benefit of adopting these advanced metrics in other contexts, including biomarker development in humans.

High Levels of Mutant Huntingtin Protein in Tear Fluid From Huntington's Disease Gene Expansion Carriers

OBJECTIVE

Huntington's disease (HD) is an autosomal dominant, fully penetrant, neurodegenerative disease that most commonly affects middle-aged adults. HD is caused by a CAG repeat expansion in the HTT gene, resulting in the expression of mutant huntingtin (mHTT). Our aim was to detect and quantify mHTT in tear fluid, which, to our knowledge, has never been measured before.

METHODS

We recruited 20 manifest and 13 premanifest HD gene expansion carriers, and 20 age-matched controls. All patients underwent detailed assessments, including the Unified Huntington's Disease Rating Scale (UHDRS) total motor score (TMS) and total functional capacity (TFC) score. Tear fluid was collected using paper Schirmer's strips. The level of tear mHTT was determined using single-molecule counting SMCxPRO technology.

RESULTS

The average tear mHTT levels in manifest (67,223 ± 80,360 fM) and premanifest patients (55,561 ± 45,931 fM) were significantly higher than those in controls (1,622 ± 2,179 fM). We noted significant correlations between tear mHTT levels and CAG repeat length, "estimated years to diagnosis," disease burden score and UHDRS TMS and TFC. The receiver operating curve demonstrated an almost perfect score (area under the curve [AUC] = 0.9975) when comparing controls to manifest patients. Similarly, the AUC between controls and premanifest patients was 0.9846. The optimal cutoff value for distinguishing between controls and manifest patients was 4,544 fM, whereas it was 6,596 fM for distinguishing between controls and premanifest patients.

CONCLUSION

Tear mHTT has potential for early and noninvasive detection of alterations in HD patients and could be integrated into both clinical trials and clinical diagnostics.

Neurodegeneration Biomarkers in Adult Spinal Muscular Atrophy (SMA) Patients Treated with Nusinersen

The objective of this study is to evaluate biomarkers for neurodegenerative disorders in adult SMA patients and their potential for monitoring the response to nusinersen. Biomarkers for neurodegenerative disorders were assessed in plasma and CSF samples obtained from a total of 30 healthy older adult controls and 31 patients with adult SMA type 2 and 3. The samples were collected before and during nusinersen treatment at various time points, approximately at 2, 6, 10, and 22 months. Using ELISA technology, the levels of total tau, pNF-H, NF-L, sAPPβ, Aβ40, Aβ42, and YKL-40 were evaluated in CSF samples. Additionally, plasma samples were used to measure NF-L and total tau levels using SIMOA technology. SMA patients showed improvements in clinical outcomes after nusinersen treatment, which were statistically significant only in walkers, in RULM (p = 0.04) and HFMSE (p = 0.05) at 24 months. A reduction in sAPPβ levels was found after nusinersen treatment, but these levels did not correlate with clinical outcomes. Other neurodegeneration biomarkers (NF-L, pNF-H, total tau, YKL-40, Aβ40, and Aβ42) were not found consistently changed with nusinersen treatment. The slow progression rate and mild treatment response of adult SMA types 2 and 3 may not lead to detectable changes in common markers of axonal degradation, inflammation, or neurodegeneration, since it does not involve large pools of damaged neurons as observed in pediatric forms. However, changes in biomarkers associated with the APP processing pathway might be linked to treatment administration. Further studies are warranted to better understand these findings.

Data-driven modelling of neurodegenerative disease progression: thinking outside the black box

Data-driven disease progression models are an emerging set of computational tools that reconstruct disease timelines for long-term chronic diseases, providing unique insights into disease processes and their underlying mechanisms. Such methods combine a priori human knowledge and assumptions with large-scale data processing and parameter estimation to infer long-term disease trajectories from short-term data. In contrast to 'black box' machine learning tools, data-driven disease progression models typically require fewer data and are inherently interpretable, thereby aiding disease understanding in addition to enabling classification, prediction and stratification. In this Review, we place the current landscape of data-driven disease progression models in a general framework and discuss their enhanced utility for constructing a disease timeline compared with wider machine learning tools that construct static disease profiles. We review the insights they have enabled across multiple neurodegenerative diseases, notably Alzheimer disease, for applications such as determining temporal trajectories of disease biomarkers, testing hypotheses about disease mechanisms and uncovering disease subtypes. We outline key areas for technological development and translation to a broader range of neuroscience and non-neuroscience applications. Finally, we discuss potential pathways and barriers to integrating disease progression models into clinical practice and trial settings.

Microglia and complement mediate early corticostriatal synapse loss and cognitive dysfunction in Huntington's disease

Huntington's disease (HD) is a devastating monogenic neurodegenerative disease characterized by early, selective pathology in the basal ganglia despite the ubiquitous expression of mutant huntingtin. The molecular mechanisms underlying this region-specific neuronal degeneration and how these relate to the development of early cognitive phenotypes are poorly understood. Here we show that there is selective loss of synaptic connections between the cortex and striatum in postmortem tissue from patients with HD that is associated with the increased activation and localization of complement proteins, innate immune molecules, to these synaptic elements. We also found that levels of these secreted innate immune molecules are elevated in the cerebrospinal fluid of premanifest HD patients and correlate with established measures of disease burden.In preclinical genetic models of HD, we show that complement proteins mediate the selective elimination of corticostriatal synapses at an early stage in disease pathogenesis, marking them for removal by microglia, the brain's resident macrophage population. This process requires mutant huntingtin to be expressed in both cortical and striatal neurons. Inhibition of this complement-dependent elimination mechanism through administration of a therapeutically relevant C1q function-blocking antibody or genetic ablation of a complement receptor on microglia prevented synapse loss, increased excitatory input to the striatum and rescued the early development of visual discrimination learning and cognitive flexibility deficits in these models. Together, our findings implicate microglia and the complement cascade in the selective, early degeneration of corticostriatal synapses and the development of cognitive deficits in presymptomatic HD; they also provide new preclinical data to support complement as a therapeutic target for early intervention.

Plasma neurofilament light-chain and phosphorylated tau as biomarkers of disease severity in Huntington's disease: Korean cohort data

OBJECTIVE

To investigate neurofilament light chain (NfL), phosphorylated tau (p-Tau) and total tau (t-Tau) as plasma markers for clinical severity in Korean Huntington's disease (HD) cohort.

METHODS

Genetically-confirmed 67 HD patients participated from 13 referral hospitals in South Korea. The subjects were evaluated with the Unified Huntington's Disease Rating Scale (UHDRS), total motor score (TMS) and total functional capacity (TFC), Mini-Mental Status Examination (K-MMSE), Montreal Cognitive Assessment (MoCA-K), and Beck's depression inventory (K-BDI). We measured plasma NfL, p-Tau and t-Tau concentrations using single-molecule array (SIMOA) assays. Stages of HD were classified based on UHDRS-TFC score and plasma markers were analyzed for correlation with clinical severity scales.

RESULTS

Plasma NfL was elevated in both 6 premanifest and 61 full manifest HD patients compared to the reference value, which increased further from premanifest to manifest HD groups. The NfL level was not significantly correlated with UHDRS TMS or TFC scores in manifest HD patients. Plasma p-Tau was also elevated in HD patients (p = 0.038). The level was the highest in stage III-V HD (n = 30) group (post-hoc p < 0.05). The p-Tau was correlated with UHDRS TFC scores (adjusted p = 0.002). Plasma t-Tau neither differed among the groups nor associated with any clinical variables.

CONCLUSIONS

This study supports plasma NfL being a biomarker for initial HD manifestation in Korean cohort, and a novel suggestion of plasma p-Tau as a potential biomarker reflecting the clinical severity in full-manifest HD.

The temporal event-based model: Learning event timelines in progressive diseases

Timelines of events, such as symptom appearance or a change in biomarker value, provide powerful signatures that characterise progressive diseases. Understanding and predicting the timing of events is important for clinical trials targeting individuals early in the disease course when putative treatments are likely to have the strongest effect. However, previous models of disease progression cannot estimate the time between events and provide only an ordering in which they change. Here, we introduce the temporal event-based model (TEBM), a new probabilistic model for inferring timelines of biomarker events from sparse and irregularly sampled datasets. We demonstrate the power of the TEBM in two neurodegenerative conditions: Alzheimer's disease (AD) and Huntington's disease (HD). In both diseases, the TEBM not only recapitulates current understanding of event orderings but also provides unique new ranges of timescales between consecutive events. We reproduce and validate these findings using external datasets in both diseases. We also demonstrate that the TEBM improves over current models; provides unique stratification capabilities; and enriches simulated clinical trials to achieve a power of 80 % with less than half the cohort size compared with random selection. The application of the TEBM naturally extends to a wide range of progressive conditions.

Plasma NfL as a prognostic biomarker for enriching HD-ISS stage 1 categorisation: a cross-sectional study

BACKGROUND

The recently proposed Huntington's Disease Integrated Staging System (HD-ISS) categorises individuals with the Huntintin genetic mutation into disease progression cohorts based on quantitative neuroimaging, cognitive, and functional markers for research purposes. Unfortunately, many research studies do not collect quantitative neuroimaging data, and so the authors of the HD-ISS have subsequently provided approximated cohort thresholds based on disease and clinical data alone. However, these are rough proxies that aim to maximise stage separation, and should not be considered as 1:1 substitutes for the HD-ISS. Notably, no wet biomarker met the stringent criteria required to be considered a landmark for HD-ISS categorisation. We have previously shown that levels of plasma neurofilament light (NfL), a neuronal marker associated with axonal injury, are associated with predicted years to clinical motor diagnosis (CMD). Our objective in the current study was to determine whether HD-ISS categorisation, particularly for stages prior to CMD, could be improved with consideration of plasma NfL levels.

METHODS

A total of 290 blood samples, and clinical measures, were collected from participants across all HD-ISS stages: n = 50 [Stage 0], n = 64 [Stage 1], n = 63 [Stage 2], n = 63 [Stage 3], as well as 50 healthy controls. Plasma NfL levels were measured using a Meso Scale Discovery assay.

FINDINGS

Cohorts differed by age, cognitive function, CAG repeat length, and select UHDRS measures. Plasma NfL levels also differed significantly across cohorts. Approximately 50% of Stage 1 participants had plasma NfL levels indicative of predicted CMD within ten years.

INTERPRETATION

Our findings suggest that plasma NfL levels may have use in enriching Stage 1 membership into sub-groups that are less than, and within, predicted 10 years until CMD.

FUNDING

This work was supported by the National Institutes of Health (NS111655 to E.A.T.); the UCSD Huntington's Disease Society of America Center of Excellence; and the UCSD Shiley-Marcos Alzheimer's Disease Research Center (NIH-NIA P30 AG062429).

Study protocol of IMAGINE-HD: Imaging iron accumulation and neuroinflammation with 7T-MRI + CSF in Huntington's disease

INTRODUCTION

Strong evidence suggests a significant role for iron accumulation in the brain in addition to the well-documented neurodegenerative aspects of Huntington's disease (HD). The putative mechanisms by which iron is linked to the HD pathogenesis are multiple, including oxidative stress, ferroptosis and neuroinflammation. However, no previous study in a neurodegenerative disease has linked the observed increase of brain iron accumulation as measured by MRI with well-established cerebrospinal fluid (CSF) and blood biomarkers for iron accumulation, or with associated processes such as neuroinflammation. This study is designed to link quantitative data from iron levels and neuroinflammation metabolites obtained from 7T MRI of HD patients, with specific and well-known clinical biofluid markers for iron accumulation, neurodegeneration and neuroinflammation. Biofluid markers will provide quantitative measures of overall iron accumulation, neurodegeneration and neuroinflammation, while MRI measurements on the other hand will provide quantitative spatial information on brain pathology, neuroinflammation and brain iron accumulation, which will be linked to clinical outcome measures.

METHODS

This is an observational cross-sectional study, IMAGINE-HD, in HD gene expansion carriers and healthy controls. We include premanifest HD gene expansion carriers and patients with manifest HD in an early or moderate stage. The study includes a 7T MRI scan of the brain, clinical evaluation, motor, functional, and neuropsychological assessments, and sampling of CSF and blood for the detection of iron, neurodegenerative and inflammatory markers. Quantitative Susceptibility Maps will be reconstructed using T2* weighted images to quantify brain iron levels and Magnetic Resonance Spectroscopy will be used to obtain information about neuroinflammation by measuring cell-specific intracellular metabolites' level and diffusion. Age and sex matched healthy subjects are included as a control group.

DISCUSSION

Results from this study will provide an important basis for the evaluation of brain iron levels and neuroinflammation metabolites as an imaging biomarker for disease stage in HD and their relationship with the salient pathomechanisms of the disease on the one hand, and with clinical outcome on the other.

sEBM: Scaling Event Based Models to Predict Disease Progression via Implicit Biomarker Selection and Clustering

The Event Based Model (EBM) is a probabilistic generative model to explore biomarker changes occurring as a disease progresses. Disease progression is hypothesized to occur through a sequence of biomarker dysregulation "events". The EBM estimates the biomarker dysregulation event sequence. It computes the data likelihood for a given dysregulation sequence, and subsequently evaluates the posterior distribution on the dysregulation sequence. Since the posterior distribution is intractable, Markov Chain Monte-Carlo is employed to generate samples under the posterior distribution. However, the set of possible sequences increases as N ! where N is the number of biomarkers (data dimension) and quickly becomes prohibitively large for effective sampling via MCMC. This work proposes the "scaled EBM" (sEBM) to enable event based modeling on large biomarker sets (e.g. high-dimensional data). First, sEBM implicitly selects a subset of biomarkers useful for modeling disease progression and infers the event sequence only for that subset. Second, sEBM clusters biomarkers with similar positions in the event sequence and only orders the "clusters", with each successive cluster corresponding to the next stage in disease progression. These two modifications used to construct the sEBM method provably reduces the possible space of event sequences by multiple orders of magnitude. The novel modifications are supported by theory and experiments on synthetic and real clinical data provides validation for sEBM to work in higher dimensional settings. Results on synthetic data with known ground truth shows that sEBM outperforms previous EBM variants as data dimensions increase. sEBM was successfully implemented with up to 300 biomarkers, which is a 6-fold increase over previous EBM applications. A real-world clinical application of sEBM is performed using 119 neuroimaging markers from publicly available Alzheimer's Disease Neuroimaging Initiative (ADNI) data to stratify subjects into 6 stages of disease progression. Subjects included cognitively normal (CN), mild cognitive impairment (MCI), and Alzheimer's Disease (AD). sEBM stage is differentiated for the 3 groups ( χ 2 p - v a l u e < 4.6 e - 32 ) . Increased sEBM stage is a strong predictor of conversion risk to AD ( p - v a l u e < 2.3 e - 14 ) for MCI subjects, as verified with a Cox proportional-hazards model adjusted for age, sex, education and APOE4 status. Like EBM, sEBM does not rely on apriori defined diagnostic labels and only uses cross-sectional data.

Application Value of Serum Neurofilament Light Protein for Disease Staging in Huntington's Disease

BACKGROUND

Neurofilament light protein (NfL) has been proven to be a sensitive biomarker for Huntington's disease (HD). However, these studies did not include HD patients at advanced stages or with larger CAG repeats (>50), leading to a knowledge gap of the characteristics of NfL.

METHODS

Serum NfL (sNfL) levels were quantified using an ultrasensitive immunoassay. Participants were assessed by clinical scales and 7.0 T magnetic resonance imaging. Longitudinal samples and clinical data were obtained.

RESULTS

Baseline samples were available from 110 controls, 90 premanifest HD (pre-HD) and 137 HD individuals. We found levels of sNfL significantly increased in HD compared to pre-HD and controls (both P < 0.0001). The increase rates of sNfL were differed by CAG repeat lengths. However, there was no difference in sNfL levels in manifest HD from early to late stages. In addition, sNfL levels were associated with cognitive measures in pre-HD and manifest HD group, respectively. The increased levels of sNfL were also closely related to microstructural changes in white matter. In the longitudinal analysis, baseline sNfL did not correlate with subsequent clinical function decline. Random forest analysis revealed that sNfL had good power for predicting disease onset.

CONCLUSIONS

Although sNfL levels are independent of disease stages in manifest HD, it is still an optimal indicator for predicting disease onset and has potential use as a surrogate biomarker of treatment effect in clinical trials. © 2023 International Parkinson and Movement Disorder Society.

Cross-cohort analysis identified an immune checkpoint-based signature to predict the clinical outcomes of neuroblastoma

BACKGROUND

Neuroblastoma (NB) places a substantial health burden on families worldwide. This study aimed to develop an immune checkpoint-based signature (ICS) based on the expression of immune checkpoints to better assess patient survival risk and potentially guide patient selection for immunotherapy of NB.

METHODS

Immunohistochemistry integrated with digital pathology was used to determine the expression levels of 9 immune checkpoints in 212 tumor tissues used as the discovery set. The GSE85047 dataset (n=272) was used as a validation set in this study. In the discovery set, the ICS was constructed using a random forest algorithm and confirmed in the validation set to predict overall survival (OS) and event-free survival (EFS). Kaplan-Meier curves with a log-rank test were drawn to compare the survival differences. A receiver operating characteristic (ROC) curve was applied to calculate the area under the curve (AUC).

RESULTS

Seven immune checkpoints, including PD-L1, B7-H3, IDO1, VISTA, T-cell immunoglobulin and mucin domain containing-3 (TIM-3), inducible costimulatory molecule (ICOS) and costimulatory molecule 40 (OX40), were identified as abnormally expressed in NB in the discovery set. OX40, B7-H3, ICOS and TIM-3 were eventually selected for the ICS model in the discovery set, and 89 patients with high risk had an inferior OS (HR 15.91, 95% CI 8.87 to 28.55, p<0.001) and EFS (HR 4.30, 95% CI 2.80 to 6.62, p<0.001). Furthermore, the prognostic value of the ICS was confirmed in the validation set (p<0.001). Multivariate Cox regression analysis demonstrated that age and the ICS were independent risk factors for OS in the discovery set (HR 6.17, 95% CI 1.78 to 21.29 and HR 1.18, 95% CI 1.12 to 1.25, respectively). Furthermore, nomogram A combining the ICS and age demonstrated significantly better prognostic value than age alone in predicting the patients' 1-year, 3-year and 5-year OS in the discovery set (1 year: AUC, 0.891 (95% CI 0.797 to 0.985) vs 0.675 (95% CI 0.592 to 0.758); 3 years: 0.875 (95% CI 0.817 to 0.933) vs 0.701 (95% CI 0.645 to 0.758); 5 years: 0.898 (95% CI 0.851 to 0.940) vs 0.724 (95% CI 0.673 to 0.775), respectively), which was confirmed in the validation set.

CONCLUSIONS

We propose an ICS that significantly differentiates between low-risk and high-risk patients, which might add prognostic value to age and provide clues for immunotherapy in NB.

Quantifying mutant huntingtin protein in human cerebrospinal fluid to support the development of huntingtin-lowering therapies

Huntington's disease (HD) is caused by a cytosine adenine guanine-repeat expansion in the huntingtin gene. This results in the production of toxic mutant huntingtin protein (mHTT), which has an elongated polyglutamine (polyQ) stretch near the protein's N-terminal end. The pharmacological lowering of mHTT expression in the brain targets the underlying driver of HD and is one of the principal therapeutic strategies being pursued to slow or stop disease progression. This report describes the characterisation and validation of an assay designed to quantify mHTT in the cerebrospinal fluid of individuals with HD, for use in registrational clinical trials. The assay was optimised, and its performance was characterised with recombinant huntingtin protein (HTT) varying in overall and polyQ-repeat length. The assay was successfully validated by two independent laboratories in regulated bioanalytical environments and showed a steep signal increase as the polyQ stretch of recombinant HTTs pivoted from wild-type to mutant protein forms. Linear mixed effects modelling confirmed highly parallel concentration-response curves for HTTs, with only a minor impact of individual slopes of the concentration-response for different HTTs (typically < 5% of the overall slope). This implies an equivalent quantitative signal behaviour for HTTs with differing polyQ-repeat lengths. The reported method may be a reliable biomarker tool with relevance across the spectrum of HD mutations, which can facilitate the clinical development of HTT-lowering therapies in HD.

Peripheral Biomarkers in Manifest and Premanifest Huntington's Disease

Huntington's disease (HD) is characterized by clinical motor impairment (e.g., involuntary movements, poor coordination, parkinsonism), cognitive deficits, and psychiatric symptoms. An inhered expansion of the CAG triplet in the huntingtin gene causing a pathogenic gain-of-function of the mutant huntingtin (mHTT) protein has been identified. In this review, we focus on known biomarkers (e.g., mHTT, neurofilament light chains) and on new biofluid biomarkers that can be quantified in plasma or peripheral blood mononuclear cells from mHTT carriers. Circulating biomarkers may fill current unmet needs in HD management: better stratification of patients amenable to etiologic treatment; the initiation of preventive treatment in premanifest HD; and the identification of peripheral pathogenic central nervous system cascades.

Group 2 innate lymphoid cells promote inhibitory synapse development and social behavior

The innate immune system plays essential roles in brain synaptic development, and immune dysregulation is implicated in neurodevelopmental diseases. Here we show that a subset of innate lymphocytes (group 2 innate lymphoid cells, ILC2s) is required for cortical inhibitory synapse maturation and adult social behavior. ILC2s expanded in the developing meninges and produced a surge of their canonical cytokine Interleukin-13 (IL-13) between postnatal days 5-15. Loss of ILC2s decreased cortical inhibitory synapse numbers in the postnatal period where as ILC2 transplant was sufficient to increase inhibitory synapse numbers. Deletion of the IL-4/IL-13 receptor (Il4ra) from inhibitory neurons phenocopied the reduction inhibitory synapses. Both ILC2 deficient and neuronal Il4ra deficient animals had similar and selective impairments in adult social behavior. These data define a type 2 immune circuit in early life that shapes adult brain function.

The updated development of blood-based biomarkers for Huntington's disease

Huntington's disease is a progressive neurodegenerative disease caused by mutation of the huntingtin (HTT) gene. The identification of mutation carriers before symptom onset provides an opportunity to intervene in the early stage of the disease course. Optimal biomarkers are of great value to reflect neuropathological and clinical progression and are sensitive to potential disease-modifying treatments. Blood-based biomarkers have the merits of minimal invasiveness, low cost, easy accessibility and safety. In this review, we summarized the updated development of blood-based biomarkers for HD from six aspects, including neuronal injuries, oxidative stress, endocrine functions, immune reactions, metabolism and differentially expressed miRNAs. The blood-based biomarkers presented and discussed in this review were close to clinical applicability and might facilitate clinical design as surrogate endpoints. Exploration and validation of robust blood-based biomarkers require further standard and systemic study design in the future.

Salivary Huntingtin protein is uniquely associated with clinical features of Huntington's disease

Measuring Huntingtin (HTT) protein in peripheral cells represents an essential step in biomarker discovery for Huntington's Disease (HD), however to date, investigations into the salivary expression of HTT has been lacking. In the current study, we quantified total HTT (tHTT) and mutant HTT (mHTT) protein in matched blood and saliva samples using single molecule counting (SMC) immunoassays: 2B7-D7F7 (tHTT) and 2B7-MW1 (mHTT). Matched samples, and clinical data, were collected from 95 subjects: n = 19 manifest HD, n = 34 premanifest HD (PM), and n = 42 normal controls (NC). Total HTT and mHTT levels were not correlated in blood and saliva. Plasma tHTT was significantly associated with age, and participant sex; whereas salivary mHTT was significantly correlated with age, CAG repeat length and CAP score. Plasma and salivary tHTT did not differ across cohorts. Salivary and plasma mHTT were significantly increased in PM compared to NC; salivary mHTT was also significantly increased in HD compared to NC. Only salivary tHTT and mHTT were significantly correlated with clinical measures. Salivary HTT is uniquely associated with clinical measures of HD and offers significant promise as a relevant, non-invasive HD biomarker. Its use could be immediately implemented into both translational and clinical research applications.

Pre- and Post-Portosystemic Shunt Placement Metabolomics Reveal Molecular Signatures for the Development of Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a common complication of advanced liver disease causing brain dysfunction. This is likely due to the accumulation of unfiltered toxins within the bloodstream. A known risk factor for developing or worsening HE is the placement of a transjugular intrahepatic portosystemic shunt (TIPS), which connects the pre-hepatic and post-hepatic circulation allowing some blood to bypass the dysfunctional liver and decreases portal hypertension. To better understand the pathophysiology of post-TIPS HE, we conducted a multi-center prospective cohort study employing metabolomic analyses on hepatic vein and peripheral vein blood samples from participants with cirrhosis undergoing elective TIPS placement, measuring chemical modifications and changes in concentrations of metabolites resulting from TIPS placement. In doing so, we identified numerous alterations in metabolites, including bile acids, glycerophosphocholines, and bilirubins possibly implicated in the development and severity of HE.

Neurofilament light oligomers in neurodegenerative diseases: quantification by homogeneous immunoassay in cerebrospinal fluid

Background

Neurofilament light (NfL) is a widely used biomarker for neurodegeneration. NfL is prone to oligomerisation, but available assays do not reveal the exact molecular nature of the protein variant measured. The objective of this study was to develop a homogeneous ELISA capable of quantifying oligomeric NfL (oNfL) in cerebrospinal fluid (CSF).

Methods

A homogeneous ELISA, based on the same capture and detection antibody (NfL21), was developed and used to quantify oNfL in samples from patients with behavioural variant frontotemporal dementia (bvFTD, n=28), non-fluent variant primary progressive aphasia (nfvPPA, n=23), semantic variant PPA (svPPA, n=10), Alzheimer's disease (AD, n=20) and healthy controls (n=20). The nature of NfL in CSF, and the recombinant protein calibrator, was also characterised by size exclusion chromatography (SEC).

Results

CSF concentration of oNfL was significantly higher in nfvPPA (p<0.0001) and svPPA patients (p<0.05) compared with controls. CSF oNfL concentration was also significantly higher in nfvPPA compared with bvFTD (p<0.001) and AD (p<0.01) patients. SEC data showed a peak fraction compatible with a full-length dimer (~135 kDa) in the in-house calibrator. For CSF, the peak was found in a fraction of lower molecular weight (~53 kDa), suggesting dimerisation of NfL fragments.

Conclusions

The homogeneous ELISA and SEC data suggest that most of the NfL in both the calibrator and human CSF is present as a dimer. In CSF, the dimer appears to be truncated. Further studies are needed to determine its precise molecular composition.

Levels of Synaptic Proteins in Brain and Neurofilament Light Chain in Cerebrospinal Fluid and Plasma of OVT73 Huntington's Disease Sheep Support a Prodromal Disease State

BACKGROUND

Synaptic changes occur early in patients with Huntington's disease (HD) and in mouse models of HD. An analysis of synaptic changes in HD transgenic sheep (OVT73) is fitting since they have been shown to have some phenotypes. They also have larger brains, longer lifespan, and greater motor and cognitive capacities more aligned with humans, and can provide abundant biofluids for in vivo monitoring of therapeutic interventions.

OBJECTIVE

The objective of this study was to determine if there were differences between 5- and 10-year-old OVT73 and wild-type (WT) sheep in levels of synaptic proteins in brain and in neurofilament light chain (NfL) in cerebrospinal fluid (CSF) and plasma.

METHODS

Mutant huntingtin (mHTT) and other proteins were measured by western blot assay in synaptosomes prepared from caudate, motor, and piriform cortex in 5-year-old and caudate, putamen, motor; and piriform cortex in 10-year-old WT and OVT73 sheep. Levels of NfL, a biomarker for neuronal damage increased in many neurological disorders including HD, were examined in CSF and plasma samples from 10-year-old WT and OVT73 sheep using the Simoa NfL Advantage kit.

RESULTS

Western blot analysis showed mHTT protein expression in synaptosomes from OVT73 sheep was  23% of endogenous sheep HTT levels at both ages. Significant changes were detected in brain levels of PDE10A, SCN4B, DARPP32, calmodulin, SNAP25, PSD95, VGLUT 1, VAMP1, and Na+/K+-ATPase, which depended on age and brain region. There was no difference in NfL levels in CSF and plasma in OVT73 sheep compared to age-matched WT sheep.

CONCLUSIONS

These results show that synaptic changes occur in brain of 5- and 10-year-old OVT73 sheep, but levels of NfL in biofluids are unaffected. Altogether, the data support a prodromal disease state in OVT73 sheep that involves the caudate, putamen and cortex.

Neurofilament light levels predict clinical progression and death in multiple system atrophy

Disease-modifying treatments are currently being trialled in multiple system atrophy. Approaches based solely on clinical measures are challenged by heterogeneity of phenotype and pathogenic complexity. Neurofilament light chain protein has been explored as a reliable biomarker in several neurodegenerative disorders but data on multiple system atrophy have been limited. Therefore, neurofilament light chain is not yet routinely used as an outcome measure in multiple system atrophy. We aimed to comprehensively investigate the role and dynamics of neurofilament light chain in multiple system atrophy combined with cross-sectional and longitudinal clinical and imaging scales and for subject trial selection. In this cohort study, we recruited cross-sectional and longitudinal cases in a multicentre European set-up. Plasma and CSF neurofilament light chain concentrations were measured at baseline from 212 multiple system atrophy cases, annually for a mean period of 2 years in 44 multiple system atrophy patients in conjunction with clinical, neuropsychological and MRI brain assessments. Baseline neurofilament light chain characteristics were compared between groups. Cox regression was used to assess survival; receiver operating characteristic analysis to assess the ability of neurofilament light chain to distinguish between multiple system atrophy patients and healthy controls. Multivariate linear mixed-effects models were used to analyse longitudinal neurofilament light chain changes and correlated with clinical and imaging parameters. Polynomial models were used to determine the differential trajectories of neurofilament light chain in multiple system atrophy. We estimated sample sizes for trials aiming to decrease neurofilament light chain levels. We show that in multiple system atrophy, baseline plasma neurofilament light chain levels were better predictors of clinical progression, survival and degree of brain atrophy than the neurofilament light chain rate of change. Comparative analysis of multiple system atrophy progression over the course of disease, using plasma neurofilament light chain and clinical rating scales, indicated that neurofilament light chain levels rise as the motor symptoms progress, followed by deceleration in advanced stages. Sample size prediction suggested that significantly lower trial participant numbers would be needed to demonstrate treatment effects when incorporating plasma neurofilament light chain values into multiple system atrophy clinical trials in comparison to clinical measures alone. In conclusion, neurofilament light chain correlates with clinical disease severity, progression and prognosis in multiple system atrophy. Combined with clinical and imaging analysis, neurofilament light chain can inform patient stratification and serve as a reliable biomarker of treatment response in future multiple system atrophy trials of putative disease-modifying agents.

Brain Alterations in Aged OVT73 Sheep Model of Huntington's Disease: An MRI Based Approach

BACKGROUND

Huntington's disease (HD) is a fatal neurodegenerative autosomal dominant disorder with prevalence of 1 : 20000 that has no effective treatment to date. Translatability of candidate therapeutics could be enhanced by additional testing in large animal models because of similarities in brain anatomy, size, and immunophysiology. These features enable realistic pre-clinical studies of biodistribution, efficacy, and toxicity.

OBJECTIVE AND METHODS

Here we non-invasively characterized alterations in brain white matter microstructure, neurochemistry, neurological status, and mutant Huntingtin protein (mHTT) levels in cerebrospinal fluid (CSF) of aged OVT73 HD sheep.

RESULTS

Similar to HD patients, CSF mHTT differentiates HD from normal sheep. Our results are indicative of a decline in neurological status, and alterations in brain white matter diffusion and spectroscopy metric that are more severe in aged female HD sheep. Longitudinal analysis of aged female HD sheep suggests that the decline is detectable over the course of a year. In line with reports of HD human studies, white matter alterations in corpus callosum correlates with a decline in gait of HD sheep. Moreover, alterations in the occipital cortex white matter correlates with a decline in clinical rating score. In addition, the marker of energy metabolism in striatum of aged HD sheep, shows a correlation with decline of clinical rating score and eye coordination.

CONCLUSION

This data suggests that OVT73 HD sheep can serve as a pre-manifest large animal model of HD providing a platform for pre-clinical testing of HD therapeutics and non-invasive tracking of the efficacy of the therapy.

The Chinese Version of UHDRS in Huntington's Disease: Reliability and Validity Assessment

BACKGROUND

The Unified Huntington's Disease Rating Scale (UHDRS) is a universal scale assessing disease severity of Huntington's disease (HD). However, the English version cannot be widely used in China, and the reliability and validity of the Chinese UHDRS have not yet been confirmed.

OBJECTIVE

To test the reliability and validity of Chinse UHDRS in patients with HD.

METHODS

Between August 2013 and August 2021, 159 HD patients, 40 premanifest HD, and 64 healthy controls were consecutively recruited from two medical centers in China and assessed by Chinese UHDRS. Internal consistency and interrater reliability of the scale were examined. Intercorrelation was performed to analyze the convergent and divergent validity of the scale. A receiver operating characteristic analysis was conducted to explore the optimal cutoff point of each cognitive test.

RESULTS

High internal consistency was found in Chinese UHDRS, and its Cronbach's alpha values of the motor, cognitive, behavioral and functional subscales were 0.954, 0.826, 0.804, and 0.954, respectively. The interrater reliability of the total motor score was 0.960. The convergent and divergent validity revealed that motor, cognitive and functional subscales strongly related to each other except for Problem Behavior Assessment. Furthermore, we not only provided the normal level of each cognitive test in controls, but also gave the optimal cutoff points of cognitive tests between controls and HD patients.

CONCLUSION

We demonstrate for the first time that the translated version of UHDRS is reliable for assessing HD patients in China. This can promote the universal use of UHDRS in clinical practice.

Cerebrospinal fluid biomarkers for assessing Huntington disease onset and severity

The identification of molecular biomarkers in CSF from individuals affected by Huntington disease may help improve predictions of disease onset, better define disease progression and could facilitate the evaluation of potential therapies. The primary objective of our study was to investigate novel CSF protein candidates and replicate previously reported protein biomarker changes in CSF from Huntington disease mutation carriers and healthy controls. Our secondary objective was to compare the discriminatory potential of individual protein analytes and combinations of CSF protein markers for stratifying individuals based on the severity of Huntington disease. We conducted a hypothesis-driven analysis of 26 pre-specified protein analytes in CSF from 16 manifest Huntington disease subjects, eight premanifest Huntington disease mutation carriers and eight healthy control individuals using parallel-reaction monitoring mass spectrometry. In addition to reproducing reported changes in previously investigated CSF biomarkers (NEFL, PDYN, and PENK), we also identified novel exploratory CSF proteins (C1QB, CNR1, GNAL, IDO1, IGF2, and PPP1R1B) whose levels were altered in Huntington disease mutation carriers and/or across stages of disease. Moreover, we report strong associations of select CSF proteins with clinical measures of disease severity in manifest Huntington disease subjects (C1QB, CNR1, NEFL, PDYN, PPP1R1B, and TTR) and with years to predicted disease onset in premanifest Huntington disease mutation carriers (ALB, C4B, CTSD, IGHG1, and TTR). Using receiver operating characteristic curve analysis, we identified PENK as being the most discriminant CSF protein for stratifying Huntington disease mutation carriers from controls. We also identified exploratory multi-marker CSF protein panels that improved discrimination of premanifest Huntington disease mutation carriers from controls (PENK, ALB and NEFL), early/mid-stage Huntington disease from premanifest mutation carriers (PPP1R1B, TTR, CHI3L1, and CTSD), and late-stage from early/mid-stage Huntington disease (CNR1, PPP1R1B, BDNF, APOE, and IGHG1) compared with individual CSF proteins. In this study, we demonstrate that combinations of CSF proteins can outperform individual markers for stratifying individuals based on Huntington disease mutation status and disease severity. Moreover, we define exploratory multi-marker CSF protein panels that, if validated, may be used to improve the accuracy of disease-onset predictions, complement existing clinical and imaging biomarkers for monitoring the severity of Huntington disease, and potentially for assessing therapeutic response in clinical trials. Additional studies with CSF collected from larger cohorts of Huntington disease mutation carriers are needed to replicate these exploratory findings.

Leukocyte Telomere Length as Potential Biomarker of HD Progression: A Follow-Up Study

The identification of biomarkers for neurodegenerative disorders such as Huntington’s disease (HD) is crucial for monitoring disease progression and therapeutic trial outcomes, especially in the pre-manifest disease stage (pre-HD). In a previous study, we observed that leukocyte telomere length (LTL) was strongly correlated with the estimated time to clinical onset in pre-HD subjects. To validate this hypothesis, we designed a follow-up study in which we analyzed LTL in 45 pre-HD stage subjects at baseline (T0) and then again after clinical onset at follow-up (T1); the follow-up interval was about 3 years, and the CAG range was 39–51 repeats; 90 peripheral blood mononuclear cell samples (PBMCs) were obtained from the Enroll-HD biorepository. In pre-HD subjects at T0, LTL was significantly reduced by 22% compared to the controls and by 14% from T0 at T1. No relationship was observed between the LTL and CAG numbers in subjects carrying different CAG repeats at T0 and at T1, suggesting that LTL reduction occurs independently of CAG number in pre-HD subjects. ROC curve analysis was used to test the validity of LTL as a potential biomarker of HD progression and showed that LTL measurement is extremely accurate in discriminating pre-HD subjects from the controls and even pre-HD from manifest HD, thus yielding a robust prognostic value in pre-HD subjects.

Current Diagnostic Methods and Non-Coding RNAs as Possible Biomarkers in Huntington's Disease

Whether as a cause or a symptom, RNA transcription is recurrently altered in pathologic conditions. This is also true for non-coding RNAs, with regulatory functions in a variety of processes such as differentiation, cell identity and metabolism. In line with their increasingly recognized roles in cellular pathways, RNAs are also currently evaluated as possible disease biomarkers. They could be informative not only to follow disease progression and assess treatment efficacy in clinics, but also to aid in the development of new therapeutic approaches. This is especially important for neurological and genetic disorders, where the administration of appropriate treatment during the disease prodromal stage could significantly delay, if not halt, disease progression. In this review we focus on the current status of biomarkers in Huntington's Disease (HD), a fatal hereditary and degenerative disease condition. First, we revise the sources and type of wet biomarkers currently in use. Then, we explore the feasibility of different RNA types (miRNA, ncRNA, circRNA) as possible biomarker candidates, discussing potential advantages, disadvantages, sources of origin and the ongoing investigations on this topic.

Neurofilaments contribution in clinic: state of the art

Neurological biomarkers are particularly valuable to clinicians as they can be used for diagnosis, prognosis, or response to treatment. This field of neurology has evolved considerably in recent years with the improvement of analytical methods, allowing the detection of biomarkers not only in cerebrospinal fluid (CSF) but also in less invasive fluids like blood. These advances greatly facilitate the repeated quantification of biomarkers, including at asymptomatic stages of the disease. Among the various informative biomarkers of neurological disorders, neurofilaments (NfL) have proven to be of particular interest in many contexts, such as neurodegenerative diseases, traumatic brain injury, multiple sclerosis, stroke, and cancer. Here we discuss these different pathologies and the potential value of NfL assay in the management of these patients, both for diagnosis and prognosis. We also describe the added value of NfL compared to other biomarkers currently used to monitor the diseases described in this review.

Benefits of global mutant huntingtin lowering diminish over time in a Huntington's disease mouse model

We have developed an inducible Huntington's disease (HD) mouse model that allows temporal control of whole-body allele-specific mutant huntingtin (mHtt) expression. We asked whether moderate global lowering of mHtt (~50%) was sufficient for long-term amelioration of HD-related deficits and, if so, whether early mHtt lowering (before measurable deficits) was required. Both early and late mHtt lowering delayed behavioral dysfunction and mHTT protein aggregation, as measured biochemically. However, long-term follow-up revealed that the benefits, in all mHtt-lowering groups, attenuated by 12 months of age. While early mHtt lowering attenuated cortical and striatal transcriptional dysregulation evaluated at 6 months of age, the benefits diminished by 12 months of age, and late mHtt lowering did not ameliorate striatal transcriptional dysregulation at 12 months of age. Only early mHtt lowering delayed the elevation in cerebrospinal fluid neurofilament light chain that we observed in our model starting at 9 months of age. As small-molecule HTT-lowering therapeutics progress to the clinic, our findings suggest that moderate mHtt lowering allows disease progression to continue, albeit at a slower rate, and could be relevant to the degree of mHTT lowering required to sustain long-term benefits in humans.

Circulating U13 Small Nucleolar RNA as a Potential Biomarker in Huntington's Disease: A Pilot Study

Plasma small RNAs have been recently explored as biomarkers in Huntington’s disease (HD). We performed an exploratory study on nine HD patients, eight healthy subjects (HS), and five psychiatric patients (PP; to control for iatrogenic confounder effects) through an Affymetrix-Gene-Chip-miRNA-Array. We validated the results in an independent population of 23 HD, 15 pre-HD, 24 PP, 28 Alzheimer’s disease (AD) patients (to control the disease-specificity) and 22 HS through real-time PCR. The microarray results showed higher levels of U13 small nucleolar RNA (SNORD13) in HD patients than controls (fold change 1.54, p = 0.003 HD vs. HS, and 1.44, p = 0.0026 HD vs. PP). In the validation population, a significant increase emerged with respect to both pre-HD and the control groups (p < 0.0001). SNORD13 correlated with the status of the mutant huntingtin carrier (r = 0.73; p < 0.001) and the disease duration (r = 0.59; p = 0.003). The receiver operating characteristic (ROC) curve analysis showed the high accuracy of SNORD13 in discriminating HD patients from other groups (AUC = 0.963). An interactome and pathway analysis on SNORD13 revealed enrichments for factors relevant to HD pathogenesis. We report the unprecedented finding of a potential disease-specific role of SNORD13 in HD. It seems to peripherally report a ‘tipping point’ in the pathogenic cascade at the neuronal level.

The Key Role of Magnetic Resonance Imaging in the Detection of Neurodegenerative Diseases-Associated Biomarkers: A Review

Neurodegenerative diseases (NDs), including chronic disease such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis, and acute diseases like traumatic brain injury and ischemic stroke are characterized by progressive degeneration, brain tissue damage and loss of neurons, accompanied by behavioral and cognitive dysfunctions. So far, there are no complete cures for NDs; thus, early and timely diagnoses are essential and beneficial to patients' treatment. Magnetic resonance imaging (MRI) has become one of the advanced medical imaging techniques widely used in the clinical examination of NDs due to its non-invasive diagnostic value. In this review, research published in English in current decade from PubMed electronic database on the use of MRI to detect specific biomarkers of NDs was collected, summarized, and discussed, which provides valuable suggestions for the early diagnosis, prevention, and treatment of NDs in the clinic.

Monitoring gait at home with radio waves in Parkinson's disease: A marker of severity, progression, and medication response

Parkinson's disease (PD) is the fastest-growing neurological disease in the world. A key challenge in PD is tracking disease severity, progression, and medication response. Existing methods are semisubjective and require visiting the clinic. In this work, we demonstrate an effective approach for assessing PD severity, progression, and medication response at home, in an objective manner. We used a radio device located in the background of the home. The device detected and analyzed the radio waves that bounce off people's bodies and inferred their movements and gait speed. We continuously monitored 50 participants, with and without PD, in their homes for up to 1 year. We collected over 200,000 gait speed measurements. Cross-sectional analysis of the data shows that at-home gait speed strongly correlates with gold-standard PD assessments, as evaluated by the Movement Disorder Society-Sponsored Revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III subscore and total score. At-home gait speed also provides a more sensitive marker for tracking disease progression over time than the widely used MDS-UPDRS. Further, the monitored gait speed was able to capture symptom fluctuations in response to medications and their impact on patients' daily functioning. Our study shows the feasibility of continuous, objective, sensitive, and passive assessment of PD at home and hence has the potential of improving clinical care and drug clinical trials.

Mutation-related magnetization-transfer, not axon density, drives white matter differences in premanifest Huntington disease: Evidence from in vivo ultra-strong gradient MRI

White matter (WM) alterations have been observed in Huntington disease (HD) but their role in the disease-pathophysiology remains unknown. We assessed WM changes in premanifest HD by exploiting ultra-strong-gradient magnetic resonance imaging (MRI). This allowed to separately quantify magnetization transfer ratio (MTR) and hindered and restricted diffusion-weighted signal fractions, and assess how they drove WM microstructure differences between patients and controls. We used tractometry to investigate region-specific alterations across callosal segments with well-characterized early- and late-myelinating axon populations, while brain-wise differences were explored with tract-based cluster analysis (TBCA). Behavioral measures were included to explore disease-associated brain-function relationships. We detected lower MTR in patients' callosal rostrum (tractometry: p = .03; TBCA: p = .03), but higher MTR in their splenium (tractometry: p = .02). Importantly, patients' mutation-size and MTR were positively correlated (all p-values < .01), indicating that MTR alterations may directly result from the mutation. Further, MTR was higher in younger, but lower in older patients relative to controls (p = .003), suggesting that MTR increases are detrimental later in the disease. Finally, patients showed higher restricted diffusion signal fraction (FR) from the composite hindered and restricted model of diffusion (CHARMED) in the cortico-spinal tract (p = .03), which correlated positively with MTR in the posterior callosum (p = .033), potentially reflecting compensatory mechanisms. In summary, this first comprehensive, ultra-strong gradient MRI study in HD provides novel evidence of mutation-driven MTR alterations at the premanifest disease stage which may reflect neurodevelopmental changes in iron, myelin, or a combination of these.

Potential disease-modifying therapies for Huntington's disease: lessons learned and future opportunities

Huntington's disease is the most frequent autosomal dominant neurodegenerative disorder; however, no disease-modifying interventions are available for patients with this disease. The molecular pathogenesis of Huntington's disease is complex, with toxicity that arises from full-length expanded huntingtin and N-terminal fragments of huntingtin, which are both prone to misfolding due to proteolysis; aberrant intron-1 splicing of the HTT gene; and somatic expansion of the CAG repeat in the HTT gene. Potential interventions for Huntington's disease include therapies targeting huntingtin DNA and RNA, clearance of huntingtin protein, DNA repair pathways, and other treatment strategies targeting inflammation and cell replacement. The early termination of trials of the antisense oligonucleotide tominersen suggest that it is time to reflect on lessons learned, where the field stands now, and the challenges and opportunities for the future.

Neurofilament Light Protein as a Potential Blood Biomarker for Huntington's Disease in Children

BACKGROUND

Juvenile-onset Huntington's disease (JOHD) is a rare and particularly devastating form of Huntington's disease (HD) for which clinical diagnosis is challenging and robust outcome measures are lacking. Neurofilament light protein (NfL) in plasma has emerged as a prognostic biomarker for adult-onset HD.

METHODS

We performed a retrospective analysis of samples and data collected between 2009 and 2020 from the Kids-HD and Kids-JHD studies. Plasma samples from children and young adults with JOHD, premanifest HD (preHD) mutation carriers, and age-matched controls were used to quantify plasma NfL concentrations using ultrasensitive immunoassay.

RESULTS

We report elevated plasma NfL concentrations in JOHD and premanifest HD mutation-carrying children. In pediatric HD mutation carriers who were within 20 years of their predicted onset and patients with JOHD, plasma NfL level was associated with caudate and putamen volumes.

CONCLUSIONS

Quantifying plasma NfL concentration may assist clinical diagnosis and therapeutic trial design in the pediatric population. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.

Translating cell therapies for neurodegenerative diseases: Huntington's disease as a model disorder

There has been substantial progress in the development of regenerative medicine strategies for CNS disorders over the last decade, with progression to early clinical studies for some conditions. However, there are multiple challenges along the translational pipeline, many of which are common across diseases and pertinent to multiple donor cell types. These include defining the point at which the preclinical data are sufficiently compelling to permit progression to the first clinical studies; scaling-up, characterization, quality control and validation of the cell product; design, validation and approval of the surgical device; and operative procedures for safe and effective delivery of cell product to the brain. Furthermore, clinical trials that incorporate principles of efficient design and disease-specific outcomes are urgently needed (particularly for those undertaken in rare diseases, where relatively small cohorts are an additional limiting factor), and all processes must be adaptable in a dynamic regulatory environment. Here we set out the challenges associated with the clinical translation of cell therapy, using Huntington's disease as a specific example, and suggest potential strategies to address these challenges. Huntington's disease presents a clear unmet need, but, importantly, it is an autosomal dominant condition with a readily available gene test, full genetic penetrance and a wide range of associated animal models, which together mean that it is a powerful condition in which to develop principles and test experimental therapeutics. We propose that solving these challenges in Huntington's disease would provide a road map for many other neurological conditions. This white paper represents a consensus opinion emerging from a series of meetings of the international translational platforms Stem Cells for Huntington's Disease and the European Huntington's Disease Network Advanced Therapies Working Group, established to identify the challenges of cell therapy, share experience, develop guidance and highlight future directions, with the aim to expedite progress towards therapies for clinical benefit in Huntington's disease.

Levels of Neurofilament Light at the Preataxic and Ataxic Stages of Spinocerebellar Ataxia Type 1

BACKGROUND AND OBJECTIVES

Neurofilament light (NfL) appears to be a promising fluid biomarker in repeat-expansion spinocerebellar ataxias (SCAs), with piloting studies in mixed SCA cohorts suggesting that NfL might be increased at the ataxic stage of SCA type 1 (SCA1). We here hypothesized that NfL is increased not only at the ataxic stage of SCA1, but also at its (likely most treatment-relevant) preataxic stage.

METHODS

We assessed serum NfL (sNfL) and CSF NfL (cNfL) levels in both preataxic and ataxic SCA1, leveraging a multicentric cohort recruited at 6 European university centers, and clinical follow-up data, including actually observed (rather than only predicted) conversion to the ataxic stage. Levels of sNfL and cNfL were assessed by single-molecule array and ELISA technique, respectively.

RESULTS

Forty individuals with SCA1 (23 preataxic, 17 ataxic) and 89 controls were enrolled, including 11 preataxic individuals converting to the ataxic stage. sNfL levels were increased at the preataxic (median 15.5 pg/mL [interquartile range 10.5-21.1 pg/mL]) and ataxic stage (31.6 pg/mL [26.2-37.7 pg/mL]) compared to controls (6.0 pg/mL [4.7-8.6 pg/mL]), yielding high age-corrected effect sizes (preataxic: r = 0.62, ataxic: r = 0.63). sNfL increases were paralleled by increases of cNfL at both the preataxic and ataxic stage. In preataxic individuals, sNfL levels increased with proximity to predicted ataxia onset, with significant sNfL elevations already 5 years before onset, and confirmed in preataxic individuals with actually observed ataxia onset. sNfL increases were detected already in preataxic individuals with SCA1 without volumetric atrophy of cerebellum or pons, suggesting that sNfL might be more sensitive to early preataxic neurodegeneration than the currently known most change-sensitive regions in volumetric MRI. Using longitudinal sNfL measurements, we estimated sample sizes for clinical trials with the reduction of sNfL as the endpoint.

DISCUSSION

sNfL levels might provide easily accessible peripheral biomarkers in both preataxic and ataxic SCA1, allowing stratification of preataxic individuals regarding proximity to onset, early detection of neurodegeneration even before volumetric MRI alterations, and potentially capture of treatment response in clinical trials.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov Identifier: NCT01037777.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that NfL levels are increased in both ataxic and preataxic SCA1 and are associated with ataxia onset.

Safety and Feasibility of Research Lumbar Puncture in Huntington's Disease: The HDClarity Cohort and Bioresource

BACKGROUND

Biomarkers are needed to monitor disease progression, target engagement and efficacy in Huntington's disease (HD). Cerebrospinal fluid (CSF) is an ideal medium to research such biomarkers due to its proximity to the brain.

OBJECTIVE

To investigate the safety and feasibility of research lumbar punctures (LP) in HD.

METHODS

HDClarity is an ongoing international biofluid collection initiative built on the Enroll-HD platform, where clinical assessments are recorded. It aims to recruit 1,200 participants. Biosamples are collected following an overnight fast: blood via venipuncture and CSF via LP. Participants are healthy controls and HD gene expansion carriers across the disease spectrum. We report on monitored data from February 2016 to September 2019.

RESULTS

Of 448 participants screened, 398 underwent at least 1 sampling visit, of which 98.24% were successful (i.e., CSF was collected), amounting to 10,610 mL of CSF and 8,200 mL of plasma. In the total 572 sampling visits, adverse events were reported in 24.13%, and headaches of any kind and post-LP headaches in 14.86% and 12.24%, respectively. Frequencies were less in manifest HD; gender, age, body mass index and disease burden score were not associated with the occurrence of the events in gene expansion carriers. Headaches and back pain were the most frequent adverse events.

CONCLUSION

HDClarity is the largest CSF collection initiative to support scientific research into HD and is now stablished as a leading resource for HD research. Our data confirm that research LP in HD are feasible and acceptable to the community, and have a manageable safety profile.

Changes in brain activity with tominersen in early-manifest Huntington’s disease

It is unknown whether alterations in EEG brain activity caused by Huntington’s disease may be responsive to huntingtin-lowering treatment. We analysed EEG recordings of 46 patients (mean age = 47.02 years; standard deviation = 10.19 years; 18 female) with early-manifest Stage 1 Huntington’s disease receiving the huntingtin-lowering antisense oligonucleotide tominersen for 4 months or receiving placebo as well as 39 healthy volunteers (mean age = 44.48 years; standard deviation = 12.94; 22 female) not receiving treatment. Patients on tominersen showed increased resting-state activity within a 4–8 Hz frequency range compared with patients receiving placebo (cluster-based permutation test, P &lt; 0.05). The responsive frequency range overlapped with EEG activity that was strongly reduced in Huntington’s disease compared with healthy controls (cluster-based permutation test, P &lt; 0.05). The underlying mechanisms of the observed treatment-related increase are unknown and may reflect neural plasticity as a consequence of the molecular pathways impacted by tominersen treatment.

Hawellek et al. report that patients with Huntington’s disease treated with the huntingtin-lowering antisense oligonucleotide tominersen exhibited increased EEG power in the theta/alpha frequency range. The underlying mechanisms of the observed changes are unknown and may reflect neural plasticity as a consequence of the molecular pathways impacted by tominersen treatment.

Blood biomarkers for Alzheimer's disease and related disorders

Alzheimer's disease (AD) is a progressive neurodegenerative disease and the single commonest cause of dementia. Many other diseases can, however, cause dementia, and differential diagnosis can be challenging, especially in early disease stages. For most neurodegenerative dementias, accumulation of brain pathologies starts many years before clinical onset; the ability to detect these pathologies paves the way for targeted disease-modifying prevention trials. AD is associated with β-amyloid and tau pathologies, which can be quantified using cerebrospinal fluid and imaging biomarkers and, more recently, using highly sensitive blood tests. While for the most part, specific biomarkers of non-AD neurodegenerative dementias are lacking, non-specific biomarkers of neurodegeneration are available. This review summarizes recent advances in the neurodegenerative dementia blood biomarker research and discusses the next steps required for clinical implementation.

Development of mAb-based polyglutamine-dependent and polyglutamine length-independent huntingtin quantification assays with cross-site validation

Huntington's disease (HD) is caused by an expansion of the CAG trinucleotide repeat domain in the huntingtin gene that results in expression of a mutant huntingtin protein (mHTT) containing an expanded polyglutamine tract in the amino terminus. A number of therapeutic approaches that aim to reduce mHTT expression either locally in the CNS or systemically are in clinical development. We have previously described sensitive and selective assays that measure human HTT proteins either in a polyglutamine-independent (detecting both mutant expanded and non-expanded proteins) or in a polyglutamine length-dependent manner (detecting the disease-causing polyglutamine repeats) on the electrochemiluminescence Meso Scale Discovery detection platform. These original assays relied upon polyclonal antibodies. To ensure an accessible and sustainable resource for the HD field, we developed similar assays employing monoclonal antibodies. We demonstrate that these assays have equivalent sensitivity compared to our previous assays through the evaluation of cellular and animal model systems, as well as HD patient biosamples. We also demonstrate cross-site validation of these assays, allowing direct comparison of studies performed in geographically distinct laboratories.

Preventing amyotrophic lateral sclerosis: insights from pre-symptomatic neurodegenerative diseases

Significant progress has been made in understanding the pre-symptomatic phase of amyotrophic lateral sclerosis. While much is still unknown, advances in other neurodegenerative diseases offer valuable insights. Indeed, it is increasingly clear that the well-recognized clinical syndromes of Alzheimer's disease, Parkinson's disease, Huntington's disease, spinal muscular atrophy and frontotemporal dementia are also each preceded by a pre-symptomatic or prodromal period of varying duration, during which the underlying disease process unfolds, with associated compensatory changes and loss of inherent system redundancy. Key insights from these diseases highlight opportunities for discovery in amyotrophic lateral sclerosis. The development of biomarkers reflecting amyloid and tau has led to a shift in defining Alzheimer's disease based on inferred underlying histopathology. Parkinson's disease is unique among neurodegenerative diseases in the number and diversity of non-genetic biomarkers of pre-symptomatic disease, most notably REM sleep behaviour disorder. Huntington's disease benefits from an ability to predict the likely timing of clinically manifest disease based on age and CAG-repeat length alongside reliable neuroimaging markers of atrophy. Spinal muscular atrophy clinical trials have highlighted the transformational value of early therapeutic intervention, and studies in frontotemporal dementia illustrate the differential role of biomarkers based on genotype. Similar advances in amyotrophic lateral sclerosis would transform our understanding of key events in pathogenesis, thereby dramatically accelerating progress towards disease prevention. Deciphering the biology of pre-symptomatic amyotrophic lateral sclerosis relies on a clear conceptual framework for defining the earliest stages of disease. Clinically manifest amyotrophic lateral sclerosis may emerge abruptly, especially among those who harbour genetic mutations associated with rapidly progressive amyotrophic lateral sclerosis. However, the disease may also evolve more gradually, revealing a prodromal period of mild motor impairment preceding phenoconversion to clinically manifest disease. Similarly, cognitive and behavioural impairment, when present, may emerge gradually, evolving through a prodromal period of mild cognitive impairment or mild behavioural impairment before progression to amyotrophic lateral sclerosis. Biomarkers are critically important to studying pre-symptomatic amyotrophic lateral sclerosis and essential to efforts to intervene therapeutically before clinically manifest disease emerges. The use of non-genetic biomarkers, however, presents challenges related to counselling, informed consent, communication of results and limited protections afforded by existing legislation. Experiences from pre-symptomatic genetic testing and counselling, and the legal protections against discrimination based on genetic data, may serve as a guide. Building on what we have learned-more broadly from other pre-symptomatic neurodegenerative diseases and specifically from amyotrophic lateral sclerosis gene mutation carriers-we present a road map to early intervention, and perhaps even disease prevention, for all forms of amyotrophic lateral sclerosis.