Congenital myopathies--clinical features and frequency of individual subtypes diagnosed over a 5-year period in the United Kingdom

Biallelic variants in RYR1 and STAC3 are predominant causes of King-Denborough Syndrome in an African cohort

King-Denborough Syndrome (KDS) is a congenital myopathy (CM) characterised by myopathy, dysmorphic features and susceptibility to malignant hyperthermia. The objective of this study was to investigate the genotype-phenotype correlation in Black African patients presenting with CM, specifically those with KDS-like phenotypes, who remained undiagnosed for over 25 years. A cohort of 67 Black African patients with CM was studied, of whom 44 were clinically evaluated and diagnosed with KDS. Whole-exome sequencing (WES) was performed as part of an international genomics study (ICGNMD) to identify potential pathogenic mutations. Genomic assessments focused on identifying relevant genes, including RYR1 and STAC3, and establishing genotype-phenotype correlations. The study identified RYR1 and STAC3 mutations as the predominant genetic causes of KDS in this cohort, with mutations in both genes exhibiting autosomal recessive inheritance. While RYR1 has previously been linked to autosomal dominant mutations, STAC3, which was formerly associated exclusively with Native American Myopathy/Bailey-Bloch Myopathy, congenital hypotonia, and susceptibility to malignant hyperthermia, is now newly associated with CM-KDS in this study. This establishes the first genotype-phenotype correlation for 44 Black African individuals with KDS. This study marks a significant milestone in research on understudied African populations with CM, emphasising the lengthy diagnostic journey these patients endured. The findings highlight the pressing need for improved access to genomic medicine in underserved regions and underscore the importance of expanding research and diagnostic capabilities in Africa. This work contributes to the advancement of genetic medicine in underrepresented populations, facilitating better diagnostic and therapeutic outcomes.

[SELENON-related myopathy with scoliosis and respiratory failure since early childhood diagnosed through reassessment during pediatric-to-adult healthcare transition: a case report]

The patient was a 33-year-old woman with no family history of a similar disorder. At one year of age, she exhibited scoliosis and respiratory failure, necessitating a tracheostomy performed at 5 years of age (1990s). During that time, the patient was provisionally diagnosed with "non-Fukuyama congenital muscular dystrophy" via muscle biopsy. Difficulties in independent walking and standing emerged by 14 years of age, progressing to significant mobility challenges by 21 years of age. The patient was referred to our department at 33 years of age for the transition to adult care. The examination revealed predominant trunk muscle weakness, persistent scoliosis, restricted neck and trunk mobility, significant restrictive ventilatory impairment, and mild intellectual developmental delay. Reanalysis of the muscle biopsy pathology was conducted, and genetic testing identified a known homozygous mutation, c.1574T>G (p.M525R), in the SELENON (SEPN1) gene, leading to a diagnosis of SELENON-related myopathy. The pediatric-to-adult healthcare transition can provide a valuable opportunity for the reassessment of diagnoses and disabilities.

Structural variation in nebulin and its implications on phenotype and inheritance: establishing a dominant distal phenotype caused by large deletions

Introduction

Structural variants (SVs) of the nebulin gene (NEB), including intragenic duplications, deletions, and copy number variation of the triplicate region, are an established cause of recessively inherited nemaline myopathies and related neuromuscular disorders. Large deletions have been shown to cause dominantly inherited distal myopathies. Here we provide an overview of 35 families with muscle disorders caused by such SVs in NEB.

Methods

Using custom Comparative Genomic Hybridization arrays, exome sequencing, short-read genome sequencing, custom Droplet Digital PCR, or Sanger sequencing, we identified pathogenic SVs in 35 families with NEB-related myopathies.

Results

In 23 families, recessive intragenic deletions and duplications or pathogenic gains of the triplicate region segregating with the disease in compound heterozygous form, together with a small variant in trans, were identified. In two families the SV was, however, homozygous. Eight families have not been described previously. In 12 families with a distal myopathy phenotype, eight unique, large deletions encompassing 52 to 97 exons in either heterozygous (n = 10) or mosaic (n = 2) state were identified.In the families where inheritance was recessive, no correlation could be made between the types of variants and the severity of the disease. In contrast, all patients with large dominant deletions in NEB had milder, predominantly distal muscle weakness.

Discussion

For the first time, we establish a clear and statistically significant association between large NEB deletions and a form of distal myopathy. In addition, we provide the hitherto largest overview of the spectrum of SVs in NEB.

Dual role of the S5 segment in type 1 ryanodine receptor channel gating

The type 1 ryanodine receptor (RyR1) is a Ca2+ release channel in the sarcoplasmic reticulum that is essential for skeletal muscle contraction. RyR1 forms a channel with six transmembrane segments, in which S5 is the fifth segment and is thought to contribute to pore formation. However, its role in channel gating remains unclear. Here, we performed a functional analysis of several disease-associated mutations in S5 and interpreted the results with respect to the published RyR1 structures to identify potential interactions associated with the mutant phenotypes. We demonstrate that S5 plays a dual role in channel gating: the cytoplasmic side interacts with S6 to reduce the channel activity, whereas the luminal side forms a rigid structural base necessary for S6 displacement in channel opening. These results deepen our understanding of the molecular mechanisms of RyR1 channel gating and provide insight into the divergent disease phenotypes caused by mutations in S5.

Novel TUBA4A variant causes congenital myopathy with focal myofibrillar disorganisation

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_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.

Best practice recommendations for speech-language pathology in children with neuromuscular disorders: A Delphi-based consensus study

PURPOSE

Speech-language pathology (SLP) is considered an essential intervention due to the high prevalence of dysphagia and dysarthria in paediatric neuromuscular disorders (pNMD). Evidence-based guidelines for SLP in pNMD are missing and children could be deprived the best of care. This study aimed to achieve consensus and present best practice recommendations on SLP intervention in pNMD.

METHOD

A modified Delphi technique was used with a panel of experienced Dutch speech-language pathologists. In two online survey rounds and a face-to-face consensus meeting, the SLP experts proposed intervention items for cases of four types of pNMD (congenital myopathy, Duchenne muscular dystrophy, myotonic dystrophy type 1, and spinal muscular atrophy type 2), covering symptoms of dysphagia, dysarthria, drooling, and oral hygiene problems. They rated the level of agreement.

RESULT

Intervention items that achieved consensus were incorporated into best practice recommendations. These recommendations cover six core intervention components (wait and see, explanation and advice, training and treatment, aids and adjustments, referral to other disciplines, and monitoring) suitable for the described symptoms.

CONCLUSION

Insight into treatment options is essential to facilitate speech-language pathologists in clinical decision-making. The current study led to best practice recommendations for speech-language pathologists working within the field of pNMD.

Phenotype-Genotype Correlation of a Cohort of Patients with Congenital Myopathy: A Single Centre Experience from India

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.

Role of Actin-Binding Proteins in Skeletal Myogenesis

Maintenance of skeletal muscle quantity and quality is essential to ensure various vital functions of the body. Muscle homeostasis is regulated by multiple cytoskeletal proteins and myogenic transcriptional programs responding to endogenous and exogenous signals influencing cell structure and function. Since actin is an essential component in cytoskeleton dynamics, actin-binding proteins (ABPs) have been recognized as crucial players in skeletal muscle health and diseases. Hence, dysregulation of ABPs leads to muscle atrophy characterized by loss of mass, strength, quality, and capacity for regeneration. This comprehensive review summarizes the recent studies that have unveiled the role of ABPs in actin cytoskeletal dynamics, with a particular focus on skeletal myogenesis and diseases. This provides insight into the molecular mechanisms that regulate skeletal myogenesis via ABPs as well as research avenues to identify potential therapeutic targets. Moreover, this review explores the implications of non-coding RNAs (ncRNAs) targeting ABPs in skeletal myogenesis and disorders based on recent achievements in ncRNA research. The studies presented here will enhance our understanding of the functional significance of ABPs and mechanotransduction-derived myogenic regulatory mechanisms. Furthermore, revealing how ncRNAs regulate ABPs will allow diverse therapeutic approaches for skeletal muscle disorders to be developed.

Critical illness-associated weakness and related motor disorders

Weakness of limb and respiratory muscles that occurs in the course of critical illness has become an increasingly common and serious complication of adult and pediatric intensive care unit patients and a cause of prolonged ventilatory support, morbidity, and prolonged hospitalization. Two motor disorders that occur singly or together, namely critical illness polyneuropathy and critical illness myopathy, cause weakness of limb and of breathing muscles, making it difficult to be weaned from ventilatory support, commencing rehabilitation, and extending the length of stay in the intensive care unit, with higher rates of morbidity and mortality. Recovery can take weeks or months and in severe cases, and may be incomplete or absent. Recent findings suggest an improved prognosis of critical illness myopathy compared to polyneuropathy. Prevention and treatment are therefore very important. Its management requires an integrated team approach commencing with neurologic consultation, creatine kinase (CK) measurement, detailed electrodiagnostic, respiratory and neuroimaging studies, and potentially muscle biopsy to elucidate the etiopathogenesis of the weakness in the peripheral and/or central nervous system, for which there may be a variety of causes. These tenets of care are being applied to new cases and survivors of the coronavirus-2 disease pandemic of 2019. This chapter provides an update to the understanding and approach to critical illness motor disorders.

Congenital myopathies

The congenital myopathies are inherited muscle disorders characterized clinically by hypotonia and weakness, usually from birth, with a static or slowly progressive clinical course. Historically, the congenital myopathies have been classified according to major morphological features seen on muscle biopsy as nemaline myopathy, central core disease, centronuclear or myotubular myopathy, and congenital fiber type disproportion. However, in the past two decades, the genetic basis of these different forms of congenital myopathy has been further elucidated with the result being improved correlation with histological and genetic characteristics. However, these notions have been challenged for three reasons. First, many of the congenital myopathies can be caused by mutations in more than one gene that suggests an impact of genetic heterogeneity. Second, mutations in the same gene can cause different muscle pathologies. Third, the same genetic mutation may lead to different pathological features in members of the same family or in the same individual at different ages. This chapter provides a clinical overview of the congenital myopathies and a clinically useful guide to its genetic basis recognizing the increasing reliance of exome, subexome, and genome sequencing studies as first-line analysis in many patients.

Mutations in proteins involved in E-C coupling and SOCE and congenital myopathies

In skeletal muscle, Ca2+ necessary for muscle contraction is stored and released from the sarcoplasmic reticulum (SR), a specialized form of endoplasmic reticulum through the mechanism known as excitation-contraction (E-C) coupling. Following activation of skeletal muscle contraction by the E-C coupling mechanism, replenishment of intracellular stores requires reuptake of cytosolic Ca2+ into the SR by the activity of SR Ca2+-ATPases, but also Ca2+ entry from the extracellular space, through a mechanism called store-operated calcium entry (SOCE). The fine orchestration of these processes requires several proteins, including Ca2+ channels, Ca2+ sensors, and Ca2+ buffers, as well as the active involvement of mitochondria. Mutations in genes coding for proteins participating in E-C coupling and SOCE are causative of several myopathies characterized by a wide spectrum of clinical phenotypes, a variety of histological features, and alterations in intracellular Ca2+ balance. This review summarizes current knowledge on these myopathies and discusses available knowledge on the pathogenic mechanisms of disease.

PIEZO2-related distal arthrogryposis type 5: Longitudinal follow-up of a three-generation family broadens phenotypic spectrum, complications, and health surveillance recommendations for this patient group

Arthrogryposis is a heterogenous condition with a wide variety of etiological causes. It has been subdivided clinically based on the presence of additional features. Dominant gain of function (GoF) pathogenic variants in PIEZO2 have been associated with several forms of arthrogryposis. Previous reports have focused on diagnosis and clinical features. We report a three-generation family with four affected individuals with a known pathogenic GoF change p.(Glu2727del) in PIEZO2. All family members presented at birth with distal arthrogryposis and ophthalmoplegia but have varied in their subsequent clinical course with differences in mobility and joint restriction. In the longer term, other features have presented including dysphagia, back pain and spinal stenosis-like symptoms, raised intraocular pressure, and progressive restrictive lung disease. As far as we know, this is the first report detailing the longitudinal follow-up of a three-generation family which highlights potential long-term complications in patients with PIEZO2-related arthrogryposis. We present this family to demonstrate the importance of long-term follow-up for the clinical management of this group of patients.

A case of giant dental calculus in a patient with centronuclear myopathy

INTRODUCTION

Centronuclear myopathy is a hereditary congenital muscle disease. It is characterized by generalized muscle hypotonia from early childhood, elongated cacial appearance, mandibular undergroth, and dental malposition. In this report, we discuss the clinical course and management of a patient with centronuclearmyopathy, who developed a giant dental calculus in the floor of the mouth and underwent surgical excision.

CASE REPORT

A 37-year-old Japanese man was referred to our hospital, and reported a swelling in the floor of the mouth. The patient affects centronuclear myopathy and has generalized muscle weakness. CT images showed a high-density area in the floor of the mouth measuring 35 × 28 × 20 mm. The lesion was clinically diagnosed as giant dental calculus, and surgically removed.

CONCLUSION

We have experienced a case of giant dental calculus in a patient with centronuclear myopathy. In dental treatment, we must consider generalized muscle weakness.

Redox Signaling and Stress in Inherited Myopathies

Significance: Reactive oxygen species (ROS) are highly reactive compounds that behave like a double-edged sword; they damage cellular structures and act as second messengers in signal transduction. Mitochondria and endoplasmic reticulum (ER) are interconnected organelles with a central role in ROS production, detoxification, and oxidative stress response. Skeletal muscle is the most abundant tissue in mammals and one of the most metabolically active ones and thus relies mainly on oxidative phosphorylation (OxPhos) to synthesize adenosine triphosphate. The impairment of OxPhos leads to myopathy and increased ROS production, thus affecting both redox poise and signaling. In addition, ROS enter the ER and trigger ER stress and its maladaptive response, which also lead to a myopathic phenotype with mitochondrial involvement. Here, we review the role of ROS signaling in myopathies due to either mitochondrial or ER dysfunction. Recent Advances: Relevant advances have been evolving over the last 10 years on the intricate ROS-dependent pathways that act as modifiers of the disease course in several myopathies. To this end, pathways related to mitochondrial biogenesis, satellite cell differentiation, and ER stress have been studied extensively in myopathies. Critical Issues: The analysis of the chemistry and the exact quantitation, as well as the localization of ROS, are still challenging due to the intrinsic labile nature of ROS and the technical limitations of their sensors. Future Directions: The mechanistic studies of the pathogenesis of mitochondrial and ER-related myopathies offer a unique possibility to discover novel ROS-dependent pathways. Antioxid. Redox Signal. 37, 301-323.

Congenital or Early Developing Neuromuscular Diseases Affecting Feeding, Swallowing and Speech – A Review of the Literature from January 1998 to August 2021

Background:

The knowledge about the impact of oral motor impairment in neuromuscular diseases (NMDs) is limited but increasing.

Objective:

The aim of this review was to collect and compile knowledge on how muscle weakness in congenital or early developing NMDs directly or indirectly affects feeding, swallowing, speech and saliva control.

Methods:

A literature search was performed in PubMed from January 1, 1998, to August 31, 2021. The keywords “feeding”, “dysphagia”, “swallowing”, “dysarthria”, “speech”, “drooling” and “sialorrhea” were used in combination with “paediatric neuromuscular disease” or specific diagnoses.

Results:

Sixty-five studies were selected for the review, 33 focused on feeding and swallowing, 11 on speech, four on a combination of feeding, swallowing, saliva control or speech and 17 general descriptions. Most of the studies reported on patients with a disorder affecting muscles. These studies show that muscle weakness and impaired motility affecting the muscles innervated by the cranial nerves may influence feeding, swallowing, and speech, and that respiratory function, general health and neurodevelopmental delay also influence these functions. Feeding impairment and breathing difficulties are common in NMDs. Lifesaving interventions such as tube feeding and ventilatory support are common in severe cases.

Conclusions:

Feeding impairment, dysphagia and dysarthria are prevalent in NMDs with congenital or early age of onset. Feeding and swallowing has been studied more than speech and saliva control. More children with NMD survive thanks to new treatment options and it is therefore urgent to follow up how these therapies may impact the development of feeding, swallowing, and speech.

Correlation of Phenotype–Genotype and Protein Structure in RYR1-Related Myopathy

Introduction

Next generation sequencing results in an explosive identification of rare variants of RYR1, making the correlation between phenotype and genotype complicated. We analyzed the data of 33 patients with RYR1-related myopathy, attempting to elucidate correlations between phenotype, genotype, and protein structure of RyR1.

Methods

Clinical, histopathologic, and genetic data were evaluated, and variants were mapped to the cryo-EM RyR1 structure. The three-dimensional structure of the variant on RyR1 was analyzed.

Results

The clinical spectrum was highly variable regardless of the mode of inheritance. Recessive variations were associated with more severe feeding problems and respiratory insufficiency in infancy (p < 0.05). Forty pathogenic and likely pathogenic variations were identified, and 14 of them were novel. Missense was the most common variation type regardless of inheritance mode. Arginine (15/45) was the most frequently involved residue. All but one dominant variation clustered in Pore forming and pVSD domains, while recessive variations enriched in Bsol (7/25) and SPRYs (6/25) domains. Analysis of the spatial structure of variants showed that dominant variants may impact RyR1 mainly by breaking down hydrogen or electrovalent bonds (10/21); recessive variants located in different domains may impact the function of RyR1 through different pathways. Variants located in RyR1 coupling sites (PY1&2 and the outermost of Bsol) may cause the most severe clinical manifestation.

Conclusion

Clinical diversity of RYR1-related myopathy was impacted by the inheritance mode, variation type, and variant location. Dominant and recessive variants have different sensitive domains impacting the function of RyR1 through different pathways.

Identification of Potential Biomarkers for Ryanodine Receptor 1 (RYR1) Mutation-Associated Myopathies Using Bioinformatics Approach

Background

Myopathies related to Ryanodine receptor 1 (RYR1) mutation are the most common nondystrophy muscle disorder in humans. Early detection and diagnosis of RYR1 mutation-associated myopathies may lead to more timely treatment of patients, which contributes to the management and preparation for malignant hyperthermia. However, diagnosis of RYR1 mutation-associated myopathies is delayed and challenging. The absence of diagnostic morphological features in muscle biopsy does not rule out the possibility of pathogenic variations in RYR1. Accordingly, it is helpful to seek biomarkers to diagnose RYR1 mutation-associated myopathies.

Methods

Skeletal muscle tissue microarray datasets of RYR1 mutation-associated myopathies or healthy persons were built in accordance with the gene expression synthesis (GEO) database. Differentially expressed genes (DEGs) were identified on the basis of R software. Genes specific to tissue/organ were identified through BioGPS. An enrichment analysis of DEGs was conducted in accordance with the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO). We also built protein-protein interaction (PPI) networks to explore the function and enrichment pathway of DEGs and the identification of hub genes. Lastly, the ROC curve was drawn for hub genes achieving specific expressions within skeletal muscle. Moreover, the area under the curve (AUC) was obtained to calculate the predictive value of key genes. The transcription factors of hub genes achieving specific expressions within skeletal muscle were predicted with the use of the iRegulon plugin.

Results

We identified 170 DEGs among 11 muscle biopsy samples of healthy subjects and 17 muscle biopsy samples of RYR1 mutation-associated myopathy patients in the dataset. Among the above DEGs, 30 genes achieving specific expressions within tissues/organs were found. GO and KEGG enrichment analysis of DEGs mainly focused on muscle contraction, actin-mediated cell contraction, actin filament-based movement, and muscular sliding. 12 hub genes were identified with the use of Cytoscape. Four hub genes were specifically expressed in skeletal muscle tissue, including MYH1 (AUC: 0.856), TNNT3 (AUC: 0.840), MYLPF (AUC: 0.786), and ATP2A1 (AUC: 0.765). The iRegulon predicted results suggested that the transcription factor MYF6 was found with the highest reliability.

Conclusions

Four skeletal muscle tissue-specific genes were identified, including MYH1, TNNT3, MYLPF, and ATP2A1, as the potential biomarkers for diagnosing and treating RYR1 mutation-associated myopathies, which provided insights into the transcriptome-level development mechanism. The transcription factor MYF6 may be a vital upstream regulator of the above biomarkers.

Congenital myopathies in adults: A diagnosis not to overlook

BACKGROUND

Congenital myopathies (CM) were traditionally classified according to the muscle histopathological features, but in recent years, molecular diagnosis has become increasingly important. CM may present a wide phenotype variability, and while adult-onset CM have been increasingly recognized, substantial diagnostic delays are still reported.

OBJECTIVES

To describe a cohort of adult CM patients, including clinical, genetic, and histopathological features, and further characterize the subgroup of adult-diagnosed patients.

MATERIALS AND METHODS

We performed a retrospective observational cohort study to characterize the CM patients evaluated in our adult Neuromuscular outpatient clinic, including the subgroup of adult-diagnosed patients.

RESULTS

We identified 19 CM patients with compatible molecular and/or histological diagnoses, of which 14 were diagnosed in adulthood. Eleven adult-diagnosed patients had symptoms since childhood and 9 had a family history of myopathy. The median age of symptoms' onset was 4 years old and the median age at diagnosis was 37 years old. The most common causative gene was RYR1, followed by TTN and MYH7. Three patients had non-specific features on muscle biopsy, all diagnosed during adulthood.

CONCLUSIONS

In our cohort, the majority of CM were diagnosed in adulthood, despite most having pediatric-onset symptoms and positive family history. The diagnostic delay may be associated with mild presentation, slow course, atypical muscle histology, and lack of awareness of adult-onset CM. Studies with larger populations are needed.

Clinical and genetic features of infancy-onset congenital myopathies from a Chinese paediatric centre

BACKGROUND

Congenital myopathies are a group of rare neuromuscular diseases characterized by specific histopathological features. The relationship between the pathologies and the genetic causes is complex, and the prevalence of myopathy-causing genes varies among patients from different ethnic groups. The aim of the present study was to characterize congenital myopathies with infancy onset among patients registered at our institution.

METHOD

This retrospective study enrolled 56 patients based on the pathological and/or genetic diagnosis. Clinical, histopathological and genetic features of the patients were analysed with long-term follow-up.

RESULTS

Twenty-six out of 43 patients who received next-generation sequencing had genetic confirmation, and RYR1 variations (12/26) were the most prevalent. Eighteen novel variations were identified in 6 disease-causing genes, including RYR1, NEB, TTN, TNNT1, DNM2 and ACTA1. Nemaline myopathy (17/55) was the most common histopathology. The onset ages ranged from birth to 1 year. Thirty-one patients were followed for 3.83 ± 3.05 years (ranging from 3 months to 11 years). No patient died before 1 year. Two patients died at 5 years and 8 years respectively. The motor abilities were stable or improved in 23 patients and deteriorated in 6 patients. Ten (10/31) patients developed respiratory involvement, and 9 patients (9/31) had mildly abnormal electrocardiograms and/or echocardiograms.

CONCLUSION

The severity of congenital myopathies in the neonatal/infantile period may vary in patients from different ethnic groups. More concern should be given to cardiac monitoring in patients with congenital myopathies even in those with static courses.

RyR1-related myopathy mutations in ATP and calcium binding sites impair channel regulation

The type 1 ryanodine receptor (RyR1) is an intracellular calcium (Ca²⁺) release channel on the sarcoplasmic/endoplasmic reticulum that is required for skeletal muscle contraction. RyR1 channel activity is modulated by ligands, including the activators Ca²⁺ and ATP. Patients with inherited mutations in RyR1 may exhibit muscle weakness as part of a heterogeneous, complex disorder known as RYR1-related myopathy (RYR1-RM) or more recently termed RYR1-related disorders (RYR1-RD). Guided by high-resolution structures of skeletal muscle RyR1, obtained using cryogenic electron microscopy, we introduced mutations into putative Ca²⁺ and ATP binding sites and studied the function of the resulting mutant channels. These mutations confirmed the functional significance of the Ca²⁺ and ATP binding sites identified by structural studies based on the effects on channel regulation. Under normal conditions, Ca²⁺ activates RyR1 at low concentrations (µM) and inhibits it at high concentrations (mM). Mutations in the Ca²⁺-binding site impaired both activating and inhibitory regulation of the channel, suggesting a single site for both high and low affinity Ca²⁺-dependent regulation of RyR1 function. Mutation of residues that interact with the adenine ring of ATP abrogated ATP binding to the channel, whereas mutating residues that interact with the triphosphate tail only affected the degree of activation. In addition, patients with mutations at the Ca²⁺ or ATP binding sites suffer from muscle weakness, therefore impaired RyR1 channel regulation by either Ca²⁺ or ATP may contribute to the pathophysiology of RYR1-RM in some patients.

Ion Channel Gene Mutations Causing Skeletal Muscle Disorders: Pathomechanisms and Opportunities for Therapy

Skeletal muscle ion channelopathies (SMICs) are a large heterogeneous group of rare genetic disorders caused by mutations in genes encoding ion channel subunits in the skeletal muscle mainly characterized by myotonia or periodic paralysis, potentially resulting in long-term disabilities. However, with the development of new molecular technologies, new genes and new phenotypes, including progressive myopathies, have been recently discovered, markedly increasing the complexity in the field. In this regard, new advances in SMICs show a less conventional role of ion channels in muscle cell division, proliferation, differentiation, and survival. Hence, SMICs represent an expanding and exciting field. Here, we review current knowledge of SMICs, with a description of their clinical phenotypes, cellular and molecular pathomechanisms, and available treatments.

Cofilin Loss in Drosophila Muscles Contributes to Muscle Weakness through Defective Sarcomerogenesis during Muscle Growth

Sarcomeres, the fundamental contractile units of muscles, are conserved structures composed of actin thin filaments and myosin thick filaments. How sarcomeres are formed and maintained is not well understood. Here, we show that knockdown of Drosophila cofilin (DmCFL), an actin depolymerizing factor, disrupts both sarcomere structure and muscle function. The loss of DmCFL also results in the formation of sarcomeric protein aggregates and impairs sarcomere addition during growth. The activation of the proteasome delays muscle deterioration in our model. Furthermore, we investigate how a point mutation in CFL2 that causes nemaline myopathy (NM) in humans affects CFL function and leads to the muscle phenotypes observed in vivo. Our data provide significant insights to the role of CFLs during sarcomere formation, as well as mechanistic implications for disease progression in NM patients.

How sarcomeres are added and maintained in a growing muscle cell is unclear. Balakrishnan et al. observed that DmCFL loss in growing muscles affects sarcomere size and addition through unregulated actin polymerization. This results in a collapse of sarcomere and muscle structure, formation of large protein aggregates, and muscle weakness.

Evaluating next-generation sequencing in neuromuscular diseases with neonatal respiratory distress

With the exception of infantile spinal muscular atrophy (SMA) and congenital myotonic dystrophy 1 (DM1), congenital myopathies and muscular dystrophies with neonatal respiratory distress pose diagnostic challenges. Next-generation sequencing (NGS) provides hope for the diagnosis of these rare diseases. We evaluated the efficiency of next-generation sequencing (NGS) in ventilated newborns with peripheral hypotonia. We compared the results of our previous study in a cohort of 19 patients analysed by Sanger sequencing from 2007 to 2012, with a diagnostic yield of 26% (5/19), and those of a new retrospective study in 28 patients from 2007 to 2018 diagnosed using MyoPanel, a neuromuscular disease panel, with a diagnostic yield of 43% (12/28 patients). Pathogenic variants were found in five genes: ACTA1 (n = 4 patients), RYR1 (n = 2), CACNA1S (n = 1), NEB (n = 3), and MTM1 (n = 2). Myopanel increased the diagnosis of congenital neuromuscular diseases, but more than half the patients remained undiagnosed. Whole exome sequencing did not seem to fully respond to this diagnostic limitation. Therefore, explorations with whole genome sequencing will be the next step.

The Phenotype and Genotype of Congenital Myopathies Based on a Large Pediatric Cohort

BACKGROUND

Congenital myopathies (CMs) are a clinically and genetically heterogeneous group of hereditary muscular disorders. The distribution of genetic and histologic subtypes has been addressed in only a few cohorts, and the relationship between phenotypes and genotypes is only partially understood.

METHODS

This is a retrospective cross-sectional data collection study conducted at a single center. The clinical, histopathological, and molecular characterization of 104 patients with CM is reported.

RESULTS

The most common histopathological subtype was core myopathy (42%). Patients with severe endomysial fibrosis were more commonly unable to walk than patients with only a mild-grade endomysial fibrosis (56% vs 16%). Inability to walk was also more prevalent in patients with severe fatty replacement (44% vs 19%). The genetic etiology was more frequently identified among those patients with "specific" histologic findings (74% vs 62%). A definite molecular diagnosis was reached in 65 of 104 patients (62%), with RYR1 (24/104) and TTN (8/104) being the most frequent causative genes. Neonatal onset occurred in 56%. Independent ambulation was achieved by 74%. Patients who walked late were more likely to become wheelchair-dependent. Respiratory support was needed in one of three patients. Gastrostomy placement was required in 15%. Cardiac involvement was observed in 3%, scoliosis in 43%, and intellectual disability in 6%.

CONCLUSIONS

This study provides an updated picture of the clinical, histopathological, and molecular landscape of CMs. Independently of the causative gene, fibrosis and fatty replacement in muscle biopsy specimens are associated with clinical severity. Mutations in TTN are responsible for a higher proportion of cases than previously thought.

A Cross-Sectional Study of Nemaline Myopathy

Objective

Nemaline myopathy (NM) is a rare neuromuscular condition with clinical and genetic heterogeneity. To establish disease natural history, we performed a cross-sectional study of NM, complemented by longitudinal assessment and exploration of pilot outcome measures.

Methods

Fifty-seven individuals with NM were recruited at 2 family workshops, including 16 examined at both time points. Participants were evaluated by clinical history and physical examination. Functional outcome measures included the Motor Function Measure (MFM), pulmonary function tests (PFTs), myometry, goniometry, and bulbar assessments.

Results

The most common clinical classification was typical congenital (54%), whereas 42% had more severe presentations. Fifty-eight percent of individuals needed mechanical support, with 26% requiring wheelchair, tracheostomy, and feeding tube. The MFM scale was performed in 44 of 57 participants and showed reduced scores in most with little floor/ceiling effect. Of the 27 individuals completing PFTs, abnormal values were observed in 65%. Last, bulbar function was abnormal in all patients examined, as determined with a novel outcome measure. Genotypes included mutations in ACTA1 (18), NEB (20), and TPM2 (2). Seventeen individuals were genetically unresolved. Patients with pathogenic ACTA1 and NEB variants were largely similar in clinical phenotype. Patients without genetic resolution had more severe disease.

Conclusion

We present a comprehensive cross-sectional study of NM. Our data identify significant disabilities and support a relatively stable disease course. We identify a need for further diagnostic investigation for the genetically unresolved group. MFM, PFTs, and the slurp test were identified as promising outcome measures for future clinical trials.

Myocardial strain assessment by 2D speckle-tracking echocardiography in patients with congenital myopathy

Background:

Congenital myopathies (CMs) are a group of rare genetic muscle disorders. Cardiac involvement can be seen in these patients. We aimed to evaluate the myocardial strain parameters by 2D speckle-tracking echocardiography (STE) in patients with CM.

Materials and Methods:

Twenty-four patients with CM whose diagnosis was confirmed by genetic analysis or muscle biopsy were included in the study, and 48 patients were involved as a control group. Left ventricular ejection fraction (LVEF%) was calculated by biplane Simpson method, and myocardial strain analysis was performed by 2D STE.

Results:

The median age of the study population was 26 (19–35 interquartile range [IQR]) and 43 (60%) were women. In the analysis performed after the exclusion of two patients with multiminicore disease (MMD) who developed heart failure, although mild, LVEF% (62 [60–65 IQR] vs. 64 [63–66 IQR], P = 0.008) and right ventricular global longitudinal strain (RVGLS) were significantly lower in the CM group (−21.8 [−19.7, −24.9 IQR] vs. −23.9 [−22.4, −25.6 IQR], P = 0.0017). Left ventricular global longitudinal strain (LVGLS) was observed similarly in both groups (−19.9 [−18.7, −20.7 IQR] vs. −20.5 [−19.3, −21.9 IQR], P = 0.069). LVEF% (33 and 46), LVGLS (−7.5 and −10.7), and RVGLS (−14.9 and −16.1) values were low in two siblings with MMD.

Conclusion:

Although LVEF% and RVGLS were significantly lower in the CM group, LVGLS was similar. The decrease in RVGLS and LVEF% was mild, and heart failure was not observed in any patient except MMD patients who were not included in the analysis.

Use of the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND) in X-Linked Myotubular Myopathy: Content Validity and Psychometric Performance

X-linked myotubular myopathy (XLMTM) is a life-threatening, congenital myopathy characterized by extreme hypotonia, weakness, delayed motor milestones, and respiratory failure, often resulting in pediatric mortality. This study evaluated the content validity and psychometric performance of the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders as a measure of neuromuscular functioning in children with X-linked myotubular myopathy. This study was conducted in two phases. Phase I assessed the content validity of the measure for use in an XLMTM pediatric population through: literature review, clinical expert interviews, caregiver interviews, and a modified-Delphi panel among clinicians. Phase II assessed psychometric performance based on the INCEPTUS observational clinical study and the ASPIRO interventional gene therapy study, including tests of reliability (internal consistency, test-retest, and interrater), validity (construct and criterion), and responsiveness based on observational and interventional clinical trial data analyses. Data established construct validity and reliability of the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders among XLMTM patients before administration of resamirigene bilparvovec, and sensitivity to study drug administration as evidenced by the significant post-administration response in ASPIRO. Findings support the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders as an appropriate neuromuscular functioning assessment in a pediatric X-linked myotubular myopathy patient population.

From Mice to Humans: An Overview of the Potentials and Limitations of Current Transgenic Mouse Models of Major Muscular Dystrophies and Congenital Myopathies

Muscular dystrophies are a group of more than 160 different human neuromuscular disorders characterized by a progressive deterioration of muscle mass and strength. The causes, symptoms, age of onset, severity, and progression vary depending on the exact time point of diagnosis and the entity. Congenital myopathies are rare muscle diseases mostly present at birth that result from genetic defects. There are no known cures for congenital myopathies; however, recent advances in gene therapy are promising tools in providing treatment. This review gives an overview of the mouse models used to investigate the most common muscular dystrophies and congenital myopathies with emphasis on their potentials and limitations in respect to human applications.

Selenoprotein N-related myopathy: a retrospective natural history study to guide clinical trials

Objective

To describe clinical features and disease progression of Selenoprotein N‐related myopathy in a large multicenter cohort of patients.

Methods

Cross‐sectional multicenter data analysis of 60 patients (53 families) with Selenoprotein N‐related myopathy and single‐center retrospective longitudinal analysis of 25 patients (21 families) over a median period of 5.3 years.

Results

The majority of patients (46/60, 77%) presented before age 2 years with hypotonia, poor head/neck control, and developmental delay. At last assessment (median age 14 years; range 2.5 to 36 years), 10/60 patients had minimal or no ambulation. Ventilatory support was initiated in 50/60 patients at a mean Forced Vital Capacity (FVC) of 38% and at a median age of 13 years. Forty‐five/60 patients developed scoliosis (at median age 12.1 years) and 18 had scoliosis surgery at a median age of 13.6 years. Five children needed nasogastric feeds and/or gastrostomy. Longitudinal data analysis on 25 patients showed progressive decline of Hammersmith functional motor scores (estimated annual change −0.55 point), time to walk 10 meter, time standing from sitting, and from lying. Sixteen patients had weights < 2nd centile. The estimated change in FVC % per year was −2.04, with a 95% CI (−2.94, −1.14).

Conclusions

This comprehensive analysis of patients with Selenoprotein N‐related myopathy further describes the clinical course of this rare condition. The observed functional motor and respiratory data provide evidence of the slow decline patients experience over time which is useful when considering therapeutic intervention.

Congenital Muscular Dystrophy and Congenital Myopathy

PURPOSE OF REVIEW

Congenital muscular dystrophies and congenital myopathies are a heterogeneous group of disorders resulting in hypotonia, muscle weakness, and dystrophic or myopathic features on muscle biopsy. This article summarizes the clinical and genetic aspects of these disorders.

RECENT FINDINGS

Historically, diagnoses of congenital muscular dystrophy and congenital myopathy have been made by clinical features and histopathology; however, recent advances in genetics have changed diagnostic practice by relying more heavily on genetic findings. This article reviews the clinical and genetic features of the most common congenital muscular dystrophies including laminin subunit alpha 2 (LAMA2)-related (merosin deficient), collagen VI-related, and α-dystroglycan-related congenital muscular dystrophies and reviews the most common congenital myopathies including nemaline rod, core, and centronuclear myopathies. With the increasing accessibility of genetic testing, the number of genes found to be associated with these disorders has increased dramatically. A wide spectrum of severity and onset (from birth to adulthood) exist across all subtypes. Progression and other features are variable depending on the subtype and severity of the specific genetic mutation.

SUMMARY

Congenital muscular dystrophy and congenital myopathy are increasingly recognized disorders. A growing appreciation for the breadth of phenotypic variability and overlap between established subtypes has challenged long-standing phenotypic and histopathologic classifications of these disorders but has driven a greater understanding of pathogenesis and opened the door to the development of novel treatments.

Mouse model of severe recessive RYR1-related myopathy

Ryanodine receptor type I (RYR1)-related myopathies (RYR1 RM) are a clinically and histopathologically heterogeneous group of conditions that represent the most common subtype of childhood onset non-dystrophic muscle disorders. There are no treatments for this severe group of diseases. A major barrier to therapy development is the lack of an animal model that mirrors the clinical severity of pediatric cases of the disease. To address this, we used CRISPR/Cas9 gene editing to generate a novel recessive mouse model of RYR1 RM. This mouse (Ryr1TM/Indel) possesses a patient-relevant point mutation (T4706M) engineered into 1 allele and a 16 base pair frameshift deletion engineered into the second allele. Ryr1TM/Indel mice exhibit an overt phenotype beginning at 14 days of age that consists of reduced body/muscle mass and myofibre hypotrophy. Ryr1TM/Indel mice become progressively inactive from that point onward and die at a median age of 42 days. Histopathological assessment shows myofibre hypotrophy, increased central nuclei and decreased triad number but no clear evidence of metabolic cores. Biochemical analysis reveals a marked decrease in RYR1 protein levels (20% of normal) as compared to only a 50% decrease in transcript. Functional studies at end stage show significantly reduced electrically evoked Ca2+ release and force production. In summary, Ryr1TM/Indel mice exhibit a post-natal lethal recessive form of RYR1 RM that pheno-copies the severe congenital clinical presentation seen in a subgroup of RYR1 RM children. Thus, Ryr1TM/Indel mice represent a powerful model for both establishing the pathomechanisms of recessive RYR1 RM and pre-clinical testing of therapies for efficacy.

Exercise Training as Part of Musculoskeletal Management for Congenital Myopathy: Where Are We Now?

Congenital myopathy is a heterogeneous group of muscle disorders characterized by muscle weakness and hypotonia. This condition is associated with a range of skeletal, respiratory, and ophthalmologic complications and requires a multidisciplinary therapeutic approach aimed at maximizing the function and independence of patients. One promising direction for therapeutic intervention is physical exercise rehabilitation, given its demonstrated ability to promote muscle and bone health of patients with a variety of neuromuscular conditions. However, there are few data to assist health care professionals identify the optimal physical activity levels and exercise type, including the intensity, frequency, and duration. This lack of empirical evidence is particularly problematic given the fact that inappropriate exercise modes can potentially cause muscle damage in patients with congenital myopathy. In this article, we discuss the rationale behind the incorporation of two types of physical exercises, strength and aerobic training, into the clinical care of patients with congenital myopathy. Given the paucity of literature on the management of congenital myopathy, we review the results of published research on the treatment of both congenital myopathy and other neuromuscular diseases that could provide helpful insights into the physical rehabilitation of patients with congenital myopathy. We also discuss the potential benefits of vibration therapy, which has been studied in patients with other neuromuscular disorders over the last two decades. We conclude by proposing directions for future research on physical rehabilitation of patients with congenital myopathy.

Congenital myopathies: an update

Congenital myopathies comprise a clinical, histopathological, and genetic heterogeneous group of rare hereditary muscle diseases that are defined by architectural abnormalities in the muscle fibres. They are subdivided by the predominant structural pathological change on muscle biopsy, resulting in five subgroups: (1) core myopathies; (2) nemaline myopathies; (3) centronuclear myopathies; (4) congenital fibre type disproportion myopathy; and (5) myosin storage myopathy. Besides the clinical features, muscle biopsy, muscle imaging, and genetic analyses are essential in the diagnosis of congenital myopathies. Using next-generation sequencing techniques, a large number of new genes are being identified as the cause of congenital myopathies as well as new mutations in known genes, broadening the phenotype-genotype spectrum of congenital myopathies. Management is performed by a multidisciplinary team specialized in neuromuscular disorders, where the (paediatric) neurologist has an essential role. To date, only supportive treatment is available, but novel pathomechanisms are being discovered and gene therapies are being explored. WHAT THIS PAPER ADDS: Many new genes are being identified in congenital myopathies, broadening the phenotype-genotype spectrum. Management is performed by a multidisciplinary team specialized in neuromuscular disorders.

Cored in the act: the use of models to understand core myopathies

The core myopathies are a group of congenital myopathies with variable clinical expression - ranging from early-onset skeletal-muscle weakness to later-onset disease of variable severity - that are identified by characteristic 'core-like' lesions in myofibers and the presence of hypothonia and slowly or rather non-progressive muscle weakness. The genetic causes are diverse; central core disease is most often caused by mutations in ryanodine receptor 1 (RYR1), whereas multi-minicore disease is linked to pathogenic variants of several genes, including selenoprotein N (SELENON), RYR1 and titin (TTN). Understanding the mechanisms that drive core development and muscle weakness remains challenging due to the diversity of the excitation-contraction coupling (ECC) proteins involved and the differential effects of mutations across proteins. Because of this, the use of representative models expressing a mature ECC apparatus is crucial. Animal models have facilitated the identification of disease progression mechanisms for some mutations and have provided evidence to help explain genotype-phenotype correlations. However, many unanswered questions remain about the common and divergent pathological mechanisms that drive disease progression, and these mechanisms need to be understood in order to identify therapeutic targets. Several new transgenic animals have been described recently, expanding the spectrum of core myopathy models, including mice with patient-specific mutations. Furthermore, recent developments in 3D tissue engineering are expected to enable the study of core myopathy disease progression and the effects of potential therapeutic interventions in the context of human cells. In this Review, we summarize the current landscape of core myopathy models, and assess the hurdles and opportunities of future modeling strategies.

Adult Diagnosis of Type 1 Fiber Predominance Myopathy Caused by Novel Mutations in the RYR1 Gene

We describe a 57-year-old patient with mild diffuse weakness that was incidentally detected when he was evaluated for restless leg syndrome. An electromyography confirmed the presence of a myopathy without suggestion of inflammatory myopathy. A muscle biopsy demonstrated type 1 fiber predominance with minimal inflammatory features suggesting a genetic myopathy. Exome sequencing revealed c.10648C > T variant (p.R3550W), and a novel variant, c.10749_10753delGGAGG (E3584Rfs*3), in the ryanodine receptor 1 (RYR1) gene transmitted through his asymptomatic father indicating these mutations are in trans. Prompted by these results, a 47-year-old sister presented for evaluation. Her examination showed mild proximal muscle weakness, and an electromyography confirmed a noninflammatory myopathy. Her genotype was identical to her affected brother confirming that in these siblings, the RYR1 mutations, transmitted in an autosomal recessive pattern, are the cause of their myopathy. The adult age at diagnosis of these affected siblings likely reflects the mild and minimally progressive nature of the myopathy.

Bayesian modeling to predict malignant hyperthermia susceptibility and pathogenicity of RYR1, CACNA1S and STAC3 variants

Aim: Identify variants in RYR1, CACNA1S and STAC3, and predict malignant hyperthermia (MH) pathogenicity using Bayesian statistics in individuals clinically treated as MH susceptible (MHS). Materials & methods: Whole exome sequencing including RYR1, CACNA1S and STAC3 performed on 64 subjects with: MHS; suspected MH event or first-degree relative; and MH negative. Variant pathogenicity was estimated using in silico analysis, allele frequency and prior data to calculate Bayesian posterior probabilities. Results: Bayesian statistics predicted CACNA1S variant p.Thr1009Lys and RYR1 variants p.Ser1728Phe and p.Leu4824Pro are likely pathogenic, and novel STAC3 variant p.Met187Thr has uncertain significance. Nearly a third of MHS subjects had only benign variants. Conclusion: Bayesian method provides new approach to predict MH pathogenicity of genetic variants.

Early-Onset Myopathies: Clinical Findings, Prevalence of Subgroups and Diagnostic Approach in a Single Neuromuscular Referral Center in Germany

BACKGROUND

Early-onset myopathies are a heterogeneous group of neuromuscular diseases with broad clinical, genetic and histopathological overlap. The diagnostic approach has considerably changed since high throughput genetic methods (next generation sequencing, NGS) became available.

OBJECTIVE

We present diagnostic subgroups in a single neuromuscular referral center and describe an algorithm for the diagnostic work-up.

METHODS

The diagnostic approach of 98 index patients was retrospectively analysed. In 56 cases targeted sequencing of a known gene was performed, in 44 patients NGS was performed using large muscle specific panels, and in 12 individuals whole exome sequencing (WES) was undertaken. One patient was diagnosed via array CGH. Clinical features of all patients are provided.

RESULTS

The final diagnosis could be found in 63 out of 98 patients (64%) with molecular genetic analysis. In 55% targeted gene sequencing could establish the genetic diagnosis. However, this rate largely depended on the presence of distinct histological or clinical features. NGS (large myopathy-related panels and WES) revealed genetic diagnosis in 58.5% (52% and 67%, respectively). The genes detected by WES in our cohort of patients were all covered by the panels. Based on our findings we propose an algorithm for a practical diagnostic approach.Prevalences:MTM1- and LAMA2-patients are the two biggest subgroups, followed by SEPN1-, RYR1- and Collagen VI-related diseases. 31% of genetically confirmed cases represents a group with overlap between "congenital myopathies (CM)" and "congenital muscular dystrophies (CMD)". In 36% of the patients a specific genetic diagnosis could not be assigned.

CONCLUSIONS

A final diagnosis can be confirmed by high throughput genetic analysis in 58.5% of the cases, which is a higher rate than reported in the literature for muscle biopsy and should in many cases be considered as a first diagnostic tool. NGS cannot replace neuromuscular expertise and a close discussion with the geneticists on NGS is mandatory. Targeted candidate gene sequencing still plays a role in selected cases with highly suspicious clinical or histological features. There is a relevant clinical and genetic overlap between the entities CM and CMD.

Congenital myopathies in the adult neuromuscular clinic: Diagnostic challenges and pitfalls

Objective

To investigate the spectrum of undiagnosed congenital myopathies (CMs) in adults presenting to our neuromuscular clinic and to identify the pitfalls responsible for diagnostic delays.

Methods

We conducted a retrospective review of patients diagnosed with CM in adulthood in our neuromuscular clinic between 2008 and 2018. Patients with an established diagnosis of CM before age 18 years were excluded.

Results

We identified 26 patients with adult-onset CM and 18 patients with pediatric-onset CM who were only diagnosed in adulthood. Among patients with adult onset, the median age at onset was 47 years, and the causative genes were RYR1 (11 families), MYH7 (3 families) and ACTA1 (2 families), and SELENON, MYH2, DNM2, and CACNA1S (1 family each). Of 33 patients who underwent muscle biopsy, only 18 demonstrated histologic abnormalities characteristic of CM. Before their diagnosis of CM, 23 patients had received other diagnoses, most commonly non-neurologic disorders. The main causes of diagnostic delays were mildness of the symptoms delaying neurologic evaluation and attribution of the symptoms to coexisting comorbidities, particularly among pediatric-onset patients.

Conclusions

CMs in adulthood represent a diagnostic challenge, as they may lack the clinical and myopathologic features classically associated with CM. Our findings underscore the need for a revision of the terminology and current classification of these disorders.

Therapeutic Aspects in Congenital Myopathies

The congenital myopathies are a genetically heterogeneous and diverse group of early-onset, nondystrophic neuromuscular disorders. While the originally reported "classical" entities within this group - Central Core Disease, Multiminicore Disease, Nemaline Myopathy, and Centronuclear Myopathy - were defined by the predominant finding on muscle biopsy, "novel" forms with multiple, subtle, and unusual histopathologic features have been described more recently, reflective of an expanding phenotypical spectrum. The main disease mechanisms concern excitation-contraction coupling, intracellular calcium homeostasis, and thin/thick filament interactions. Management to date has been mainly supportive. Therapeutic strategies currently at various stages of exploration include genetic interventions aimed at direct correction of the underlying genetic defect, enzyme replacement therapy, and pharmacologic approaches, either specifically targeting the principal effect of the underlying gene mutation, or addressing its downstream consequences more generally. Clinical trial development is accelerating but will require more robust natural history data and tailored outcome measures.

SELENON (SEPN1) protects skeletal muscle from saturated fatty acid-induced ER stress and insulin resistance

Selenoprotein N (SELENON) is an endoplasmic reticulum (ER) protein whose loss of function leads to a congenital myopathy associated with insulin resistance (SEPN1-related myopathy). The exact cause of the insulin resistance in patients with SELENON loss of function is not known. Skeletal muscle is the main contributor to insulin-mediated glucose uptake, and a defect in this muscle-related mechanism triggers insulin resistance and glucose intolerance. We have studied the chain of events that connect the loss of SELENON with defects in insulin-mediated glucose uptake in muscle cells and the effects of this on muscle performance. Here, we show that saturated fatty acids are more lipotoxic in SELENON-devoid cells, and blunt the insulin-mediated glucose uptake of SELENON-devoid myotubes by increasing ER stress and mounting a maladaptive ER stress response. Furthermore, the hind limb skeletal muscles of SELENON KO mice fed a high-fat diet mirrors the features of saturated fatty acid-treated myotubes, and show signs of myopathy with a compromised force production. These findings suggest that the absence of SELENON together with a high-fat dietary regimen increases susceptibility to insulin resistance by triggering a chronic ER stress in skeletal muscle and muscle weakness. Importantly, our findings suggest that environmental cues eliciting ER stress in skeletal muscle (such as a high-fat diet) affect the pathological phenotype of SEPN1-related myopathy and can therefore contribute to the assessment of prognosis beyond simple genotype-phenotype correlations.

Congenital myopathies are mainly associated with a mild cardiac phenotype

BACKGROUND

To evaluate the prevalence of cardiac involvement in patients with congenital myopathies and the association to specific genotypes.

METHODS

We evaluated patients with physical examination, electrocardiogram, echocardiography, and 48-h Holter monitoring. Follow-up was performed for major events.

RESULTS

We included 130 patients, 55 men (42%), with a mean age of 34 ± 17 years. A genetic diagnosis was established in 97 patients (75%). Right bundle branch block was observed in three patients: 2/34 patients with a ryanodine receptor 1 (RYR1) and 1/6 with a tropomyosin two gene (TPM2) gene mutation. Echocardiography showed left-ventricular hypertrophy in five patients: 2/17 and 3/34 patients with a Dynamin 2 (DNM2) and a RYR1 mutation, respectively. One patient with a myosin heavy-chain (MYH7) mutation had dilated cardiomyopathy and heart failure. On Holter monitoring, frequent ventricular premature contractions were observed in one patient with a DNM2 mutation. Two patients with a TPM2 and a RYR1 mutation, respectively, had a single short run of non-sustained ventricular tachycardia. Atrioventricular nodal re-entry tachycardia was observed in a 20-year-old man with an actin 1 gene mutation. During follow-up (median 8.4 years), four patients died, all of non-cardiac causes.

CONCLUSION

Congenital myopathies are generally associated with a mild cardiac phenotype. Our findings substantiate the literature and indicate that, except for patients with specific genotypes, such as MYH7 and TTN mutations, repeated cardiac assessments can be minimized, given a normal initial cardiac screening at time of diagnosis.

Neonatal hypotonia and neuromuscular conditions

The differential diagnosis of neonatal hypotonia is a complex task, as in newborns hypotonia can be the presenting sign of different underlying causes, including peripheral and central nervous system involvement and genetic and metabolic diseases. This chapter describes how a combined approach, based on the combination of clinical signs and new genetic techniques, can help not only to establish when the hypotonia is related to peripheral involvement but also to achieve an accurate and early diagnosis of the specific neuromuscular diseases with neonatal onset. The early identification of such disorders is important, as this allows early intervention with disease-specific standards of care and, more importantly, because of the possibility to treat some of them, such as spinal muscular atrophy, with therapeutic approaches that have recently become available.

New mutations found by Next-Generation Sequencing screening of Spanish patients with Nemaline Myopathy

Nemaline Myopathy (NM) is a rare genetic disorder that encompasses a large spectrum of myopathies characterized by hypotonia and generalized muscle weakness. To date, mutations in thirteen different genes have been associated with NM. The most frequently responsible genes are NEB (50% of cases) and ACTA1 (15–25% of cases). In this report all known NM related genes were screened by Next Generation Sequencing in five Spanish patients in order to genetically confirm the clinical and histological diagnosis of NM. Four mutations in NEB (c.17779_17780delTA, c.11086A>C, c.21076C>T and c.2310+5G>A) and one mutation in ACTA1 (c.871A>T) were found in four patients. Three of the four mutations in NEB were novel. A cDNA sequencing assay of the novel variants c.17779_17780delTA, c.11086A>C and c.2310+5G>A revealed that the intronic variant c.2310+5G>A affected the splicing process. Mutations reported here could help clinicians and geneticists in NM diagnosis.