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Congenital myopathies (CMs) are a kind of non-progressive or slow-progressive muscle diseases caused by genetic mutations, which are currently defined and categorized mainly according to their clinicopathological features. CMs exhibit pleiotropy and genetic heterogeneity. Currently, supportive treatment and pharmacological remission are the mainstay of treatment, with no cure available. Some adeno-associated viruses show promising prospects in the treatment of MTM1 and BIN1-associated myopathies; however, such gene-level therapeutic interventions target only specific mutation types and are not generalizable. Thus, it is particularly crucial to identify the specific causative genes. Here, we outline the pathogenic mechanisms based on the classification of causative genes: excitation-contraction coupling and triadic assembly (RYR1, MTM1, DNM2, BIN1), actin-myosin interaction and production of myofibril forces (NEB, ACTA1, TNNT1, TPM2, TPM3), as well as other biological processes. Furthermore, we provide a comprehensive overview of recent therapeutic advancements and potential treatment modalities of CMs. Despite ongoing research endeavors, targeted strategies and collaboration are imperative to address diagnostic uncertainties and explore potential treatments., (© 2024. The Author(s).)

Background and Objectives: The diagnostic process for myofibrillar myopathies (MFM) and distal myopathies (DM) is particularly complex because of the large number of causative genes, the existence of still molecularly undefined disease entities, and the overlapping features between the 2 categories. This study aimed to characterize a large cohort of patients affected by MFM and DM and identify the most important diagnostic and prognostic aspects of these diseases., Methods: Patients with either a myopathological diagnosis of MFM or a clinical diagnosis of DM were included in this retrospective multicentric national study. Demographic, genetic, clinical, and histopathologic data of anonymized patients were collected from the neuromuscular centers of the Italian Association of Myology network., Results: Data regarding 132 patients with MFM (mean age 57.0 ± 15.8 years, 49% female) and 298 patients with DM (mean age 50.7 ± 15.9 years, 40% female) were gathered from 20 neuromuscular centers. 69 patients fulfilled the criteria for both groups (distal myopathies with myofibrillar pathology, DM-MP). Molecular confirmation was achieved in 63% of the patients. Fifty-two percent of the patients with MFM carried pathogenic variants in either DES (n = 30), MYOT (n = 20), or DNAJB6 (n = 18), which were also the most frequent disease-causing genes in DM-MP, while GNE (n = 44) and MYH7 (n = 23) were the genes most commonly carrying pathogenic variants in DM. The mean age at onset varied from <25 years in patients with causative variants in MYH7 and DYSF to 59 years in patients with myotilinopathies. Cardiac involvement was reported in 29% of patients with MFM and 16% of patients with DM, with DES and MYH7 variants significantly associated with the development of cardiomyopathy. Respiratory impairment was more prevalent in patients with TTN and DES variants and rare in other disorders such as GNE myopathy and dysferlinopathies, which were instead associated, together with DNAJB6 -related and PLIN4 -related myopathies, with the risk of losing ambulation during the disease course., Discussion: The Italian cohort of patients with MFM and DM recapitulates the phenotypic heterogeneity and the partial overlap between the 2 groups. However, in relative contrast to the encountered phenotypic variability, only 5 genes accounted for most of the molecular diagnoses. Specific genetic entities are associated with significantly increased risk of developing cardiorespiratory complications or loss of ambulation, which has relevant prognostic implications.

Myofibrillar myopathy (MFM) is a group of hereditary myopathies that mainly involves striated muscles. This study aimed to use tandem mass tag (TMT)-based proteomics to investigate the underlying pathomechanisms of two of the most common MFM subtypes, desminopathy and titinopathy. Muscles from 7 patients with desminopathy, 5 with titinopathy and 5 control individuals were included. Samples were labelled with TMT and then underwent high-resolution liquid chromatography-mass spectrometry analysis. Compared with control samples, there were 436 differentially abundant proteins (DAPs) in the desminopathy group and 269 in the titinopathy group. When comparing the desminopathy with the titinopathy group, there were 113 DAPs. In desminopathy, mitochondrial ATP production, muscle contraction, and cytoskeleton organization were significantly suppressed. Activated cellular components and pathways were mostly related to extracellular matrix (ECM). In titinopathy, mitochondrial-related pathways and the cellular component ECM were downregulated, while gluconeogenesis was activated. Direct comparison between desminopathy and titinopathy revealed hub genes that were all involved in glycolytic process. The disparity in glycolysis in the two MFM subtypes is likely due to fiber type switching. This study has revealed disorganization of cytoskeleton and mitochondrial dysfunction as the common pathophysiological processes in MFM, and glycolysis and ECM as the differential pathomechanism between desminopathy and titinopathy. This offers a future direction for targeted therapy for MFM., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

Oculopharyngodistal myopathy (OPDM) is an inherited myopathy manifesting with ptosis, dysphagia and distal weakness. Pathologically it is characterised by rimmed vacuoles and intranuclear inclusions on muscle biopsy. In recent years CGG • CCG repeat expansion in four different genes were identified in OPDM individuals in Asian populations. None of these have been found in affected individuals of non-Asian ancestry. In this study we describe the identification of CCG expansions in ABCD3, ranging from 118 to 694 repeats, in 35 affected individuals across eight unrelated OPDM families of European ancestry. ABCD3 transcript appears upregulated in fibroblasts and skeletal muscle from OPDM individuals, suggesting a potential role of over-expression of CCG repeat containing ABCD3 transcript in progressive skeletal muscle degeneration. The study provides further evidence of the role of non-coding repeat expansions in unsolved neuromuscular diseases and strengthens the association between the CGG • CCG repeat motif and a specific pattern of muscle weakness., (© 2024. The Author(s).)

Truncation of the protein-protein interaction SH3 domain of the membrane remodeling Bridging Integrator 1 (BIN1, Amphiphysin 2) protein leads to centronuclear myopathy. Here, we assessed the impact of a set of naturally observed, previously uncharacterized BIN1 SH3 domain variants using conventional in vitro and cell-based assays monitoring the BIN1 interaction with dynamin 2 (DNM2) and identified potentially harmful ones that can be also tentatively connected to neuromuscular disorders. However, SH3 domains are typically promiscuous and it is expected that other, so far unknown partners of BIN1 exist besides DNM2, that also participate in the development of centronuclear myopathy. In order to shed light on these other relevant interaction partners and to get a holistic picture of the pathomechanism behind BIN1 SH3 domain variants, we used affinity interactomics. We identified hundreds of new BIN1 interaction partners proteome-wide, among which many appear to participate in cell division, suggesting a critical role of BIN1 in the regulation of mitosis. Finally, we show that the identified BIN1 mutations indeed cause proteome-wide affinity perturbation, signifying the importance of employing unbiased affinity interactomic approaches., Competing Interests: BZ, EE, BM, LN, MP, ZD, SO, GT, JL, GG No competing interests declared, (© 2024, Zambo et al.)

Objective: To explore the clinical and genetic characteristics of two newborns with Central nuclear myopathy (CNM)., Methods: Two newborns with CNM diagnosed clinically at Wuhan Children's Hospital Affiliated to Tongji Medical College, Huazhong University of Science and Technology in April 2019 and November 2021 were selected as the study subjects, and their clinical data was collected. Both newborns and their parents were subjected chromosomal karyotyping analysis and whole exome sequencing (WES). Candidate variants were verified by Sanger sequencing. Pathogenicity of the candidate variants was evaluated based on the guidelines from the American College of Medical Genetics and Genomics (ACMG)., Results: Patient 1 was a male neonate and Patient 2 was a 20-day-old male infant. Both newborns had featured difficulty in breathing and swallowing. WES revealed that both had harbored hemizygous variants of the MTM1 gene, which were verified by Sanger sequencing. Patient 1 had harbored a c.1261A>G variant. Based on the ACMG guidelines, it was rated as pathogenic (PVS1+PM2&#95;Supporting+PP3). Patient 2 harbored a c.342delT variant, which was also rated as pathogenic (PVS1+PM2&#95;Supporting+PP3)., Conclusion: The c.1261A>G and c.342delT variants of the MTM1 gene probably underlay the pathogenesis of CNM in the two patients.

Background: Congenital myopathies are severe genetic diseases with a strong impact on patient autonomy and often on survival. A large number of patients do not have a genetic diagnosis, precluding genetic counseling and appropriate clinical management. Our objective was to find novel pathogenic variants and genes associated with congenital myopathies and to decrease diagnostic odysseys and dead-end., Methods: To identify pathogenic variants and genes implicated in congenital myopathies, we established and conducted the MYOCAPTURE project from 2009 to 2018 to perform exome sequencing in a large cohort of 310 families partially excluded for the main known genes., Results: Pathogenic variants were identified in 156 families (50%), among which 123 families (40%) had a conclusive diagnosis. Only 44 (36%) of the resolved cases were linked to a known myopathy gene with the corresponding phenotype, while 55 (44%) were linked to pathogenic variants in a known myopathy gene with atypical signs, highlighting that most genetic diagnosis could not be anticipated based on clinical-histological assessments in this cohort. An important phenotypic and genetic heterogeneity was observed for the different genes and for the different congenital myopathy subtypes, respectively. In addition, we identified 14 new myopathy genes not previously associated with muscle diseases (20% of all diagnosed cases) that we previously reported in the literature, revealing novel pathomechanisms and potential therapeutic targets., Conclusions: Overall, this approach illustrates the importance of massive parallel gene sequencing as a comprehensive tool for establishing a molecular diagnosis for families with congenital myopathies. It also emphasizes the contribution of clinical data, histological findings on muscle biopsies, and the availability of DNA samples from additional family members to the diagnostic success rate. This study facilitated and accelerated the genetic diagnosis of congenital myopathies, improved health care for several patients, and opened novel perspectives for either repurposing of existing molecules or the development of novel treatments., (© 2024. The Author(s).)

Two recent papers have highlighted that STIM1, a key component of Store-operated Ca2+-entry, is able to translocate to the nucleus and participate in nuclear Ca 2+ -handling and in DNA repair. These finding opens new avenues on the role that this Ca 2+ -sensing protein may have in health and disease., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Background: Congenital myopathies are a clinical, histopathological and genetic heterogeneous group of inherited muscle disorders that are defined on peculiar architectural abnormalities in the muscle fibres. Although there have been at least 33 different genetic causes of the disease, a significant percentage of congenital myopathies remain genetically unresolved. The present study aimed to report a novel TUBA4A variant in two unrelated Chinese patients with sporadic congenital myopathy., Methods: A comprehensive strategy combining laser capture microdissection, proteomics and whole-exome sequencing was performed to identify the candidate genes. In addition, the available clinical data, myopathological changes, the findings of electrophysiological examinations and thigh muscle MRIs were also reviewed. A cellular model was established to assess the pathogenicity of the TUBA4A variant., Results: We identified a recurrent novel heterozygous de novo c.679C>T (p.L227F) variant in the TUBA4A (NM&#95;006000), encoding tubulin alpha-4A, in two unrelated patients with clinicopathologically diagnosed sporadic congenital myopathy. The prominent myopathological changes in both patients were muscle fibres with focal myofibrillar disorganisation and rimmed vacuoles. Immunofluorescence showed ubiquitin-positive TUBA4A protein aggregates in the muscle fibres with rimmed vacuoles. Overexpression of the L227F mutant TUBA4A resulted in cytoplasmic aggregates which colocalised with ubiquitin in cellular model., Conclusion: Our findings expanded the phenotypic and genetic manifestations of TUBA4A as well as tubulinopathies, and added a new type of congenital myopathy to be taken into consideration in the differential diagnosis., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

The myotubularin family, encompassing myotubularin 1 (MTM1) and 14 myotubularin-related proteins (MTMRs), represents a conserved group of phosphatases featuring a protein tyrosine phosphatase domain. Nine members are characterized by an active phosphatase domain C(X) 5 R, dephosphorylating the D3 position of PtdIns(3)P and PtdIns(3,5)P2. Mutations in myotubularin genes result in human myopathies, and several neuropathies including X-linked myotubular myopathy and Charcot-Marie-Tooth type 4B. MTM1, MTMR6 and MTMR14 also contribute to Ca 2+ signaling and Ca 2+ homeostasis that play a key role in many MTM-dependent myopathies and neuropathies. Here we explore the evolving roles of MTM1/MTMRs, unveiling their influence on critical aspects of Ca 2+ signaling pathways., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Marek Michalak reports a relationship with University of Alberta that includes: funding grants. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Membrane tubulation coupled with fission (MTCF) is a widespread phenomenon but mechanisms for their coordination remain unclear, partly because of the lack of assays to monitor dynamics of membrane tubulation and subsequent fission. Using polymer cushioned bilayer islands, we analyze the membrane tubulator Bridging Integrator 1 (BIN1) mixed with the fission catalyst dynamin2 (Dyn2). Our results reveal this mixture to constitute a minimal two-component module that demonstrates MTCF. MTCF is an emergent property and arises because BIN1 facilitates recruitment but inhibits membrane binding of Dyn2 in a dose-dependent manner. MTCF is therefore apparent only at high Dyn2 to BIN1 ratios. Because of their mutual involvement in T-tubules biogenesis, mutations in BIN1 and Dyn2 are associated with centronuclear myopathies and our analysis links the pathology with aberrant MTCF. Together, our results establish cushioned bilayer islands as a facile template for the analysis of membrane tubulation and inform of mechanisms that coordinate MTCF., Competing Interests: Competing interests statement:The authors declare no competing interest.

Myofibrillar myopathy (MFM) is a rare genetic disorder characterized by muscular dystrophy that is often associated with cardiac disease. This disease is caused by mutations in several genes, among them DES (encoding desmin) is the most frequently affected. Peripheral blood mononuclear cells from 5 different MFM patients with different DES mutations were reprogrammed into induced pluripotent stem cells (IPSC) using non-integrative vectors. For each patient, one IPSC clone was selected and demonstrated pluripotency hallmarks without genomic abnormalities. SNP profiles were identical to the cells of origin and all the clones have the capacity to differentiate into all three germ layers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

X-linked myotubular myopathy (XLMTM) is a rare congenital myopathy. In February 2021, a male neonate was admitted to the West China Second University Hospital, Sichuan University, with clinical manifestations of hypotonia, accompanied by distinctive facial features, and requiring continuous ventilatory support. He was born prematurely at 36 +2 weeks gestation and developed respiratory distress postnatally, followed by difficulty in weaning from mechanical ventilation. Additional clinical features included hypotonia of the limbs, swallowing dysfunction, and specific facial characteristics (elongated limbs, narrow face, high-arched palate, wrist drop, empty scrotum, elongated fingers/toes). Genetic testing confirmed the diagnosis of XLMTM. Whole-exome sequencing analysis of the family revealed no mutations in the father, paternal grandfather, or paternal grandmother, while the mother had a heterozygous mutation. The pathogenic mutation was identified as MTM1 gene ( OMIM : 300415), chromosome position chrX-150649714, with a nucleotide change of c.868-2A>C. The patient exhibited typical facial features. Genetic testing is crucial for accurate diagnosis of XLMTM in infants presenting with abnormal muscle tone and distinctive facial features.

Tubular aggregate myopathies comprise a rare group of disorders with characteristic pathological findings and heterogeneous phenotypes, including myasthenic syndrome. We describe a patient with tubular aggregate myopathy who presented with fatiguable weakness improving with pyridostigmine, respiratory involvement and possible cardiac manifestations. We highlight the utility of muscle biopsy in atypical myasthenic syndrome., Competing Interests: Competing interests: AC reports a consulting relationship with UCB Biosciences Inc and Argenx US, Inc. KG reports a consulting or advisory and speaking lecturer relationship with Alexion Pharmaceuticals Inc, and a consulting or advisory relationship with UCB Biosciences Inc and Argenx US, Inc., (© Author(s) (or their employer(s)) 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

Tubular aggregate myopathy (TAM) and Stormorken syndrome (STRMK) are clinically overlapping disorders characterized by childhood-onset muscle weakness and a variable occurrence of multisystemic signs, including short stature, thrombocytopenia, and hyposplenism. TAM/STRMK is caused by gain-of-function mutations in the Ca2+ sensor STIM1 or the Ca2+ channel ORAI1, both of which regulate Ca2+ homeostasis through the ubiquitous store-operated Ca2+ entry (SOCE) mechanism. Functional experiments in cells have demonstrated that the TAM/STRMK mutations induce SOCE overactivation, resulting in excessive influx of extracellular Ca2+. There is currently no treatment for TAM/STRMK, but SOCE is amenable to manipulation. Here, we crossed Stim1R304W/+ mice harboring the most common TAM/STRMK mutation with Orai1R93W/+ mice carrying an ORAI1 mutation partially obstructing Ca2+ influx. Compared with Stim1R304W/+ littermates, Stim1R304W/+Orai1R93W/+ offspring showed a normalization of bone architecture, spleen histology, and muscle morphology; an increase of thrombocytes; and improved muscle contraction and relaxation kinetics. Accordingly, comparative RNA-Seq detected more than 1,200 dysregulated genes in Stim1R304W/+ muscle and revealed a major restoration of gene expression in Stim1R304W/+Orai1R93W/+ mice. Altogether, we provide physiological, morphological, functional, and molecular data highlighting the therapeutic potential of ORAI1 inhibition to rescue the multisystemic TAM/STRMK signs, and we identified myostatin as a promising biomarker for TAM/STRMK in humans and mice.

A transverse-tubule (T-tubule) is an invagination of the plasma membrane penetrating deep into muscle cells. An extensive membrane network of T-tubules is crucial for rapid and synchronized signal transmission from the cell surface to the entire sarcoplasmic reticulum for Ca2+ release, leading to muscle contraction. T-tubules are also indispensable for the formation and positioning of other muscle organelles. Their structure and physiological roles are relatively well established; however, the mechanisms shaping T-tubules require further elucidation. Centronuclear myopathy (CNM), an inherited muscular disorder, accompanies structural defects in T-tubules. Membrane traffic-related genes, including MTM1 (Myotubularin 1), DNM2 (Dynamin 2), and BIN1 (Bridging Integrator-1), were identified as causative genes of CNM. In addition, causative genes for other muscle diseases are also reported to be involved in the formation and maintenance of T-tubules. This review summarizes current knowledge on the mechanisms of how T-tubule formation and maintenance is regulated., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Japanese Biochemical Society.)

The Myotubular and Centronuclear Myopathy Registry is an international research database containing key longitudinal data on a diverse and growing cohort of individuals affected by this group of rare and ultra-rare neuromuscular conditions. It can inform and support all areas of translational research including epidemiological and natural history studies, clinical trial feasibility planning, recruitment for clinical trials or other research studies, stand-alone clinical studies, standards of care development, and provision of real-world evidence data. For ten years, it has also served as a valuable communications tool and provided a link between the scientific and patient communities. With the anticipated advent of disease-modifying therapies for these conditions, the registry is a key resource for the generation of post-authorisation data for regulatory decision-making, real world evidence, and patient-reported outcome measures. In this paper we present some key data from the current 444 registered individuals with the following genotype split: MTM1 n=270, DNM2 n=42, BIN1 n=4, TTN n=4, RYR1 n=12, other n=4, unknown n=108. The data presented are consistent with the current literature and the common understanding of a strong genotype/phenotype correlations in CNM, most notably the data supports the current knowledge that XLMTM is typically the most severe form of CNM. Additionally, we outline the ways in which the registry supports research, and, more generally, the importance of continuous investment and development to maintain the relevance of registries for all stakeholders. Further information on the registry and contact details are available on the registry website at www.mtmcnmregistry.org., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Background: Congenital myopathies (CMs) are a diverse group of inherited muscle disorders with broad genotypic and phenotypic heterogeneity. While the literature on CM is available from European countries, comprehensive data from the Indian subcontinent is lacking., Objectives: This study aims to describe the clinical and histopathological characteristics of a cohort of genetically confirmed CMs from India and attempts to do phenotype-genotype correlation., Methods: A retrospective chart review of genetically confirmed CMs was evaluated between January 2016 and December 2020 at the neuromuscular clinic. The clinical, genetic, and follow-up data were recorded in a pre-structured proforma as per the medical records, and the data was analyzed., Results: A total of 31(M: F = 14 : 17) unrelated patients were included. The median age at onset and duration of illness are 2.0(IQR:1-8) years and 6.0(IQR:3-10) years respectively. Clinical features observed were proximodistal weakness (54.8%), facial weakness (64.5%), and myopathic facies (54.8%), followed by ptosis (33.3%), and ophthalmoplegia (19.4%). Muscle histopathology was available in 38.7% of patients, and centronuclear myopathy was the most common histopathology finding. The pathogenic genetic variants were identified in RYR1 (29.0%), DNM2 (19.4%), SELENON (12.9%), KBTBD13 (9.7%), NEB (6.5%), and MYPN (6.5%) genes. Novel mutations were observed in 30.3% of the cohort. Follow-up details were available in 77.4% of children, and the median duration of follow-up and age at last follow-up was 4.5 (Range 0.5-11) years and 13 (Range 3-35) years, respectively. The majority were ambulant with minimal assistance at the last follow-up. Mortality was noted in 8.3% due to respiratory failure in Centronuclear myopathy 1 and congenital myopathy 3 with rigid spines (SELENON)., Conclusion: This study highlights the various phenotypes and patterns of genetic mutations in a cohort of pediatric patients with congenital myopathy from India. Centronuclear myopathy was the most common histological classification and the mutations in RYR1 followed by DNM2 gene were the common pathogenic variants identified. The majority were independent in their activities of daily living during the last follow-up, highlighting the fact that the disease has slow progression irrespective of the genotype.

Background: X-linked myotubular myopathy (XLMTM) is a rare, life-threatening congenital muscle disease caused by mutations in the MTM1 gene that result in profound muscle weakness, significant respiratory insufficiency, and high infant mortality. There is no approved disease-modifying therapy for XLMTM. Resamirigene bilparvovec (AT132; rAAV8-Des-hMTM1) is an investigational adeno-associated virus (AAV8)-mediated gene replacement therapy designed to deliver MTM1 to skeletal muscle cells and achieve long-term correction of XLMTM-related muscle pathology. The clinical trial ASPIRO (NCT03199469) investigating resamirigene bilparvovec in XLMTM is currently paused while the risk:benefit balance associated with this gene therapy is further investigated., Methods: Muscle biopsies were taken before treatment and 24 and 48 weeks after treatment from ten boys with XLMTM in a clinical trial of resamirigene bilparvovec (ASPIRO; NCT03199469). Comprehensive histopathological analysis was performed., Findings: Baseline biopsies uniformly showed findings characteristic of XLMTM, including small myofibres, increased internal or central nucleation, and central aggregates of organelles. Biopsies taken at 24 weeks post-treatment showed marked improvement of organelle localisation, without apparent increases in myofibre size in most participants. Biopsies taken at 48 weeks, however, did show statistically significant increases in myofibre size in all nine biopsies evaluated at this timepoint. Histopathological endpoints that did not demonstrate statistically significant changes with treatment included the degree of internal/central nucleation, numbers of triad structures, fibre type distributions, and numbers of satellite cells. Limited (predominantly mild) treatment-associated inflammatory changes were seen in biopsy specimens from five participants., Interpretation: Muscle biopsies from individuals with XLMTM treated with resamirigene bilparvovec display statistically significant improvement in organelle localisation and myofibre size during a period of substantial improvements in muscle strength and respiratory function. This study identifies valuable histological endpoints for tracking treatment-related gains with resamirigene bilparvovec, as well as endpoints that did not show strong correlation with clinical improvement in this human study., Funding: Astellas Gene Therapies (formerly Audentes Therapeutics, Inc.)., Competing Interests: Declaration of interests MWL has received research funding from Astellas Gene Therapies∗ to his academic institution (Medical College of Wisconsin) and to his company (Diverge Translational Science Laboratory) for work related to the present manuscript; has received research grants or contracts to his academic institution (Medical College of Wisconsin) from Solid Biosciences, Kate Therapeutics, Taysha Therapeutics, Ultragenyx, and Prothelia; has received consulting fees from Astellas Gene Therapies∗, Encoded Therapeutics, Modis Therapeutics, Lacerta Therapeutics, AGADA Biosciences, Dynacure, Affinia, Voyager, BioMarin, Locanabio, and Vertex Pharmaceuticals; has received speaker fees and reimbursement for travel related to sponsored research from Astellas Gene Therapies∗; has received personal fees for scientific advisory board participation for Astellas Gene Therapies∗ and Solid Biosciences, and his institution has received payment from Taysha Therapeutics for his advisory board participation; he is currently CEO, founder, and owner of Diverge Translational Science Laboratory, which continues to work under contracts from many gene therapy companies including Astellas Gene Therapies∗, Solid Biosciences, Rocket Pharma, Kate Therapeutics, Carbon Biosciences, Dynacure, Nationwide Children's Hospital, Taysha Gene Therapies, and Ultragenyx. BS (Schoser) has received grants/contracts, honoraria, and support for attending meetings from Astellas Gene Therapies∗ has participated in Advisory Boards for Dynacure. MM has received personal fees and study funding to her institution from Astellas Gene Therapies∗ in relation to the present manuscript. CAS has received royalties from Elsevier for the book “Muscle Biopsy. A Practical Approach”. KAJ has received consulting fees from Astellas Gene Therapies∗ in relation to the present manuscript and other activities. PBS has received research funding from Astellas Gene Therapies∗ to support clinical trial investigations relating to the present manuscript; has received research contracts from Biogen, Dyne, Fulcrum, Pfizer, PTC Therapeutics, Reveragen, Sanofi, Sarepta, and Solid Biosciences; has received consulting fees from Alexion, Argenx, Biogen, Novartis Gene Therapies, Pfizer, UCB, and Sarepta; has received honoraria for lectures or presentations from Alexion, Argenx, Biogen, Catalyst, CSL Behring, Genentech, and Grifols; and has participated on Independent Data Monitoring Committees for Encoded Therapeutics, Excision BioTherapeutics, and Taysha. NLK reports research grants paid to her institution from AMO Pharma, Argenx, Astellas Gene Therapies∗, Biogen, Biohaven, Novartis, NS Pharma, Sarepta, Reveragen, Roche, and Scholar Rock; has received payment for educational presentations from Sarepta; and has participated in a Data Safety Monitoring Board for Sarepta and Advisory Boards for Argenx, BioMarin, Fibrogen, Roche, and Sarepta. BKS has received institutional research grants or contracts to serve as an INCEPTUS and ASPIRO study site from Astellas Gene Therapies∗. JJD has received research grants from NIH, CIHR, and Astellas Gene Therapies∗; has received support for attending annual meetings from the World Muscle Society (as Executive Board Member) and TREAT NMD (as Chair of Executive Board); and receives annual honoraria as a Scientific Advisory Board member for the RYR1 Foundation. WMF has received support for study materials and study personnel relating to the present manuscript from Astellas Gene Therapies∗; consulting fees from Sarepta, PTC Therapeutics, Novartis, and Roche; personal compensation from Novartis and Biogen, and institutional funding from Roche, for lectures; and has served on Scientific Advisory Boards for DGM and Glykogenosis e.V. CGB reports study funding relating to the present manuscript paid to NINDS; and has participated in data safety monitoring or advisory boards without financial compensation, in his capacity of representing NIH. AMS is a principal investigator in the ASPIRO study. AB has received speaker's honoraria from Pfizer and Roche; and has participated in advisory boards at for Pfizer and Roche. SN, ARF, DNS, ET, and URQ report no conflicts of interests. MB and MJP are full-time employees of Diverge Translational Science Laboratory. EO and SD report no conflicts of interest. PK is a full-time employee of Diverge Translational Science Laboratory. SNK report no conflicts of interest. HM is a full-time employee of Diverge Translational Science Laboratory. MVA, CW, and HGD report no conflicts of interest. AHB received study funding relating to the present manuscript; reports grants or contracts received from NIH, MDA (USA), and the Chan Zuckerberg Initiative, and from AFM Telethon, Alexion Pharmaceuticals Inc., Avidity, Dynacure SAS, Kate Therapeutics, and Pfizer Inc. He has received consulting fees from Astellas Gene Therapies∗, Dynacure, GLG Inc., Guidepoint Global, Kate Therapeutics, and Roche; has received support for attending meetings from Kate Therapeutics and MDA; holds equity in Kate Therapeutics and Kinea Bio, and is an inventor on a US patent describing a method for gene therapy of XLMTM. SC, EC, JL, CS, WM, BS (Sepulveda), FV are former employees of Astellas Gene Therapies∗. ESJ and SR are former employees and stockholders in Astellas Gene Therapies∗. SP was Chief Medical Officer and a stockholder in Astellas Gene Therapies∗ when the study was designed and initiated; he is no longer a stockholder and currently consults independently with a wide variety of companies and academic institutions primarily on Clinical Development matters. ∗Formerly Audentes Therapeutics, Inc., (Copyright © 2023. Published by Elsevier B.V.)

Background: X-linked myotubular myopathy (XLMTM) is a rare congenital myopathy resulting from dysfunction of the protein myotubularin encoded by the MTM1 gene. XLMTM has a high neonatal and infantile mortality rate due to a severe myopathic phenotype and respiratory failure. However, in a minority of XLMTM cases, patients present with milder phenotypes and achieve ambulation and adulthood. Notable facial dysmorphia is also present., Methods: We investigated the genotype-phenotype correlations in newly diagnosed XLMTM patients in a patients' cohort (previously published data plus three novel variants, n = 414). Based on the facial gestalt difference between XLMTM patients and unaffected controls, we investigated the use of the Face2Gene application., Results: Significant associations between severe phenotype and truncating variants ( p < 0.001), frameshift variants ( p < 0.001), nonsense variants ( p = 0.006), and in/del variants ( p = 0.036) were present. Missense variants were significantly associated with the mild and moderate phenotype ( p < 0.001). The Face2Gene application showed a significant difference between XLMTM patients and unaffected controls ( p = 0.001)., Conclusions: Using genotype-phenotype correlations could predict the disease course in most XLMTM patients, but still with limitations. The Face2Gene application seems to be a practical, non-invasive diagnostic approach in XLMTM using the correct algorithm.

Myofibrillar myopathies (MFMs) are a group of rare genetic disorders that affect the function of skeletal, cardiac and smooth muscle.MFM exhibits a considerable degree of clinical heterogeneity. In numerous instances of MFM, muscle weakness is the predominant manifestation. Certain MFM subtypes are distinguished by respiratory and cardiac impairment.There is little information available about anaesthetic management in MFM, and even less is known about obstetric anaesthesia.A successful case of a patient with MFM undergoing a caesarean section under combined neuraxial anaesthesia is reported. The patient experienced no complications, and functional recovery was swift., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Polyhydramnios can be caused by genetic defects at times. However, to establish an accurate diagnosis and provide a precise prenatal consultation in a given case is still a great challenge toward obstetricians. To uncover the genetic cause of polyhydramnios in the two consecutive pregnancies, we performed whole-exome sequencing of DNA for the second suffering fetuses, their parents, and targeted sanger sequencing of other members of this family. We discovered a hemizygous truncating variant in MTM1 gene, c.438&#95;439 del (p. H146Q fs*10) in this Chinese family. In the light of the molecular discoveries, the fetus's clinical phenotype was considered to be a good fit for X-linked myotubular myopathy (XLMTM). There is no related research to the prenatal manifestations of MTM1-related XLMTM among Chinese population, and this is the first one to present. Though the etiology of polyhydramnios is complicated, WES may provide us with a creative avenue in prenatal diagnosis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Background: X-linked myotubular myopathy is a rare, life-threatening, congenital muscle disease observed mostly in males, which is caused by mutations in MTM1. No therapies are approved for this disease. We aimed to assess the safety and efficacy of resamirigene bilparvovec, which is an adeno-associated viral vector serotype 8 delivering human MTM1., Methods: ASPIRO is an open-label, dose-escalation trial at seven academic medical centres in Canada, France, Germany, and the USA. We included boys younger than 5 years with X-linked myotubular myopathy who required mechanical ventilator support. The trial was initially in two parts. Part 1 was planned as a safety and dose-escalation phase in which participants were randomly allocated (2:1) to either the first dose level (1·3 × 10 14 vector genomes [vg]/kg bodyweight) of resamirigene bilparvovec or delayed treatment, then, for later participants, to either a higher dose (3·5 × 10 14 vg/kg bodyweight) of resamirigene bilparvovec or delayed treatment. Part 2 was intended to confirm the dose selected in part 1. Resamirigene bilparvovec was administered as a single intravenous infusion. An untreated control group comprised boys who participated in a run-in study (INCEPTUS; NCT02704273) or those in the delayed treatment cohort who did not receive any dose. The primary efficacy outcome was the change from baseline to week 24 in hours of daily ventilator support. After three unexpected deaths, dosing at the higher dose was stopped and the two-part feature of the study design was eliminated. Because of changes to the study design during its implementation, analyses were done on an as-treated basis and are deemed exploratory. All treated and control participants were included in the safety analysis. The trial is registered with ClinicalTrials.gov, NCT03199469. Outcomes are reported as of Feb 28, 2022. ASPIRO is currently paused while deaths in dosed participants are investigated., Findings: Between Aug 3, 2017 and June 1, 2021, 30 participants were screened for eligibility, of whom 26 were enrolled; six were allocated to the lower dose, 13 to the higher dose, and seven to delayed treatment. Of the seven children whose treatment was delayed, four later received the higher dose (n=17 total in the higher dose cohort), one received the lower dose (n=7 total in the lower dose cohort), and two received no dose and joined the control group (n=14 total, including 12 children from INCEPTUS). Median age at dosing or enrolment was 12·1 months (IQR 10·0-30·9; range 9·5-49·7) in the lower dose cohort, 31·1 months (16·0-64·7; 6·8-72·7) in the higher dose cohort, and 18·7 months (10·1-31·5; 5·9-39·3) in the control cohort. Median follow-up was 46·1 months (IQR 41·0-49·5; range 2·1-54·7) for lower dose participants, 27·6 months (24·6-29·1; 3·4-41·0) for higher dose participants, and 28·3 months (9·7-46·9; 5·7-32·7) for control participants. At week 24, lower dose participants had an estimated 77·7 percentage point (95% CI 40·22 to 115·24) greater reduction in least squares mean hours per day of ventilator support from baseline versus controls (p=0·0002), and higher dose participants had a 22·8 percentage point (6·15 to 39·37) greater reduction from baseline versus controls (p=0·0077). One participant in the lower dose cohort and three in the higher dose cohort died; at the time of death, all children had cholestatic liver failure following gene therapy (immediate causes of death were sepsis; hepatopathy, severe immune dysfunction, and pseudomonal sepsis; gastrointestinal haemorrhage; and septic shock). Three individuals in the control group died (haemorrhage presumed related to hepatic peliosis; aspiration pneumonia; and cardiopulmonary failure)., Interpretation: Most children with X-linked myotubular myopathy who received MTM1 gene replacement therapy had important improvements in ventilator dependence and motor function, with more than half of dosed participants achieving ventilator independence and some attaining the ability to walk independently. Investigations into the risk for underlying hepatobiliary disease in X-linked myotubular myopathy, and the need for monitoring of liver function before gene replacement therapy, are ongoing., Funding: Astellas Gene Therapies., Competing Interests: Declaration of interests PBS has received funding and provision of study materials from Astellas Gene Therapies (formerly Audentes Therapeutics) to support clinical trial investigations relating to the present manuscript; has received research grants or contracts from Biogen, Novartis Gene Therapies, Pfizer, PTC Therapeutics, Reveragen, Sanofi, Sarepta, and Solid Biosciences; has received consulting fees for advisory board participation from Alexion, Argenx, Biogen, Genentech, Novartis Gene Therapies, UCB, Sanofi, and Sarepta; and has received honoraria for lectures or presentations from Alexion, Argenx, Biogen, Catalyst, CSL Behring, Genentech, and Grifols. NLK has received research funding from Astellas Gene Therapies to her institute as a study site for the ASPIRO clinical trial; has received support from Astellas Gene Therapies for registration fees to attend and present at the International Congress on Neuromuscular Diseases 2022 (travel costs paid personally); has received research grants from Argenx, Biohaven, Biogen, Novartis, Sarepta, and Scholar Rock, consulting fees for participation on medical advisory boards for Argenx, BioMarin, Capacity Bio, and Sarepta, and honoraria for gene therapy lectures for Sarepta; and is on a data safety monitoring board for Sarepta. JJD has received research grants or contracts from Astellas Gene Therapies to his institute as a study site for the ASPIRO clinical trial and for preclinical studies; and has received an honorarium for a sponsored symposium and support for travel to an international meeting to present data from Astellas Gene Therapies. WM-F has received support for study materials and study personnel relating to the present manuscript from Astellas Gene Therapies; consulting fees from Sarepta, PTC Therapeutics, Novartis, and Roche; personal compensation from Novartis and Biogen and institutional funding from Roche, for lectures; and has served on scientific advisory boards for Deutsche Gesellschaft für Muskelkranke and Glykogenosis. CGB has received research grants, contracts, or travel support for various invited lectures at academic meetings from Noelia Foundation, Muscular Dystrophy UK, and Cure CMD; holds a patent for COL6A1 intron 11 pseudoexon skipping technologies unrelated to the present manuscript; has participated (without fees) in advisory boards for Solid Biosciences (IGNITE trial), Rocket Pharma, and Nationwide Children's Hospital; and is Chair of the Scientific Advisory Board of the MDUK Oxford Neuromuscular Centre. LS has received consulting fees and honoraria for lectures from Astellas Gene Therapies; and is coordinating investigator of the European NatHis-CNM study, funded by Dynacure. BKS has received institutional research grants or contracts for her institution to serve as an INCEPTUS and ASPIRO study site from Astellas Gene Therapies. AB reports institutional grants or contracts from PTC Therapeutics; has received payments or honoraria from Roche, Biogen, and Pfizer; and has participated in advisory boards at Roche and Pfizer. ARF has been a member of an independent data monitoring committee for a different clinical trial for MTM1-related myopathy and DNM2-related myopathy (the trial was terminated early). LNA has received grants or contracts from Astellas Gene Therapies via her institution to provide training and quality control services supporting the ASPIRO clinical trial programme. AHB reports research grants or contracts from the NIH, MDA (USA), AFM Telethon, Alexion Pharmaceuticals, Astellas Gene Therapies, Dynacure SAS, Pfizer, Kate Therapeutics, Chan Zuckerberg Initiative, and Avidity; has received consulting fees from Astellas Gene Therapies, Kate Therapeutics, and Roche Pharmaceuticals; has received honoraria for lectures or presentations from GLG and Guidepoint Global; has received support for travel and meeting attendance at the Muscular Dystrophy Association and World Muscle Society; is an executive board member at the World Muscle Society; is an inventor on and has received royalties for a patent for adeno-associated virus gene therapy for X-linked myotubular myopathy; and holds stocks in Kate Therapeutics and Kinea Bio. AB-B has received consulting fees from Astellas Gene Therapies and research funding from the Myotubular Trust for preclinical work related to the present manuscript; and holds a patent on systemic gene replacement therapy for treatment of X-linked myotubular myopathy. MKC has received consulting fees and institutional research funding supporting preclinical experiments for a US investigational new drug application relating to the gene therapy in the present manuscript; holds a patent for a systemic gene replacement therapy for treatment of X-linked myotubular myopathy; and has received option payments from Wake Forest University for the patent. TD has received consulting fees from Astellas Gene Therapies for study training on CHOP INTEND measurement in ASPIRO. RJG reports limited consulting fees from Astellas Gene Therapies for work on the ASPIRO study design and clinical outcome measures. JC is an employee of Astellas Gene Therapies. VMacB has received study funding relating to the present manuscript, in the form of a research grant and consulting fees from Astellas Gene Therapies paid both directly to her and her institution. ESJ was a former employee of Astellas Gene Therapies and formerly held stock in Astellas Gene Therapies. JL, FMa, WM, and FV were formerly employees of Astellas Gene Therapies. MM has received study funding relating to the present publication from Astellas Gene Therapies, formerly held stock in Astellas Gene Therapies, and was formerly employed by Astellas Gene Therepies. CH is an employee of Astellas Pharma Global Development. MN was formerly employed by Astellas Gene Therepies. MWL has received research funding from Astellas Gene Therapies to his academic institution (Medical College of Wisconsin) and to his company (Diverge Translational Science Laboratory) for work related to the present manuscript; has received research grants or contracts to his academic institution from Solid Biosciences, Kate Therapeutics, Taysha Therapeutics, Ultragenyx, and Prothelia; has received consulting fees from Astellas Gene Therapies, Encoded Therapeutics, Modis Therapeutics, Lacerta Therapeutics, AGADA Biosciences, Dynacure, Affinia, Voyager, BioMarin, Locanabio, and Vertex Pharmaceuticals; has received speaker fees and reimbursement for travel related to sponsored research from Astellas Gene Therapies; has received personal fees for scientific advisory board participation for Astellas Gene Therapies and Solid Biosciences; and his institution has received payment from Taysha Therapeutics for his advisory board participation. MWL is currently Chief Executive Officer, founder, and owner of Diverge Translational Science Laboratory, which continues to work under contracts from many gene therapy companies including Astellas Gene Therapies, Solid Biosciences, Rocket Pharma, Kate Therapeutics, Carbon Biosciences, Dynacure, Nationwide Children's Hospital, Taysha Gene Therapies, and Ultragenyx. SP was an employee at Astellas Gene Therapies from February, 2014, to June, 2019, and was the senior physician overseeing the study relating to the present manuscript. SR reports holding stock in Astellas Gene Therapies and was formerly employed by Astellas Gene Therapies. All other authors declare no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY-NC-ND 4.0 license. Published by Elsevier Ltd.. All rights reserved.)

Competing Interests: Declaration of Competing Interest None.

Competing Interests: NCV was Principal Investigator of the Unite-CNM trial on Dynacure, and is a member of the scientific advisory board of ZNM Zusammen Stark!. HJ has acted in an advisory capacity for Audentes and Astellas, two companies involved in the development of treatments for X-linked myotubular myopathy. AAR and AF declare no competing interests. All authors are members of the European Reference Network for rare neuromuscular diseases. The authors are grateful to all patients and their families who participated in the natural history studies and the ASPIRO trial, and to the international patient organisations ZNM Zusammen Stark!, the Myotubular Trust, and the MTM-CNM Family Connection.

Myotubular myopathy is a rare disease of genetic origin characterized by significant muscle weakness leading to respiratory disorders and for which no treatment exists today. In this paper, we show that inhibition of the activity of the enzyme PI3KC2β prevents the development of this myopathy in a mouse model of the disease, thus identifying a therapeutic target to treat myotubular myopathy in humans., (© 2023 médecine/sciences – Inserm.)

Autosomal dominant centronuclear myopathy (AD-CNM) is a rare congenital myopathy characterized by muscle weakness and centrally located nuclei in muscle fibers in the absence of any regeneration. AD-CNM is due to mutations in the DNM2 gene encoding dynamin 2 (DNM2), a large GTPase involved in intracellular membrane trafficking and a regulator of actin and microtubule cytoskeletons. DNM2 mutations are associated with a broad clinical spectrum ranging from severe neonatal to less severe late-onset forms. The histopathological signature includes nuclear centralization, predominance and atrophy of type 1 myofibers and radiating sarcoplasmic strands. To explain the muscle dysfunction, several pathophysiological mechanisms affecting key mechanisms of muscle homeostasis have been identified. They include defects in excitation-contraction coupling, muscle regeneration, mitochondria or autophagy. Several therapeutic approaches are under development by modulating the expression of DNM2 in a pan-allelic manner or by allele-specific silencing targeting only the mutated allele, which open the era of clinical trials for this pathology., (© 2023 médecine/sciences – Inserm.)

Myo-inositol belongs to one of the sugar alcohol groups known as cyclitols. Phosphatidylinositols are one of the derivatives of Myo-inositol, and constitute important mediators in many intracellular processes such as cell growth, cell differentiation, receptor recycling, cytoskeletal organization, and membrane fusion. They also have even more functions that are essential for cell survival. Mutations in genes encoding phosphatidylinositols and their derivatives can lead to many disorders. This review aims to perform an in-depth analysis of these connections. Many authors emphasize the significant influence of phosphatidylinositols and phosphatidylinositols' phosphates in the pathogenesis of myotubular myopathies, neurodegenerative disorders, carcinogenesis, and other less frequently observed diseases. In our review, we have focused on three of the most often mentioned groups of disorders. Inositols are the topic of many studies, and yet, there are no clear results of successful clinical trials. Analysis of the available literature gives promising results and shows that further research is still needed.

X-linked myotubular myopathy (XLMTM) is a severe congenital disease characterized by profound muscle weakness, respiratory failure, and early death. No approved therapy for XLMTM is currently available. Adeno-associated virus (AAV)-mediated gene replacement therapy has shown promise as an investigational therapeutic strategy. We aimed to characterize the transcriptomic changes in muscle biopsies of individuals with XLMTM who received resamirigene bilparvovec (AT132; rAAV8-Des-hMTM1) in the ASPIRO clinical trial and to identify potential biomarkers that correlate with therapeutic outcome. We leveraged RNA-sequencing data from the muscle biopsies of 15 study participants and applied differential expression analysis, gene co-expression analysis, and machine learning to characterize the transcriptomic changes at baseline (pre-dose) and at 24 and 48 weeks after resamirigene bilparvovec dosing. As expected, MTM1 expression levels were significantly increased after dosing (p < 0.0001). Differential expression analysis identified upregulated genes after dosing that were enriched in several pathways, including lipid metabolism and inflammatory response pathways, and downregulated genes were enriched in cell-cell adhesion and muscle development pathways. Genes involved in inflammatory and immune pathways were differentially expressed between participants exhibiting ventilator support reduction of either greater or less than 6 h/day after gene therapy compared to pre-dosing. Co-expression analysis identified similarly regulated genes, which were grouped into modules. Finally, the machine learning model identified five genes, including MTM1, as potential RNA biomarkers to monitor the progress of AAV gene replacement therapy. These findings further extend our understanding of AAV-mediated gene therapy in individuals with XLMTM at the transcriptomic level., Competing Interests: Declaration of interests G.A., P.P., F.V., and F.U. were formerly employees and/or stockholders of Astellas Gene Therapies (formerly known as Audentes Therapeutics). H.-J.C., M.J.S.-D., and N.L. are employees and/or stockholders of Astellas Gene Therapies (formerly known as Audentes Therapeutics). C.C. is a consultant for Astellas Gene Therapies (formerly known as Audentes Therapeutics). F.M. was formerly the senior vice president of translational science at Audentes Therapeutics. S.B. has a sponsored research agreement with Astellas Gene Therapies (formerly Audentes Therapeutics)., (Copyright © 2023 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Centronuclear and myotubular myopathies (CNM) are rare and severe genetic diseases associated with muscle weakness and atrophy as well as intracellular disorganization of myofibres. The main mutated proteins control lipid and membrane dynamics and are the lipid phosphatase myotubularin (MTM1), and the membrane remodelling proteins amphiphysin 2 (BIN1) and dynamin 2 (DNM2). There is no available therapy. Here, to validate a novel therapeutic strategy for BIN1- and DNM2-CNM, we evaluated adeno-associated virus-mediated MTM1 (AAV-MTM1 ) overexpression in relevant mouse models. Early systemic MTM1 overexpression prevented the development of the CNM pathology in Bin1mck-/- mice, while late intramuscular MTM1 expression partially reverted the established phenotypes after only 4 weeks of treatment. However, AAV-MTM1 injection did not change the DNM2-CNM mouse phenotypes. We investigated the mechanism of the rescue of the myopathy in BIN1-CNM and found that the lipid phosphatase activity of MTM1 was essential for the rescue of muscle atrophy and myofibre hypotrophy but dispensable for the rescue of myofibre disorganization including organelle mis-position and T-tubule defects. Furthermore, the improvement of T-tubule organization correlated with normalization of key regulators of T-tubule morphogenesis, dysferlin and caveolin. Overall, these data support the inclusion of BIN1-CNM patients in an AAV-MTM1 clinical trial., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Guarantors of Brain.)

X-linked myotubular myopathy (XLMTM) is a fatal congenital disorder caused by mutations in the MTM1 gene. Currently, there are no approved treatments, although AAV8-mediated gene transfer therapy has shown promise in animal models and preliminarily in patients. However, 4 patients with XLMTM treated with gene therapy have died from progressive liver failure, and hepatobiliary disease has now been recognized more broadly in association with XLMTM. In an attempt to understand whether loss of MTM1 itself is associated with liver pathology, we have characterized what we believe to be a novel liver phenotype in a zebrafish model of this disease. Specifically, we found that loss-of-function mutations in mtm1 led to severe liver abnormalities including impaired bile flux, structural abnormalities of the bile canaliculus, and improper endosome-mediated trafficking of canalicular transporters. Using a reporter-tagged Mtm1 zebrafish line, we established localization of Mtm1 in the liver in association with Rab11, a marker of recycling endosomes, and canalicular transport proteins and demonstrated that hepatocyte-specific reexpression of Mtm1 could rescue the cholestatic phenotype. Last, we completed a targeted chemical screen and found that Dynasore, a dynamin-2 inhibitor, was able to partially restore bile flow and transporter localization to the canalicular membrane. In summary, we demonstrate, for the first time to our knowledge, liver abnormalities that were directly caused by MTM1 mutation in a preclinical model, thus establishing the critical framework for better understanding and comprehensive treatment of the human disease.

Aims: Dynamin-2 is a large GTPase, a member of the dynamin superfamily that regulates membrane remodelling and cytoskeleton dynamics. Mutations in the dynamin-2 gene (DNM2) cause autosomal dominant centronuclear myopathy (CNM), a congenital neuromuscular disorder characterised by progressive weakness and atrophy of the skeletal muscles. Cognitive defects have been reported in some DNM2-linked CNM patients suggesting that these mutations can also affect the central nervous system (CNS). Here we studied how a dynamin-2 CNM-causing mutation influences the CNS function., Methods: Heterozygous mice harbouring the p.R465W mutation in the dynamin-2 gene (HTZ), the most common causing autosomal dominant CNM, were used as disease model. We evaluated dendritic arborisation and spine density in hippocampal cultured neurons, analysed excitatory synaptic transmission by electrophysiological field recordings in hippocampal slices, and evaluated cognitive function by performing behavioural tests., Results: HTZ hippocampal neurons exhibited reduced dendritic arborisation and lower spine density than WT neurons, which was reversed by transfecting an interference RNA against the dynamin-2 mutant allele. Additionally, HTZ mice showed defective hippocampal excitatory synaptic transmission and reduced recognition memory compared to the WT condition., Conclusion: Our findings suggest that the dynamin-2 p.R465W mutation perturbs the synaptic and cognitive function in a CNM mouse model and support the idea that this GTPase plays a key role in regulating neuronal morphology and excitatory synaptic transmission in the hippocampus., (© 2023 British Neuropathological Society.)

Myofibrillar myopathies (MFMs) are a group of hereditary neuromuscular disorders sharing common histological features, such as myofibrillar derangement, Z-disk disintegration, and the accumulation of degradation products into protein aggregates. They are caused by mutations in several genes that encode either structural proteins or molecular chaperones. Nevertheless, the mechanisms by which mutated genes result in protein aggregation are still unknown. To unveil the role of myotilin and αB-crystallin in the pathogenesis of MFM, we injected zebrafish fertilized eggs at the one-cell stage with expression plasmids harboring cDNA sequences of human wildtype or mutated MYOT (p.Ser95Ile) and human wildtype or mutated CRYAB (p.Gly154Ser). We evaluated the effects on fish survival, motor behavior, muscle structure and development. We found that transgenic zebrafish showed morphological defects that were more severe in those overexpressing mutant genes. which developed a myopathic phenotype consistent with that of human myofibrillar myopathy, including the formation of protein aggregates. Results indicate that pathogenic mutations in myotilin and αB-crystallin genes associated with MFM cause a structural and functional impairment of the skeletal muscle in zebrafish, thereby making this non-mammalian organism a powerful model to dissect disease pathogenesis and find possible druggable targets.

Congenital myopathies define a genetically heterogeneous group of disorders associated with severe muscle weakness, for which no therapies are currently available. Here we investigated the repurposing of tamoxifen in mouse models of mild or severe forms of centronuclear myopathies due to mutations in BIN1 (encoding amphiphysin 2) or DNM2 (encoding dynamin 2), respectively. Exposure to a tamoxifen-enriched diet from 3 weeks of age resulted in significant improvement in muscle contractility without increase in fibre size in both models, underlying an increase in the capacity of the muscle fibres to produce more force. In addition, the histological alterations were fully rescued in the BIN1-centronuclear myopathies mouse model. To assess the mechanism of the rescue, transcriptome analyses and targeted protein studies were performed. Although tamoxifen is known to modulate the transcriptional activity of the oestrogen receptors, correction of the disease transcriptomic signature was marginal on tamoxifen treatment. Conversely, tamoxifen lowered the abnormal increase in dynamin 2 protein level in both centronuclear myopathies models. Of note, it was previously reported that dynamin 2 increase is a main pathological cause of centronuclear myopathies. The Akt/mTOR muscle hypertrophic pathway and protein markers of the ubiquitin-proteasome system (the E3 ubiquitin ligase cullin 3) and autophagy (p62) were increased in both models of centronuclear myopathies. Normalization of dynamin 2 level mainly correlated with the normalization of cullin 3 protein level on tamoxifen treatment, supporting the idea that the ubiquitin-proteasome system is a main target for the tamoxifen effect in the amelioration of these diseases. Overall, our data suggest that tamoxifen antagonizes disease development probably through dynamin 2 level regulation. In conclusion, the beneficial effect of tamoxifen on muscle function supports the suggestion that tamoxifen may serve as a common therapy for several autosomal forms of centronuclear myopathies., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Centronuclear myopathy (CNM) is a heterogeneous group of muscle disorders primarily characterized by muscle weakness and variable degrees of respiratory dysfunction caused by mutations in MTM1, DNM2, RYR1, TTN and BIN1. X-linked myotubular myopathy has been the focus of recent natural history studies and clinical trials. Data on respiratory function for other genotypes is limited. To better understand the respiratory properties of the CNM spectrum, we performed a retrospective study in a non-selective Dutch CNM cohort. Respiratory dysfunction was defined as an FVC below 70% of predicted and/or a daytime pCO2 higher than 6 kPa. We collected results of other pulmonary function values (FEV1/FVC ratio) and treatment data from the home mechanical ventilation centres. Sixty-one CNM patients were included. Symptoms of respiratory weakness were reported by 15/47 (32%) patients. Thirty-three individuals (54%) with different genotypes except autosomal dominant (AD)-BIN1-related CNM showed respiratory dysfunction. Spirometry showed decreased FVC, FEV1 & PEF values in all but two patients. Sixteen patients were using HMV (26%), thirteen of them only during night-time. In conclusion, this study provides insight into the prevalence of respiratory symptoms in four genetic forms of CNM in the Netherlands and offers the basis for future natural history studies., Competing Interests: Declaration of Competing Interest N. Voermans was PI of the phase I/II Unite-CNM trial for Dynacure. This has not caused a conflict of interest for this manuscript. None of the other authors reported a conflict of interest. The authors received no financial support for the research, authorship, and/or publication of this article., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

Background: X-linked myotubular myopathy (XLMTM) is a rare, life-threatening congenital myopathy with multisystem involvement, often requiring invasive ventilator support, gastrostomy tube feeding, and wheelchair use. Understanding healthcare resource utilization in patients with XLMTM is important for development of targeted therapies but data are limited., Methods: We analyzed individual medical codes as governed by Healthcare Common Procedure Coding System, Current Procedural Terminology, and International Classification of Diseases, 10th Revision (ICD-10) for a defined cohort of XLMTM patients within a US medical claims database. Using third-party tokenization software, we defined a cohort of XLMTM patient tokens from a de-identified dataset in a research registry of diagnostically confirmed XLMTM patients and de-identified data from a genetic testing company. After approval of an ICD-10 diagnosis code for XLMTM (G71.220) in October 2020, we identified additional patients., Results: A total of 192 males with a diagnosis of XLMTM were included: 80 patient tokens and 112 patients with the new ICD-10 code. From 2016 to 2020, the annual number of patients with claims increased from 120 to 154 and the average number of claims per patient per year increased from 93 to 134. Of 146 patients coded with hospitalization claims, 80 patients (55%) were first hospitalized between 0 and 4 years of age. Across all patients, 31% were hospitalized 1-2 times, 32% 3-9 times, and 14% ≥ 10 times. Patients received care from multiple specialty practices: pulmonology (53%), pediatrics (47%), neurology (34%), and critical care medicine (31%). The most common conditions and procedures related to XLMTM were respiratory events (82%), ventilation management (82%), feeding difficulties (81%), feeding support (72%), gastrostomy (69%), and tracheostomy (64%). Nearly all patients with respiratory events had chronic respiratory claims (96%). The most frequent diagnostic codes were those investigating hepatobiliary abnormalities., Conclusions: This innovative medical claims analysis shows substantial healthcare resource use in XLMTM patients that increased over the last 5 years. Most patients required respiratory and feeding support and experienced multiple hospitalizations throughout childhood and beyond for those that survived. This pattern delineation will inform outcome assessments with the emergence of novel therapies and supportive care measures., (© 2023. The Author(s).)

Competing Interests: Declaration of Competing Interest The authors declare no competing interests.

Centronuclear myopathies (CNMs) are a group of inherited rare muscle disorders characterised by the abnormal position of the nucleus in the center of the muscle fiber. One of CNM is the X-Linked Myotubular Myopathy, caused by mutations in the myotubularin (MTM1) gene (XLMTM), characterised by profound muscle hypotonia and weakness, severe bulbar and respiratory involvement. Here, we generated an induced pluripotent stem cell (iPSC) line from a patient with a severe form of XLMTM. Dermal fibroblasts were reprogrammed to pluripotency using a non-integrating mRNA-based protocol. This new MTM1-mutant iPSC line could facilitate disease-modelling and therapy development studies for XLMTM., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Liani G Devito reports financial support was provided by The Francis Crick Institute., (Copyright © 2023. Published by Elsevier B.V.)

Phosphoinositides (PIs) are membrane lipids that regulate signal transduction and vesicular trafficking. X-linked centronuclear myopathy (XLCNM), also called myotubular myopathy, results from loss-of-function mutations in the MTM1 gene, which encodes the myotubularin phosphatidylinositol 3-phosphate (PtdIns3P) lipid phosphatase. No therapy for this disease is currently available. Previous studies showed that loss of expression of the class II phosphoinositide 3-kinase (PI3K) PI3KC2β (PI3KC2B) protein improved the phenotypes of an XLCNM mouse model. PI3Ks are well known to have extensive scaffolding functions and the importance of the catalytic activity of this PI3K for rescue remains unclear. Here, using PI3KC2β kinase-dead mice, we show that the selective inactivation of PI3KC2β kinase activity is sufficient to fully prevent muscle atrophy and weakness, histopathology, and sarcomere and triad disorganization in Mtm1-knockout mice. This rescue correlates with normalization of PtdIns3P level and mTORC1 activity, a key regulator of protein synthesis and autophagy. Conversely, lack of PI3KC2β kinase activity did not rescue the histopathology of the BIN1 autosomal CNM mouse model. Overall, these findings support the development of specific PI3KC2β kinase inhibitors to cure myotubular myopathy.

Purpose: Congenital myopathies are a heterogeneous group of diseases affecting the skeletal muscles and characterized by high clinical, genetic, and histological variability. Magnetic Resonance (MR) is a valuable tool for the assessment of involved muscles (i.e., fatty replacement and oedema) and disease progression. Machine Learning is becoming increasingly applied for diagnostic purposes, but to our knowledge, Self-Organizing Maps (SOMs) have never been used for the identification of the patterns in these diseases. The aim of this study is to evaluate if SOMs may discriminate between muscles with fatty replacement (S), oedema (E) or neither (N)., Methods: MR studies of a family affected by tubular aggregates myopathy (TAM) with the histologically proven autosomal dominant mutation of the STIM1 gene, were examined: for each patient, in two MR assessments (i.e., t0 and t1, the latter after 5 years), fifty-three muscles were evaluated for muscular fatty replacement on the T1w images, and for oedema on the STIR images, for reference. Sixty radiomic features were collected from each muscle at t0 and t1 MR assessment using 3DSlicer software, in order to obtain data from images. A SOM was created to analyze all datasets using three clusters (i.e., 0, 1 and 2) and results were compared with radiological evaluation., Results: Six patients with TAM STIM1-mutation were included. At t0 MR assessments, all patients showed widespread fatty replacement that intensifies at t1, while oedema mainly affected the muscles of the legs and appears stable at follow-up. All muscles with oedema showed fatty replacement, too. At t0 SOM grid clustering shows almost all N muscles in Cluster 0 and most of the E muscles in Cluster 1; at t1 almost all E muscles appear in Cluster 1., Conclusion: Our unsupervised learning model appears to be able to recognize muscles altered by the presence of edema and fatty replacement., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Lupi et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Myofibrillar myopathies (MFM) are a group of chronic muscle diseases pathophysiologically characterized by accumulation of protein aggregates and structural failure of muscle fibers. A subtype of MFM is caused by heterozygous mutations in the filamin C ( FLNC ) gene, exhibiting progressive muscle weakness, muscle structural alterations and intracellular protein accumulations. Here, we characterize in depth the pathogenicity of two novel truncating FLNc variants (p.Q1662X and p.Y2704X) and assess their distinct effect on FLNc stability and distribution as well as their impact on protein quality system (PQS) pathways. Both variants cause a slowly progressive myopathy with disease onset in adulthood, chronic myopathic alterations in muscle biopsy including the presence of intracellular protein aggregates. Our analyses revealed that p.Q1662X results in FLNc haploinsufficiency and p.Y2704X in a dominant-negative FLNc accumulation. Moreover, both protein-truncating variants cause different PQS alterations: p.Q1662X leads to an increase in expression of several genes involved in the ubiquitin-proteasome system (UPS) and the chaperone-assisted selective autophagy (CASA) system, whereas p.Y2704X results in increased abundance of proteins involved in UPS activation and autophagic buildup. We conclude that truncating FLNC variants might have different pathogenetic consequences and impair PQS function by diverse mechanisms and to varying extents. Further studies on a larger number of patients are necessary to confirm our observations.