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Magnesium (Mg) is a vital element for various metabolic and physiological functions in the human body, including its crucial role in skeletal muscle health. Hypomagnesaemia is frequently reported in many muscle diseases, and it also seems to contribute to the pathogenesis of skeletal muscle impairment in patients with neuromuscular diseases. The aim of this scoping review is to analyze the role of Mg in skeletal muscle, particularly its biological effects on muscle tissue in neuromuscular diseases (NMDs) in terms of biological effects and clinical implications. This scoping review followed the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews) guidelines. From the 305 studies identified, 20 studies were included: 4 preclinical and 16 clinical studies. Preclinical research has demonstrated that Mg plays a critical role in modulating pathways affecting skeletal muscle homeostasis and oxidative stress in muscles. Clinical studies have shown that Mg supplementation can improve muscle mass, respiratory muscle strength, and exercise recovery and reduce muscle soreness and inflammation in athletes and patients with various conditions. Despite the significant role of Mg in muscle health, there is a lack of research on Mg supplementation in NMDs. Given the potential similarities in pathogenic mechanisms between NMDs and Mg deficiency, further studies on the effects of Mg supplementation in NMDs are warranted. Overall, maintaining optimal Mg levels through dietary intake or supplementation may have important implications for improving muscle health and function, particularly in conditions associated with muscle weakness and atrophy.

In vivo, muscle and neuronal cells are post-mitotic, and their function is predominantly regulated by proteostasis, a multilayer molecular process that maintains a delicate balance of protein homeostasis. The ubiquitin-proteasome system (UPS) is a key regulator of proteostasis. A dysfunctional UPS is a hallmark of muscle ageing and is often impacted in neuromuscular disorders (NMDs). Malfunction of the UPS often results in aberrant protein accumulation which can lead to protein aggregation and/or mis-localization affecting its function. Deubiquitinating enzymes (DUBs) are key players in the UPS, controlling protein turnover and maintaining the free ubiquitin pool. Several mutations in DUB encoding genes are linked to human NMDs, such as ATXN3, OTUD7A, UCHL1 and USP14, whilst other NMDs are associated with dysregulation of DUB expression. USP5, USP9X and USP14 are implicated in synaptic transmission and remodeling at the neuromuscular junction. Mice lacking USP19 show increased maintenance of lean muscle mass. In this review, we highlight the involvement of DUBs in muscle physiology and NMDs, particularly in processes affecting muscle regeneration, degeneration and inflammation following muscle injury. DUBs have recently garnered much respect as promising drug targets, and their roles in muscle maturation, regeneration and degeneration may provide the framework for novel therapeutics to treat muscular disorders including NMDs, sarcopenia and cachexia., (© 2024 The Author(s).)

Cytoplasmic and nuclear iron-sulfur (Fe-S) enzymes that are essential for genome maintenance and replication depend on the cytoplasmic Fe-S assembly (CIA) machinery for cluster acquisition. The core of the CIA machinery consists of a complex of CIAO1, MMS19 and FAM96B. The physiological consequences of loss of function in the components of the CIA pathway have thus far remained uncharacterized. Our study revealed that patients with biallelic loss of function in CIAO1 developed proximal and axial muscle weakness, fluctuating creatine kinase elevation, and respiratory insufficiency. In addition, they presented with CNS symptoms including learning difficulties and neurobehavioral comorbidities, along with iron deposition in deep brain nuclei, mild normocytic to macrocytic anemia, and gastrointestinal symptoms. Mutational analysis revealed reduced stability of the variants compared with WT CIAO1. Functional assays demonstrated failure of the variants identified in patients to recruit Fe-S recipient proteins, resulting in compromised activities of DNA helicases, polymerases, and repair enzymes that rely on the CIA complex to acquire their Fe-S cofactors. Lentivirus-mediated restoration of CIAO1 expression reversed all patient-derived cellular abnormalities. Our study identifies CIAO1 as a human disease gene and provides insights into the broader implications of the cytosolic Fe-S assembly pathway in human health and disease.

Neuromuscular diseases encompass a heterogeneous array of disorders characterized by varying onset ages, clinical presentations, severity, and progression. While these conditions can stem from acquired or inherited causes, this review specifically focuses on disorders arising from genetic abnormalities, excluding metabolic conditions. The pathogenic defect may primarily affect the anterior horn cells, the axonal or myelin component of peripheral nerves, the neuromuscular junction, or skeletal and/or cardiac muscles. While inherited neuromuscular disorders have been historically deemed not treatable, the advent of gene-based and molecular therapies is reshaping the treatment landscape for this group of condition. With the caveat that many products still fail to translate the positive results obtained in pre-clinical models to humans, both the technological development (e.g., implementation of tissue-specific vectors) as well as advances on the knowledge of pathogenetic mechanisms form a collective foundation for potentially curative approaches to these debilitating conditions. This review delineates the current panorama of therapies targeting the most prevalent forms of inherited neuromuscular diseases, emphasizing approved treatments and those already undergoing human testing, offering insights into the state-of-the-art interventions., (© 2024. The Author(s).)

Motor neuron (MN) demise is a hallmark of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Post-transcriptional gene regulation can control RNA's fate, and defects in RNA processing are critical determinants of MN degeneration. N 6 -methyladenosine (m 6 A) is a post-transcriptional RNA modification that controls diverse aspects of RNA metabolism. To assess the m 6 A requirement in MNs, we depleted the m 6 A methyltransferase-like 3 (METTL3) in cells and mice. METTL3 depletion in embryonic stem cell-derived MNs has profound and selective effects on survival and neurite outgrowth. Mice with cholinergic neuron-specific METTL3 depletion display a progressive decline in motor behavior, accompanied by MN loss and muscle denervation, culminating in paralysis and death. Reader proteins convey m 6 A effects, and their silencing phenocopies METTL3 depletion. Among the m 6 A targets, we identified transactive response DNA-binding protein 43 (TDP-43) and discovered that its expression is under epitranscriptomic control. Thus, impaired m 6 A signaling disrupts MN homeostasis and triggers neurodegeneration conceivably through TDP-43 deregulation., Competing Interests: Declaration of interests F.L. is a co-founder and president of a startup company working on antisense oligonucleotide therapeutics., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Bi-allelic variants in VWA1, encoding Von Willebrand Factor A domain containing 1 protein localized to the extracellular matrix (ECM), were linked to a neuromuscular disorder with manifestation in child- or adulthood. Clinical findings indicate a neuromyopathy presenting with muscle weakness. Given that pathophysiological processes are still incompletely understood, and biomarkers are still missing, we aimed to identify blood biomarkers of pathophysiological relevance: white blood cells (WBC) and plasma derived from six VWA1-patients were investigated by proteomics. Four proteins, BET1, HNRNPDL, NEFM and PHGDH, known to be involved in neurological diseases and dysregulated in WBC were further validated by muscle-immunostainings unravelling HNRNPDL as a protein showing differences between VWA1-patients, healthy controls and patients suffering from neurogenic muscular atrophy and BICD2-related neuromyopathy. Immunostaining studies of PHGDH indicate its involvement in apoptotic processes via co-localisation with caspase-3. NEFM showed an increase in cells within the ECM in biopsies of all patients studied. Plasma proteomics unravelled dysregulation of 15 proteins serving as biomarker candidates among which a profound proportion of increased ones (6/11) are mostly related to antioxidative processes and have even partially been described as blood biomarkers for other entities of neuromuscular disorders before. CRP elevated in plasma also showed an increase in the extracellular space of VWA1-mutant muscle. Results of our combined studies for the first time describe pathophysiologically relevant biomarkers for VWA1-related neuromyopathy and suggest that VWA1-patient derived blood might hold the potential to study disease processes of clinical relevance, an important aspect for further preclinical studies., (© 2024 The Authors. Journal of Cellular and Molecular Medicine published by Foundation for Cellular and Molecular Medicine and John Wiley & Sons Ltd.)

The Blood-Brain Barrier (BBB) is a selective structural and functional barrier between the circulatory system and the cerebral environment, playing an essential role in maintaining cerebral homeostasis by limiting the passage of harmful molecules. Exosomes, nanovesicles secreted by virtually all cell types into body fluids, have emerged as a major mediator of intercellular communication. Notably, these vesicles can cross the BBB and regulate its physiological functions. However, the precise molecular mechanisms by which exosomes regulate the BBB remain unclear. Recent research studies focused on the effect of exosomes on the BBB, particularly in the context of their involvement in the onset and progression of various cerebral disorders, including solid and metastatic brain tumors, stroke, neurodegenerative, and neuroinflammatory diseases. This review focuses on discussing and summarizing the current knowledge about the role of exosomes in the physiological and pathological modulation of the BBB. A better understanding of this regulation will improve our understanding of the pathogenesis of cerebral diseases and will enable the design of effective treatment strategies.

Water transport across the biological membranes is mediated by aquaporins (AQPs). AQP4 and AQP1 are the predominantly expressed AQPs in the skeletal muscle. Since the discovery of AQP4, several studies have highlighted reduced AQP4 levels in Duchenne muscular dystrophy (DMD) patients and mouse models, and other neuromuscular disorders (NMDs) such as sarcoglycanopathies and dysferlinopathies. AQP4 loss is attributed to the destabilizing dystrophin-associated protein complex (DAPC) in DMD leading to compromised water permeability in the skeletal muscle fibers. However, AQP4 knockout (KO) mice appear phenotypically normal. AQP4 ablation does not impair physical activity in mice but limits them from achieving the performance demonstrated by wild-type mice. AQP1 levels were found to be upregulated in DMD models and are thought to compensate for AQP4 loss. Several groups investigated the expression of other AQPs in the skeletal muscle; however, these findings remain controversial. In this review, we summarize the role of AQP4 with respect to skeletal muscle function and findings in NMDs as well as the implications from a clinical perspective.

Neuromuscular disorders (NMDs) are a large group of diseases associated with either alterations of skeletal muscle fibers, motor neurons or neuromuscular junctions. Most of these diseases is characterized with muscle weakness or wasting and greatly alter the life of patients. Animal models do not always recapitulate the phenotype of patients. The development of innovative and representative human preclinical models is thus strongly needed for modeling the wide diversity of NMDs, characterization of disease-associated variants, investigation of novel genes function, or the development of therapies. Over the last decade, the use of patient's derived induced pluripotent stem cells (hiPSC) has resulted in tremendous progress in biomedical research, including for NMDs. Skeletal muscle is a complex tissue with multinucleated muscle fibers supported by a dense extracellular matrix and multiple cell types including motor neurons required for the contractile activity. Major challenges need now to be tackled by the scientific community to increase maturation of muscle fibers in vitro, in particular for modeling adult-onset diseases affecting this tissue (neuromuscular disorders, cachexia, sarcopenia) and the evaluation of therapeutic strategies. In the near future, rapidly evolving bioengineering approaches applied to hiPSC will undoubtedly become highly instrumental for investigating muscle pathophysiology and the development of therapeutic strategies.

Poliomyelitis-like illness is a common clinical manifestation of neurotropic viral infections. Functional loss and death of motor neurons often lead to reduced muscle tone and paralysis, causing persistent motor sequelae among disease survivors. Despite several reports demonstrating the molecular basis of encephalopathy, the pathogenesis behind virus-induced flaccid paralysis remained largely unknown. The present study for the first time aims to elucidate the mechanism responsible for limb paralysis by studying clinical isolates of Japanese encephalitis virus (JEV) and Chandipura virus (CHPV) responsible for causing acute flaccid paralysis (AFP) in vast regions of Southeast Asia and the Indian subcontinent. An experimental model for studying virus-induced AFP was generated by intraperitoneal injection of 10-day-old BALB/c mice. Progressive decline in motor performance of infected animals was observed, with paralysis being correlated with death of motor neurons (MNs). Furthermore, we demonstrated that upon infection, MNs undergo an extrinsic apoptotic pathway in a RIG-I-dependent fashion via transcription factors pIRF-3 and pIRF-7. Both gene-silencing experiments using specific RIG-I-short interfering RNA and in vivo morpholino abrogated cellular apoptosis, validating the important role of pattern recognition receptor (PRR) RIG-I in MN death. Hence, from our experimental observations, we hypothesize that host innate response plays a significant role in deterioration of motor functioning upon neurotropic virus infections. IMPORTANCE Neurotropic viral infections are an increasingly common cause of immediate or delayed neuropsychiatric sequelae, cognitive impairment, and movement disorders or, in severe cases, death. Given the highest reported disability-adjusted life years and mortality rate worldwide, a better understanding of molecular mechanisms for underlying clinical manifestations like AFP will help in development of more effective tools for therapeutic solutions.

Neuromuscular diseases (NMDs) are dysfunctions that involve skeletal muscle and cause incorrect communication between the nerves and muscles. The specific causes of NMDs are not well known, but most of them are caused by genetic mutations. NMDs are generally progressive and entail muscle weakness and fatigue. Muscular impairments can differ in onset, severity, prognosis, and phenotype. A multitude of possible injury sites can make diagnosis of NMDs difficult. Mitochondria are crucial for cellular homeostasis and are involved in various metabolic pathways; for this reason, their dysfunction can lead to the development of different pathologies, including NMDs. Most NMDs due to mitochondrial dysfunction have been associated with mutations of genes involved in mitochondrial biogenesis and metabolism. This review is focused on some mitochondrial routes such as the TCA cycle, OXPHOS, and β-oxidation, recently found to be altered in NMDs. Particular attention is given to the alterations found in some genes encoding mitochondrial carriers, proteins of the inner mitochondrial membrane able to exchange metabolites between mitochondria and the cytosol. Briefly, we discuss possible strategies used to diagnose NMDs and therapies able to promote patient outcome.

Mitochondrial diseases are caused by variants in both mitochondrial and nuclear genomes. A nuclear gene HPDL (4-hydroxyphenylpyruvate dioxygenase-like), which encodes an intermembrane mitochondrial protein, has been recently implicated in causing a neurodegenerative disease characterized by pediatric-onset spastic movement phenotypes. Here, we report six Chinese patients with bi-allelic HPDL pathogenic variants from four unrelated families showing neuropathic symptoms of variable severity, including developmental delay/intellectual disability, spasm, and hypertonia. Seven different pathogenic variants are identified, of which five are novel. Both fibroblasts and immortalized lymphocytes derived from patients show impaired mitochondrial respiratory function, which is also observed in HPDL-knockdown (KD) HeLa cells. In these HeLa cells, overexpression of a wild-type HPDL gene can rescue the respiratory phenotype of oxygen consumption rate. In addition, a decreased activity of the oxidative phosphorylation (OXPHOS) complex II is observed in patient-derived lymphocytes and HPDL-KD HeLa cells, further supporting an essential role of HPDL in the mitochondrial respiratory chain. Collectively, our data expand the clinical and mutational spectra of this mitochondrial neuropathy and further delineate the possible disease mechanism involving the impairment of the OXPHOS complex II activity due to the bi-allelic inactivations of HPDL., (Copyright © 2021 Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, and Genetics Society of China. Published by Elsevier Ltd. All rights reserved.)

Mitochondrial dysfunction is considered the major contributor to skeletal muscle wasting in different conditions. Genetically determined neuromuscular disorders occur as a result of mutations in the structural proteins of striated muscle cells and therefore are often combined with cardiac phenotype, which most often manifests as a cardiomyopathy. The specific roles played by mitochondria and mitochondrial energetic metabolism in skeletal muscle under muscle-wasting conditions in cardiomyopathies have not yet been investigated in detail, and this aspect of genetic muscle diseases remains poorly characterized. This review will highlight dysregulation of mitochondrial representation and bioenergetics in specific skeletal muscle disorders caused by mutations that disrupt the structural and functional integrity of muscle cells.

Amyloidosis refers to an etiologically heterogeneous group of protein misfolding diseases, pathologically characterized by extracellular amyloid fibrils producing congophillic amorphous deposits in organs and tissues, which may lead to severe organ dysfunction and mortality. Clinical presentations vary and are often nonspecific, depending on what organs or tissues are affected. In systemic amyloidosis, the peripheral nervous system is commonly affected, whereas the skeletal muscles are only rarely involved. Immunoglobulin light chain (AL) amyloidosis and hereditary transthyretin (ATTRv) amyloidosis are the most frequent types of systemic amyloidosis involving the neuromuscular system. Localized amyloidosis can occur in skeletal muscle, so-called isolated amyloid myopathy. Amyloid neuropathy typically involves small myelinated and unmyelinated sensory and autonomic nerve fibers early in the course of the disease, followed by large myelinated fiber sensory and motor deficits. The relentlessly progressive nature with motor, painful sensory and severe autonomic dysfunction, profound weight loss, and systemic features are distinct characteristics of amyloid neuropathy. Amyloid myopathy presentation differs between systemic amyloidosis and isolated amyloid myopathy. Long-standing symptoms, distal predominant myopathy, markedly elevated creatine kinase level, and lack of peripheral neuropathy or systemic features are highly suggestive of isolated amyloid myopathy. In ATTR and AL amyloidosis, early treatment correlates with favorable outcomes. Therefore, awareness of these disorders and active screening for amyloidosis in patients with neuropathy or myopathy are crucial in detecting these patients in the everyday practice of neuromuscular medicine. Herein, we review the clinical manifestations of neuromuscular amyloidosis and provide a diagnostic approach to this disorder., (© 2021 Wiley Periodicals LLC.)

The neuromuscular junction (NMJ) is the peripheral synapse formed between a motor neuron axon terminal and a muscle fibre. NMJs are thought to be the primary site of peripheral pathology in many neuromuscular diseases, but innervation/denervation status is often assessed qualitatively with poor systematic criteria across studies, and separately from 3D morphological structure. Here, we describe the development of 'NMJ-Analyser', to comprehensively screen the morphology of NMJs and their corresponding innervation status automatically. NMJ-Analyser generates 29 biologically relevant features to quantitatively define healthy and aberrant neuromuscular synapses and applies machine learning to diagnose NMJ degeneration. We validated this framework in longitudinal analyses of wildtype mice, as well as in four different neuromuscular disease models: three for amyotrophic lateral sclerosis (ALS) and one for peripheral neuropathy. We showed that structural changes at the NMJ initially occur in the nerve terminal of mutant TDP43 and FUS ALS models. Using a machine learning algorithm, healthy and aberrant neuromuscular synapses are identified with 95% accuracy, with 88% sensitivity and 97% specificity. Our results validate NMJ-Analyser as a robust platform for systematic and structural screening of NMJs, and pave the way for transferrable, and cross-comparison and high-throughput studies in neuromuscular diseases.

Inflammasomes are molecular hubs that are assembled and activated by a host in response to various microbial and non-microbial stimuli and play a pivotal role in maintaining tissue homeostasis. The NLRP3 is a highly promiscuous inflammasome that is activated by a wide variety of sterile triggers, including misfolded protein aggregates, and drives chronic inflammation via caspase-1-mediated proteolytic cleavage and secretion of proinflammatory cytokines, interleukin-1β and interleukin-18. These cytokines further amplify inflammatory responses by activating various signaling cascades, leading to the recruitment of immune cells and overproduction of proinflammatory cytokines and chemokines, resulting in a vicious cycle of chronic inflammation and tissue damage. Neuromuscular diseases are a heterogeneous group of muscle disorders that involve injury or dysfunction of peripheral nerves, neuromuscular junctions and muscles. A growing body of evidence suggests that dysregulation, impairment or aberrant NLRP3 inflammasome signaling leads to the initiation and exacerbation of pathological processes associated with neuromuscular diseases. In this review, we summarize the available knowledge about the NLRP3 inflammasome in neuromuscular diseases that affect the peripheral nervous system and amyotrophic lateral sclerosis, which affects the central nervous system. In addition, we also examine whether therapeutic targeting of the NLRP3 inflammasome components is a viable approach to alleviating the detrimental phenotype of neuromuscular diseases and improving clinical outcomes.

GDP-mannose-pyrophosphorylase-B (GMPPB) facilitates the generation of GDP-mannose, a sugar donor required for glycosylation. GMPPB defects cause muscle disease due to hypoglycosylation of α-dystroglycan (α-DG). Alpha-DG is part of a protein complex, which links the extracellular matrix with the cytoskeleton, thus stabilizing myofibers. Mutations of the catalytically inactive homolog GMPPA cause alacrima, achalasia, and mental retardation syndrome (AAMR syndrome), which also involves muscle weakness. Here, we showed that Gmppa-KO mice recapitulated cognitive and motor deficits. As structural correlates, we found cortical layering defects, progressive neuron loss, and myopathic alterations. Increased GDP-mannose levels in skeletal muscle and in vitro assays identified GMPPA as an allosteric feedback inhibitor of GMPPB. Thus, its disruption enhanced mannose incorporation into glycoproteins, including α-DG in mice and humans. This increased α-DG turnover and thereby lowered α-DG abundance. In mice, dietary mannose restriction beginning after weaning corrected α-DG hyperglycosylation and abundance, normalized skeletal muscle morphology, and prevented neuron degeneration and the development of motor deficits. Cortical layering and cognitive performance, however, were not improved. We thus identified GMPPA defects as the first congenital disorder of glycosylation characterized by α-DG hyperglycosylation, to our knowledge, and we have unraveled underlying disease mechanisms and identified potential dietary treatment options.

Skeletal muscle formation is a complex process that requires tight spatiotemporal control of key myogenic factors. Emerging evidence suggests that RNA processing is crucial for the regulation of these factors, and that multiple post-transcriptional regulatory pathways work dependently and independently of one another to enable precise control of transcripts throughout muscle development and repair. Moreover, disruption of these pathways is implicated in neuromuscular disease, and the recent development of RNA-mediated therapies shows enormous promise in the treatment of these disorders. We discuss the overlapping post-transcriptional regulatory pathways that mediate muscle development, how these pathways are disrupted in neuromuscular disorders, and advances in RNA-mediated therapies that present a novel approach to the treatment of these diseases., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Tripartite motif (TRIM) proteins are RING E3 ubiquitin ligases defined by a shared domain structure. Several of them are implicated in rare genetic diseases, and mutations in TRIM32 and TRIM-like malin are associated with Limb-Girdle Muscular Dystrophy R8 and Lafora disease, respectively. These two proteins are evolutionary related, share a common ancestor, and both display NHL repeats at their C-terminus. Here, we revmniew the function of these two related E3 ubiquitin ligases discussing their intrinsic and possible common pathophysiological pathways.

Duchenne muscular dystrophy (DMD) affects 1 in 3500 live male births. To date, there is no effective cure for DMD, and the identification of novel molecular targets involved in disease progression is important to design more effective treatments and therapies to alleviate DMD symptoms. Here, we show that protein levels of the Bromodomain and extra-terminal domain (BET) protein BRD4 are significantly increased in the muscle of the mouse model of DMD, the mdx mouse, and that pharmacological inhibition of the BET proteins has a beneficial outcome, tempering oxidative stress and muscle damage. Alterations in reactive oxygen species (ROS) metabolism are an early event in DMD onset and they are tightly linked to inflammation, fibrosis, and necrosis in skeletal muscle. By restoring ROS metabolism, BET inhibition ameliorates these hallmarks of the dystrophic muscle, translating to a beneficial effect on muscle function. BRD4 direct association to chromatin regulatory regions of the NADPH oxidase subunits increases in the mdx muscle and JQ1 administration reduces BRD4 and BRD2 recruitment at these regions. JQ1 treatment reduces NADPH subunit transcript levels in mdx muscles, isolated myofibers and DMD immortalized myoblasts. Our data highlight novel functions of the BET proteins in dystrophic skeletal muscle and suggest that BET inhibitors may ameliorate the pathophysiology of DMD.

The RYR1 gene, which encodes the sarcoplasmic reticulum calcium release channel or type 1 ryanodine receptor (RyR1) of skeletal muscle, was sequenced in 1988 and RYR1 variations that impair calcium homeostasis and increase susceptibility to malignant hyperthermia were first identified in 1991. Since then, RYR1-related myopathies (RYR1-RM) have been described as rare, histopathologically and clinically heterogeneous, and slowly progressive neuromuscular disorders. RYR1 variants can lead to dysfunctional RyR1-mediated calcium release, malignant hyperthermia susceptibility, elevated oxidative stress, deleterious post-translational modifications, and decreased RyR1 expression. RYR1-RM-affected individuals can present with delayed motor milestones, contractures, scoliosis, ophthalmoplegia, and respiratory insufficiency.Historically, RYR1-RM-affected individuals were diagnosed based on morphologic features observed in muscle biopsies including central cores, cores and rods, central nuclei, fiber type disproportion, and multi-minicores. However, these histopathologic features are not always specific to RYR1-RM and often change over time. As additional phenotypes were associated with RYR1 variations (including King-Denborough syndrome, exercise-induced rhabdomyolysis, lethal multiple pterygium syndrome, adult-onset distal myopathy, atypical periodic paralysis with or without myalgia, mild calf-predominant myopathy, and dusty core disease) the overlap among diagnostic categories is ever increasing. With the continuing emergence of new clinical subtypes along the RYR1 disease spectrum and reports of adult-onset phenotypes, nuanced nomenclatures have been reported (RYR1- [related, related congenital, congenital] myopathies). In this narrative review, we provide historical highlights of RYR1 research, accounts of the main diagnostic disease subtypes and propose RYR1-related disorders (RYR1-RD) as a unified nomenclature to describe this complex and evolving disease spectrum.

A hallmark of neurodegeneration is defective protein quality control. The E3 ligase Listerin (LTN1/Ltn1) acts in a specialized protein quality control pathway-Ribosome-associated Quality Control (RQC)-by mediating proteolytic targeting of incomplete polypeptides produced by ribosome stalling, and Ltn1 mutation leads to neurodegeneration in mice. Whether neurodegeneration results from defective RQC and whether defective RQC contributes to human disease have remained unknown. Here we show that three independently-generated mouse models with mutations in a different component of the RQC complex, NEMF/Rqc2, develop progressive motor neuron degeneration. Equivalent mutations in yeast Rqc2 selectively interfere with its ability to modify aberrant translation products with C-terminal tails which assist with RQC-mediated protein degradation, suggesting a pathomechanism. Finally, we identify NEMF mutations expected to interfere with function in patients from seven families presenting juvenile neuromuscular disease. These uncover NEMF's role in translational homeostasis in the nervous system and implicate RQC dysfunction in causing neurodegeneration.

Spinal muscular atrophy (SMA) occurs as a result of cell-ubiquitous depletion of the essential survival motor neuron (SMN) protein. Characteristic disease pathology is driven by a particular vulnerability of the ventral motor neurons of the spinal cord to decreased SMN. Perhaps not surprisingly, many other organ systems are also impacted by SMN depletion. The normal kidney expresses very high levels of SMN protein, equivalent to those found in the nervous system and liver, and levels are dramatically lowered by ~90-95% in mouse models of SMA. Taken together, these data suggest that renal pathology may be present in SMA. We have addressed this using an established mouse model of severe SMA. Nephron number, as assessed by gold standard stereological techniques, was significantly reduced. In addition, morphological assessment showed decreased renal vasculature, particularly of the glomerular capillary knot, dysregulation of nephrin and collagen IV, and ultrastructural changes in the trilaminar filtration layers of the nephron. To explore the molecular drivers underpinning this process, we correlated these findings with quantitative PCR measurements and protein analyses of glial cell-line-derived neurotrophic factor, a crucial factor in ureteric bud branching and subsequent nephron development. Glial cell-line-derived neurotrophic factor levels were significantly reduced at early stages of disease in SMA mice. Collectively, these findings reveal significant renal pathology in a mouse model of severe SMA, further reinforcing the need to develop and administer systemic therapies for this neuromuscular disease., (© The Author(s) 2020. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Inborn errors of Riboflavin (Rf) transport and metabolism have been recently related to severe human neuromuscular disorders, as resulting in profound alteration of human flavoproteome and, therefore, of cellular bioenergetics. This explains why the interest in studying the "flavin world", a topic which has not been intensively investigated before, has increased much over the last few years. This also prompts basic questions concerning how Rf transporters and FAD (flavin adenine dinucleotide) -forming enzymes work in humans, and how they can create a coordinated network ensuring the maintenance of intracellular flavoproteome. The concept of a coordinated cellular "flavin network", introduced long ago studying humans suffering for Multiple Acyl-CoA Dehydrogenase Deficiency (MADD), has been, later on, addressed in model organisms and more recently in cell models. In the frame of the underlying relevance of a correct supply of Rf in humans and of a better understanding of the molecular rationale of Rf therapy in patients, this review wants to deal with theories and existing experimental models in the aim to potentiate possible therapeutic interventions in Rf-related neuromuscular diseases.

Alongside playing structural roles, the extracellular matrix (ECM) acts as an interaction platform for cellular homeostasis, organ development, and maintenance. The necessity of the ECM is highlighted by the diverse, sometimes very serious diseases that stem from defects in its components. The neuromuscular junction (NMJ) is a large peripheral motor synapse differing from its central counterparts through the ECM included at the synaptic cleft. Such synaptic basal lamina (BL) is specialized to support NMJ establishment, differentiation, maturation, stabilization, and function and diverges in molecular composition from the extrasynaptic ECM. Mutations, toxins, and autoantibodies may compromise NMJ integrity and function, thereby leading to congenital myasthenic syndromes (CMSs), poisoning, and autoimmune diseases, respectively, and all these conditions may involve synaptic ECM molecules. With neurotransmission degraded or blocked, muscle function is impaired or even prevented. At worst, this can be fatal. The article reviews the synaptic BL composition required for assembly and function of the NMJ molecular machinery through the lens of studies primarily with mouse models but also with human patients. In-depth focus is given to collagen XIII, a postsynaptic-membrane-spanning but also shed ECM protein that in recent years has been revealed to be a significant component for the NMJ. Its deficiency in humans causes CMS, and autoantibodies against it have been recognized in autoimmune myasthenia gravis. Mouse models have exposed numerous details that appear to recapitulate human NMJ phenotypes relatively faithfully and thereby can be readily used to generate information necessary for understanding and ultimately treating human diseases. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc., (© 2019 Wiley Periodicals, Inc.)

Skeletal muscle and the nervous system depend on efficient protein quality control, and they express chaperones and cochaperones at high levels to maintain protein homeostasis. Mutations in many of these proteins cause neuromuscular diseases, myopathies, and hereditary motor and sensorimotor neuropathies. In this review, we cover mutations in DNAJB6, DNAJB2, αB-crystallin (CRYAB, HSPB5), HSPB1, HSPB3, HSPB8, and BAG3, and discuss the molecular mechanisms by which they cause neuromuscular disease. In addition, previously unpublished results are presented, showing downstream effects of BAG3 p.P209L on DNAJB6 turnover and localization., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Immunohistochemistry- and/or immunofluorescence-based analysis of muscular proteins represents a standard procedure in the diagnostic management of patients suffering from neuromuscular diseases such as "Caveolinopathies" which are caused by mutations in the CAV3 gene encoding for caveolin-3. Human caveolin-3 is a 151 amino acid sized transmembrane protein localized within caveolae, predominantly expressed in cardiac and skeletal muscle cells and involved in a diversity of cellular functions crucial for muscle cell homeostasis. Loss of caveolin-3 protein abundance is indicative for the presence of pathogenic mutations within the corresponding gene and thus for the diagnosis of "Caveolinopathies." Moreover, description of abnormal immunoreactivity findings for the caveolin-3 protein is increasing in the context of other neuromuscular diseases suggesting that profound knowledge of abnormal caveolin-3-expression and/or distribution findings can be decisive also for the diagnosis of other neurological diseases as well as for a better understanding of the biology of the protein. Here, we summarize the current knowledge about the caveolin-3, report on a protocol for immunofluorescence-based analysis of the protein in the diagnostic workup of neuromuscular patients-also considering problems encountered-and confirm as well as summarize already published abnormal histological findings in muscular pathologies beyond "Caveolinopathies."

The bioactive sphingolipid metabolite, sphingosine 1-phosphate (S1P), and the signaling pathways triggered by its binding to specific G protein-coupled receptors play a critical regulatory role in many pathophysiological processes, including skeletal muscle and nervous system degeneration. The signaling transduced by S1P binding appears to be much more complex than previously thought, with important implications for clinical applications and for personalized medicine. In particular, the understanding of S1P/S1P receptor signaling functions in specific compartmentalized locations of the cell is worthy of being better investigated, because in various circumstances it might be crucial for the development or/and the progression of neuromuscular diseases, such as Charcot-Marie-Tooth disease, myasthenia gravis, and Duchenne muscular dystrophy.

Dynamin 2 (DNM2) encodes a ubiquitously expressed large GTPase with membrane fission capabilities that participates in the endocytosis of clathrin-coated vesicles. Heterozygous mutations in DNM2 are associated with two distinct neuromuscular disorders, Charcot-Marie-Tooth disease (CMT) and autosomal dominant centronuclear myopathy (CNM). Despite extensive investigations in cell culture, the role of dynamin 2 in normal muscle development is poorly understood and the consequences of DNM2 mutations at the molecular level in vivo are not known. To address these gaps in knowledge, we developed transgenic zebrafish expressing either wild-type dynamin 2 or dynamin 2 with either a CNM or CMT mutation. Taking advantage of the live imaging capabilities of the zebrafish embryo, we establish the localization of wild-type and mutant dynamin 2 in vivo, showing for the first time distinctive dynamin 2 subcellular compartments. Additionally, we demonstrate that CNM-related DNM2 mutations are associated with protein mislocalization and aggregation. Lastly, we define core phenotypes associated with our transgenic mutant fish, including impaired motor function and altered muscle ultrastructure, making them the ideal platform for drug screening. Overall, using the power of the zebrafish, we establish novel insights into dynamin 2 localization and dynamics and provide the necessary groundwork for future studies examining dynamin 2 pathomechanisms and therapy development., (© The Author(s) 2019. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

The high level of complexity underlying the heterogeneous pathophysiology of neuromuscular diseases is a fundamental limiting factor in understanding the role of physical activity in their onset and/or clinical evolution. To overcome this difficulty, it is essential to rely on and deep knowledge of the aetiology and on the physiological adaptations to physical exercise, in order to predict how they can impact on the clinical history of each disease. This paper illustrates the possible strategies of intervention in some neuromuscular disorders, through the analysis of their supposed pathogenic mechanisms. Nevertheless, no clear conclusions can be inferred so far., (©2019 Gaetano Conte Academy - Mediterranean Society of Myology, Naples, Italy.)

We previously identified DNAJC11, a mitochondrial outer membrane protein of unknown function, as a novel genetic cause in modeled neuromuscular disease. To understand the physiological role of DNAJC11, we employed a proteomic approach for the identification of the DNAJC11 interactome, through the expression of DNAJC11-FLAG in HEK293FT cells and transgenic mice. Our analysis confirmed known DNAJC11-interacting proteins including members of the MICOS complex that organize mitochondrial cristae formation. Moreover, we identified in both biological systems novel mitochondrial interactions including VDACs that exchange metabolites across the outer mitochondrial membrane. In HEK293FT cells, DNAJC11 preferentially interacted with ribosomal subunits and chaperone proteins including Hsp70 members, possibly correlating DNAJC11 with cotranslational folding and import of mitochondrial proteins in metabolically active cells. Instead, the DNAJC11 interactome in the mouse cerebrum was enriched for synaptic proteins, supporting the importance of DNAJC11 in synapse and neuronal integrity. Moreover, we demonstrated that the DUF3395 domain is critically involved in DNAJC11 protein-protein interactions, while the J-domain determines its mitochondrial localization. Collectively, these results provide a functional characterization for DNAJC11 domains, while the identified interactome networks reveal an emerging role of DNAJC11 in mitochondrial biogenesis and response to microenvironment changes and requirements.

Autophagy is the major intracellular machinery for degrading proteins, lipids, polysaccharides, and organelles. This cellular process is essential for the maintenance of the correct cellular balance in both physiological and stress conditions. Because of its role in maintaining cellular homeostasis, dysregulation of autophagy leads to various disease manifestations, such as inflammation, metabolic alterations, aging, and neurodegeneration. A common feature of many neurologic and neuromuscular diseases is the alteration of the autophagy-lysosomal pathways. For this reason, autophagy is considered a target for the prevention and/or cure of these diseases. Dietary intake of polyphenols has been demonstrated to prevent/ameliorate several of these diseases. Thus, natural products that can modulate the autophagy machinery are considered a promising therapeutic strategy. In particular, curcumin, a phenolic compound widely used as a dietary supplement, exerts an important effect in modulating autophagy. Herein, we report on the current knowledge concerning the role of curcumin in modulating the autophagy machinery in various neurological and neuromuscular diseases as well as its role in restoring the autophagy molecular mechanism in several cell types that have different effects on the progression of neurological and neuromuscular disorders.

Enterovirus D68 (EV-D68) is an emerging virus that has been identified as a cause of recent outbreaks of acute flaccid myelitis (AFM), a poliomyelitis-like spinal cord syndrome that can result in permanent paralysis and disability. In experimental mouse models, EV-D68 spreads to, infects, and kills spinal motor neurons following infection by various routes of inoculation. The topography of virus-induced motor neuron loss correlates with the pattern of paralysis. The mechanism(s) by which EV-D68 spreads to target motor neurons remains unclear. We sought to determine the capacity of EV-D68 to spread by the neuronal route and to determine the role of known EV-D68 receptors, sialic acid and intracellular adhesion molecule 5 (ICAM-5), in neuronal infection. To do this, we utilized a microfluidic chamber culture system in which human induced pluripotent stem cell (iPSC) motor neuron cell bodies and axons can be compartmentalized for independent experimental manipulation. We found that EV-D68 can infect motor neurons via their distal axons and spread by retrograde axonal transport to the neuronal cell bodies. Virus was not released from the axons via anterograde axonal transport after infection of the cell bodies. Prototypic strains of EV-D68 depended on sialic acid for axonal infection and transport, while contemporary circulating strains isolated during the 2014 EV-D68 outbreak did not. The pattern of infection did not correspond with the ICAM-5 distribution and expression in either human tissue, the mouse model, or the iPSC motor neurons. IMPORTANCE Enterovirus D68 (EV-D68) infections are on the rise worldwide. Since 2014, the United States has experienced biennial spikes in EV-D68-associated acute flaccid myelitis (AFM) that have left hundreds of children paralyzed. Much remains to be learned about the pathogenesis of EV-D68 in the central nervous system (CNS). Herein we investigated the mechanisms of EV-D68 CNS invasion through neuronal pathways. A better understanding of EV-D68 infection in experimental models may allow for better prevention and treatment strategies of EV-D68 CNS disease., (Copyright © 2019 American Society for Microbiology.)

Animals require different types of muscle for survival, for example for circulation, motility, reproduction and digestion. Much emphasis in the muscle field has been placed on understanding how transcriptional regulation generates diverse types of muscle during development. Recent work indicates that alternative splicing and RNA regulation are as critical to muscle development, and altered function of RNA-binding proteins causes muscle disease. Although hundreds of genes predicted to bind RNA are expressed in muscles, many fewer have been functionally characterized. We present a cross-species view summarizing what is known about RNA-binding protein function in muscle, from worms and flies to zebrafish, mice and humans. In particular, we focus on alternative splicing regulated by the CELF, MBNL and RBFOX families of proteins. We discuss the systemic nature of diseases associated with loss of RNA-binding proteins in muscle, focusing on mis-regulation of CELF and MBNL in myotonic dystrophy. These examples illustrate the conservation of RNA-binding protein function and the marked utility of genetic model systems in understanding mechanisms of RNA regulation., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Objective: The aim of this phase 2 trial was to ascertain the feasibility and effect of community-based aerobic exercise training for people with 2 of the more common neuromuscular diseases: Charcot-Marie-Tooth disease type 1A (CMT) and inclusion body myositis (IBM)., Methods: A randomized single-blinded crossover trial design was used to compare a 12-week aerobic training program using recombinant exercise bicycles compared to a control period. The training occurred 3 times per week in community gyms local to the participants. Support was available from trained gym staff and a research physiotherapist. The 2 disease groups were analyzed separately. The primary outcome measure was peak oxygen uptake (VO 2 peak) during a maximal exercise test, with secondary measures of muscle strength, function, and patient-reported measures., Results: Data from 23 people with CMT and 17 people with IBM were included in the analysis. Both disease groups had high levels of participation and demonstrated improvements in VO 2 peak, with a moderate effect size in the CMT participants (Cohen d = 0.53) and a strong effect size in the IBM group (Cohen d = 1.72). No major changes were observed in the secondary outcome measures. Qualitative interviews revealed that participants valued the support of gym instructors and the research physiotherapists in overcoming challenges to participation., Conclusion: Twelve weeks of aerobic training in community gyms was feasible, safe, and improved aerobic capacity in people with CMT and IBM., Classification of Evidence: This study provides Class II evidence that for patients with CMT type 1A and IBM, an aerobic training program increases aerobic capacity., (Copyright © 2019 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.)

Increased proteolytic activity has been widely associated with skeletal muscle atrophy. However, elevated proteolysis is also critical for the maintenance of cellular homeostasis by disposing cytotoxic proteins and non-functioning organelles. We recently demonstrated that exercise activates autophagy and re-establishes proteostasis in cardiac diseases. Here, we characterized the impact of exercise on skeletal muscle autophagy and proteostasis in a model of neurogenic myopathy induced by sciatic nerve constriction in rats. Neurogenic myopathy, characterized by progressive atrophy and impaired contractility, was paralleled by accumulation of autophagy-related markers and loss of acute responsiveness to both colchicine and chloroquine. These changes were correlated with elevated levels of damaged proteins, chaperones and pro-apoptotic markers compared to control animals. Sustained autophagy inhibition using chloroquine in rats (50 mg.kg -1 .day -1 ) or muscle-specific deletion of Atg7 in mice was sufficient to impair muscle contractility in control but not in neurogenic myopathy, suggesting that dysfunctional autophagy is critical in skeletal muscle pathophysiology. Finally, 4 weeks of aerobic exercise training (moderate treadmill running, 5x/week, 1 h/day) prior to neurogenic myopathy improved skeletal muscle autophagic flux and proteostasis. These changes were followed by spared muscle mass and better contractility properties. Taken together, our findings suggest the potential value of exercise in maintaining skeletal muscle proteostasis and slowing down the progression of neurogenic myopathy.

Skeletal muscle is critical for mobility and many metabolic functions integral to survival and long-term health. Alcohol can affect skeletal muscle physiology and metabolism, which will have immediate and long-term consequences on health. While skeletal muscle abnormalities, including morphological, biochemical, and functional impairments, are well-documented in adults that excessively consume alcohol, there is a scarcity of information about the skeletal muscle in the offspring prenatally exposed to alcohol ("prenatal alcohol exposure"; PAE). This minireview examines the available studies addressing skeletal muscle abnormalities due to PAE. Growth restriction, fetal alcohol myopathy, and abnormalities in the neuromuscular system, which contribute to deficits in locomotion, are some direct, immediate consequences of PAE on skeletal muscle morphology and function. Long-term health consequences of PAE-related skeletal abnormalities include impaired glucose metabolism in the skeletal muscle, resulting in glucose intolerance and insulin resistance, leading to an increased risk of type 2 diabetes. In general, there is limited information on the morphological, biochemical, and functional features of skeletal abnormalities in PAE offspring. There is a need to understand how PAE affects muscle growth and function at the cellular level during early development to improve the immediate and long-term health of offspring suffering from PAE.

Despite recent rapid advances in sequencing technologies, a significant proportion of patients with rare genetic disorders do not receive a genetic diagnosis after exhaustive testing, and even fewer have a potential therapeutic target identified. Taking rare neuromuscular and neurodegenerative disorders as a paradigm that can be extended to other rare Mendelian disorders, this viewpoint explores the opportunities that are brought about by the integration of genomics and proteomics, as well as the limitations and remaining challenges of this newly emerging field of proteogenomics. The relevance of combining proteomic findings with genetic results for diagnosis and gene discovery is illustrated, highlighting the insights the combined analysis provides into the underlying biology and aetiology as well as the limitations of the experimental techniques. A final discussion focuses on the importance of mechanisms to enable the sharing, reuse, and analysis of source experimental data and describes some of the international initiatives that are making progress in this area., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Bone modeling is a process that starts with fetal life and continues during adolescence. Complex factors such as hormones, nutritional and environmental factors affect this process. In addition to these factors, physical conditioning and medications that have toxic effects on bony tissue should be carefully considered in patient follow-up. Osteoporosis is a significant problem in pediatric population because of ongoing growth and development of skeletal system. Two types of osteoporosis are primary and secondary types and children with neuromuscular disabilities constitute a major group with secondary osteoporosis. Low bone mass in patients with cerebral palsy, spina bifida, and Duchenne muscular dystrophy cause increased bone fragility in even slight traumas. Maximizing peak bone mass and prevention of bone loss are very important to reduce the fracture risk in neuromuscular diseases. This article aims to review the determinants of bone physiology and bone loss in children with cerebral palsy, spina bifida, and Duchenne muscular dystrophy., (Copyright © 2017 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved.)

Introduction: Pierson syndrome is caused by a mutation of LAMB2, encoding for laminin β2. Clinical phenotype is variable but usually associates congenital nephrotic syndrome (CNS) and ocular abnormalities. Neuromuscular impairment has also been described., Methods: We report on a 15-year old girl, suffering from Pierson Syndrome, who developed severe bone deformations during puberty. This patient initially displayed CNS and microcoria, leading to the clinical diagnosis of Pierson syndrome. Genetic analysis revealed a truncating mutation and a splice site mutation of LAMB2. The patient received a renal transplantation (R-Tx) at the age of 3. After R-Tx, renal evolution was simple, the patient receiving low-dose corticosteroids, tacrolimus and mycophenolate mofetil. At the age of 12, bone deformations progressively appeared. At the time of bone impairment, renal function was subnormal (glomerular filtration rate using iohexol clearance 50mL/min per 1.73m 2 ), and parameters of calcium/phosphate metabolism were normal (calcium 2.45mmol/L, phosphorus 1.30mmol/L, PTH 81ng/L, ALP 334U/L, 25OH-D 73nmol/L). Radiographs showed major deformations such as scoliosis, genu varum and diffuse epiphyseal abnormalities. A high resolution scanner (HR-pQCT) was performed, demonstrating a bone of "normal low" quantity and quality; major radial and cubital deformations were observed. Stainings of laminin β2 were performed on bone and renal samples from the patient and healthy controls: as expected, laminin β2 was expressed in the control kidney but not in the patient's renal tissue, and a similar pattern was observed in bone., Conclusion: This is the first case of skeletal impairment ever described in Pierson syndrome. Integrin α3β1, receptor for laminin β2, are found in podocytes and osteoblasts, and the observation of both the presence of laminin β2 staining in healthy bone and its absence in the patient's bone raises the question of a potential role of laminin β2 in bone physiology., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: Mitochondrial dysfunction may represent a pathogenic factor in Huntington disease (HD). Physical exercise leads to enhanced mitochondrial function in healthy participants. However, data on effects of physical exercise on HD skeletal muscle remains scarce. We aimed at investigating adaptations of the skeletal muscle mitochondria to endurance training in HD patients., Methods: Thirteen HD patients and 11 healthy controls completed 26 weeks of endurance training. Before and after the training phase muscle biopsies were obtained from M. vastus lateralis. Mitochondrial respiratory chain complex activities, mitochondrial respiratory capacity, capillarization, and muscle fiber type distribution were determined from muscle samples., Results: Citrate synthase activity increased during the training intervention in the whole cohort (P = 0.006). There was no group x time interaction for citrate synthase activity during the training intervention (P = 0.522). Complex III (P = 0.008), Complex V (P = 0.043), and succinate cytochrome c reductase (P = 0.008) activities increased in HD patients and controls by endurance training. An increase in mass-specific mitochondrial respiratory capacity was present in HD patients during the endurance training intervention. Overall capillary-to-fiber ratio increased in HD patients by 8.4% and in healthy controls by 6.4% during the endurance training intervention., Conclusions: Skeletal muscle mitochondria of HD patients are equally responsive to an endurance-training stimulus as in healthy controls. Endurance training is a safe and feasible option to enhance indices of energy metabolism in skeletal muscle of HD patients and may represent a potential therapeutic approach to delay the onset and/or progression of muscular dysfunction., Trial Registration: ClinicalTrials.gov NCT01879267 . Registered May 24, 2012.

Muscular dystrophies are characterized by weakness and wasting of skeletal muscle tissues. Several drugs targeting the myostatin pathway have been used in clinical trials to increase muscle mass and function but most showed limited efficacy. Here we show that the expression of components of the myostatin signaling pathway is downregulated in muscle wasting or atrophying diseases, with a decrease of myostatin and activin receptor, and an increase of the myostatin antagonist, follistatin. We also provide in vivo evidence in the congenital myotubular myopathy mouse model (knock-out for the myotubularin coding gene Mtm1) that a down-regulated myostatin pathway can be reactivated by correcting the underlying gene defect. Our data may explain the poor clinical efficacy of anti-myostatin approaches in several of the clinical studies and the apparent contradictory results in mice regarding the efficacy of anti-myostatin approaches and may inform patient selection and stratification for future trials.

The aim of this study is to compare the rates of clinically relevant and clinically irrelevant neuronal autoantibodies among patients presenting with new neurological symptoms. We reviewed 401 neurological patients who were tested for the Mayo-Clinic paraneoplastic panel from January 2014 to December 2014 at the Johns Hopkins Hospital. We divided antibody-positive patients into two groups: clinically relevant (CR), in which a recognizable autoimmune or paraneoplastic syndrome was confirmed, and clinically irrelevant (CI), in which an autoimmune/paraneoplastic etiology was initially suspected but an alternative diagnosis was eventually found. We used Fisher's exact test for categorical variables and Mann-Whitney U test for continuous variables to identify differences between the two groups. Fifty-three patients tested positive for one or more neuronal autoantibodies. There were 17 CR (65% females, mean age 56 years), 33 CI, and 3 indeterminate patients. Compared to CI patients, CR patients were more likely to present with movement disorders or stiff person syndrome, have inflammatory CSF markers, cancer or smoking history, concomitant hyponatremia, and classical onconeuronal antibodies. CI patients were more likely to have a neuromuscular presentation, a chronic course, and antibodies against synaptic antigens. By combining the most robust differentiating factors, we developed a simple scale that predicted clinical relevance with an odds ratio of 50.3 (CI 8.2-309.9, P < 0.0001) if the score was ≥ 2. Up to 62% of neuronal autoantibody-positive patients are ultimately found to have an alternative diagnosis. Several clinical and laboratory factors can differentiate CR from CI patients to aid in interpretation of positive results.

Neuromuscular diseases are both genetic and acquired conditions resulting in progressive muscle weakness and wasting which lead to disability and reduced survival. The availability of high-quality human biomaterial is crucial to support biomedical research with potential applications at all stages of development, from molecular pathophysiology to drug discovery, clinical trials and evaluation of biomarkers. Although significant progress has been made over the last few years in the diagnosis of these rare conditions, the genetic defect and underlying pathological abnormality remain unknown in approximately 1/3 of cases. Moreover, to date no definitive cure is available for most neuromuscular disorders, nor are there sufficiently reliable and specific biomarkers to monitor disease progression and response to treatment. This is in part due to the rarity and genetic heterogeneity of neuromuscular diseases and the lack of access to patient samples. The availability of the national MRC Centre Biobank for Neuromuscular Diseases in Newcastle and London has addressed this bottleneck and supported neuromuscular research. Nine years after the establishment of the MRC Centre Biobank, many high profile research publications have highlighted the positive impact of neuromuscular biobanking for translational research and proven this facility to be a unique repository source for diagnostics, basic science research, industry, drug development, and therapy., (Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.)

Objective: Acute neuromuscular weakness related to hypokalemia is a readily treatable disorder associated with diverse aetiologies. In this study we aim to report clinical pattern and biochemical features to identify the different aetiologies of the hypokalemic neuromuscular weakness., Methods: Retrospective reviews of the medical record were analysed. Evaluation included demography, clinical features, investigations performed to ascertain the aetiologies. All the patients were categorised in to 3 groups; Idiopathic hypokalemic paralysis (IHP), dengue associated hypokalemic paralysis (DHP) and secondary group (SG) which included renal tubular acidosis (RTA- 1 and 2), thyrotoxic periodic paralysis (TPP) and Gitelman's syndrome (GS)., Results: Forty patients were analysed and the mean age was 31.78 (range, 14-60) years and 35 (87.5%) were male.The underlying aetiologies comprised of IHP in 20, DHP in 12, RTA-2 in 4, RTA-1 in 2, TPP, GS in one each. Weakness on Medical Research Council (MRC) grade was 2.6±1.19 (range 0-4). Comparison of various clinical and laboratory parameters revealed that more patient in IHP and SG had recurrent attack (p=0.001). DHP group had low platelet (p=0.001), high creatine phosphokinase (CPK) (p=0.01) and serum glutamic oxaloacetic transaminase (SGOT) (p=0.008). SG had significantly lower serum potassium (p=0.04) and more time to improve (p=0.02). Recovery time correlated negatively with serum potassium (r=-0.44, p=0.004) and grade of weakness (r= 0.42,p=0.007)., Conclusion: In half of the patients, secondary causes were identified. After IHP, the DHP emerged as second common cause in post monsoon season. SG had significantly lower serum potassium, recurrent attack and more time to improve.

Spinal muscular atrophy (SMA) is a common and often fatal neuromuscular disorder caused by low levels of the Survival Motor Neuron (SMN) protein. Amongst the earliest detectable consequences of SMN deficiency are profound defects of the neuromuscular junctions (NMJs). In model mice these synapses appear disorganized, fail to mature and are characterized by poorly arborized nerve terminals. Given one role of the SMN protein in orchestrating the assembly of spliceosomal snRNP particles and subsequently regulating the alternative splicing of pre-mRNAs, a plausible link between SMN function and the distal neuromuscular SMA phenotype is an incorrectly spliced transcript or transcripts involved in establishing or maintaining NMJ structure. In this study, we explore the effects of one such transcript-Z+Agrin-known to be a critical organizer of the NMJ. We confirm that low SMN protein reduces motor neuronal levels of Z+Agrin. Repletion of this isoform of Agrin in the motor neurons of SMA model mice increases muscle fiber size, enhances the post-synaptic NMJ area, reduces the abnormal accumulation of intermediate filaments in nerve terminals of the neuromuscular synapse and improves the innervation of muscles. While these effects are independent of changes in SMN levels or increases in motor neuron numbers they nevertheless have a significant effect on the overall disease phenotype, enhancing mean survival in severely affected SMA model mice by ∼40%. We conclude that Agrin is an important target of the SMN protein and that mitigating NMJ defects may be one strategy in treating human spinal muscular atrophy., (© The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

The mechanism underlying selective motor neuron (MN) death remains an essential question in the MN disease field. The MN disease spinal muscular atrophy (SMA) is attributable to reduced levels of the ubiquitous protein SMN. Here, we report that SMN levels are widely variable in MNs within a single genetic background and that this heterogeneity is seen not only in SMA MNs but also in MNs derived from controls and amyotrophic lateral sclerosis (ALS) patients. Furthermore, cells with low SMN are more susceptible to cell death. These findings raise the important clinical implication that some SMN-elevating therapeutics might be effective in MN diseases besides SMA. Supporting this, we found that increasing SMN across all MN populations using an Nedd8-activating enzyme inhibitor promotes survival in both SMA and ALS-derived MNs. Altogether, our work demonstrates that examination of human neurons at the single-cell level can reveal alternative strategies to be explored in the treatment of degenerative diseases., (Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.)

Emerging evidence revealed that abrogated cell cycle entry into highly differentiated mature neurons and muscles is having detrimental consequences in response to cell cycle checkpoints disruption, altered signaling cascades, pathophysiological and external stimuli, for instance, Aβ, Parkin, p-tau, α-synuclein, impairment in TRK, Akt/GSK3β, MAPK/Hsp90, and oxidative stress. These factors, reinitiate undesired cell division by triggering new DNA synthesis, replication, and thus exquisitely forced mature cell to enter into a disturbed and vulnerable state that often leads to death as reported in many neuro- and myodegenerative disorders. A pertinent question arises how to reverse this unwanted pathophysiological phenomenon is attributed to the usage of cell cycle inhibitors to prevent the degradation of crucial cell cycle arresting proteins, cyclin inhibitors, chaperones and E3 ligases. Herein, we identified the major culprits behind the forceful cell cycle re-entry, elucidated the cyclin re-expression based on disturbed signaling mechanisms in neuromuscular degeneration together with plausible therapeutic strategies., (Copyright © 2016 Elsevier B.V. All rights reserved.)