Adult-onset spinal muscular atrophy: An update

Early signs of neurodegenerative diseases: Possible mechanisms and targets for Golgi stress

The Golgi apparatus plays a crucial role in mediating the modification, transport, and sorting of intracellular proteins and lipids. The morphological changes occurring in the Golgi apparatus are exceptionally important for maintaining its function. When exposed to external pressure or environmental stimulation, the Golgi apparatus undergoes adaptive changes in both structure and function, which are known as Golgi stress. Although certain signal pathway responses or post-translational modifications have been observed following Golgi stress, further research is needed to comprehensively summarize and understand the related mechanisms. Currently, there is evidence linking Golgi stress to neurodegenerative diseases; however, the role of Golgi stress in the progression of neurodegenerative diseases such as Alzheimer's disease remains largely unexplored. This review focuses on the structural and functional alterations of the Golgi apparatus during stress, elucidating potential mechanisms underlying the involvement of Golgi stress in regulating immunity, autophagy, and metabolic processes. Additionally, it highlights the pivotal role of Golgi stress as an early signaling event implicated in the pathogenesis and progression of neurodegenerative diseases. Furthermore, this study summarizes prospective targets that can be therapeutically exploited to mitigate neurodegenerative diseases by targeting Golgi stress. These findings provide a theoretical foundation for identifying novel breakthroughs in preventing and treating neurodegenerative diseases.

Genetic characterization of non-5q proximal spinal muscular atrophy in a French cohort: the place of whole exome sequencing

Proximal spinal muscular atrophy (SMA) is defined by a degeneration of the anterior horn cells resulting in muscle weakness predominantly in the proximal lower limbs. While most patients carry a biallelic deletion in the SMN1 gene (localized in chromosome 5q), little is known regarding patients without SMN1-mutation, and a genetic diagnosis is not always possible. Here, we report a cohort of 24 French patients with non-5q proximal SMA from five neuromuscular centers who all, except two, had next-generation sequencing (NGS) gene panel, followed by whole exome sequencing (WES) if gene panel showed a negative result. The two remaining patients benefited directly from WES or whole genome sequencing (WGS). A total of ten patients with causative variants were identified, nine of whom were index cases (9/23 families = 39%). Eight variants were identified by gene panel: five variants in DYNC1H1, and three in BICD2. Compound heterozygous causative variants in ASAH1 were identified directly by WES, and one variant in DYNC1H1 was identified directly by WGS. No causative variant was found using WES in patients with a previous panel with negative results (14 cases). We thus recommend using primarily NGS panels in patients with non-5q-SMA and using WES, especially when several members of the same family are affected and/or when trio analyses are possible, or WGS as second-line testing if available.

Diagnosis and management of Becker muscular dystrophy: the French guidelines

Becker muscular dystrophy (BMD) is one of the most frequent among neuromuscular diseases, affecting approximately 1 in 18,000 male births. It is linked to a genetic mutation on the X chromosome. In contrast to Duchenne muscular dystrophy, for which improved care and management have changed the prognosis and life expectancy of patients, few guidelines have been published for management of BMD. Many clinicians are inexperienced in managing the complications of this disease. In France, a committee of experts from a wide range of disciplines met in 2019 to establish recommendations, with the goal of improving care of patients with BMD. Here, we present the tools to provide diagnosis of BMD as quickly as possible and for differential diagnoses. Then, we describe the multidisciplinary approach essential for optimum management of BMD. We give recommendations for the initial assessment and follow-up of the neurological, respiratory, cardiac, and orthopedic consequences of males who present with BMD. Finally, we describe the optimal therapeutic management of these complications. We also provide guidance on cardiac management for female carriers.

Transient Receptor Potential Vanilloid 4: a Double-Edged Sword in the Central Nervous System

Transient receptor potential vanilloid 4 (TRPV4) is a nonselective cation channel that can be activated by diverse stimuli, such as heat, mechanical force, hypo-osmolarity, and arachidonic acid metabolites. TRPV4 is widely expressed in the central nervous system (CNS) and participates in many significant physiological processes. However, accumulative evidence has suggested that deficiency, abnormal expression or distribution, and overactivation of TRPV4 are involved in pathological processes of multiple neurological diseases. Here, we review the latest studies concerning the known features of this channel, including its expression, structure, and its physiological and pathological roles in the CNS, proposing an emerging therapeutic strategy for CNS diseases.

Transcript-Targeted Therapy Based on RNA Interference and Antisense Oligonucleotides: Current Applications and Novel Molecular Targets

The development of novel target therapies based on the use of RNA interference (RNAi) and antisense oligonucleotides (ASOs) is growing in an exponential way, challenging the chance for the treatment of the genetic diseases and cancer by hitting selectively targeted RNA in a sequence-dependent manner. Multiple opportunities are taking shape, able to remove defective protein by silencing RNA (e.g., Inclisiran targets mRNA of protein PCSK9, permitting a longer half-life of LDL receptors in heterozygous familial hypercholesteremia), by arresting mRNA translation (i.e., Fomivirsen that binds to UL123-RNA and blocks the translation into IE2 protein in CMV-retinitis), or by reactivating modified functional protein (e.g., Eteplirsen able to restore a functional shorter dystrophin by skipping the exon 51 in Duchenne muscular dystrophy) or a not very functional protein. In this last case, the use of ASOs permits modifying the expression of specific proteins by modulating splicing of specific pre-RNAs (e.g., Nusinersen acts on the splicing of exon 7 in SMN2 mRNA normally not expressed; it is used for spinal muscular atrophy) or by downregulation of transcript levels (e.g., Inotersen acts on the transthryretin mRNA to reduce its expression; it is prescribed for the treatment of hereditary transthyretin amyloidosis) in order to restore the biochemical/physiological condition and ameliorate quality of life. In the era of precision medicine, recently, an experimental splice-modulating antisense oligonucleotide, Milasen, was designed and used to treat an 8-year-old girl affected by a rare, fatal, progressive form of neurodegenerative disease leading to death during adolescence. In this review, we summarize the main transcriptional therapeutic drugs approved to date for the treatment of genetic diseases by principal regulatory government agencies and recent clinical trials aimed at the treatment of cancer. Their mechanism of action, chemical structure, administration, and biomedical performance are predominantly discussed.

Evaluation of exonic copy numbers of SMN1 and SMN2 genes in SMA

SMA is a neuromuscular disease and occurs primarily through autosomal recessive inheritance. Identification of deletions in the SMN1 gene especially in the exon 7 and exon 8 regions (hot spot), are used in carrier testing. The exact copy numbers of those exons in the SMN1 and SMN2 genes in 113 patients who presented with a pre-diagnosis of SMA were determined using MLPA method. We aimed to reveal both the most common copy number profiles of different SMA types. It was found that the frequency of homozygous deletions in SMN1 was 15.9%, while heterozygous deletions was 16.9%. The most common SMN-MLPA profile was 0-0-3-3. In the cases with homozygous deletion, SMA type III diagnosis was observed most frequently (44%), and the rate of consanguineous marriage was found 33%. Two cases with the same exonic copy number profile but with different clinical subtypes were identified in a family. We also detected distinct exonic deletion and duplication MLPA profiles for the first time. We created "the SMA signature" that can be added to patient reports. Furthermore, our data are important for revealing potential local profiles of SMA and describing the disease in genetic reports in a way that is clear and comprehensive.

Genetic architecture of motor neuron diseases

Motor neuron diseases (MNDs) are rare and frequently fatal neurological disorders in which motor neurons within the brainstem and spinal cord regions slowly die. MNDs are primarily caused by genetic mutations, and > 100 different mutant genes in humans have been discovered thus far. Given the fact that many more MND-related genes have yet to be discovered, the growing body of genetic evidence has offered new insights into the diverse cellular and molecular mechanisms involved in the aetiology and pathogenesis of MNDs. This search may aid in the selection of potential candidate genes for future investigation and, eventually, may open the door to novel interventions to slow down disease progression. In this review paper, we have summarized detailed existing research findings of different MNDs, such as amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), spinal bulbar muscle atrophy (SBMA) and hereditary spastic paraplegia (HSP) in relation to their complex genetic architecture.

Urine-Derived Stem Cells Express 571 Neuromuscular Disorders Causing Genes, Making Them a Potential in vitro Model for Rare Genetic Diseases

Background: Neuromuscular disorders (NMDs) are a heterogeneous group of genetic diseases, caused by mutations in genes involved in spinal cord, peripheral nerve, neuromuscular junction, and muscle functions. To advance the knowledge of the pathological mechanisms underlying NMDs and to eventually identify new potential drugs paving the way for personalized medicine, limitations regarding the availability of neuromuscular disease-related biological samples, rarely accessible from patients, are a major challenge. Aim: We characterized urinary stem cells (USCs) by in-depth transcriptome and protein profiling to evaluate whether this easily accessible source of patient-derived cells is suitable to study neuromuscular genetic diseases, focusing especially on those currently involved in clinical trials. Methods: The global transcriptomics of either native or MyoD transformed USCs obtained from control individuals was performed by RNA-seq. The expression of 610 genes belonging to 16 groups of disorders (http://www.musclegenetable.fr/) whose mutations cause neuromuscular diseases, was investigated on the RNA-seq output. In addition, protein expression of 11 genes related to NMDs including COL6A, EMD, LMNA, SMN, UBA1, DYNC1H1, SOD1, C9orf72, DYSF, DAG1, and HTT was analyzed in native USCs by immunofluorescence and/or Western blot (WB). Results: RNA-seq profile of control USCs shows that 571 out of 610 genes known to be involved in NMDs, are expressed in USCs. Interestingly, the expression levels of the majority of NMD genes remain unmodified following USCs MyoD transformation. Most genes involved in the pathogenesis of all 16 groups of NMDs are well represented except for channelopathies and malignant hyperthermia related genes. All tested proteins showed high expression values, suggesting consistency between transcription and protein representation in USCs. Conclusion: Our data suggest that USCs are human cells, obtainable by non-invasive means, which might be used as a patient-specific cell model to study neuromuscular disease-causing genes and that they can be likely adopted for a variety of in vitro functional studies such as mutation characterization, pathway identification, and drug screening.

Newborn Screening for Spinal Muscular Atrophy: Ontario Testing and Follow-up Recommendations

BACKGROUND

Spinal muscular atrophy (SMA) is characterized by the progressive loss of motor neurons causing muscle atrophy and weakness. Nusinersen, the first effective SMA therapy was approved by Health Canada in June 2017 and has been added to the provincial formulary of all but one Canadian province. Access to this effective therapy has triggered the inclusion of SMA in an increasing number of Newborn Screening (NBS) programs. However, the range of disease-modifying SMN2 gene copy numbers encountered in survival motor neuron 1 (SMN1)-null individuals means that neither screen-positive definition nor resulting treatment decisions can be determined by SMN1 genotype alone. We outline an approach to this challenge, one that specifically addresses the case of SMA newborns with four copies of SMN2.

OBJECTIVES

To develop a standardized post-referral evaluation pathway for babies with a positive SMA NBS screen result.

METHODS

An SMA NBS pilot trial in Ontario using first-tier MassARRAY and second-tier multi-ligand probe amplification (MLPA) was launched in January 2020. Prior to this, Ontario pediatric neuromuscular disease and NBS experts met to review the evidence regarding the diagnosis and treatment of children with SMA as it pertained to NBS. A post-referral evaluation algorithm was developed, outlining timelines for patient retrieval and management.

CONCLUSIONS

Ontario's pilot NBS program has created a standardized path to facilitate early diagnosis of SMA and initiation of treatment. The goal is to provide timely access to those SMA infants in need of therapy to optimize motor function and prolong survival.

Findings regarding emotion regulation strategies and quality of life's domains in families having children with spinal muscular atrophy

The severity of motor impairment and the psycho-emotional and social consequences of spinal muscular atrophy (SMA) impact both children and their families, who must adapt using cognitive-emotional strategies. We aimed to determine whether the domains of quality of life and the consequent emotion regulation strategies could be related, and if so, to what quantitative, at a statistically significant level. This study was conducted at the Dr. N. Robanescu National Clinical Center of Neurorehabilitation for Children and included 33 mothers questioned using the PedsQL-Family Impact Module (PedsQL-FIM) and Cognitive Emotion Regulation Questionnaire (CERQ). Statistical analysis of PedsQL-FIM data showed high positive Spearman's rho correlations between communication and social functioning (p=0.719), daily activities and cognitive functioning (p=0.704), family relationships and daily activities (p=0.705). The analysis of the Spearman's rho correlation coefficients reflected some moderate positive correlations between CERQ subscales: self-blame and catastrophizing (p=0.577), acceptance and refocus on planning (p=0.577), acceptance and putting into perspective (p=0.532), refocus on planning and positive reappraisal (p=0.630), positive reappraisal and putting into perspective (p=0.609). Maladaptive strategies affect family relationships, cognitive and social functioning, emotional functioning, and communication inside the family. Positive correlations were found between the adaptive strategies (acceptance, refocus on planning, putting into perspective, positive reappraisal) in the participants within our study group, showing their interest in attitude changing and actively solving the family tasks related to children's illness.

Severe cervical compressive polydiscopathic myelopathy with features of motor neuron disease: A case report

Cervical myelopathy is part of ALS mimic syndrome and should be considered in patients with clinical signs of motor neuron disease.

Clinical and radiological profile of patients with spinal muscular atrophy type 4

BACKGROUND AND PURPOSE

Spinal muscular atrophy (SMA) is the most important cause of motor neuron disease in childhood, and continues to represent the leading genetic cause of infant death. Adulthood-onset SMA (SMA type 4) is rare, with few isolated cases reported. The objective of the present study was to describe a cohort of patients with SMA type 4.

METHODS

A cross-sectional study was conducted to characterize clinical, genetic, radiological and neurophysiological features of patients with adulthood-onset SMA. Correlation analysis of functional assessment with genetic, radiological and neurophysiological data was performed.

RESULTS

Twenty patients with SMA type 4 were identified in a Brazilian cohort of 227 patients with SMA. The most common clinical symptom was limb-girdle muscle weakness, observed in 15 patients (75%). The most frequent neurological findings were absent tendon reflexes in 18 (90%) and fasciculations in nine patients (45%). Sixteen patients (80%) had the homozygous deletion of exon 7 in the SMN1 gene, with 12 patients (60%) showing four copies of the SMN2 gene. The functional scales Hammersmith Functional Motor Scale Expanded, Amyotrophic Lateral Sclerosis Functional Rating Scale Revised, Revised Upper Limb Module and Spinal Muscular Atrophy Functional Rating Scale, as well as the six-minute walk and the Time Up and Go tests showed a correlation with duration of disease. Motor Unit Number Index was correlated both with duration of disease and with performance in functional assessment. Radiological studies exhibited a typical pattern, with involvement of biceps femoris short head and gluteus minimus in all patients.

CONCLUSION

This study represents the largest cohort of patients with SMA type 4 and provides functional, genetic, radiological and neurophysiological features that can be used as potential biomarkers for the new specific genetic therapies for SMA.

Glial cells involvement in spinal muscular atrophy: Could SMA be a neuroinflammatory disease?

Spinal muscular atrophy (SMA) is a severe, inherited disease characterized by the progressive degeneration and death of motor neurons of the anterior horns of the spinal cord, which results in muscular atrophy and weakness of variable severity. Its early-onset form is invariably fatal in early childhood, while milder forms lead to permanent disability, physical deformities and respiratory complications. Recently, two novel revolutionary therapies, antisense oligonucleotides and gene therapy, have been approved, and might prove successful in making long-term survival of these patients likely. In this perspective, a deep understanding of the pathogenic mechanisms and of their impact on the interactions between motor neurons and other cell types within the central nervous system (CNS) is crucial. Studies using SMA animal and cellular models have taught us that the survival and functionality of motor neurons is highly dependent on a whole range of other cell types, namely glial cells, which are responsible for a variety of different functions, such as neuronal trophic support, synaptic remodeling, and immune surveillance. Thus, it emerges that SMA is likely a non-cell autonomous, multifactorial disease in which the interaction of different cell types and disease mechanisms leads to motor neurons failure and loss. This review will introduce the different glial cell types in the CNS and provide an overview of the role of glial cells in motor neuron degeneration in SMA. Furthermore, we will discuss the relevance of these findings so far and the potential impact on the success of available therapies and on the development of novel ones.

Golgi Fragmentation in Neurodegenerative Diseases: Is There a Common Cause?

In most mammalian cells, the Golgi complex forms a continuous ribbon. In neurodegenerative diseases, the Golgi ribbon of a specific group of neurons is typically broken into isolated elements, a very early event which happens before clinical and other pathological symptoms become evident. It is not known whether this phenomenon is caused by mechanisms associated with cell death or if, conversely, it triggers apoptosis. When the phenomenon was studied in diseases such as Parkinson’s and Alzheimer’s or amyotrophic lateral sclerosis, it was attributed to a variety of causes, including the presence of cytoplasmatic protein aggregates, malfunctioning of intracellular traffic and/or alterations in the cytoskeleton. In the present review, we summarize the current findings related to these and other neurodegenerative diseases and try to search for clues on putative common causes.

Atypical Motor Neuron Disease variants: Still a diagnostic challenge in Neurology

Motor neuron disease (MND) represents a wide and heterogeneous expanding group of disorders involving the upper or lower motor neurons, mainly represented by amyotrophic lateral sclerosis (ALS), primary lateral sclerosis, progressive muscular atrophy and progressive bulbar palsy. Primary motor neuronopathies are characterized by progressive degenerative loss of anterior horn cell motoneurons (lower motor neurons) or loss of giant pyramidal Betz cells (upper motor neurons). Despite its well-known natural history, pathophysiological and clinical characteristics for the most common MND, atypical clinical presentation and neurodegenerative mechanisms are commonly observed in rare clinical entities, so-called atypical variants of MND-ALS, including flail-leg syndrome, flail-arm syndrome, facial-onset sensory and motor neuronopathy (FOSMN), finger extension weakness and downbeat nystagmus (FEWDON-MND) and long-lasting and juvenile MND-ALS. Herein, we provide a review article presenting clinical, genetic, pathophysiological and neuroimaging findings of atypical variants of MND-ALS in clinical practice.

TDP-43 post-translational modifications in health and disease

INTRODUCTION

Nuclear factor TDP-43 is a ubiquitously expressed RNA binding protein that plays a key causative role in several neurodegenerative diseases, especially in the ALS/FTD spectrum. In addition, its aberrant aggregation and expression has been recently observed in other type of diseases, such as myopathies and Niemann-Pick C, a lysosomal storage disease. Areas covered: This review aims to specifically cover the post-translational modifications (PTMs) that can affect TDP-43 function and cellular status both in health and disease. To this date, these include phosphorylation, formation of C-terminal fragments, disulfide bridge formation, ubiquitination, acetylation, and sumoylation. Recently published articles on these subjects have been reviewed in this manuscript. Expert opinion: Targeting aberrant TDP-43 expression in neurodegenerative diseases is a very challenging task due to the fact that both its overexpression and downregulation are considerably toxic to cells. This characteristic makes it difficult to therapeutically target this protein in a generalized manner. An alternative approach could be the identification of specific aberrant PTMs that promote its aggregation or toxicity, and developing novel therapeutic approaches toward their selective modification.