Amyotrophic lateral sclerosis--a model of corticofugal axonal spread

Heterozygous knockout of Synaptotagmin13 phenocopies ALS features and TP53 activation in human motor neurons

Spinal motor neurons (MNs) represent a highly vulnerable cellular population, which is affected in fatal neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA). In this study, we show that the heterozygous loss of SYT13 is sufficient to trigger a neurodegenerative phenotype resembling those observed in ALS and SMA. SYT13+/- hiPSC-derived MNs displayed a progressive manifestation of typical neurodegenerative hallmarks such as loss of synaptic contacts and accumulation of aberrant aggregates. Moreover, analysis of the SYT13+/- transcriptome revealed a significant impairment in biological mechanisms involved in motoneuron specification and spinal cord differentiation. This transcriptional portrait also strikingly correlated with ALS signatures, displaying a significant convergence toward the expression of pro-apoptotic and pro-inflammatory genes, which are controlled by the transcription factor TP53. Our data show for the first time that the heterozygous loss of a single member of the synaptotagmin family, SYT13, is sufficient to trigger a series of abnormal alterations leading to MN sufferance, thus revealing novel insights into the selective vulnerability of this cell population.

Diagnostic accuracy and confounders of vagus nerve ultrasound in amyotrophic lateral sclerosis-a single-center case series and pooled individual patient data meta-analysis

BACKGROUND

Several single-center studies proposed utility of vagus nerve (VN) ultrasound for detecting disease severity, autonomic dysfunction, and bulbar phenotype in amyotrophic lateral sclerosis (ALS). However, the resulting body of literature shows opposing results, leaving considerable uncertainty on the clinical benefits of VN ultrasound in ALS.

METHODS

Relevant studies were identified up to 04/2024 and individual patient data (IPD) obtained from the respective authors were pooled with a so far unpublished cohort (from Munich). An IPD meta-analysis of 109 patients with probable or definite ALS (El Escorial criteria) and available VN cross-sectional area (CSA) was performed, with age, sex, ALS Functional Rating Scale-revised (ALSFRS-R), disease duration, and bulbar phenotype as independent variables.

RESULTS

Mean age was 65 years (± 12) and 47% of patients (± 12) had bulbar ALS. Mean ALSFRS-R was 38 (± 7), and mean duration was 18 months (± 18). VN atrophy was highly prevalent [left: 67% (± 5), mean CSA 1.6mm2 (± 0.6); right: 78% (± 21), mean CSA 1.8 mm2 (± 0.7)]. VN CSA correlated with disease duration (mean slope: left - 0.01; right - 0.01), but not with ALSFRS-R (mean slope: left 0.004; mean slope: right - 0.002). Test accuracy for phenotyping bulbar vs. non-bulbar ALS was poor (summary receiver operating characteristic area under the curve: left 0.496; right 0.572).

CONCLUSION

VN atrophy in ALS is highly prevalent and correlates with disease duration, but not with ALSFRS-R. VN CSA is insufficient to differentiate bulbar from non-bulbar ALS phenotypes. Further studies are warranted to analyze the link between VN atrophy, autonomic impairment, and survival in ALS.

Tissue-specific landscape of protein aggregation and quality control in an aging vertebrate

Protein aggregation is a hallmark of age-related neurodegeneration. Yet, aggregation during normal aging and in tissues other than the brain is poorly understood. Here, we leverage the African turquoise killifish to systematically profile protein aggregates in seven tissues of an aging vertebrate. Age-dependent aggregation is strikingly tissue specific and not simply driven by protein expression differences. Experimental interrogation in killifish and yeast, combined with machine learning, indicates that this specificity is linked to protein-autonomous biophysical features and tissue-selective alterations in protein quality control. Co-aggregation of protein quality control machinery during aging may further reduce proteostasis capacity, exacerbating aggregate burden. A segmental progeria model with accelerated aging in specific tissues exhibits selectively increased aggregation in these same tissues. Intriguingly, many age-related protein aggregates arise in wild-type proteins that, when mutated, drive human diseases. Our data chart a comprehensive landscape of protein aggregation during vertebrate aging and identify strong, tissue-specific associations with dysfunction and disease.

Pathological insights derived from neuroimaging in amyotrophic lateral sclerosis: emerging clinical applications

PURPOSE OF REVIEW

Neuroimaging has been instrumental in shaping current understanding of the pathoanatomical signature of amyotrophic lateral sclerosis (ALS) across clinically well defined patient cohorts. The potential utility of imaging as an objective disease marker, however, remains poorly defined.

RECENT FINDINGS

Increasingly advanced quantitative and computational imaging studies have highlighted emerging clinical applications for neuroimaging as a complementary clinical modality for diagnosis, monitoring, and modelling disease propagation. Multimodal neuroimaging has demonstrated novel approaches for capturing primary motor disease. Extra-motor subcortical dysfunction is increasingly recognized as key modulators of disease propagation.

SUMMARY

The neural signature of cortical and subcortical dysfunction in ALS has been well defined at the population level. Objective metrics of focal primary motor dysfunction are increasingly sensitive and translatable to the individual patient level. Integrity of extra-motor subcortical abnormalities are recognized to represent critical pathways of the ALS disease 'connectome', predicting pathological spread. Neuroimaging plays a pivotal role in capturing upper motor neuron pathology in ALS. Their potential clinical role as objective disease markers for disease classification, longitudinal monitoring, and prognosis in ALS have become increasingly well defined.

Update on recent advances in amyotrophic lateral sclerosis

In the last few years, our understanding of disease molecular mechanisms underpinning ALS has advanced greatly, allowing the first steps in translating into clinical practice novel research findings, including gene therapy approaches. Similarly, the recent advent of assistive technologies has greatly improved the possibility of a more personalized approach to supportive and symptomatic care, in the context of an increasingly complex multidisciplinary line of actions, which remains the cornerstone of ALS management. Against this rapidly growing background, here we provide an comprehensive update on the most recent studies that have contributed towards our understanding of ALS pathogenesis, the latest results from clinical trials as well as the future directions for improving the clinical management of ALS patients.

Non-motor symptoms in patients with amyotrophic lateral sclerosis: current state and future directions

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive degeneration of both upper and lower motor neurons. A defining histopathological feature in approximately 97% of all ALS cases is the accumulation of phosphorylated trans-activation response (TAR) DNA-binding protein 43 protein (pTDP-43) aggregates in the cytoplasm of neurons and glial cells within the central nervous system. Traditionally, it was believed that the accumulation of TDP-43 aggregates and subsequent neurodegeneration primarily occurs in motor neurons. However, contemporary evidence suggests that as the disease progresses, other systems and brain regions are also affected. Despite this, there has been a limited number of clinical studies assessing the non-motor symptoms in ALS patients. These studies often employ various outcome measures, resulting in a wide range of reported frequencies of non-motor symptoms in ALS patients. The importance of assessing the non-motor symptoms reflects in a fact that they have a significant impact on patients' quality of life, yet they frequently go underdiagnosed and unreported during clinical evaluations. This review aims to provide an up-to-date overview of the current knowledge concerning non-motor symptoms in ALS. Furthermore, we address their diagnosis and treatment in everyday clinical practice.

Temporal and spatial progression of microstructural cerebral degeneration in ALS: A multicentre longitudinal diffusion tensor imaging study

OBJECTIVE

The corticospinal tract (CST) reveals progressive microstructural alterations in ALS measurable by DTI. The aim of this study was to evaluate fractional anisotropy (FA) along the CST as a longitudinal marker of disease progression in ALS.

METHODS

The study cohort consisted of 114 patients with ALS and 110 healthy controls from the second prospective, longitudinal, multicentre study of the Canadian ALS Neuroimaging Consortium (CALSNIC-2). DTI and clinical data from a harmonized protocol across 7 centres were collected. Thirty-nine ALS patients and 61 controls completed baseline and two follow-up visits and were included for longitudinal analyses. Whole brain-based spatial statistics and hypothesis-guided tract-of-interest analyses were performed for cross-sectional and longitudinal analyses.

RESULTS

FA was reduced at baseline and longitudinally in the CST, mid-corpus callosum (CC), frontal lobe, and other ALS-related tracts, with alterations most evident in the CST and mid-CC. CST and pontine FA correlated with functional impairment (ALSFRS-R), upper motor neuron function, and clinical disease progression rate. Reduction in FA was largely located in the upper CST; however, the longitudinal decline was greatest in the lower CST. Effect sizes were dependent on region, resulting in study group sizes between 17 and 31 per group over a 9-month interval. Cross-sectional effect sizes were maximal in the upper CST; whereas, longitudinal effect sizes were maximal in mid-callosal tracts.

CONCLUSIONS

Progressive microstructural alterations in ALS are most prominent in the CST and CC. DTI can provide a biomarker of cerebral degeneration in ALS, with longitudinal changes in white matter demonstrable over a reasonable observation period, with a feasible number of participants, and within a multicentre framework.

Frontotemporal dementia-like disease progression elicited by seeded aggregation and spread of FUS

RNA binding proteins have emerged as central players in the mechanisms of many neurodegenerative diseases. In particular, a proteinopathy of fused in sarcoma (FUS) is present in some instances of familial Amyotrophic lateral sclerosis (ALS) and about 10% of sporadic Frontotemporal lobar degeneration (FTLD). Here we establish that focal injection of sonicated human FUS fibrils into brains of mice in which ALS-linked mutant or wild-type human FUS replaces endogenous mouse FUS is sufficient to induce focal cytoplasmic mislocalization and aggregation of mutant and wild-type FUS which with time spreads to distal regions of the brain. Human FUS fibril-induced FUS aggregation in the mouse brain of humanized FUS mice is accelerated by an ALS-causing FUS mutant relative to wild-type human FUS. Injection of sonicated human FUS fibrils does not induce FUS aggregation and subsequent spreading after injection into naïve mouse brains containing only mouse FUS, indicating a species barrier to human FUS aggregation and its prion-like spread. Fibril-induced human FUS aggregates recapitulate pathological features of FTLD including increased detergent insolubility of FUS and TAF15 and amyloid-like, cytoplasmic deposits of FUS that accumulate ubiquitin and p62, but not TDP-43. Finally, injection of sonicated FUS fibrils is shown to exacerbate age-dependent cognitive and behavioral deficits from mutant human FUS expression. Thus, focal seeded aggregation of FUS and further propagation through prion-like spread elicits FUS-proteinopathy and FTLD-like disease progression.

Frontotemporal dementia-like disease progression elicited by seeded aggregation and spread of FUS

RNA binding proteins have emerged as central players in the mechanisms of many neurodegenerative diseases. In particular, a proteinopathy of fu sed in s arcoma (FUS) is present in some instances of familial Amyotrophic lateral sclerosis (ALS) and about 10% of sporadic FTLD. Here we establish that focal injection of sonicated human FUS fibrils into brains of mice in which ALS-linked mutant or wild-type human FUS replaces endogenous mouse FUS is sufficient to induce focal cytoplasmic mislocalization and aggregation of mutant and wild-type FUS which with time spreads to distal regions of the brain. Human FUS fibril-induced FUS aggregation in the mouse brain of humanized FUS mice is accelerated by an ALS-causing FUS mutant relative to wild-type human FUS. Injection of sonicated human FUS fibrils does not induce FUS aggregation and subsequent spreading after injection into naïve mouse brains containing only mouse FUS, indicating a species barrier to human FUS aggregation and its prion-like spread. Fibril-induced human FUS aggregates recapitulate pathological features of FTLD including increased detergent insolubility of FUS and TAF15 and amyloid-like, cytoplasmic deposits of FUS that accumulate ubiquitin and p62, but not TDP-43. Finally, injection of sonicated FUS fibrils is shown to exacerbate age-dependent cognitive and behavioral deficits from mutant human FUS expression. Thus, focal seeded aggregation of FUS and further propagation through prion-like spread elicits FUS-proteinopathy and FTLD-like disease progression.

Abnormal brain functional network dynamics in amyotrophic lateral sclerosis patients with depression

Since depression is common in amyotrophic lateral sclerosis (ALS) patients, we aimed to explore the specific brain functional network dynamics in ALS patients with depression (ALS-D) compared with healthy controls (HCs) and ALS patients without depressive symptoms (ALS-ND). According to the DSM-V, 32 ALS-D patients were selected from a large and newly diagnosed ALS cohort. Then, 32 demographic- and cognitive-matched ALS-ND patients were also selected, and 64 HCs were recruited. These participants underwent resting-state fMRI scans, and functional connectivity state analysis and dynamic graph theory were applied to evaluate brain functional network dynamics. Moreover, the Hamilton Depression Rating Scale (HDRS) was used to quantify depressive symptoms in the ALS-D patients. Four distinct states were identified in the ALS-D patients and controls. Compared with that in HCs, the fraction rate (FR) in state 2 was significantly decreased in ALS-D patients, and the FR in state 4 was significantly increased in ALS-D patients. Compared with that of HCs, the dwell time in state 4 was significantly increased in the ALS-D patients. Moreover, compared with that in the ALS-D patients, the FR in state 3 was significantly decreased in the ALS-ND patients. Among the ALS-D patients, there was the suggestion of a positive association between HDRS scores and dwell time of state 4, but this association did not reach statistical significance (r = 0.354; p = 0.055). Depression is an important feature of ALS patients, and we found a special pattern of brain functional network dynamics in ALS-D patients. Our findings may play an important role in understanding the mechanism underlying depression in ALS patients and help develop therapeutic interventions for depressed ALS patients.

Nanoplastics and Neurodegeneration in ALS

Plastic production, which exceeds one million tons per year, is of global concern. The constituent low-density polymers enable spread over large distances and micro/nano particles (MNPLs) induce organ toxicity via digestion, inhalation, and skin contact. Particles have been documented in all human tissues including breast milk. MNPLs, especially weathered particles, can breach the blood-brain barrier, inducing neurotoxicity. This has been documented in non-human species, and in human-induced pluripotent stem cell lines. Within the brain, MNPLs initiate an inflammatory response with pro-inflammatory cytokine production, oxidative stress with generation of reactive oxygen species, and mitochondrial dysfunction. Glutamate and GABA neurotransmitter dysfunction also ensues with alteration of excitatory/inhibitory balance in favor of reduced inhibition and resultant neuro-excitation. Inflammation and cortical hyperexcitability are key abnormalities involved in the pathogenic cascade of amyotrophic lateral sclerosis (ALS) and are intricately related to the mislocalization and aggregation of TDP-43, a hallmark of ALS. Water and many foods contain MNPLs and in humans, ingestion is the main form of exposure. Digestion of plastics within the gut can alter their properties, rendering them more toxic, and they cause gut microbiome dysbiosis and a dysfunctional gut-brain axis. This is recognized as a trigger and/or aggravating factor for ALS. ALS is associated with a long (years or decades) preclinical period and neonates and infants are exposed to MNPLs through breast milk, milk substitutes, and toys. This endangers a time of intense neurogenesis and establishment of neuronal circuitry, setting the stage for development of neurodegeneration in later life. MNPL neurotoxicity should be considered as a yet unrecognized risk factor for ALS and related diseases.

Neuronal Circuit Dysfunction in Amyotrophic Lateral Sclerosis

The primary neural circuit affected in Amyotrophic Lateral Sclerosis (ALS) patients is the corticospinal motor circuit, originating in upper motor neurons (UMNs) in the cerebral motor cortex which descend to synapse with the lower motor neurons (LMNs) in the spinal cord to ultimately innervate the skeletal muscle. Perturbation of these neural circuits and consequent loss of both UMNs and LMNs, leading to muscle wastage and impaired movement, is the key pathophysiology observed. Despite decades of research, we are still lacking in ALS disease-modifying treatments. In this review, we document the current research from patient studies, rodent models, and human stem cell models in understanding the mechanisms of corticomotor circuit dysfunction and its implication in ALS. We summarize the current knowledge about cortical UMN dysfunction and degeneration, altered excitability in LMNs, neuromuscular junction degeneration, and the non-cell autonomous role of glial cells in motor circuit dysfunction in relation to ALS. We further highlight the advances in human stem cell technology to model the complex neural circuitry and how these can aid in future studies to better understand the mechanisms of neural circuit dysfunction underpinning ALS.

Potential of neuroimaging as a biomarker in amyotrophic lateral sclerosis: from structure to metabolism

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by motor neuron degeneration. The development of ALS involves metabolite alterations leading to tissue lesions in the nervous system. Recent advances in neuroimaging have significantly improved our understanding of the underlying pathophysiology of ALS, with findings supporting the corticoefferent axonal disease progression theory. Current studies on neuroimaging in ALS have demonstrated inconsistencies, which may be due to small sample sizes, insufficient statistical power, overinterpretation of findings, and the inherent heterogeneity of ALS. Deriving meaningful conclusions solely from individual imaging metrics in ALS studies remains challenging, and integrating multimodal imaging techniques shows promise for detecting valuable ALS biomarkers. In addition to giving an overview of the principles and techniques of different neuroimaging modalities, this review describes the potential of neuroimaging biomarkers in the diagnosis and prognostication of ALS. We provide an insight into the underlying pathology, highlighting the need for standardized protocols and multicenter collaborations to advance ALS research.

Cognitive function in amyotrophic lateral sclerosis: a cross-sectional and prospective pragmatic clinical study with review of the literature

BACKGROUND

Amyotrophic lateral sclerosis (ALS) can present with either bulbar or spinal symptoms, and in some cases, both types of symptoms may be present. In addition, cognitive impairment has been observed in ALS. The study aimed to evaluate the frontal and general cognitive performance in ALS not only cross-sectionally but also longitudinally.

METHODS AND MATERIALS

The Frontal Assessment Battery (FAB) and the Montreal Cognitive Assessment (MoCA) were employed to assess cognitive function in 52 adults with ALS and 52 cognitively healthy individuals. The statistical analyses encompassed the Pearson Chi square test, the Skillings-Mack test, the Spearman's rank correlation coefficient, and the Proportional Odds Logistic Regression Model (POLR).

RESULTS

Cross-sectionally, lower cognitive performance was associated with ALS diagnosis, older age, and motor functional decline. The cognitive impairment of individuals with bulbar and spinal-bulbar symptoms showed faster deterioration compared to those with spinal symptoms. The spinal subgroup consistently performed worst in delayed recall and attention, while the spinal-bulbar and bulbar subgroups exhibited inferior scores in delayed recall, attention, visuospatial skills, orientation, and verbal fluency.

CONCLUSION

The incorporation of cognitive screening in the diagnostic workup of ALS may be beneficial, as early detection can enhance symptom management and improve the quality of life for both individuals with ALS and their care partners.

Choroid plexus enlargement in amyotrophic lateral sclerosis patients and its correlation with clinical disability and blood-CSF barrier permeability

BACKGROUND

Using in vivo neuroimaging techniques, growing evidence has demonstrated that the choroid plexus (CP) volume is enlarged in patients with several neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. However, although animal and postmortem findings suggest that CP abnormalities are likely important pathological mechanisms underlying amyotrophic lateral sclerosis (ALS), the third most common neurodegenerative disease, no available study has been conducted to thoroughly assess CP abnormalities and their clinical relevance in vivo in ALS patients to date. Thus, we aimed to determine whether in vivo CP enlargement may occur in ALS patients. We also aimed to identify the relationships of CP volume with clinical disabilities and blood-CSF barrier (BCSFB) permeability in ALS patients.

METHODS

In this retrospective study, based on structural MRI data, CP volume was assessed using a Gaussian mixture model and underwent further manual correction in 155 ALS patients and 105 age- and sex-matched HCs from October 2021 to April 2023. The ALS Functional Rating Scale-Revised (ALSFRS-R) was used to assess clinical disability. The CSF/serum albumin quotient (Qalb) was used to assess BCSFB permeability. Moreover, all the ALS patients completed genetic testing, and according to genetic testing, the ALS patients were further divided into genetic ALS subgroup and sporadic ALS subgroup.

RESULTS

We found that compared with HCs, ALS patients had a significantly higher CP volume (p < 0.001). Moreover, compared with HCs, CP volume was significantly increased in both ALS patients with and without known genetic mutations after family-wise error correction (p = 0.006 and p < 0.001, respectively), while there were no significant differences between the two ALS groups. Furthermore, the CP volume was significantly correlated with the ALSFRS-r score (r = -0.226; p = 0.005) and the Qalb (r = 0.479; p < 0.001) in ALS patients.

CONCLUSION

Our study first demonstrates CP enlargement in vivo in ALS patients, and continues to suggest an important pathogenetic role for CP abnormalities in ALS. Moreover, assessing CP volume is likely a noninvasive and easy-to-implement approach for screening BCSFB dysfunction in ALS patients.

The Corticospinal System and Amyotrophic Lateral Sclerosis: IFCN handbook chapter

Corticospinal neurons located in motor areas of the cerebral neocortex project corticospinal axons which synapse with the spinal network; a parallel corticobulbar system projects to the cranial motor network and to brainstem motor pathways. The primate corticospinal system has a widespread cortical origin and an extensive range of different fibre diameters, including thick, fast-conducting axons. Direct cortico-motoneuronal (CM) projections from the motor cortex to arm and hand alpha motoneurons are a recent evolutionary feature, that is well developed in dexterous primates and particularly in humans. Many of these projections originate from the caudal subdivision of area 4 ('new' M1: primary motor cortex). They arise from corticospinal neurons of varied soma size, including those with fast- and relatively slow-conducting axons. This CM system has been shown to be involved in the control of skilled movements, carried out with fractionation of the distal extremities and at low force levels. During movement, corticospinal neurons are activated quite differently from 'lower' motoneurons, and there is no simple or fixed functional relationship between a so-called 'upper' motoneuron and its target lower motoneuron. There are key differences in the organisation and function of the corticospinal and CM system in primates versus non-primates, such as rodents. These differences need to be recognized when making the choice of animal model for understanding disorders such as amyotrophic lateral sclerosis (ALS). In this neurodegenerative brain disease there is a selective loss of fast-conducting corticospinal axons, and their synaptic connections, and this is reflected in responses to non-invasive cortical stimuli and measures of cortico-muscular coherence. The loss of CM connections influencing distal limb muscles results in a differential loss of muscle strength or 'split-hand' phenotype. Importantly, there is also a unique impairment in the coordination of skilled hand tasks that require fractionation of digit movement. Scores on validated tests of skilled hand function could be used to assess disease progression.

In-depth analysis of data from the RAS-ALS study reveals new insights in rasagiline treatment for amyotrophic lateral sclerosis

BACKGROUND AND PURPOSE

In 2016, we concluded a randomized controlled trial testing 1 mg rasagiline per day add-on to standard therapy in 252 amyotrophic lateral sclerosis (ALS) patients. This article aims at better characterizing ALS patients who could possibly benefit from rasagiline by reporting new subgroup analysis and genetic data.

METHODS

We performed further exploratory in-depth analyses of the study population and investigated the relevance of single nucleotide polymorphisms (SNPs) related to the dopaminergic system.

RESULTS

Placebo-treated patients with very slow disease progression (loss of Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised [ALSFRS-R] per month before randomization of ≤0.328 points) showed a per se survival probability after 24 months of 0.85 (95% confidence interval = 0.65-0.94). The large group of intermediate to fast progressing ALS patients showed a prolonged survival in the rasagiline group compared to placebo after 6 and 12 months (p = 0.02, p = 0.04), and a reduced decline of ALSFRS-R after 18 months (p = 0.049). SNP genotypes in the MAOB gene and DRD2 gene did not show clear associations with rasagiline treatment effects.

CONCLUSIONS

These results underline the need to consider individual disease progression at baseline in future ALS studies. Very slow disease progressors compromise the statistical power of studies with treatment durations of 12-18 months using clinical endpoints. Analysis of MAOB and DRD2 SNPs revealed no clear relationship to any outcome parameter. More insights are expected from future studies elucidating whether patients with DRD2CC genotype (Rs2283265) show a pronounced benefit from treatment with rasagiline, pointing to the opportunities precision medicine could open up for ALS patients in the future.

The central pattern of weakness of ALS: Morphological correlates in whole-body muscle MRI

OBJECTIVE

Monosynaptically cortically innervated α-motoneurons are early and strongly involved in amyotrophic lateral sclerosis (ALS). Consequently, the muscles that receive the strongest direct corticomotoneuronal input are the clinically most affected. To objectify this concept in vivo through morphological image correlates, whole-body magnetic resonance imaging (MRI) with muscle signal analysis was performed in patients with ALS compared to healthy controls.

METHODS

Modified Dixon-based whole-body MRI was acquired in patients with ALS (n = 33) and matched healthy controls (n = 30). Manual labeling of limb muscle MRI was performed, and a specific subset of nine muscles, selected as pairs of muscle groups with different corticomotoneuronal input, was analyzed per subject based on their volume, fat fraction, and functional remaining muscle area (fRMA).

RESULTS

Statistical analysis of 978 muscles in total revealed significantly decreased volumes, decreased fRMA, and increased fat fraction in the muscles of patients with ALS compared to controls. The clinical degree of pareses of directly innervated muscles was significantly worse than that of less directly innervated muscles in each comparison. The muscles receiving stronger direct corticomotoneuronal input showed more pronounced morphological involvement compared to those with less monosynaptic corticomotoneuronal input (fRMA, significant in three pairwise comparisons).

INTERPRETATION

In conclusion, whole-body MRI-based muscle analysis provided additional evidence for a characteristic pattern of pareses in ALS. This technical approach (parameterization and quantification of muscle alterations from MRI) to patients with ALS could pave the way for the future establishment of a diagnostic algorithm of muscle MRI for ALS and may serve as a biomarker.

Unraveling the Heterogeneity of ALS-A Call to Redefine Patient Stratification for Better Outcomes in Clinical Trials

Despite tremendous efforts in basic research and a growing number of clinical trials aiming to find effective treatments, amyotrophic lateral sclerosis (ALS) remains an incurable disease. One possible reason for the lack of effective causative treatment options is that ALS may not be a single disease entity but rather may represent a clinical syndrome, with diverse genetic and molecular causes, histopathological alterations, and subsequent clinical presentations contributing to its complexity and variability among individuals. Defining a way to subcluster ALS patients is becoming a central endeavor in the field. Identifying specific clusters and applying them in clinical trials could enable the development of more effective treatments. This review aims to summarize the available data on heterogeneity in ALS with regard to various aspects, e.g., clinical, genetic, and molecular.

The glymphatic system and Amyotrophic lateral sclerosis

The glymphatic system and the meningeal lymphatic vessels provide a pathway for transport of solutes and clearance of toxic material from the brain. Of specific relevance to ALS, this is applicable for TDP-43 and glutamate, both major elements in disease pathogenesis. Flow is propelled by arterial pulsation, respiration, posture, as well as the positioning and proportion of aquaporin-4 channels (AQP4). Non-REM slow wave sleep is the is key to glymphatic drainage which discontinues during wakefulness. In Parkinson's disease and Alzheimer's disease, sleep impairment is known to predate the development of characteristic clinical features by several years and is associated with progressive accumulation of toxic proteinaceous products. While sleep issues are well described in ALS, consideration of preclinical sleep impairment or the potential of a failing glymphatic system in ALS has rarely been considered. Here we review how the glymphatic system may impact ALS. Preclinical sleep impairment as an unrecognized major risk factor for ALS is considered, while potential therapeutic options to improve glymphatic flow are explored.

Casein kinase 1 inhibitor avoids TDP-43 pathology propagation in a patient-derived cellular model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a fatal neurodegenerative disease without a cure to reverse its progression. Its main hallmark is the nuclear protein TDP-43, which undergoes different post-translational modifications leading to a loss of function in the nucleus and an increase in toxicity in the cytoplasm. Previous reports have indicated that pathogenic TDP-43 exhibits prion-like propagation in various contexts. With the aim of advancing therapeutics focused on preventing the propagation of TDP-43 pathology, we studied the potential role of pathogenic TDP-43 in lymphoblasts from sporadic ALS patients. We used lymphoblastoid cell lines from sporadic ALS patients as a source of pathogenic forms of TDP-43, and healthy human cells (lymphoblasts, myoblasts, neuroblastoma SH-SY5Y, or osteosarcoma U2OS) as recipient cells to investigate the seeding and spread of TDP-43 proteinopathy. Furthermore, we evaluated the potential of targeting TDP-43 phosphorylation with a CK-1 inhibitor to prevent the propagation of the pathology. The results presented herein indicate that pathogenic forms of TDP-43 are secreted into the extracellular medium of sporadic ALS lymphoblasts and could be transported by extracellular vesicles, spreading TDP-43 pathology to healthy cells. Moreover, tunneling nanotubes have also been discovered in pathological cells and may be involved in the transport of TDP-43. Interestingly, targeting TDP-43 phosphorylation with an in-house designed CK-1 inhibitor (IGS2.7) was sufficient to halt TDP-43 pathology transmission, in addition to its known effects on restoring the homeostasis of TDP-43 protein in patients-derived cells.

Unraveling the Genetic Landscape of Neurological Disorders: Insights into Pathogenesis, Techniques for Variant Identification, and Therapeutic Approaches

Genetic abnormalities play a crucial role in the development of neurodegenerative disorders (NDDs). Genetic exploration has indeed contributed to unraveling the molecular complexities responsible for the etiology and progression of various NDDs. The intricate nature of rare and common variants in NDDs contributes to a limited understanding of the genetic risk factors associated with them. Advancements in next-generation sequencing have made whole-genome sequencing and whole-exome sequencing possible, allowing the identification of rare variants with substantial effects, and improving the understanding of both Mendelian and complex neurological conditions. The resurgence of gene therapy holds the promise of targeting the etiology of diseases and ensuring a sustained correction. This approach is particularly enticing for neurodegenerative diseases, where traditional pharmacological methods have fallen short. In the context of our exploration of the genetic epidemiology of the three most prevalent NDDs-amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease, our primary goal is to underscore the progress made in the development of next-generation sequencing. This progress aims to enhance our understanding of the disease mechanisms and explore gene-based therapies for NDDs. Throughout this review, we focus on genetic variations, methodologies for their identification, the associated pathophysiology, and the promising potential of gene therapy. Ultimately, our objective is to provide a comprehensive and forward-looking perspective on the emerging research arena of NDDs.

Neurite orientation dispersion and density imaging quantifies microstructural impairment in the thalamus and its connectivity in amyotrophic lateral sclerosis

AIMS

To evaluate microstructural impairment in the thalamus and thalamocortical connectivity using neurite orientation dispersion and density imaging (NODDI) in amyotrophic lateral sclerosis (ALS).

METHODS

This study included 47 healthy controls and 43 ALS patients, whose structural and diffusion-weighted data were collected. We used state-of-the-art parallel transport tractography to identify thalamocortical pathways in individual spaces. Thalamus was then parcellated into six subregions based on its connectivity pattern with the priori defined cortical (i.e., prefrontal/motor/somatosensory/temporal/posterior-parietal/occipital) regions. For each of the thalamic and cortical subregions and thalamo-cortical tracts, we compared the following NODDI metrics between groups: orientation dispersion index (ODI), neurite density index (NDI), and isotropic volume fraction (ISO). We also used these metrics to conduct receiver operating characteristic curve (ROC) analyses and Spearman correlation.

RESULTS

In ALS patients, we found decreased ODI and increased ISO in the thalamic subregion connecting the left motor cortex and other extramotor (e.g., somatosensory and occipital) cortex (Bonferroni-corrected p < 0.05). NDI decreased in the bilateral thalamo-motor and thalamo-somatosensory tracts and in the right thalamo-posterior-parietal and thalamo-occipital tracts (Bonferroni-corrected p < 0.05). NDI reduction in the bilateral thalamo-motor tract (p = 0.017 and 0.009) and left thalamo-somatosensory tract (p = 0.029) was correlated with disease severity. In thalamo-cortical tracts, NDI yielded a higher effect size during between-group comparisons and a greater area under ROC (p < 0.05) compared with conventional diffusion tensor imaging metrics.

CONCLUSIONS

Microstructural impairment in the thalamus and thalamocortical connectivity is the hallmark of ALS. NODDI improved the detection of disrupted thalamo-cortical connectivity in ALS.

Structural and Functional Brain Network Connectivity at Different King's Stages in Patients With Amyotrophic Lateral Sclerosis

BACKGROUND AND OBJECTIVES

There is currently no validated disease-stage biomarker for amyotrophic lateral sclerosis (ALS). The identification of quantitative and reproducible markers of disease stratification in ALS is fundamental for study design definition and inclusion of homogenous patient cohorts into clinical trials. Our aim was to assess the rearrangements of structural and functional brain connectivity underlying the clinical stages of ALS, to suggest objective, reproducible measures provided by MRI connectomics mirroring disease staging.

METHODS

In this observational study, patients with ALS and healthy controls (HCs) underwent clinical evaluation and brain MRI on a 3T scanner. Patients were classified into 4 groups, according to the King's staging system. Structural and functional brain connectivity matrices were obtained using diffusion tensor and resting-state fMRI data, respectively. Whole-brain network-based statistics (NBS) analysis and comparisons of intraregional and inter-regional connectivity values using analysis of covariance models were performed between groups. Correlations between MRI and clinical/cognitive measures were tested using Pearson coefficient.

RESULTS

One hundred four patients with ALS and 61 age-matched and sex-matched HCs were included. NBS and regional connectivity analyses demonstrated a progressive decrease of intranetwork and internetwork structural connectivity of sensorimotor regions at increasing ALS stages in our cohort, compared with HCs. By contrast, functional connectivity showed divergent patterns between King's stages 3 (increase in basal ganglia and temporal circuits [p = 0.04 and p = 0.05, respectively]) and 4 (frontotemporal decrease [p = 0.03]), suggesting a complex interplay between opposite phenomena in late stages of the disease. Intraregional sensorimotor structural connectivity was correlated with ALS Functional Rating Scale-revised (ALSFRS-r) score (r = 0.31, p < 0.001) and upper motor neuron burden (r = -0.25, p = 0.01). Inter-regional frontal-sensorimotor structural connectivity was also correlated with ALSFRS-r (r = 0.24, p = 0.02). No correlations with cognitive measures were found.

DISCUSSION

MRI of the brain allows to demonstrate and quantify increasing disruption of structural connectivity involving the sensorimotor networks in ALS, mirroring disease stages. Frontotemporal functional disconnection seems to characterize only advanced disease phases. Our findings support the utility of MRI connectomics to stratify patients and stage brain pathology in ALS in a reproducible way, which may mirror clinical progression.

Glymphatic dysfunction in patients with early-stage amyotrophic lateral sclerosis

Recently, an astrocytic aquaporin 4-dependent drainage system, that is, the glymphatic system, has been identified in the live murine and human brain. Growing evidence suggests that glymphatic function is impaired in patients with several neurodegenerative diseases, including Alzheimer's and Parkinson's disease. As the third most common neurodegenerative disease, although animal studies have indicated that early glymphatic dysfunction is likely an important pathological mechanism underpinning amyotrophic lateral sclerosis (ALS), no available study has been conducted to thoroughly assess glymphatic function in vivo in ALS patients to date, particularly in patients with early-stage ALS. Thus, using diffusion tensor imaging analysis along the perivascular space (ALPS) index, an approximate measure of glymphatic function in vivo, we aimed to explore whether glymphatic function is impaired in patients with patients with early-stage ALS, and the diagnostic performance of the ALPS index in distinguishing between patients with early-stage ALS and healthy subjects. We also aimed to identify the relationships between glymphatic dysfunction and clinical disabilities and sleep problems in patients with early-stage ALS. In this retrospective study, King's Stage 1 ALS patients were defined as patients with early-stage ALS. We enrolled 56 patients with early-stage ALS and 32 age- and sex-matched healthy control subjects. All participants completed clinical screening, sleep assessment and ALPS index analysis. For the sleep assessment, the Pittsburgh Sleep Quality Index, Epworth Sleepiness Scale and polysomnography were used. Compared with healthy control subjects, patients with early-stage ALS had a significantly lower ALPS index after family-wise error correction (P < 0.05). Moreover, receiver operating characteristic analysis showed that the area under the curve for the ALPS index was 0.792 (95% confidence interval 0.700-0.884). Partial correlation analyses showed that the ALPS index was significantly correlated with clinical disability and sleep disturbances in patients with early-stage ALS. Multivariate analysis showed that sleep efficiency (r = 0.419, P = 0.002) and periodic limb movements in sleep index (r = -0.294, P = 0.017) were significant predictive factors of the ALPS index in patients with early-stage ALS. In conclusion, our study continues to support an important role for glymphatic dysfunction in ALS pathology, and we provide additional insights into the early diagnostic value of glymphatic dysfunction and its correlation with sleep disturbances in vivo in patients with early-stage ALS. Moreover, we suggest that early improvement of glymphatic function may be a promising strategy for slowing the neurodegenerative process in ALS. Future studies are needed to explore the diagnostic and therapeutic value of glymphatic dysfunction in individuals with presymptomatic-stage neurodegenerative diseases.

Betz cells of the primary motor cortex

Betz cells, named in honor of Volodymyr Betz (1834-1894), who described them as "giant pyramids" in the primary motor cortex of primates and other mammalian species, are layer V extratelencephalic projection (ETP) neurons that directly innervate α-motoneurons of the brainstem and spinal cord. Despite their large volume and circumferential dendritic architecture, to date, no single molecular criterion has been established that unequivocally distinguishes adult Betz cells from other layer V ETP neurons. In primates, transcriptional signatures suggest the presence of at least two ETP neuron clusters that contain mature Betz cells; these are characterized by an abundance of axon guidance and oxidative phosphorylation transcripts. How neurodevelopmental programs drive the distinct positional and morphological features of Betz cells in humans remains unknown. Betz cells display a distinct biphasic firing pattern involving early cessation of firing followed by delayed sustained acceleration in spike frequency and magnitude. Few cell type-specific transcripts and electrophysiological characteristics are conserved between rodent layer V ETP neurons of the motor cortex and primate Betz cells. This has implications for the modeling of disorders that affect the motor cortex in humans, such as amyotrophic lateral sclerosis (ALS). Perhaps vulnerability to ALS is linked to the evolution of neural networks for fine motor control reflected in the distinct morphomolecular architecture of the human motor cortex, including Betz cells. Here, we discuss histological, molecular, and functional data concerning the position of Betz cells in the emerging taxonomy of neurons across diverse species and their role in neurological disorders.

The preferences of people with amyotrophic lateral sclerosis on riluzole treatment in Europe

The Patient Preference Survey aims to understand unmet needs related to riluzole management in people with Amyotrophic Lateral Sclerosis (ALS) and to identify which characteristics of a new formulation could better match their preferences. The survey involved 117 people with ALS (PALS) treated with riluzole in four European countries. The dysphagic PALS were least satisfied with the riluzole tablet and oral suspension and with ease in self-administration; up to 68% of respondents postponed or missed the treatment due to swallowing difficulties and need of caregiver assistance. Overall, 51% of tablet and 53% of oral suspension users regularly crushed or mixed riluzole with beverages, respectively; PALS who always manipulated riluzole showed low satisfaction with the formulation and considered the risk of choking and pneumonia the most worrisome event. The survey evaluated the driving factors in choosing/switching the therapy: 67% of PALS declared a low risk of choking. The research finally evaluated which attributes of a new formulation would be preferred: the most relevant were ease of use (4.3/5), convenient/portable packaging (4.0/5) and oral-dissolving properties without tongue motility (3.9/5). The Patient Preference Survey suggests that patients have several unmet needs and preferences that could be addressed by a different formulation, e.g. using oral film technologies.

History of ALS and the competing theories on pathogenesis: IFCN handbook chapter

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder of the human motor system, first described in the 19th Century. The etiology of ALS appears to be multifactorial, with a complex interaction of genetic, epigenetic, and environmental factors underlying the onset of disease. Importantly, there are no known naturally occurring animal models, and transgenic mouse models fail to faithfully reproduce ALS as it manifests in patients. Debate as to the site of onset of ALS remain, with three competing theories proposed, including (i) the dying-forward hypothesis, whereby motor neuron degeneration is mediated by hyperexcitable corticomotoneurons via an anterograde transsynaptic excitotoxic mechanism, (ii) dying-back hypothesis, proposing the ALS begins in the peripheral nervous system with a toxic factor(s) retrogradely transported into the central nervous system and mediating upper motor neuron dysfunction, and (iii) independent hypothesis, suggesting that upper and lower motor neuron degenerated independently. Transcranial magnetic stimulation studies, along with pathological and genetic findings have supported the dying forward hypothesis theory, although the science is yet to be settled. The review provides a historical overview of ALS, discusses phenotypes and likely pathogenic mechanisms.

TDP-43 as a therapeutic target in neurodegenerative diseases: Focusing on motor neuron disease and frontotemporal dementia

A common feature of adult-onset neurodegenerative diseases is the presence of characteristic pathological accumulations of specific proteins. These pathological protein depositions can vary in their protein composition, cell-type distribution, and intracellular (or extracellular) location. For example, abnormal cytoplasmic protein deposits which consist of the TDP-43 protein are found within motor neurons in patients with amyotrophic lateral sclerosis (ALS, a common form of motor neuron disease) and frontotemporal dementia (FTD). The presence of these insoluble intracellular TDP-43 inclusions suggests that restoring TDP-43 homeostasis represents a potential therapeutical strategy, which has been demonstrated in alleviating neurodegenerative symptoms in cell and animal models of ALS/FTD. We have reviewed the mechanisms that lead to disrupted TDP-43 homeostasis and discussed how small molecule-based therapies could be applied in modulating these mechanisms. This review covers recent advancements and challenges in small molecule-based therapies that could be used to clear pathological forms of TDP-43 through various protein homeostasis mechanisms and advance the way towards finding effective therapeutical drug discoveries for neurodegenerative diseases characterized by TDP-43 proteinopathies, especially ALS and FTD. We also consider the wider insight of these therapeutic strategies for other neurodegenerative diseases.

Somatosensory pathway dysfunction in patients with amyotrophic lateral sclerosis in a completely locked-in state

OBJECTIVE

To investigate somatosensory pathway function in patients with amyotrophic lateral sclerosis (ALS) dependent on invasive ventilation and in a completely locked-in state (CLIS).

METHODS

We examined median nerve somatosensory evoked potentials (SEPs) in 17 ALS patients in a CLIS, including 11 patients with sporadic ALS, one with familial ALS with genes not examined, four with a Cu/Zn superoxide-dismutase-1 (SOD1) gene variant (Val118Leu, Gly93Ser, Cys146Arg), and one with a fused-in-sarcoma gene variant (P525L). We evaluated N9, N13, N20 and P25, and central conduction time (CCT); the data were compared with those of 73 healthy controls.

RESULTS

N20 and N13 were abolished in 12 and 10 patients, and their latencies was prolonged in four and three patients, respectively. The CCT was prolonged in five patients with measurable N13 and N20. Two patients with SOD1 gene mutations had absent or slightly visible N9. Compared to the CCT and latencies and amplitudes of N13 and N20 in the controls, those in the patient cohort were significantly abnormal.

CONCLUSIONS

The central somatosensory pathway is severely involved in patients with ALS in a CLIS.

SIGNIFICANCE

Our findings suggest that median nerve SEP cannot be utilized for communication in patients with ALS in a CLIS.

Neuronal dysfunction caused by FUSR521G promotes ALS-associated phenotypes that are attenuated by NF-κB inhibition

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are related neurodegenerative diseases that belong to a common disease spectrum based on overlapping clinical, pathological and genetic evidence. Early pathological changes to the morphology and synapses of affected neuron populations in ALS/FTD suggest a common underlying mechanism of disease that requires further investigation. Fused in sarcoma (FUS) is a DNA/RNA-binding protein with known genetic and pathological links to ALS/FTD. Expression of ALS-linked FUS mutants in mice causes cognitive and motor defects, which correlate with loss of motor neuron dendritic branching and synapses, in addition to other pathological features of ALS/FTD. The role of ALS-linked FUS mutants in causing ALS/FTD-associated disease phenotypes is well established, but there are significant gaps in our understanding of the cell-autonomous role of FUS in promoting structural changes to motor neurons, and how these changes relate to disease progression. Here we generated a neuron-specific FUS-transgenic mouse model expressing the ALS-linked human FUSR521G variant, hFUSR521G/Syn1, to investigate the cell-autonomous role of FUSR521G in causing loss of dendritic branching and synapses of motor neurons, and to understand how these changes relate to ALS-associated phenotypes. Longitudinal analysis of mice revealed that cognitive impairments in juvenile hFUSR521G/Syn1 mice coincide with reduced dendritic branching of cortical motor neurons in the absence of motor impairments or changes in the neuromorphology of spinal motor neurons. Motor impairments and dendritic attrition of spinal motor neurons developed later in aged hFUSR521G/Syn1 mice, along with FUS cytoplasmic mislocalisation, mitochondrial abnormalities and glial activation. Neuroinflammation promotes neuronal dysfunction and drives disease progression in ALS/FTD. The therapeutic effects of inhibiting the pro-inflammatory nuclear factor kappa B (NF-κB) pathway with an analog of Withaferin A, IMS-088, were assessed in symptomatic hFUSR521G/Syn1 mice and were found to improve cognitive and motor function, increase dendritic branches and synapses of motor neurons, and attenuate other ALS/FTD-associated pathological features. Treatment of primary cortical neurons expressing FUSR521G with IMS-088 promoted the restoration of dendritic mitochondrial numbers and mitochondrial activity to wild-type levels, suggesting that inhibition of NF-κB permits the restoration of mitochondrial stasis in our models. Collectively, this work demonstrates that FUSR521G has a cell-autonomous role in causing early pathological changes to dendritic and synaptic structures of motor neurons, and that these changes precede motor defects and other well-known pathological features of ALS/FTD. Finally, these findings provide further support that modulation of the NF-κB pathway in ALS/FTD is an important therapeutic approach to attenuate disease.

Synaptic remodeling follows upper motor neuron hyperexcitability in a rodent model of TDP-43

Amyotrophic Lateral Sclerosis (ALS) is an incurable disease characterized by relentlessly progressive degeneration of the corticomotor system. Cortical hyperexcitability has been identified as an early pre-symptomatic biomarker of ALS. This suggests that hyperexcitability occurs upstream in the ALS pathological cascade and may even be part of the mechanism that drives development of symptoms or loss of motor neurons in the spinal cord. However, many studies also indicate a loss to the synaptic machinery that mediates synaptic input which raises the question of which is the driver of disease, and which is a homeostatic response. Herein, we used an inducible mouse model of TDP-43 mediated ALS that permits for the construction of detailed phenotypic timelines. Our work comprehensively describes the relationship between intrinsic hyperexcitability and altered synaptic input onto motor cortical layer 5 pyramidal neurons over time. As a result, we have constructed the most complete timeline of electrophysiological changes following induction of TDP-43 dysfunction in the motor cortex. We report that intrinsic hyperexcitability of layer 5 pyramidal neurons precedes changes to excitatory synaptic connections, which manifest as an overall loss of inputs onto layer 5 pyramidal neurons. This finding highlights the importance of hyperexcitability as a primary mechanism of ALS and re-contextualizes synaptic changes as possibly representing secondary adaptive responses. Recognition of the relationship between intrinsic hyperexcitability and reduced excitatory synaptic input has important implications for the development of useful therapies against ALS. Novel strategies will need to be developed that target neuronal output by managing excitability against synapses separately.

Dysautonomia in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease, characterized in its typical presentation by a combination of lower and upper motor neuron symptoms, with a progressive course and fatal outcome. Due to increased recognition of the non-motor symptoms, it is currently considered a multisystem disorder with great heterogeneity, regarding genetical, clinical, and neuropathological features. Often underestimated, autonomic signs and symptoms have been described in patients with ALS, and various method analyses have been used to assess autonomic nervous system involvement. The aim of this paper is to offer a narrative literature review on autonomic disturbances in ALS, based on the scarce data available to date.

TDP-43 differentially propagates to induce antero- and retrograde degeneration in the corticospinal circuits in mouse focal ALS models

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by TDP-43 inclusions in the cortical and spinal motor neurons. It remains unknown whether and how pathogenic TDP-43 spreads across neural connections to progress degenerative processes in the cortico-spinal motor circuitry. Here we established novel mouse ALS models that initially induced mutant TDP-43 inclusions in specific neuronal or cell types in the motor circuits, and investigated whether TDP-43 and relevant pathological processes spread across neuronal or cellular connections. We first developed ALS models that primarily induced TDP-43 inclusions in the corticospinal neurons, spinal motor neurons, or forelimb skeletal muscle, by using adeno-associated virus (AAV) expressing mutant TDP-43. We found that TDP-43 induced in the corticospinal neurons was transported along the axons anterogradely and transferred to the oligodendrocytes along the corticospinal tract (CST), coinciding with mild axon degeneration. In contrast, TDP-43 introduced in the spinal motor neurons did not spread retrogradely to the cortical or spinal neurons; however, it induced an extreme loss of spinal motor neurons and subsequent degeneration of neighboring spinal neurons, suggesting a degenerative propagation in a retrograde manner in the spinal cord. The intraspinal degeneration further led to severe muscle atrophy. Finally, TDP-43 induced in the skeletal muscle did not propagate pathological events to spinal neurons retrogradely. Our data revealed that mutant TDP-43 spread across neuro-glial connections anterogradely in the corticospinal pathway, whereas it exhibited different retrograde degenerative properties in the spinal circuits. This suggests that pathogenic TDP-43 may induce distinct antero- and retrograde mechanisms of degeneration in the motor system in ALS.

Structural and microstructural neuroimaging signature of C9orf72-associated ALS: A multiparametric MRI study

BACKGROUND

ALS patients with hexanucleotide expansion in C9orf72 are characterized by a specific clinical phenotype, including more aggressive disease course and cognitive decline. Computerized multiparametric MRI with gray matter volumetry and diffusion tensor imaging (DTI) to analyze white matter structural connectivity is a potential in vivo biomarker.

OBJECTIVE

The objective of this study was to develop a multiparametric MRI signature in a large cohort of ALS patients with C9orf72 mutations. The aim was to investigate how morphological features of C9orf72-associated ALS differ in structural MRI and DTI compared to healthy controls and ALS patients without C9orf72 mutations.

METHODS

Atlas-based volumetry (ABV) and whole brain-based DTI-based analyses were performed in a cohort of n = 51 ALS patients with C9orf72 mutations and compared with both n = 51 matched healthy controls and n = 51 C9orf72 negative ALS patients, respectively. Subsequently, Spearman correlation analysis of C9orf72 ALS patients' data with clinical parameters (age of onset, sex, ALS-FRS-R, progression rate, survival) as well as ECAS and p-NfH in CSF was performed.

RESULTS

The whole brain voxel-by-voxel comparison of fractional anisotropy (FA) maps between C9orf72 ALS patients and controls showed significant bilateral alterations in axonal structures of the white matter at group level, primarily along the corticospinal tracts and in fibers projecting to the frontal lobes. For the frontal lobes, these alterations were also significant between C9orf72 positive and C9orf72 negative ALS patients. In ABV, patients with C9orf72 mutations showed lower volumes of the frontal, temporal, and parietal lobe, with the lowest values in the gray matter of the superior frontal and the precentral gyrus, but also in hippocampi and amygdala. Compared to C9orf72 negative ALS, the differences were shown to be significant for cerebral gray matter (p = 0.04), especially in the frontal (p = 0.01) and parietal lobe (p = 0.01), and in the thalamus (p = 0.004). A correlation analysis between ECAS and averaged regional FA values revealed significant correlations between cognitive performance in ECAS and frontal association fibers. Lower FA values in the frontal lobes were associated with worse performance in all cognitive domains measured (language, verbal fluency, executive functions, memory and spatial perception). In addition, there were significant negative correlations between age of onset and atlas-based volumetry results for gray matter.

CONCLUSIONS

This study demonstrates a distinct pattern of DTI alterations of the white matter and ubiquitous volume reductions of the gray matter early in the disease course of C9orf72-associated ALS. Alterations were closely linked to a more aggressive cognitive phenotype. These results are in line with an expected pTDP43 propagation pattern of cortical affection and thus strengthen the hypothesis that an underlying developmental disorder is present in ALS with C9orf72 expansions. Thus, multiparametric MRI could contribute to the assessment of the disease as an in vivo biomarker even in the early phase of the disease.

Integrative proteomics highlight presynaptic alterations and c-Jun misactivation as convergent pathomechanisms in ALS

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease mainly affecting upper and lower motoneurons. Several functionally heterogeneous genes have been associated with the familial form of this disorder (fALS), depicting an extremely complex pathogenic landscape. This heterogeneity has limited the identification of an effective therapy, and this bleak prognosis will only improve with a greater understanding of convergent disease mechanisms. Recent evidence from human post-mortem material and diverse model systems has highlighted the synapse as a crucial structure actively involved in disease progression, suggesting that synaptic aberrations might represent a shared pathological feature across the ALS spectrum. To test this hypothesis, we performed the first comprehensive analysis of the synaptic proteome from post-mortem spinal cord and human iPSC-derived motoneurons carrying mutations in the major ALS genes. This integrated approach highlighted perturbations in the molecular machinery controlling vesicle release as a shared pathomechanism in ALS. Mechanistically, phosphoproteomic analysis linked the presynaptic vesicular phenotype to an accumulation of cytotoxic protein aggregates and to the pro-apoptotic activation of the transcription factor c-Jun, providing detailed insights into the shared pathobiochemistry in ALS. Notably, sub-chronic treatment of our iPSC-derived motoneurons with the fatty acid docosahexaenoic acid exerted a neuroprotective effect by efficiently rescuing the alterations revealed by our multidisciplinary approach. Together, this study provides strong evidence for the central and convergent role played by the synaptic microenvironment within the ALS spinal cord and highlights a potential therapeutic target that counteracts degeneration in a heterogeneous cohort of human motoneuron cultures.

Saccadic oscillations as a biomarker of clinical symptoms in amyotrophic lateral sclerosis

BACKGROUND

Among eye movements in amyotrophic lateral sclerosis (ALS), we identified the characteristics of square-wave jerks (SWJs) seen during times without visual fixation (VF) and analyzed their relationships with clinical parameters.

MATERIALS AND METHODS

Clinical symptoms were evaluated and eye movements were tested using electronystagmography in 15 patients with ALS (10 men, 5 women; mean age, 66.9 ± 10.5 years). SWJs with and without VF were recorded, and their characteristics were identified. Relationships between each SWJ parameter and clinical symptoms were evaluated. Results were compared with eye movement data from 18 healthy individuals.

RESULTS

The frequency of SWJs without VF was significantly higher in the ALS group than in the healthy group (P < 0.001). When the condition was changed from VF to no-VF in the ALS group, the frequency of SWJs was significantly higher in healthy subjects (P = 0.004). A positive correlation was seen between frequency of SWJs and percentage predicted forced vital capacity (%FVC) (R = 0.546, P = 0.035).

CONCLUSION

The frequency of SWJs was higher with VF in healthy people, and was suppressed without VF. In contrast, the frequency of SWJs was not suppressed without VF in ALS patients. This suggests that SWJs without VF have some clinical significance in ALS patients. Moreover, a relationship was noted between the parameters of SWJs without VF in ALS patients and results of pulmonary function tests, suggesting that SWJs during times without VF may offer a clinical parameter of ALS.

Brain imaging signatures in amyotrophic lateral sclerosis: Correlation with peripheral motor degeneration

OBJECTIVE

This study aimed to explore the clinical significance of brain imaging signatures in the context of clinical neurological deficits in association with upper and lower motor neuron degeneration in amyotrophic lateral sclerosis (ALS).

METHODS

We performed brain MRI examinations to quantitatively evaluate (1) gray matter volume and (2) white matter tract fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD). Image-derived indices were correlated with (1) global neurological deficits of MRC muscle strength sum score, revised amyotrophic lateral sclerosis functional rating scale (ALSFRS-R), and forced vital capacity (FVC), and (2) focal scores of University of Pennsylvania Upper motor neuron score (Penn score) and the summation of compound muscle action potential Z scores (CMAP Z sum score).

RESULTS

There were 39 ALS patients and 32 control subjects matched for age and gender. Compared to controls, ALS patients had a lower gray matter volume in the precentral gyrus of the primary motor cortex, which was correlated with FA of corticofugal tracts. The gray matter volume of the precentral gyrus was correlated with FVC, MRC sum score, and CMAP Z sum score, while the FA of the corticospinal tract was linearly associated with CMAP Z sum score and Penn score on multivariate linear regression model.

INTERPRETATION

This study indicated that clinical assessment of muscle strength and routine measurements on nerve conduction studies provided surrogate markers of brain structural changes for ALS. Furthermore, these findings suggested parallel involvement of both upper and lower motor neurons in ALS.

Nuclear Expression of TDP-43 Is Linked with Morphology and Ubiquitylation of Cytoplasmic Aggregates in Amyotrophic Lateral Sclerosis

The transactive response DNA-binding protein of 43 kDa (TDP-43) is a pathological protein of amyotrophic lateral sclerosis (ALS). TDP-43 pathology is characterized by a combination of the cytoplasmic aggregation and nuclear clearance of this protein. However, the mechanisms underlying TDP-43 pathology have not been fully clarified. The aim of this study was to evaluate the relationships between the expression level of nuclear TDP-43 and the pathological properties of cytoplasmic aggregates in autopsied ALS cases. We included 22 consecutively autopsied cases with sporadic TDP-43-related ALS. The motor neuron systems were neuropathologically assessed. We identified 790 neurons with cytoplasmic TDP-43 inclusions from the lower motor neuron system of included cases. Nuclear TDP-43 disappeared in 84% (n = 660) and expressed in 16% (n = 130) of neurons with cytoplasmic inclusions; the former was defined as TDP-43 cytoplasmic immunoreactivity (c-ir), and the latter was defined as nuclear and cytoplasmic immunoreactivity (n/c-ir). Morphologically, diffuse cytoplasmic inclusions were significantly more prevalent in TDP-43 n/c-ir neurons than in c-ir neurons, while skein-like and round inclusions were less prevalent in n/c-ir neurons. The cytoplasmic inclusions of TDP-43 n/c-ir neurons were phosphorylated but poorly ubiquitylated when compared with those of c-ir neurons. TDP-43 n/c-ir neurons became less dominant than the c-ir neurons among cases with a prolonged disease duration. The expression level of nuclear TDP-43 was significantly lower in n/c-ir neurons than in normal neurons without cytoplasmic inclusions. Our results indicate that the maturation of cytoplasmic TDP-43 inclusions correlates with the depletion of nuclear TDP-43 in each affected neuron. This finding supports the view that an imbalance between nuclear and cytoplasmic TDP-43 may be an essential pathway to TDP-43 pathology.

Patterns of synaptic loss in human amyotrophic lateral sclerosis spinal cord: a clinicopathological study

Amyotrophic Lateral Sclerosis (ALS) is mainly characterized by the degeneration of corticospinal neurons and spinal α-motoneurons; vulnerable cells display prominent pTDP-43 inclusions. Evidence gathered from genetics, murine models, and iPSC-derived neurons point to the early involvement of synapses in the disease course and their crucial role in the pathogenic cascade. However, pathology studies, with specimens from large post-mortem cohorts, mapping the pattern of synaptic disturbances over clinical and neuropathological hallmarks of disease progression, are currently not available. Thus, the appearance and progression of synaptic degeneration in human ALS patients are currently not known, preventing a full validation of the murine and in vitro models. Here, we investigated the loss of synaptophysin-positive terminals in cervical, thoracic, and lumbar spinal cord samples from a retrospective cohort of n = 33 ALS patients and n = 8 healthy controls, and we correlated the loss of synapses against clinicodemographic features and neuropathological ALS stage. We found that, although dorsal and intermediate spinal cord laminae do not lose synapses, ALS patients displayed a substantial but variable loss of synapses in the ventral horn of lumbar and cervical spinal cord. The amount of synaptic loss was predicted by disease duration, by the clinical site of onset, and by the loss of α-motoneurons, although not by the fraction of pTDP-43-immunopositive α-motoneurons. Taken together, our findings validate the synaptic pathology observed in other models and suggest that pathogenic pathways unfolding in the spinal microenvironment are critical to the progressive disassembly of local synaptic connectivity.

Low T-cell reactivity to TDP-43 peptides in ALS

Background

Dysregulation of the immune system in amyotrophic lateral sclerosis (ALS) includes changes in T-cells composition and infiltration of T cells in the brain and spinal cord. Recent studies have shown that cytotoxic T cells can directly induce motor neuron death in a mouse model of ALS and that T cells from ALS patients are cytotoxic to iPSC-derived motor neurons from ALS patients. Furthermore, a clonal expansion to unknown epitope(s) was recently found in familial ALS and increased peripheral and intrathecal activation of cytotoxic CD8+ T cells in sporadic ALS.

Results

Here, we show an increased activation of peripheral T cells from patients with sporadic ALS by IL-2 treatment, suggesting an increase of antigen-experienced T cells in ALS blood. However, a putative antigen for T-cell activation in ALS has not yet been identified. Therefore, we investigated if peptides derived from TDP-43, a key protein in ALS pathogenesis, can act as epitopes for antigen-mediated activation of human T cells by ELISPOT and flow cytometry. We found that TDP-43 peptides induced only a weak MHCI or MHCII-restricted activation of both naïve and antigen-experienced T cells from healthy controls and ALS patients. Interestingly, we found less activation in T cells from ALS patients to TDP-43 and control stimuli. Furthermore, we found no change in the levels of naturally occurring auto-antibodies against full-length TDP-43 in ALS.

Conclusion

Our data suggests a general increase in antigen-experienced T cells in ALS blood, measured by in-vitro culture with IL-2 for 14 days. Furthermore, it suggests that TDP-43 is a weak autoantigen.

Guideline "Motor neuron diseases" of the German Society of Neurology (Deutsche Gesellschaft für Neurologie)

INTRODUCTION

In 2021, the Deutsche Gesellschaft für Neurology published a new guideline on diagnosis and therapy of motor neuron disorders. Motor neuron disorders affect upper motor neurons in the primary motor cortex and/or lower motor neurons in the brain stem and spinal cord. The most frequent motor neuron disease amyotrophic lateral sclerosis (ALS) is a rapidly progressive disease with an average life expectancy of 2-4 years with a yearly incidence of 3.1/100,000 in Central Europe (Rosenbohm et al. in J Neurol 264(4):749-757, 2017. https://doi.org/10.1007/s00415-017-8413-3 ). It is considered a rare disease mainly due to its low prevalence as a consequence of short disease duration.

RECOMMENDATIONS

These guidelines comprise recommendations regarding differential diagnosis, neuroprotective therapies and multidisciplinary palliative care including management of respiration and nutrition as well as provision of assistive devices and end-of-life situations.

CONCLUSION

Diagnostic and therapeutic guidelines are necessary due the comparatively high number of cases and the aggressive disease course. Given the low prevalence and the severe impairment of patients, it is often impossible to generate evidence-based data so that ALS guidelines are partially dependent on expert opinion.

Thermodynamic and kinetic approaches for drug discovery to target protein misfolding and aggregation

INTRODUCTION

Protein misfolding diseases, including Alzheimer's and Parkinson's diseases, are characterized by the aberrant aggregation of proteins. These conditions are still largely untreatable, despite having a major impact on our healthcare systems and societies.

AREAS COVERED

We describe drug discovery strategies to target protein misfolding and aggregation. We compare thermodynamic approaches, which are based on the stabilization of the native states of proteins, with kinetic approaches, which are based on the slowing down of the aggregation process. This comparison is carried out in terms of the current knowledge of the process of protein misfolding and aggregation, the mechanisms of disease and the therapeutic targets.

EXPERT OPINION

There is an unmet need for disease-modifying treatments that target protein misfolding and aggregation for the over 50 human disorders known to be associated with this phenomenon. With the approval of the first drugs that can prevent misfolding or inhibit aggregation, future efforts will be focused on the discovery of effective compounds with these mechanisms of action for a wide range of conditions.

Verification of propagation hypothesis in patients with sporadic hand onset amyotrophic lateral sclerosis

OBJECTIVE

If lesions in sporadic amyotrophic lateral sclerosis (ALS) originate from a single focal onset site and spread contiguously by prion-like cell-to-cell propagation at a constant speed, the lesion spread time should be proportional to the anatomical distance. We verify this model in the patients.

METHODS

In 29 sporadic ALS patients with hand onset followed by spread to shoulder and leg, we retrospectively evaluated the inter/intra-regional spread time ratio: time interval of symptoms from hand-to-leg divided by that from hand-to-shoulder. We also obtained the corresponding inter-/intra-regional distance ratios of spinal cord from magnetic resonance imaging of 12 patients, and those of primary motor cortex from coordinates using neuroimaging software.

RESULTS

Inter-/intra-regional spread time ratios ranged from 0.29 to 6.00 (median 1.20). Distance ratios ranged from 1.85 to 2.86 in primary motor cortex and from 5.79 to 8.67 in spinal cord. Taken together with clinical manifestations, of 27 patients with the requisite information available, lesion spreading was consistent with the model in primary motor cortex in 4 (14.8%) patients, and in spinal cord in only 1 (3.7%) patient. However, in more patients (12 of 29 patients: 41.4%), the inter-regional spread times in a long anatomical distance of hand-to-leg were shorter than or equal to the intra-regional spread times in a short anatomical distance of hand-to-shoulder.

CONCLUSION

Contiguous cell-to-cell propagation at a constant speed might not play a major role at least in distant lesion spreading of ALS. Several mechanisms can be responsible for progression in ALS.

Patterns of small involuntary fixation saccades (SIFSs) in different neurodegenerative diseases: the role of noise

During the attempt to steadily fixate at a single spot, sequences of small involuntary fixation saccades (SIFSs, known also as microsaccades οr intrusions) occur which form spatio-temporal patterns such as square wave jerks (SWJs), a pattern characterised by alternating centrifugal and centripetal movements of similar magnitude. In many neurodegenerative disorders, SIFSs exhibit elevated amplitudes and frequencies. Elevated SIFS amplitudes have been shown to favour the occurrence of SWJs ("SWJ coupling"). We analysed SIFSs in different subject groups comprising both healthy controls (CTR) and patients with amyotrophic lateral sclerosis (ALS) and progressive supranuclear palsy (PSP), i.e. two neurodegenerative diseases with completely different neuropathological basis and different clinical phenotypes. We show that, across these groups, the relations between SIFS amplitude and the relative frequency of SWJ-like patterns and other SIFS characteristics follow a common law. As an explanation, we propose that physiological and technical noise comprises a small, amplitude-independent component that has little effect on large SIFSs, but causes considerable deviations from the intended amplitude and direction of small ones. Therefore, in contrast to large SIFSs, successive small SIFSs have a lower chance to meet the SWJ similarity criteria. In principle, every measurement of SIFSs is affected by an amplitude-independent noise background. Therefore, the dependence of SWJ coupling on SIFS amplitude will probably be encountered in almost any group of subjects. In addition, we find a positive correlation between SIFS amplitude and frequency in ALS, but none in PSP, suggesting that the elevated amplitudes might arise at different sites in the two disorders.

Loss of hypothalamic MCH decreases food intake in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is associated with impaired energy metabolism, including weight loss and decreased appetite which are negatively correlated with survival. Neural mechanisms underlying metabolic impairment in ALS remain unknown. ALS patients and presymptomatic gene carriers have early hypothalamic atrophy. The lateral hypothalamic area (LHA) controls metabolic homeostasis through the secretion of neuropeptides such as orexin/hypocretin and melanin-concentrating hormone (MCH). Here, we show loss of MCH-positive neurons in three mouse models of ALS based on SOD1 or FUS mutations. Supplementation with MCH (1.2 µg/d) through continuous intracerebroventricular delivery led to weight gain in male mutant Sod1^G86R mice. MCH supplementation increased food intake, rescued expression of the key appetite-related neuropeptide AgRP (agouti-related protein) and modified respiratory exchange ratio, suggesting increased carbohydrate usage during the inactive phase. Importantly, we document pTDP-43 pathology and neurodegeneration in the LHA of sporadic ALS patients. Neuronal cell loss was associated with pTDP-43-positive inclusions and signs of neurodegeneration in MCH-positive neurons. These results suggest that hypothalamic MCH is lost in ALS and contributes to the metabolic changes, including weight loss and decreased appetite.

Sequential alterations in diffusion metrics as correlates of disease severity in amyotrophic lateral sclerosis

BACKGROUND AND OBJECTIVE

The neuropathology of amyotrophic lateral sclerosis (ALS) follows a regional distribution pattern in the brain with four stages. Using diffusion tensor imaging (DTI), this pattern can be translated into a tract-based staging scheme to assess cerebral progression in vivo. This study investigates the association between the sequential alteration pattern and disease severity in patients with ALS.

METHODS

DTI data of 325 patients with ALS and 130 healthy controls were analyzed in a tract of interest (TOI)-based approach. Patients were categorized according to their ALS-FRS-R scores into groups with declining functionality. The fractional anisotropy (FA) values in the tracts associated with neuropathological stages were group-wise compared with healthy controls.

RESULTS

The FA in the tracts associated with ALS stages showed a decrease which could be related to the disease severity stratification, i.e., at the group level, the lower the ALS-FRS-R of the categorized patient group, the higher was the effect size of the stage-related tract. In the patient group with the highest ALS-FRS-R, Cohen's d showed a medium effect size in the corticospinal tract and small effect sizes in the other stage-related tracts. Overall, the lower the ALS-FRS-R of the categorized patient group the higher was the effect size of the comparison with healthy controls.

CONCLUSION

The progression of white matter alterations across tracts according to the model of sequential tract involvement is associated with clinical disease severity in patients with ALS, suggesting the use of staging-based DTI as a technical marker for disease progression.

Brain Vascular Health in ALS Is Mediated through Motor Cortex Microvascular Integrity

Brain vascular health appears to be critical for preventing the development of amyotrophic lateral sclerosis (ALS) and slowing its progression. ALS patients often demonstrate cardiovascular risk factors and commonly suffer from cerebrovascular disease, with evidence of pathological alterations in their small cerebral blood vessels. Impaired vascular brain health has detrimental effects on motor neurons: vascular endothelial growth factor levels are lowered in ALS, which can compromise endothelial cell formation and the integrity of the blood-brain barrier. Increased turnover of neurovascular unit cells precedes their senescence, which, together with pericyte alterations, further fosters the failure of toxic metabolite removal. We here provide a comprehensive overview of the pathogenesis of impaired brain vascular health in ALS and how novel magnetic resonance imaging techniques can aid its detection. In particular, we discuss vascular patterns of blood supply to the motor cortex with the number of branches from the anterior and middle cerebral arteries acting as a novel marker of resistance and resilience against downstream effects of vascular risk and events in ALS. We outline how certain interventions adapted to patient needs and capabilities have the potential to mechanistically target the brain microvasculature towards favorable motor cortex blood supply patterns. Through this strategy, we aim to guide novel approaches to ALS management and a better understanding of ALS pathophysiology.

Differenzialdiagnose der Amyotrophen Lateralsklerose in der klinischen Praxis

Die Diagnose der Amyotrophen Lateralsklerose (ALS) beruht vorwiegend auf klinischen Kriterien und kann aufgrund des heterogenen Erscheinungsbildes gerade in frühen Krankheitsstadien mitunter schwierig sein. Wegweisend sind der Nachweis einer kombinierten Pathologie des oberen und unteren Motoneurons, der fokale Onset, das Ausbreitungsmuster (Spreading), das typische Verteilungsmuster der Paresen, das Vorhandensein oder Fehlen nicht-motorischer Zusatzsymptome sowie Art und Geschwindigkeit der Krankheitsprogredienz. Dieser Review stellt Charakteristika der ALS sowohl im Hinblick auf die klinische Untersuchung als auch apparativer Zusatzdiagnostik in Abgrenzung zu den wichtigsten Differenzialdiagnosen in Form von Einschlusskörperchenmyositis, Chronisch Inflammatorischer Demyelinisierender Polyneuropathie (CIDP), Mulifokaler Motorischer Neuropathie (MMN), adulter Form der Spinalen Muskelatrophie (SMA), Kennedy-Syndrom und Hereditärer Spastischer Paralyse (HSP) dar.