Motor Neuron Research Articles

Cell type–specific gene therapy confers protection against motor neuron disease caused by a TFG variant

Cell type–specific gene therapy confers protection against motor neuron disease caused by a TFG variant

Actuating Extracellular Matrices Decouple the Mechanical and Biochemical Effects of Muscle Contraction on Motor Neurons

AbstractEmerging in vivo evidence suggests that repeated muscle contraction, or exercise, impacts peripheral nerves. However, the difficulty of isolating the muscle‐specific impact on motor neurons in vivo, as well as the inability to decouple the biochemical and mechanical impacts of muscle contraction in this setting, motivates investigating this phenomenon in vitro. This study demonstrates that tuning the mechanical properties of fibrin enables longitudinal culture of highly contractile skeletal muscle monolayers, enabling functional characterization of and long‐term secretome harvesting from exercised tissues. Motor neurons stimulated with exercised muscle‐secreted factors significantly upregulate neurite outgrowth and migration, with an effect size dependent on muscle contraction intensity. Actuating magnetic microparticles embedded within fibrin hydrogels enable dynamically stretching motor neurons and non‐invasively mimicking the mechanical effects of muscle contraction. Interestingly, axonogenesis is similarly upregulated in both mechanically and biochemically stimulated motor neurons, but RNA sequencing reveals different transcriptomic signatures between groups, with biochemical stimulation having a greater impact on cell signaling related to axonogenesis and synapse maturation. This study leverages actuating extracellular matrices to robustly validate a previously hypothesized role for muscle contraction in regulating motor neuron growth and maturation from the bottom‐up through both mechanical and biochemical signaling.

Working with people living with motor neurone disease and the impact on professionals’ emotional and psychological well-being: A scoping review

Background: Integrated multidisciplinary care is required to manage the progressive and debilitating symptoms associated with motor neurone disease. Professionals can find providing the level of care required by this population clinically and emotionally challenging. To support those working with these patients it is important to understand the experience of the entire multidisciplinary team involved and the impact of working with motor neurone disease on their emotional and psychological well-being. Aim: To identify what is known about (1) healthcare professionals’ experience of working with motor neurone disease and (2) the impact of this work on their emotional and psychological well-being. Design: Scoping review. Review protocol registered on Open Science Framework. Sources: Five electronic databases were searched in January 2023 and 2024. Grey literature and hand searches were completed. Results: Fifty-one sources published between 1990 and 2023 were included. A total of 1692 healthcare professionals are represented. Three main categories were identified: (1) The demands of providing motor neurone disease care. (2) Factors influencing professionals’ ability to provide desired levels of care. (3) The emotional impact of working with motor neurone disease. Subcategories are depicted within these. Conclusion: Positive experiences included job satisfaction, enhanced perspective and receiving gratitude, while negative implications such as stress, emotional exhaustion and burnout also featured. The demands of motor neurone disease patient care, the organisation of services and resources required to meet patient and family needs and the emotional burden for professionals involved, warrant greater recognition in clinical practice, guidelines and future research.

The therapeutic potential of Apigenin in amyotrophic lateral sclerosis through ALDH1A2/Nrf2/ARE signaling

BackgroundAmyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by motor neuron loss leading to muscle weakness and atrophy. Apigenin (APG), known for its antioxidant properties, holds potential as a therapeutic compound in ALS.MethodsWe used the Tg(SOD1*G93A)1Gur/J transgenic mouse model of ALS to investigate the therapeutic effects of APG. Key measured included motor function via the ALSTDI score, molecular markers of oxidative stress (OS) and apoptosis in spinal cord tissues. Techniques used included pathological, Western blotting, flow cytometry, and qRT-PCR to assess the effect of ALDH1A2.ResultsAPG treatment attenuated weight loss and improved motor function scores in ALS mice compared to untreated ALS models. Molecular analyses revealed a significant upregulation of ALDH1A2 in APG-treated groups, along with a reduction in markers of OS and apoptosis. In vitro studies in NSC34 cells further confirmed the protective effects of APG against SOD1*G93A mutation-induced cytotoxicity. In addition, suppression of ALDH1A2 by shRNA exacerbated disease markers that were ameliorated by APG treatment.ConclusionsOur results suggest that APG attenuates the progression of ALS pathology by regulating OS and apoptosis through ALDH1A2. These results support further investigation of APG as a potential therapeutic agent for the treatment of ALS.Graphical

Split hand and minipolymyoclonus in spinocerebellar ataxia type 3: a case report

BackgroundSpinocerebellar ataxia type 3 (SCA3), also known as Machado–Joseph disease, is an autosomal dominant neurodegenerative disorder caused by CAG repeat expansion in exon 10 of ATXN3. Extra-cerebellar manifestations, including external ophthalmoplegia, dystonia, Parkinsonism, and peripheral neuropathy, are predominantly present in SCA3 cases. Here, we report a case of SCA3 presenting with a split hand and minipolymyoclonus.Case presentationA 73-year-old female patient presented with a 5-year history of ataxic gait. Neurological examination revealed cerebellar ataxia and minipolymyoclonus in the digits on both sides and muscle atrophy in the right hand, consistent with the split hand pattern. Electrodiagnostic studies demonstrated decreased amplitude of compound muscle action potentials and neurogenic motor unit potentials, indicating lower motor neuron involvement.ConclusionsOur patient’s case indicated a split hand and minipolymyoclonus in SCA3. Clinicians should consider these extra-cerebellar manifestations in patients with SCA3. Although neither split hand nor minipolymyoclonus are likely to directly result in a specific etiological diagnosis, a common pathophysiological mechanism for both may be lower motor neuron involvement. This extracerebellar manifestation contributes to narrowing down the diagnostic possibilities for cases presenting with progressive cerebellar ataxia.

N-Butylidenephthalide recovered calcium homeostasis to ameliorate neurodegeneration of motor neurons derived from amyotrophic lateral sclerosis iPSCs

n-Butylidenephthalide recovered calcium homeostasis to ameliorate neurodegeneration of motor neurons derived from amyotrophic lateral sclerosis iPSCs

Exploiting speech tremors: machine learning for early diagnosis of amyotrophic lateral sclerosis

Abstract Neurodegenerative diseases pose significant challenges in healthcare, with Amyotrophic Lateral Sclerosis (ALS) being one such rare yet debilitating condition affecting motor neurons. Machine learning (ML) and artificial intelligence (AI) have emerged as powerful tools in healthcare, offering insights and solutions for various medical conditions. This study investigates the application of ML to enhance early ALS diagnosis through the analysis of tremors in sustained speech. By focusing on tremor detection as a diagnostic marker, the research employs ML algorithms to develop predictive models capable of distinguishing ALS patients from healthy controls. The dataset comprises 54 patients from the Republican Research and Clinical Centre of Neurology and Neurosurgery in Belarus, Minsk. The study adopts a two-faceted approach: (1) Exploratory voice analysis to identify tremors associated with ALS in speech samples. (2) Development of ML algorithms to construct predictive models for early ALS diagnosis based on the identified tremors. The ML models exhibit promising results in distinguishing ALS patients from healthy controls based on speech analysis. Tremor detection in sustained speech proves to be an effective marker for early ALS diagnosis. While initial findings are encouraging, larger-scale studies are required to validate the clinical applicability of this approach. The successful application of ML and AI in early ALS diagnosis by leveraging innovative approaches, such as tremor detection in sustained speech, we can enhance early diagnosis and improve patient outcomes in neurodegenerative diseases like ALS on a broader scale.

Quantitative and Computational Spinal Imaging in Neurodegenerative Conditions and Acquired Spinal Disorders: Academic Advances and Clinical Prospects

Introduction: Quantitative spinal cord imaging has facilitated the objective appraisal of spinal cord pathology in a range of neurological conditions both in the academic and clinical setting. Diverse methodological approaches have been implemented, encompassing a range of morphometric, diffusivity, susceptibility, magnetization transfer, and spectroscopy techniques. Advances have been fueled both by new MRI platforms and acquisition protocols as well as novel analysis pipelines. The quantitative evaluation of specific spinal tracts and grey matter indices has the potential to be used in diagnostic and monitoring applications. The comprehensive characterization of spinal disease burden in pre-symptomatic cohorts, in carriers of specific genetic mutations, and in conditions primarily associated with cerebral disease, has contributed important academic insights. Methods: A narrative review was conducted to examine the clinical and academic role of quantitative spinal cord imaging in a range of neurodegenerative and acquired spinal cord disorders, including hereditary spastic paraparesis, hereditary ataxias, motor neuron diseases, Huntington’s disease, and post-infectious or vascular disorders. Results: The clinical utility of specific methods, sample size considerations, academic role of spinal imaging, key radiological findings, and relevant clinical correlates are presented in each disease group. Conclusions: Quantitative spinal cord imaging studies have demonstrated the feasibility to reliably appraise structural, microstructural, diffusivity, and metabolic spinal cord alterations. Despite the notable academic advances, novel acquisition protocols and analysis pipelines are yet to be implemented in the clinical setting.

Direct conversion of urine-derived cells into functional motor neuron-like cells by defined transcription factors

Direct cell-type conversion of somatic cells into cell types of interest has garnered great attention because it circumvents rejuvenation and preserves the hallmarks of cellular aging (unlike induced pluripotent stem cells [iPSCs]) and is more suitable for modeling diseases with strong age-related and epigenetic contributions. Fibroblasts are commonly used for direct conversion; however, obtaining these cells requires highly invasive skin biopsies. Urine-derived cells (UDCs) are an alternative cell source and can be obtained via noninvasive procedures. Herein, induced motor neuron-like cells (iMNs) were generated from UDCs by transducing transcription factors involved in motor neuron (MN) differentiation. iMNs exhibited neuronal morphology, upregulation of pan-neuron and MN markers, and MN functionality, including spontaneous calcium oscillation and bungarotoxin-positive neuromuscular junction formation, when co-cultured with myotubes. Altogether, the findings of this study indicated that UDCs can be converted to functional MNs. This technology may allow us to understand disease pathogenesis and progression and discover biomarkers and drugs for MN-related diseases at the population level.

SMN2 gene copy number affects the incidence and prognosis of motor neuron diseases in Japan

BackgroundThe copy number status (CNS) of the survival motor neuron (SMN) gene may influence the risk and prognosis of amyotrophic lateral sclerosis (ALS) and lower motor neuron diseases (LMND) other than spinal muscular atrophy (SMA). However, previous studies of this association, mainly from Europe, have yielded controversial results, suggesting possible regional differences. Here, we investigated the effect of the SMN gene in Japanese patients with ALS and LMND.MethodsWe examined the SMN copy numbers and clinical histories of 487 Japanese patients with sporadic ALS (281 men; mean age at onset 61.5 years), 50 with adult LMND (50 men; mean age at onset 58.4 years) and 399 Japanese controls (171 men; mean age 62.2 years). Patients with pathogenic mutations in ALS-causing genes were excluded. SMN1 and SMN2 copy numbers were determined using the droplet digital polymerase chain reaction.ResultsThe frequency of a copy number of one for the SMN2 gene was higher in patients with ALS (38.0%) than in healthy controls (30.8%) (odds ratio (OR) = 1.37, 95% confidence interval (CI) = 1.04–1.82, p < 0.05). The SMN2 copy number affected the survival time of patients with ALS (median time: 0 copies, 34 months; 1 copy, 39 months; 2 copies, 44 months; 3 copies, 54 months; log-rank test, p < 0.05). Cox regression analysis revealed that the SMN2 copy number was associated with increased mortality (hazard ratio = 0.84, 95% CI = 0.72–0.98, p < 0.05). Also, null SMN2 cases were significantly more frequent in the LMND group (12.0%) than in the control group (4.8%) (OR = 2.73, 95% CI = 1.06–6.98, p < 0.05).ConclusionsOur findings suggest that SMN2 copy number reduction may adversely affect the onset and prognosis of MND, including ALS and LMND, in Japanese.

Host genetics and gut microbiota influence lipid metabolism and inflammation: potential implications for ALS pathophysiology in SOD1G93A mice

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disorder characterized by the progressive loss of motor neurons, with genetic and environmental factors contributing to its complex pathogenesis. Dysregulated immune responses and altered energetic metabolism are key features, with emerging evidence implicating the gut microbiota (GM) in disease progression. We investigated the interplay among genetic background, GM composition, metabolism, and immune response in two distinct ALS mouse models: 129Sv_G93A and C57Ola_G93A, representing rapid and slow disease progression, respectively.Using 16 S rRNA sequencing and fecal metabolite analysis, we characterized the GM composition and metabolite profiles in non-transgenic (Ntg) and SOD1G93A mutant mice of both strains. Our results revealed strain-specific differences in GM composition and functions, particularly in the abundance of taxa belonging to Erysipelotrichaceae and the levels of short and medium-chain fatty acids in fecal samples. The SOD1 mutation induces significant shifts in GM colonization in both strains, with C57Ola_G93A mice showing changes resembling those in 129 Sv mice, potentially affecting disease pathogenesis. ALS symptom progression does not significantly alter microbiota composition, suggesting stability.Additionally, we assessed systemic immunity and inflammatory responses revealing strain-specific differences in immune cell populations and cytokine levels.Our findings underscore the substantial influence of genetic background on GM composition, metabolism, and immune response in ALS mouse models. These strain-specific variations may contribute to differences in disease susceptibility and progression rates. Further elucidating the mechanisms underlying these interactions could offer novel insights into ALS pathogenesis and potential therapeutic targets.

Can resting lung function predict the response of a person living with motor neuron disease to a hypoxic challenge test?

People living with MND (PlwMND) are at risk of altitude-related hypoxia during flight. The Hypoxic Challenge Test (HCT) determines whether in-flight oxygen is required but can be expensive and inaccessible. To assist with travel recommendations, we investigated the relationship between altitude simulation-induced hypoxemia and baseline lung function. Retrospective audit of clinical database of PlwMND who had HCT and lung function. Pearson's correlation assessed relationships between oxygen saturation at altitude (AltSpO2) and lung function. Univariate logistic regression analysis and receiver operator characteristic (ROC) curves determined associations between lung function and HCT pass or fail. Between 2004-2023, 50 PlwMND were identified (median (IQR) diagnosis to HCT = 11.6 (16.9) months, mean ± SD forced vital capacity (FVC) = 2.4 ± 0.9 liters). Ten patients dropped below 85% SpO2 during testing (HCT fail). Baseline SpO2 was associated with AltSpO2 (r = 0.64) and predicted HCT pass or fail (OR 2.0 [95% CI 1.2-3.4], area under ROC curve (AUC) =0.8 [0.6-1.0]), as did FVC (AUC = 0.8 [0.6-0.9]). PlwMND with a FVC > 2.7L or a resting SpO2 > 97% are likely to pass HCT, whereas all those with FVC < 1L and SpO2 < 92% failed. PlwMND with FVC >2.7L or SpO2 >97% are unlikely to require oxygen or ventilatory supports for airline travel. A FVC below 2.7L will require a HCT to confidently determine HCT outcome, with testing still required for FVC <1L or baseline SpO2 <92%, to provide evidence to the airlines for in-flight respiratory support.

SMN depletion impairs skeletal muscle formation and maturation in a mouse model of SMA.

Spinal muscular atrophy (SMA) is characterized by low levels of the ubiquitously expressed Survival Motor Neuron (SMN) protein, leading to progressive muscle weakness and atrophy. Skeletal muscle satellite cells play a crucial role in muscle fiber maintenance, repair, and remodelling. While the effects of SMN depletion in muscle are well documented, its precise role in satellite cell function remains largely unclear. Using the Smn2B/- mouse model, we investigated SMN-depleted satellite cell biology through single fiber culture studies. Myofibers from Smn2B/- mice were smaller in size, shorter in length, had reduced myonuclear domain size, and reduced sub-synaptic myonuclear clusters-all suggesting impaired muscle function and integrity. These changes were accompanied by a reduction in the number of myonuclei in myofibers from Smn2B/- mice across all disease stages examined. Although the number of satellite cells in myofibers was significantly reduced, those remaining retained their capacity for myogenic activation and proliferation. These findings support the idea that a dysregulated myogenic process could be occurring as early in muscle stem cells during muscle formation and maturation in SMA. Targeting those pathways could offer additional options for combinatorial therapies for SMA.

Genetic testing for monogenic forms of motor neuron disease/amyotrophic lateral sclerosis in unaffected family members.

Motor neuron disease (MND), also referred to as amyotrophic lateral sclerosis (ALS), is a monogenic disease in a minority of cases, with autosomal dominant inheritance. Increasing numbers of people with MND are requesting genetic testing, and indeed receiving a genetic diagnosis. Consequently, requests for genetic counselling and predictive testing (i.e. of unaffected family members) are similarly expected to rise, alongside pre-symptomatic clinical trials. Despite this, there is no evidence-based guideline for predictive genetic testing in MND. This paper provides an overview of the genomic basis of MND, focusing specifically on the most common monogenic causes of MND. It then lays out the complexities of MND predictive testing, including the genetic landscape characterised by incomplete penetrance, clinical and genetic heterogeneity, and an oligogenic mechanism of pathogenesis in some cases. Additionally, there is limited research on the psychosocial impact of predictive genetic testing for MND, with studies suggesting potential difficulty in adjusting to the news, in part due to a lack of support and follow-up. This underscores a case for evidence-based, disease-specific guidance for predictive testing in MND.

Comprehensive newborn screening for severe combined immunodeficiency, X-linked agammaglobulinemia, and spinal muscular atrophy: the Chinese experience.

Newborn screening (NBS) for severe combined immunodeficiency (SCID), X-linked agammaglobulinemia (XLA), and spinal muscular atrophy (SMA) enables early diagnosis and intervention, significantly improving patient outcomes. Advances in real-time polymerase chain reaction (PCR) technology have been instrumental in facilitating their inclusion in NBS programs. We employed multiplex real-time PCR to simultaneously detect T-cell receptor excision circles (TRECs), kappa-deleting recombination excision circles (KRECs), and the absence of the survival motor neuron (SMN) 1 gene in dried blood spots from 103,240 newborns in Zhejiang Province, China, between July 2021 and December 2022. Of all the samples, 122 were requested further evaluation. After flow cytometry evaluation and/or genetic diagnostics, we identified one patient with SCID, two patients with XLA, nine patients with SMA [one of whom also had Wiskott-Aldrich Syndrome (WAS)], and eight patients with other medical conditions. The positive predictive values (PPVs) of NBS for SCID, XLA, and SMA were 2.44%, 2.78%, and 100%, respectively. The estimated prevalence rates in the Chinese population were 1 in 103,240 for SCID, 1 in 51,620 for XLA, and 1 in 11,471 for SMA. This study represents the first large-scale screening in mainland China using a TREC/KREC/SMN1 multiplex assay, providing valuable epidemiological data. Our findings suggest that this multiplex assay is an effective screening method for SCID, XLA, and SMA, potentially supporting the universal implementation of NBS programs across China.

Possible changes in motor neuron discharge characteristics in presymptomatic amyotrophic lateral sclerosis.

Possible changes in motor neuron discharge characteristics in presymptomatic amyotrophic lateral sclerosis.

Hibernation reduces GABA signaling in the brainstem to enhance motor activity of breathing at cool temperatures

BackgroundNeural circuits produce reliable activity patterns despite disturbances in the environment. For this to occur, neurons elicit synaptic plasticity during perturbations. However, recent work suggests that plasticity not only regulates circuit activity during disturbances, but these modifications may also linger to stabilize circuits during future perturbations. The implementation of such a regulation scheme for real-life environmental challenges of animals remains unclear. Amphibians provide insight into this problem in a rather extreme way, as circuits that generate breathing are inactive for several months during underwater hibernation and use compensatory plasticity to promote ventilation upon emergence.ResultsUsing ex vivo brainstem preparations and electrophysiology, we find that hibernation in American bullfrogs reduces GABAA receptor (GABAAR) inhibition in respiratory rhythm generating circuits and motor neurons, consistent with a compensatory response to chronic inactivity. Although GABAARs are normally critical for breathing, baseline network output at warm temperatures was not affected. However, when assessed across a range of temperatures, hibernators with reduced GABAAR signaling had greater activity at cooler temperatures, enhancing respiratory motor output under conditions that otherwise strongly depress breathing.ConclusionsHibernation reduces GABAAR signaling to promote robust respiratory output only at cooler temperatures. Although frogs do not ventilate lungs during underwater hibernation, we suggest this would be beneficial for stabilizing breathing when the animal passes through a large temperature range during emergence in the spring. More broadly, these results demonstrate that compensatory synaptic plasticity can increase the operating range of circuits in harsh environments, thereby promoting adaptive behavior in conditions that suppress activity.

Tracing ALS Degeneration: Insights from Spinal Cord and Cortex Transcriptomes

Background/Objectives: Amyotrophic Lateral Sclerosis is a progressive neurodegenerative disorder characterized by the loss of upper and lower motor neurons. Key factors contributing to neuronal death include mitochondrial energy damage, oxidative stress, and excitotoxicity. The frontal cortex is crucial for action initiation, planning, and voluntary movements whereas the spinal cord facilitates communication with the brain, walking, and reflexes. By investigating transcriptome data from the frontal cortex and spinal cord, we aim to elucidate common pathological mechanisms and pathways involved in ALS for understanding the disease progression and identifying potential therapeutic targets. Methods: In this study, we quantified gene and transcript expression patterns, predicted variants, and assessed their functional effects using computational tools. It also includes predicting variant-associated regulatory effects, constructing functional interaction networks, and performing a gene enrichment analysis. Results: We found novel genes for the upregulation of immune response, and the downregulation of metabolic-related and defective degradation processes in both the spinal cord and frontal cortex. Additionally, we observed the dysregulation of histone regulation and blood pressure-related genes specifically in the frontal cortex. Conclusions: These results highlight the distinct and shared molecular disruptions in ALS, emphasizing the critical roles of immune response and metabolic dysfunction in neuronal degeneration. Targeting these pathways may provide new therapeutic avenues to combat neurodegeneration and preserve neuronal health.

Nanoparticles encapsulating phosphatidylinositol derivatives promote neuroprotection and functional improvement in preclinical models of ALS via a long-lasting activation of TRPML1 lysosomal channel

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease currently incurable, in which motor neuron degeneration leads to voluntary skeletal muscle atrophy. Molecularly, ALS is characterized by protein aggregation, synaptic and organellar dysfunction, and Ca2+ dyshomeostasis. Of interest, autophagy dysfunction is emerging as one of the main putative targets of ALS therapy. A tune regulation of this cleansing process is affordable by a proper stimulation of TRPML1, one of the main lysosomal channels. However, TRPML1 activation by PI(3,5)P2 has low open probability to remain in an active conformation. To overcome this drawback we developed a lipid-based formulation of PI(3,5)P2 whose putative therapeutic potential has been tested in in vitro and in vivo ALS models.Pharmacodynamic properties of PI(3,5)P2 lipid-based formulations (F1 and F2) on TRPML1 activity have been characterized by means of patch-clamp electrophysiology and Fura-2AM video-imaging in motor neuronal cells. Once selected for the ability to stabilize TRPML1 activity, the most effective preparation F1 was studied in vivo to measure neuromuscular function and survival of SOD1G93A ALS mice, thereby establishing its therapeutic profile.F1, but not PI(3,5)P2 alone, stabilized the open state of the lysosomal channel TRPML1 and increased the persistence of intracellular calcium concentration ([Ca2+]i). Then, F1 was effective in delaying motor neuron loss, improving innervated endplants and muscle performance in SOD1G93A mice, extending overall lifespan by an average of 10 days. Of note F1 prevented gliosis and autophagy dysfunction in ALS mice by restoring PI(3,5)P2 level.Our novel self-assembling lipidic formulation for PI(3,5)P2 delivery exerts a neuroprotective effect in preclinical models of ALS mainly regulating dysfunctional autophagy through TRPML1 activity stabilization.

Axon demyelination and degeneration in a zebrafish spastizin model of hereditary spastic paraplegia.

Hereditary spastic paraplegias (HSPs) are a diverse set of neurological disorders characterized by progressive spasticity and weakness in the lower limbs caused by damage to the axons of the corticospinal tract. More than 88 genetic mutations have been associated with HSP, yet the mechanisms underlying these disorders are not well understood. We replicated the pathophysiology of one form of HSP known as spastic paraplegia 15 (SPG15) in zebrafish. This disorder is caused in humans by mutations in the ZFYVE26 gene, which codes for a protein called SPASTIZIN. We show that, in zebrafish, the significant reduction of Spastizin caused degeneration of large motor neurons. Motor neuron degeneration is associated with axon demyelination in the spinal cord and impaired locomotion in the spastizin mutants. Our findings reveal that the reduction in Spastizin compromises axonal integrity and affects the myelin sheath, ultimately recapitulating the pathophysiology of HSPs.