Effects of gene replacement therapy with resamirigene bilparvovec (AT132) on skeletal muscle pathology in X-linked myotubular myopathy: results from a substudy of the ASPIRO open-label clinical trial.

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.).

[The dynamin-2-gene related centronuclear myopathy]. / La myopathie centronucléaire liée au gène de la dynamine 2.

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.

Title: La myopathie centronucléaire liée au gène de la dynamine 2. Abstract: La myopathie centronucléaire autosomique dominante (AD-CNM) est une myopathie congénitale rare caractérisée par une faiblesse musculaire et par la présence de noyaux centraux dans les fibres musculaires en absence de tout processus de régénération. L'AD-CNM est due à des mutations du gène DNM2 codant la dynamine 2 (DNM2), une volumineuse GTPase impliquée dans le trafic membranaire intracellulaire et un régulateur des cytosquelettes d'actine et de microtubules. Les mutations de la DNM2 sont associées à un large éventail clinique allant de formes sévères néonatales à des formes moins graves à début plus tardif. La signature histopathologique inclut une centralisation nucléaire, une prédominance et une atrophie des fibres lentes, ainsi que des travées sarcoplasmiques en rayons de roue. Pour expliquer la dysfonction musculaire, plusieurs mécanismes physiopathologiques affectant des étapes clés de l'homéostasie musculaire ont été identifiés. Ils incluent des défauts du couplage excitation-contraction, de la régénération musculaire, des mitochondries ou de l'autophagie. Plusieurs approches thérapeutiques sont en développement, en particulier la modulation de l'expression de la DNM2 pan-allélique ou ne ciblant que l'allèle muté, ouvrant ainsi la porte à des essais cliniques dans cette pathologie.

[Microtubular network and functionality of the striated skeletal muscle]. / Réseau microtubulaire et fonctionnalité du muscle strié squelettique.

Striated skeletal muscles are made of post-mitotic and multinucleated cells: muscle fibers, in which nuclei are regularly spaced and positioned at their periphery. The specific positioning of nuclei, necessary for the proper functioning of the muscle, is mainly regulated by the microtubule network and partner proteins. Many muscular pathologies present alterations in both the organization of the microtubule network and nuclear positioning, as observed in Duchenne Muscular Dystrophy, centronuclear myopathies or various neuromuscular diseases. The importance of the microtubule interactome and its influence in the maintenance of skeletal muscle homeostasis is a key issue in understanding muscle diseases.

Title: Réseau microtubulaire et fonctionnalité du muscle strié squelettique. Abstract: Les muscles striés squelettiques sont constitués de cellules post-mitotiques et multinucléées : les fibres musculaires, dans lesquelles les noyaux sont régulièrement espacés et positionnés à leur périphérie. Ce positionnement spécifique des noyaux, nécessaire au bon fonctionnement du muscle, est essentiellement régulé par le réseau microtubulaire et ses partenaires protéiques. De nombreuses pathologies musculaires présentent une altération à la fois de l'organisation du réseau microtubulaire et du positionnement nucléaire, comme observé dans la Dystrophie Musculaire de Duchenne, les myopathies centronucléaires ou certaines maladies neuromusculaires. L'importance de l'interactome microtubulaire et son influence dans le maintien de l'homéostasie du muscle strié squelettique est un enjeu capital dans la compréhension des pathologies musculaires.

A brief history of the congenital myopathies - the myopathological perspective.

Congenital myopathies are defined by early clinical onset, slow progression, hereditary nature and disease-specific myopathological lesions - however, with exceptions - demanding special techniques in regard to morphological diagnostic and research work-up. To identify an index disease in a family requires a muscle biopsy - and no congenital myopathy has ever been first described at autopsy. The nosographic history commenced when - in addition to special histopathological techniques in the earliest classical triad of central core disease, 1956, nemaline myopathy, 1963, and centronuclear myopathy, 1966/67, within a decade - electron microscopy and enzyme histochemistry were applied to unfixed frozen muscle tissue and, thus, revolutionized diagnostic and research myopathology. During the following years, the list of structure-defined congenital myopathies grew to some 40 conditions. Then, the introduction of immunohistochemistry allowed myopathological documentation of proteins and their abnormalities in individual congenital myopathies. Together with the diagnostic evolution of molecular genetics, many more congenital myopathies were described, without new disease-specific lesions or only already known ones. These were nosographically defined by individual mutations in hitherto congenital myopathies-unrelated genes. This latter development may also affect the nomenclature of congenital myopathies in that the mutant gene needs to be attached to the individually identified congenital myopathies with or without the disease-specific lesion, such as CCD-RYR1 or CM-RYR1. This principle is similar to that of the nomenclature of Congenital Disorders of Glycosylation. Retroactive molecular characterization of originally and first described congenital myopathies has only rarely been achieved.

The Genetic Background of Abnormalities in Metabolic Pathways of Phosphoinositides and Their Linkage with the Myotubular Myopathies, Neurodegenerative Disorders, and Carcinogenesis.

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.

Whole exome sequencing discloses a pathogenic MTM1 gene mutation in a continuous polyhydramnios family in China: Case report and literature review.

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_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.

High-throughput transcriptome analyses from ASPIRO, a phase 1/2/3 study of gene replacement therapy for X-linked myotubular myopathy.

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.

Loss of Mtm1 causes cholestatic liver disease in a model of X-linked myotubular myopathy.

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.

Arrhythmias in patients with X-linked myotubular myopathy. / Arritmias en pacientes con miopatía miotubular ligada al cromosoma X.

INTRODUCTION: Myotubular myopathy is a congenital muscle disease caused by a mutation in the myotubularin (MTM1) gene. The X-linked myotubular myopathy (XLMTM) affects males with early-onset symptoms such as muscle weakness, hypotonia, and respiratory distress. To our knowledge, cardiac involvement has not been previously described in this condition, in contrast to other types of congenital myopathies such as nemaline myopathy or core myopathy. CASE REPORTS: We report two clinical cases of XLMTM that started with severe sinus bradycardia or auriculoventricular block from the first days of life, with pathologic 24-hours Holter monitoring in both cases. A primary cardiac affection was excluded by electrophysiological studies and normal heart rate was recovered with proper respiratory support. DISCUSSION: These cases with sever bradyarrhythmia in a well know pathology such the XLMTM represents a nuance on the usual differential diagnostics of congenital myopathies.

TITLE: Arritmias en pacientes con miopatía miotubular ligada al cromosoma X.Introducción. La miopatía miotubular es una enfermedad muscular congénita causada por una mutación en el gen de la miotubularina (MTM1). La miopatía miotubular ligada al cromosoma X (XLMTM) afecta a los hombres con síntomas de aparición temprana como debilidad muscular, hipotonía y dificultad respiratoria. Hasta donde sabemos, la afectación cardíaca en estos pacientes no se ha descrito previamente, a diferencia de otros tipos de miopatías congénitas, como la miopatía nemalínica o la miopatía con cores. Casos clínicos. Presentamos dos casos clínicos de XLMTM que comenzaron con bradicardia sinusal grave o bloqueo auriculoventricular desde los primeros días de vida, con Holter patológico en ambos casos. Se descartó una afectación cardíaca primaria por estudios electrofisiológicos y se recuperó la frecuencia cardíaca normal con soporte respiratorio adecuado. Conclusión. Estos casos con bradicardia grave en una patología bien conocida, como la XLMTM, suponen un matiz en el diagnóstico diferencial habitual de las miopatías congénitas.

A Possible Case of Centronuclear Myopathy: A Case Report.

Congenital myopathies (CMs) are a group of diseases that primarily affect the muscle fiber, especially the contractile apparatus and the different components that condition its normal functioning. They present as muscle weakness and hypotonia at birth or during the first year of life. Centronuclear CM is characterized by a high incidence of nuclei located centrally and internally in muscle fibers. Clinical case: a 22-year-old male patient with symptoms of muscle weakness since early childhood, with difficulty in performing physical activity according to his age, with the presence of a long face, a waddling gait, and a global decrease in muscle mass. Electromyography was performed, showing a neurogenic pattern and not the expected myopathic one, neuroconduction with reduced amplitude of the motor potential of the peroneal nerve and axonal and myelin damage of the posterior tibial nerves. The microscopic study of the studied striated muscle fragments stained with hematoxylin-eosin and Masson's trichrome showed the presence of fibers with central nuclei, diagnosing CM. The patient meets most of the description for CM, with involvement of all striated muscles, although it is important to note the neurogenic pattern present in this case, due to the denervation of damaged muscle fibers, which contain terminal axonal segments. Neuroconduction shows the involvement of motor nerves, but with normal sensory studies, axonal polyneuropathy is unlikely, due to normal sensory potentials. Different pathological findings have been described depending on the mutated gene in this disease, but all coincide with the presence of fibers with central nuclei for diagnosis by this means, which is so important in institutions where it is not possible to carry out genetic studies, and allowing early specific treatment, according to the stage through which the patient passes.

Novel p.Asp27Glu ACTA1 variant features congenital myopathy with finger flexor weakness, cardiomyopathy, and cardiac conduction defects.

Pathogenic variants in the skeletal muscle α-actin 1 gene (ACTA1) cause a spectrum of myopathies with clinical and myopathological diversity. Clinical presentations occur from the prenatal period to adulthood, commonly with proximal-predominant weakness and rarely preferential distal weakness. Myopathological findings are wide-ranging, with nemaline rods being most frequent. Associated cardiomyopathy is rare and conduction defects are not reported. We describe a family with congenital myopathy with prominent finger flexor weakness and cardiomyopathy with cardiac conduction defects. The proband, a 48-year-old Caucasian male, his 73-year-old mother, 41-year-old sister, and 19-year-old nephew presented with prominent finger flexor weakness on a background of neonatal hypotonia and delayed motor milestones. All had progressive cardiomyopathy with systolic dysfunction and/or left ventricular dilation. The proband and sister had intraventricular conduction delay and left anterior fascicular block, respectively. The mother had atrial fibrillation. Muscle biopsy in the proband and sister demonstrated congenital fiber-type disproportion and rare nemaline rods in the proband. A novel dominant variant in ACTA1 (c.81C>A, p.Asp27Glu) segregated within the family. This family expands the genotypic and phenotypic spectrum of ACTA1-related myopathy, highlighting preferential finger flexor involvement with cardiomyopathy and conduction disease. We emphasize early and ongoing cardiac surveillance in ACTA1-related myopathy.

Novel Filamin C Myofibrillar Myopathy Variants Cause Different Pathomechanisms and Alterations in Protein Quality Systems.

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.

X-Linked Myotubular Myopathy in a Female Patient with a Pathogenic Variant in the MTM1 Gene.

X-linked centronuclear myopathy is caused by pathogenic variants in the MTM1 gene, which encodes myotubularin, a phosphatidylinositol 3-phosphate (PI3P) phosphatase. This form of congenital myopathy predominantly affects males. This study presents a case of X-linked myotubular myopathy in a female carrier of a pathogenic c.1261-10A>G variant in the MTM1 gene.

Inactivating the lipid kinase activity of PI3KC2ß is sufficient to rescue myotubular myopathy in mice.

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) PI3KC2ß (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 PI3KC2ß kinase-dead mice, we show that the selective inactivation of PI3KC2ß 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 PI3KC2ß kinase activity did not rescue the histopathology of the BIN1 autosomal CNM mouse model. Overall, these findings support the development of specific PI3KC2ß kinase inhibitors to cure myotubular myopathy.

Collagen VI in the Musculoskeletal System.

Collagen VI exerts several functions in the tissues in which it is expressed, including mechanical roles, cytoprotective functions with the inhibition of apoptosis and oxidative damage, and the promotion of tumor growth and progression by the regulation of cell differentiation and autophagic mechanisms. Mutations in the genes encoding collagen VI main chains, COL6A1, COL6A2 and COL6A3, are responsible for a spectrum of congenital muscular disorders, namely Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) and myosclerosis myopathy (MM), which show a variable combination of muscle wasting and weakness, joint contractures, distal laxity, and respiratory compromise. No effective therapeutic strategy is available so far for these diseases; moreover, the effects of collagen VI mutations on other tissues is poorly investigated. The aim of this review is to outline the role of collagen VI in the musculoskeletal system and to give an update about the tissue-specific functions revealed by studies on animal models and from patients' derived samples in order to fill the knowledge gap between scientists and the clinicians who daily manage patients affected by collagen VI-related myopathies.

X-linked myotubular myopathy: a clinical report and a review of the mild phenotype. / Miopatía miotubular ligada al cromosoma X: informe clínico y revisión del fenotipo leve.

INTRODUCTION: X-linked myotubular myopathy is a rare centronuclear myopathy that affects approximately 1 in 50,000 male newborns caused by pathogenic variants in the myotubularin 1 gene (MTM1). The clinical severity varies, however the need for ventilatory support occurs almost invariably. CASE REPORT: We report the case of a 4-year-old boy presenting mild muscle hypotonia at 12 months-old, expressive language disorder, global developmental delay, and a sensory processing disorder. Clinical exome sequencing identified the hemizygous variant c.722G>A p.(Arg241His) in exon 9 of the myotubularin 1 gene (NM_000252.2). The mother is a heterozygous carrier of the same variant. A diagnosis of a mild form of maternal inherited X-linked myotubular myopathy was established. The child presented significant improvement with speech, occupational, and physical therapies, with no respiratory intercurrences or ventilator dependency. CONCLUSION: The presentation of a mild form of this myotubular myopathy, being less commonly reported, added challenge to the diagnosis. The combination of mild hypotonia, feeding difficulties and expressive language disorder should raise suspicion of a neuromuscular disease. There is a lack of verified motor or developmental scores specific to this myopathy to further determine prognosis and need of other therapies. While currently the severity myotubular myopathy is classified according to ventilator dependency, this may be insufficient and unapplicable to milder cases. There is an evident need for a grading system for mild and moderate cases assessing muscle weakness and fatigue, daily life limitations, motor developmental delay, early phenotypical scores, or recurrent respiratory infections.

TITLE: Miopatía miotubular ligada al cromosoma X: informe clínico y revisión del fenotipo leve.Introducción. La miopatía miotubular ligada al X es una miopatía centronuclear rara que afecta aproximadamente a 1 de cada 50.000 recién nacidos varones causada por variantes patógenas en el gen de la miotubularina 1 (MTM1). La gravedad clínica varía; sin embargo, la necesidad de soporte ventilatorio ocurre casi invariablemente. Caso clínico. Presentamos el caso de un niño de 4 años que presentaba hipotonía muscular leve a los 12 meses, trastorno del lenguaje expresivo, retraso global del desarrollo y trastorno del procesamiento sensorial. La secuenciación clínica del exoma identificó la variante hemicigótica c.722G>A p.(Arg241His) en el exón 9 del gen de la miotubularina 1 (NM_000252.2). La madre es portadora heterocigota de la misma variante. Se estableció el diagnóstico de una forma leve de miopatía miotubular ligada al cromosoma X de herencia materna. El niño presentó una mejoría significativa con terapias del habla, ocupacional y física, sin intercurrencias respiratorias ni dependencia de ventilador. Conclusión. La presentación de una forma leve de esta miopatía miotubular, al notificarse más raramente, añadió desafío al diagnóstico. La combinación de hipotonía leve, dificultades de alimentación y trastorno del lenguaje expresivo debe hacer sospechar una enfermedad neuromuscular. Se carece de puntuaciones motoras o de desarrollo verificadas específicas de esta miopatía para determinar el pronóstico y la necesidad de otras terapias. Aunque actualmente la gravedad de la miopatía miotubular se clasifica según la dependencia del ventilador, esto puede ser insuficiente e inaplicable a los casos más leves. Es evidente la necesidad de un sistema de clasificación para los casos leves y moderados que evalúe la debilidad muscular y la fatiga, las limitaciones de la vida diaria, el retraso del desarrollo motor, las puntuaciones fenotípicas tempranas o las infecciones respiratorias recurrentes.

Identification of a novel mutation in the HACD1 gene in an Iranian family with autosomal recessive congenital myopathy, with fibre-type disproportion.

Congenital fibre-type disproportion (CFTD) with myopathy, is a genetically heterogeneous disease in which there is relative hypotrophy of type-1-muscle-fibres compared to type-2-fibres on skeletal muscle biopsy. The classical characteristics of CFTD are infantile hypotonia and nonprogressive muscle weakness with a broad range of clinical manifestations. Pathogenic mutations in the HACD1 gene encoding 3-hydroxyacyl-CoA-dehydratase-1 have recently been reported to be associated with this disease. Whole-exome sequencing (WES) was conducted in a 12-year-old girl born to consanguineous parents from the Iranian-Azeri-Turkish population. She was diagnosed with congenital myopathy at the age of 4-month-old due to hypotonia and abnormal electromyography. DNAs were extracted from the blood samples of the proband and her parents, and subjected to PCR-Sanger-sequencing to confirm the WES result. WES data analysis identified a homozygous single nucleotide change (A>T) at position c.785-2 located in intron 6 of the HACD1 gene (NC_000010.11(NM_014241.4):c.785-2A>T). This novel mutation located at the splice-acceptor site is disturbing the splicing procedure. The absence of this mutation among our control group (100 normal healthy adults from the same ethnic group) and not being reported in any other population database confirms the pathogenicity of this mutation. Bioinformatics analysis also classified this variant as a pathogenic mutation. PCR-Sanger-sequencing data analysis confirmed the WES result in the proband and showed that the parents were carriers for the mutation. A substitution (NC_000010.11(NM_014241.4):c.785-2A>T) mutation resulted in the removal of the splicing acceptor site at the HACD1 gene. This pathogenic mutation is associated with CFTD disease.

Absence of myofibrillar myopathy in Quarter Horses with a histopathological diagnosis of type 2 polysaccharide storage myopathy and lack of association with commercial genetic tests.

BACKGROUND: Genetic tests for variants in MYOT (P2; rs1138656462), FLNC (P3a; rs1139799323 or P3b; rs1142918816) and MYOZ3 (P4; rs1142544043) genes are offered commercially to diagnose myofibrillar myopathy (MFM) and type 2 polysaccharide storage myopathy (PSSM2) in Quarter Horses (QH). OBJECTIVES: To determine if PSSM2-QH has histopathological features of MFM. To compare genotype and allele frequencies of variants P2, P3, P4 between control-QH and PSSM2-QH diagnosed by histopathology. STUDY DESIGN: Retrospective cross-sectional. METHODS: The study includes a total of 229 healthy control-QH, 163 PSSM2-QH GYS1 mutation negative. Desmin stains of gluteal/semimembranosus muscle were evaluated. Purported disease alleles P2, P3a, P3b, P4 were genotyped by pyrosequencing. Genotype, allele frequency and total number of variant alleles or loci were compared between phenotypes using additive/genotypic and dominant models and quantitative effects evaluated by multivariable logistic regression. RESULTS: Histopathological features of MFM were absent in all QH. A P variant allele at any locus was not associated (P > .05) with a histopathological diagnosis of PSSM2 and one or more P variants were common in control-QH (57%) and PSSM2-QH (61%). Allele frequencies (control/PSSM2) were: 0.24/0.21 (P2), 0.07/0.12 (P3a), 0.07/0.11 (P3b) and 0.06/0.08 (P4). P3a and P3b loci were not independent (r2  = 0.894); and not associated with PSSM2 histopathology comparing the haplotype of both P3a and P3b variants to other haplotypes. A receiver operator curve did not accurately predict the PSSM2 phenotype (AUC = 0.67, 95% CI 0.62-0.72), and there was no difference in the total number of variant loci or total variant allele count between control-QH and PSSM2-QH. MAIN LIMITATIONS: P3a and P3b were not in complete linkage disequilibrium. CONCLUSIONS: The P2, P3 and P4 variants in genes associated with human MFM were not associated with PSSM2 in 392 QH. Their use would improperly diagnose PSSM2/MFM in 57% of healthy QH and fail to diagnose PSSM2 in 40% of QH with histopathological evidence of PSSM2.

CONTEXTO: Testes genéticos para detecção das mutações MYOT (P2; rs1138656462), FLNC (P3a; rs1139799323 ou P3b; rs1142918816) e MYOZ3 (P4; rs1142544043) são oferecidos comercialmente para diagnosticar miopatia miofibrilar (MMF) e miopatia por acúmulo de polissacarídeo tipo 2 (PSSM2) em cavalos Quarto de Milha (QM). HIPÓTESES/OBJETIVOS: Determinar se PSSM2-QM tem características similares à MMF. Comparar o genótipo e a frequência dos alelos variantes P2, P3, e P4 entre cavalos QM controle, e PSSM2-QM diagnosticados por histologia. MÉTODOS: 229 cavalos QH saudáveis como controle, e 163 PSSM2-QM positivos na histologia e negativos para a mutação GYS1. METODOLOGIA: Amostras dos músculos glúteo/semimembranoso foram avaliadas após coloração com desmina. Os pretensos genes alelos P2, P3a, P3b e P4 foram genotipados por pirosequenciamento. Genótipo, frequência alélica, e número total de variância alélica ou loci foram comparados entre os fenótipos usado aditivo/genotípico e modelos dominantes e efeitos quantitativos através de regressão logística multivariável. RESULTADOS: Características histopatológicas de MMF não foram encontradas em nenhum QM. Uma variante alélica P em qualquer uma dos loci não foi associada (P > .05) com o diagnóstico histopatológicos de PSSM2 e uma ou mais variante P foram comuns em QM controles (57%) e PSSM2-QM (61%). Frequência alélica (controle/PSSM2) foram: 0.24/0.21 (P2), 0.07/0.12 (P3a), 0.07/0.11 (P3b), e 0.06/0.08 (P4). P3a e P3b loci não foram independentes (r2  = 0.894); e não foram associados com achados histopatológicos de PSSM quando comparando o haplótipo de ambas as variantes P3a e P3b com os outros haplótipos. A curva característica de operação do receptor não previu acuradamente o fenótipo PSSM2 (AUC = 0.67, 95% IC 0.62-0.72), e não houve diferença no número dotal de variantes no loci ou na contagem de variantes alélicas total entre QM controles e PSSM2-QM. PRINCIPAIS LIMITAÇÕES: P3a e P3b não estavam em desequilíbrio de ligação. CONCLUSÕES: As variantes P2, P3 e P4 em genes associados com MMF em humanos não foram associadas com PSSM em 392 QM. O seu uso diagnosticaria impropriamente PSSM2 e MMF em 57% dos cavalos saudáveis utilizados como controle e não diagnosticaria PSSM2 em 40% dos QM com evidência histológica de PSSM2.

Tamoxifen improves muscle structure and function of Bin1- and Dnm2-related centronuclear myopathies.

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.

Bi-Allelic DES Gene Variants Causing Autosomal Recessive Myofibrillar Myopathies Affecting Both Skeletal Muscles and Cardiac Function.

Mutations in the human desmin gene (DES) may cause both autosomal dominant and recessive cardiomyopathies leading to heart failure, arrhythmias and atrio-ventricular blocks, or progressive myopathies. Cardiac conduction disorders, arrhythmias and cardiomyopathies usually associated with progressive myopathy are the main manifestations of autosomal dominant desminopathies, due to mono-allelic pathogenic variants. The recessive forms, due to bi-allelic variants, are very rare and exhibit variable phenotypes in which premature sudden cardiac death could also occur in the first or second decade of life. We describe a further case of autosomal recessive desminopathy in an Italian boy born of consanguineous parents, who developed progressive myopathy at age 12, and dilated cardiomyopathy four years later and died of intractable heart failure at age 17. Next Generation Sequencing (NGS) analysis identified the homozygous loss-of-function variant c.634C>T; p.Arg212*, which was likely inherited from both parents. Furthermore, we performed a comparison of clinical and genetic results observed in our patient with those of cases so far reported in the literature.