Diaphragmatic dysfunction in SEPN1-related myopathy

SEPN1-related myopathy depends on the oxidoreductase ERO1A and is druggable with the chemical chaperone TUDCA

Selenoprotein N (SEPN1) is a protein of the endoplasmic reticulum (ER) whose inherited defects originate SEPN1-related myopathy (SEPN1-RM). Here, we identify an interaction between SEPN1 and the ER-stress-induced oxidoreductase ERO1A. SEPN1 and ERO1A, both enriched in mitochondria-associated membranes (MAMs), are involved in the redox regulation of proteins. ERO1A depletion in SEPN1 knockout cells restores ER redox, re-equilibrates short-range MAMs, and rescues mitochondrial bioenergetics. ERO1A knockout in a mouse background of SEPN1 loss blunts ER stress and improves multiple MAM functions, including Ca2+ levels and bioenergetics, thus reversing diaphragmatic weakness. The treatment of SEPN1 knockout mice with the ER stress inhibitor tauroursodeoxycholic acid (TUDCA) mirrors the results of ERO1A loss. Importantly, muscle biopsies from patients with SEPN1-RM exhibit ERO1A overexpression, and TUDCA-treated SEPN1-RM patient-derived primary myoblasts show improvement in bioenergetics. These findings point to ERO1A as a biomarker and a viable target for intervention and to TUDCA as a pharmacological treatment for SEPN1-RM.

Respiratory function in LAMA2-related muscular dystrophy and SELENON-related congenital myopathy, a 1.5-year natural history study

INTRODUCTION

LAMA2-related muscular dystrophy (LAMA2-MD) and SELENON(SEPN1)-related congenital myopathy (SELENON-RM) are rare neuromuscular diseases with respiratory impairment from a young age. Prospective natural history studies are needed for prevalence estimations, respiratory characterization, optimizing clinical care and selecting outcome measures for trial readiness.

METHODS

Our prospective 1.5-year natural history study included spirometry (forced vital capacity (FVC); difference between upright and supine vital capacity (dVC)), respiratory muscle strength tests (sniff nasal inspiratory pressure (SNIP)) (age≥5 years), and diaphragm ultrasound (thickness; thickening; echogenicity; all ages).

RESULTS

Twenty-six LAMA2-MD patients (M = 8, median 21 [9; 31] years) and 11 SELENON-RM patients (M = 8, 20 [10; 33] years) were included. At baseline, 17 (85 %) LAMA2-MD (FVC%: 59 % [33; 68]) and all SELENON-RM patients (FVC%: 34 % [31; 46]) had an impaired respiratory function (FVC%<80 %). Nine (35 %) LAMA2-MD and eight (73 %) SELENON-RM patients received mechanical ventilation at baseline, and two additional SELENON-RM patients started during follow-up. Contrarily to LAMA2-MD, SELENON-RM patients had severe diaphragm atrophy (diaphragm thickness z-score: 2.5 [-3.1; -2.1]) and dysfunction (diaphragm thickness ratio: 1.2 [1.0; 1.7]; dVC: 30 % [7.7; 41]). SNIP was low in both neuromuscular diseases and correlated with motor function. In SELENON-RM, respiratory function decreased during follow-up.

CONCLUSION

The majority of LAMA2-MD and all SELENON-RM patients had respiratory impairment. SELENON-RM patients showed lower respiratory function which was progressive, more prevalent mechanical ventilation, and more severe diaphragm atrophy and dysfunction than LAMA2-MD patients. Spirometry (FVC%, dVC) and respiratory muscle strength tests (SNIP) are useful in clinical care and as outcome measure in clinical trials.

CLINICAL TRIAL NUMBER

NCT04478981.

Sleep in pediatric neuromuscular disorders

Sleep disordered breathing (SDB) is prevalent among children with neuromuscular disorders (NMD). The combination of respiratory muscle weakness, altered drive, and chest wall distortion due to scoliosis make sleep a stressful state in this population. Symptomatology can range from absent to snoring, nocturnal awakenings, morning headaches, and excessive daytime sleepiness. Sequelae of untreated SDB includes cardiovascular effects, metabolic derangements, and neurocognitive concerns which can be compounded by those innate to the NMD. The clinician should have a low threshold for obtaining polysomnography and recognize the nuances of individual disorders due to disproportionately impacted muscle groups such as hypoventilation in ambulating patients from diaphragm weakness. Non-invasive or invasive ventilation are the mainstay of treatment. In this review we explore the diagnosis and treatment of SDB in children with various NMD.

Limitations of the apnea-hypopnea index in children and young adults with neuromuscular disorders

There are no validated criteria to initiate noninvasive ventilation (NIV) in children and young adults with neuromuscular disease (NMD). In order to analyze NIV initiation criteria, we reviewed the polysomnography (PSG) criteria that led to the initiation of NIV in 61 consecutive patients with NMD, median age 4.1 (0.8-21) years, who had a PSG during their routine care. NIV was initiated on abnormal PSG data (apnea-hypopnea index (AHI) > 10 events/h and/or a transcutaneous carbon dioxide pressure > 50 mmHg and/or a pulse oximetry 〈 90%, both during at least 2% sleep time or 〉 5 consecutive minutes) in 11 (18%) patients. Six of these 11 patients had an AHI ≤ 10 events/h and would not have been ventilated if only AHI was retained. However, one of these 6 patients had isolated nocturnal hypoxemia, 3 isolated nocturnal hypercapnia and 2 abnormal respiratory events. Six (10%) patients with a normal PSG were started on NIV on clinical criteria. Our results show the limitation of the AHI when taken as the unique PSG criterion for NIV initiation in young patients with NMD and underline the need to include also abnormalities of overnight gas exchange into the NIV decision-making process.

Sex-Specific Patterns of Diaphragm Phospholipid Content and Remodeling during Aging and in a Model of SELENON-Related Myopathy

Growing evidence shows that the lipid bilayer is a key site for membrane interactions and signal transduction. Surprisingly, phospholipids have not been widely studied in skeletal muscles, although mutations in genes involved in their biosynthesis have been associated with muscular diseases. Using mass spectrometry, we performed a phospholipidomic profiling in the diaphragm of male and female, young and aged, wild type and SelenoN knock-out mice, the murine model of an early-onset inherited myopathy with severe diaphragmatic dysfunction. We identified 191 phospholipid (PL) species and revealed an important sexual dimorphism in PLs in the diaphragm, with almost 60% of them being significantly different between male and female animals. In addition, 40% of phospholipids presented significant age-related differences. Interestingly, SELENON protein absence was responsible for remodeling of 10% PL content, completely different in males and in females. Expression of genes encoding enzymes involved in PL remodeling was higher in males compared to females. These results establish the diaphragm PL map and highlight an important PL remodeling pattern depending on sex, aging and partly on genotype. These differences in PL profile may contribute to the identification of biomarkers associated with muscular diseases and muscle aging.

SELENON-Related Myopathy Across the Life Span, a Cross-Sectional Study for Preparing Trial Readiness

BACKGROUND

SELENON(SEPN1)-related myopathy (SELENON-RM) is a rare congenital neuromuscular disease characterized by proximal and axial muscle weakness, spinal rigidity, scoliosis and respiratory impairment. No curative treatment options exist, but promising preclinical studies are ongoing. Currently, natural history data are lacking, while selection of appropriate clinical and functional outcome measures is needed to reach trial readiness.

OBJECTIVE

We aim to identify all Dutch and Dutch-speaking Belgian SELENON-RM patients, deep clinical phenotyping, trial readiness and optimization of clinical care.

METHODS

This cross-sectional, single-center, observational study comprised neurological examination, functional measurements including Motor Function Measurement 20/32 (MFM-20/32) and accelerometry, questionnaires, muscle ultrasound, respiratory function tests, electro- and echocardiography, and dual-energy X-ray absorptiometry.

RESULTS

Eleven patients with genetically confirmed SELENON-RM were included (20±13 (3-42) years, 73% male). Axial and proximal muscle weakness were most pronounced. The mean MFM-20/32 score was 71.2±15.1%, with domain 1 (standing and transfers) being most severely affected. Accelerometry showed a strong correlation with MFM-20/32. Questionnaires revealed impaired quality of life, pain and problematic fatigue. Muscle ultrasound showed symmetrically increased echogenicity in all muscles. Respiratory function, and particularly diaphragm function, was impaired in all patients, irrespective of the age. Cardiac assessment showed normal left ventricular systolic function in all patients but abnormal left ventricular global longitudinal strain in 43% of patients and QRS fragmentation in 80%. Further, 80% of patients showed decreased bone mineral density on dual-energy X-ray absorptiometry scan and 55% of patients retrospectively experienced fragility long bone fractures.

CONCLUSIONS

We recommend cardiorespiratory follow-up as a part of routine clinical care in all patients. Furthermore, we advise vitamin D supplementation and optimization of calcium intake to improve bone quality. We recommend management interventions to reduce pain and fatigue. For future clinical trials, we propose MFM-20/32, accelerometry and muscle ultrasound to capture disease severity and possibly disease progression.

CAR T-Cell Therapy for Relapsed/Refractory Diffuse Large B-Cell Lymphoma with Progressive Muscular Dystrophy: A Case Report

Muscular dystrophies are a heterogeneous group of genetically inherited degenerative disorders defined by dystrophic features on pathological assessment of muscle biopsy specimens. Muscular dystrophies and lymphoma are not common concomitant diseases. Chimeric antigen receptor (CAR) T-cell immunotherapy for lymphoma patients with inherited degenerative diseases, such as muscular dystrophies, has not been previously reported. We report a relapsed/refractory diffuse large B-cell lymphoma (DLBCL) patient with progressive muscular dystrophy (PMD) characterized by progressive muscle weakness that affected the limb, axial and facial muscles. He was identified to be a germline DYSF p.R204* homozygous mutation carrier. The patient received a murine monoclonal anti-CD19 and anti-CD22 CAR T-cell “cocktail” and suffered from a mild case of grade 1 cytokine release syndrome (CRS). One month after the CAR T-cell infusion, he achieved complete remission of his lymphoma without minimal residual disease (MRD), as assessed by radiography. One year after the infusion, the Deauville score was stable at 1. Currently, patient has been in remission for over three years after receiving anti-CD19 and anti-CD22 CAR T-cell therapy. This case provides evidence for the use of CAR T-cell therapy in lymphoma patients with inherited degenerative disorders. Achieving remission of the lymphoma and subsequent administration of γ-globulin as well as zoledronic acid reduced the muscular dystrophy symptoms.

Novel SEPN1 Mutations in Exon 1 Are Common in Rigid Spine With Muscular Dystrophy Type 1 in Chinese Patients

Congenital muscular dystrophy with early rigid spine, also known as the rigid spine with muscular dystrophy type 1 (RSMD1), is caused by SEPN1 mutation. We investigated the clinical manifestations, pathological features, and genetic characteristics of 8 Chinese RSMD1 patients in order to improve diagnosis and management of the disease. Eight patients presented with delayed motor development, muscle weakness, hypotonia, and a myopathic face with high palatine arches. All patients could walk independently, though with poor running and jumping, and most had a rigid spine, lordosis, or scoliosis. The symptoms of respiratory involvement were present early, and upper respiratory tract infections and pneumonia often occurred. Five patients had severe pneumonia, pulmonary hypertension, and respiratory failure. Lung function tests showed variable restrictive ventilation dysfunction. Polysomnography suggested hypoxia and hypoventilation. The serum creatine kinase (CK) level was normal or mildly increased. Muscle biopsy indicated chronic myopathic changes and minicores. Muscle magnetic resonance imaging (MRI) showed diffuse fatty infiltration of the gluteus maximus and thigh muscle. SEPN1 gene analysis revealed 16 compound heterozygous variants, 81.3% of which are unreported, including 7 exon 1 variants. Our study expands the spectrum of clinical and genetic findings in RSMD1 to improve diagnosis, management, and standards of care. SEPN1 mutations in exon 1 are common and easily missed, and exon 1 should be carefully analyzed when RSMD1 is suspected, which will provide valuable genetic counseling for the family and useful information for future natural history studies and clinical trials.

Defining and identifying satellite cell-opathies within muscular dystrophies and myopathies

Muscular dystrophies and congenital myopathies arise from specific genetic mutations causing skeletal muscle weakness that reduces quality of life. Muscle health relies on resident muscle stem cells called satellite cells, which enable life-course muscle growth, maintenance, repair and regeneration. Such tuned plasticity gradually diminishes in muscle diseases, suggesting compromised satellite cell function. A central issue however, is whether the pathogenic mutation perturbs satellite cell function directly and/or indirectly via an increasingly hostile microenvironment as disease progresses. Here, we explore the effects on satellite cell function of pathogenic mutations in genes (myopathogenes) that associate with muscle disorders, to evaluate clinical and muscle pathological hallmarks that define dysfunctional satellite cells. We deploy transcriptomic analysis and comparison between muscular dystrophies and myopathies to determine the contribution of satellite cell dysfunction using literature, expression dynamics of myopathogenes and their response to the satellite cell regulator PAX7. Our multimodal approach extends current pathological classifications to define Satellite Cell-opathies: muscle disorders in which satellite cell dysfunction contributes to pathology. Primary Satellite Cell-opathies are conditions where mutations in a myopathogene directly affect satellite cell function, such as in Progressive Congenital Myopathy with Scoliosis (MYOSCO) and Carey-Fineman-Ziter Syndrome (CFZS). Primary satellite cell-opathies are generally characterised as being congenital with general hypotonia, and specific involvement of respiratory, trunk and facial muscles, although serum CK levels are usually within the normal range. Secondary Satellite Cell-opathies have mutations in myopathogenes that affect both satellite cells and muscle fibres. Such classification aids diagnosis and predicting probable disease course, as well as informing on treatment and therapeutic development.

ERS Statement on pediatric long term noninvasive respiratory support

Long term noninvasive respiratory support, comprising continuous positive airway pressure (CPAP) and noninvasive ventilation (NIV), in children is expanding worldwide, with increasing complexities of children being considered for this type of ventilator support and expanding indications such as palliative care. There have been improvements in equipment and interfaces. Despite growing experience, there are still gaps in a significant number of areas: there is a lack of validated criteria for CPAP/NIV initiation, optimal follow-up and monitoring; weaning and long term benefits have not been evaluated. Therapeutic education of the caregivers and the patient is of paramount importance, as well as continuous support and assistance, in order to achieve optimal adherence. The preservation or improvement of the quality of life of the patient and caregivers should be a concern for all children treated with long term CPAP/NIV. As NIV is a highly specialised treatment, patients are usually managed by an experienced pediatric multidisciplinary team. This Statement written by experts in the field of pediatric long term CPAP/NIV aims to emphasize on the most recent scientific input and should open up to new perspectives and research areas.

An infant with congenital respiratory insufficiency and diaphragmatic paralysis: A novel BICD2 phenotype?

Monoallelic pathogenic variants in BICD2 are associated with autosomal dominant Spinal Muscular Atrophy Lower Extremity Predominant 2A and 2B (SMALED2A, SMALED2B). As part of the cellular vesicular transport, complex BICD2 facilitates the flow of constitutive secretory cargoes from the trans-Golgi network, and its dysfunction results in motor neuron loss. The reported phenotypes among patients with SMALED2A and SMALED2B range from a congenital onset disorder of respiratory insufficiency, arthrogryposis, and proximal or distal limb weakness to an adult-onset disorder of limb weakness and contractures. We report an infant with congenital respiratory insufficiency requiring mechanical ventilation, congenital diaphragmatic paralysis, decreased lung volume, and single finger camptodactyly. The infant displayed appropriate antigravity limb movements but had radiological, electrophysiological, and histopathological evidence of myopathy. Exome sequencing and long-read whole-genome sequencing detected a novel de novo BICD2 variant (NM_001003800.1:c.[1543G>A];[=]). This is predicted to encode p.(Glu515Lys); p.Glu515 is located in the coiled-coil 2 mutation hotspot. We hypothesize that this novel phenotype of diaphragmatic paralysis without clear appendicular muscle weakness and contractures of large joints is a presentation of BICD2-related disease.

Natural history, outcome measures and trial readiness in LAMA2-related muscular dystrophy and SELENON-related myopathy in children and adults: protocol of the LAST STRONG study

BACKGROUND

SELENON (SEPN1)-related myopathy (SELENON-RM) is a rare congenital myopathy characterized by slowly progressive proximal muscle weakness, early onset spine rigidity and respiratory insufficiency. A muscular dystrophy caused by mutations in the LAMA2 gene (LAMA2-related muscular dystrophy, LAMA2-MD) has a similar clinical phenotype, with either a severe, early-onset due to complete Laminin subunit α2 deficiency (merosin-deficient congenital muscular dystrophy type 1A (MDC1A)), or a mild, childhood- or adult-onset due to partial Laminin subunit α2 deficiency. For both muscle diseases, no curative treatment options exist, yet promising preclinical studies are ongoing. Currently, there is a paucity on natural history data and appropriate clinical and functional outcome measures are needed to reach trial readiness.

METHODS

LAST STRONG is a natural history study in Dutch-speaking patients of all ages diagnosed with SELENON-RM or LAMA2-MD, starting August 2020. Patients have four visits at our hospital over a period of 1.5 year. At all visits, they undergo standardized neurological examination, hand-held dynamometry (age ≥ 5 years), functional measurements, questionnaires (patient report and/or parent proxy; age ≥ 2 years), muscle ultrasound including diaphragm, pulmonary function tests (spirometry, maximal inspiratory and expiratory pressure, sniff nasal inspiratory pressure; age ≥ 5 years), and accelerometry for 8 days (age ≥ 2 years); at visit one and three, they undergo cardiac evaluation (electrocardiogram, echocardiography; age ≥ 2 years), spine X-ray (age ≥ 2 years), dual-energy X-ray absorptiometry (DEXA-)scan (age ≥ 2 years) and full body magnetic resonance imaging (MRI) (age ≥ 10 years). All examinations are adapted to the patient's age and functional abilities. Correlation between key parameters within and between subsequent visits will be assessed.

DISCUSSION

Our study will describe the natural history of patients diagnosed with SELENON-RM or LAMA2-MD, enabling us to select relevant clinical and functional outcome measures for reaching clinical trial-readiness. Moreover, our detailed description (deep phenotyping) of the clinical features will optimize clinical management and will establish a well-characterized baseline cohort for prospective follow-up.

CONCLUSION

Our natural history study is an essential step for reaching trial readiness in SELENON-RM and LAMA2-MD.

TRIAL REGISTRATION

This study has been approved by medical ethical reviewing committee Region Arnhem-Nijmegen (NL64269.091.17, 2017-3911) and is registered at ClinicalTrial.gov ( NCT04478981 ).

Hypoxia and Hypoxia-Inducible Factor Signaling in Muscular Dystrophies: Cause and Consequences

Muscular dystrophies (MDs) are a group of inherited degenerative muscle disorders characterized by a progressive skeletal muscle wasting. Respiratory impairments and subsequent hypoxemia are encountered in a significant subgroup of patients in almost all MD forms. In response to hypoxic stress, compensatory mechanisms are activated especially through Hypoxia-Inducible Factor 1 α (HIF-1α). In healthy muscle, hypoxia and HIF-1α activation are known to affect oxidative stress balance and metabolism. Recent evidence has also highlighted HIF-1α as a regulator of myogenesis and satellite cell function. However, the impact of HIF-1α pathway modifications in MDs remains to be investigated. Multifactorial pathological mechanisms could lead to HIF-1α activation in patient skeletal muscles. In addition to the genetic defect per se, respiratory failure or blood vessel alterations could modify hypoxia response pathways. Here, we will discuss the current knowledge about the hypoxia response pathway alterations in MDs and address whether such changes could influence MD pathophysiology.

Calcium and Redox Liaison: A Key Role of Selenoprotein N in Skeletal Muscle

Selenoprotein N (SEPN1) is a type II glycoprotein of the endoplasmic reticulum (ER) that senses calcium levels to tune the activity of the sarcoplasmic reticulum calcium pump (SERCA pump) through a redox-mediated mechanism, modulating ER calcium homeostasis. In SEPN1-depleted muscles, altered ER calcium homeostasis triggers ER stress, which induces CHOP-mediated malfunction, altering excitation–contraction coupling. SEPN1 is localized in a region of the ER where the latter is in close contact with mitochondria, i.e., the mitochondria-associated membranes (MAM), which are important for calcium mobilization from the ER to mitochondria. Accordingly, SEPN1-depleted models have impairment of both ER and mitochondria calcium regulation and ATP production. SEPN1-related myopathy (SEPN1-RM) is an inherited congenital muscle disease due to SEPN1 loss of function, whose main histopathological features are minicores, i.e., areas of mitochondria depletion and sarcomere disorganization in muscle fibers. SEPN1-RM presents with weakness involving predominantly axial and diaphragmatic muscles. Since there is currently no disease-modifying drug to treat this myopathy, analysis of SEPN1 function in parallel with that of the muscle phenotype in SEPN1 loss of function models should help in understanding the pathogenic basis of the disease and possibly point to novel drugs for therapy. The present essay recapitulates the novel biological findings on SEPN1 and how these reconcile with the muscle and bioenergetics phenotype of SEPN1-related myopathy.

Progression or Not - A Small Natural History Study of Genetical Confirmed Congenital Myopathies

BACKGROUND

Clinical characteristics of patients with congenital myopathies (CM) are well known but there is a lack of knowledge about the natural history and course of disease of the different genetic subtypes. In 2010 we assessed the national cohort of Danish patients with CM to decide genetic diagnosing and describe genotype- phenotype relationships.AIM of this follow-up study was to evaluate the course of disease since the initial study and to evaluate the applicability of standard assessment methods to reflect change over time and patients own opinion on the course of disease.

METHODS

All available genetically diagnosed patients studied by us in 2010 (n = 41) were invited to the follow-up study; assessment of motor function (MFM-32), muscle strength (MRC %)and respiratory function (FVC %) and prime assessor were the same as in the initial study. Patients were asked whether the course of disease had progresses, was stable or had improved.

RESULTS

23 patients (15-61 y) accepted the invitation. Mean follow-up time was 7.7 years. Loss of muscle strength was more prominent in patients with mutations in DNM2, RYR1 and TPM2/3 genes and deterioration in FVC % was more evident in patients carrying NEB and ACTA1 gene mutations. MFM-sum score was less sensitive to change compared to MRC-sum score. In general, agreement between the patient's own opinion of the course of disease and results of assessments was good.

CONCLUSION

The number of patients in the study is too small to be conclusive, but the results indicate that CM can be stable or slowly progressive depending on the genetic subtype.

Respiratory management of children with spinal muscular atrophy (SMA)

Spinal muscular atrophy (SMA) causes a predominantly bilateral proximal muscle weakness and atrophy. The respiratory muscles are also involved with a weakness of the intercostal muscles and a relatively spared diaphragm. This respiratory muscle weakness translates into a cough impairment, resulting in poor clearance of airway secretions and recurrent pulmonary infections, restrictive lung disease due to a poor or insufficient chest wall and lung growth, nocturnal hypoventilation and, finally, respiratory failure. Systematic and regular monitoring of respiratory muscle performance is necessary in children with SMA in order to anticipate respiratory complications, such as acute and chronic respiratory failure, and guide clinical care. This monitoring is based in clinical practice on volitional and noninvasive tests, such as vital capacity, sniff nasal inspiratory pressure, maximal static pressures, peak expiratory flow and peak cough flow because of their simplicity, availability and ease. In young children, those with poor cooperation or severe respiratory muscle weakness, other, mostly invasive, tests may be required to evaluate respiratory muscle performance. A sleep study, or at least overnight monitoring of nocturnal gas exchange is mandatory for detecting nocturnal alveolar hypoventilation. Training for patients and caregivers in cough-assisted techniques is recommended when respiratory muscle strength falls below 50% of predicted or in case of recurrent or severe respiratory infections. Noninvasive ventilation (NIV) should be initiated in case of isolated nocturnal hypoventilation and followed by a pediatric respiratory team with expertise in NIV. Multidisciplinary (neurology and respiratory) pediatric management is crucial for optimal care of children with SMA. © 2020 French Society of Pediatrics. Published by Elsevier Masson SAS. All rights reserved.

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.

The clinical, histologic, and genotypic spectrum of SEPN1-related myopathy: A case series

OBJECTIVE

To clarify the prevalence, long-term natural history, and severity determinants of SEPN1-related myopathy (SEPN1-RM), we analyzed a large international case series.

METHODS

Retrospective clinical, histologic, and genetic analysis of 132 pediatric and adult patients (2-58 years) followed up for several decades.

RESULTS

The clinical phenotype was marked by severe axial muscle weakness, spinal rigidity, and scoliosis (86.1%, from 8.9 ± 4 years), with relatively preserved limb strength and previously unreported ophthalmoparesis in severe cases. All patients developed respiratory failure (from 10.1±6 years), 81.7% requiring ventilation while ambulant. Histopathologically, 79 muscle biopsies showed large variability, partly determined by site of biopsy and age. Multi-minicores were the most common lesion (59.5%), often associated with mild dystrophic features and occasionally with eosinophilic inclusions. Identification of 65 SEPN1 mutations, including 32 novel ones and the first pathogenic copy number variation, unveiled exon 1 as the main mutational hotspot and revealed the first genotype-phenotype correlations, bi-allelic null mutations being significantly associated with disease severity (p = 0.017). SEPN1-RM was more severe and progressive than previously thought, leading to loss of ambulation in 10% of cases, systematic functional decline from the end of the third decade, and reduced lifespan even in mild cases. The main prognosis determinants were scoliosis/respiratory management, SEPN1 mutations, and body mass abnormalities, which correlated with disease severity. We propose a set of severity criteria, provide quantitative data for outcome identification, and establish a need for age stratification.

CONCLUSION

Our results inform clinical practice, improving diagnosis and management, and represent a major breakthrough for clinical trial readiness in this not so rare disease.

Defective endoplasmic reticulum-mitochondria contacts and bioenergetics in SEPN1-related myopathy

SEPN1-related myopathy (SEPN1-RM) is a muscle disorder due to mutations of the SEPN1 gene, which is characterized by muscle weakness and fatigue leading to scoliosis and life-threatening respiratory failure. Core lesions, focal areas of mitochondria depletion in skeletal muscle fibers, are the most common histopathological lesion. SEPN1-RM underlying mechanisms and the precise role of SEPN1 in muscle remained incompletely understood, hindering the development of biomarkers and therapies for this untreatable disease. To investigate the pathophysiological pathways in SEPN1-RM, we performed metabolic studies, calcium and ATP measurements, super-resolution and electron microscopy on in vivo and in vitro models of SEPN1 deficiency as well as muscle biopsies from SEPN1-RM patients. Mouse models of SEPN1 deficiency showed marked alterations in mitochondrial physiology and energy metabolism, suggesting that SEPN1 controls mitochondrial bioenergetics. Moreover, we found that SEPN1 was enriched at the mitochondria-associated membranes (MAM), and was needed for calcium transients between ER and mitochondria, as well as for the integrity of ER-mitochondria contacts. Consistently, loss of SEPN1 in patients was associated with alterations in body composition which correlated with the severity of muscle weakness, and with impaired ER-mitochondria contacts and low ATP levels. Our results indicate a role of SEPN1 as a novel MAM protein involved in mitochondrial bioenergetics. They also identify a systemic bioenergetic component in SEPN1-RM and establish mitochondria as a novel therapeutic target. This role of SEPN1 contributes to explain the fatigue and core lesions in skeletal muscle as well as the body composition abnormalities identified as part of the SEPN1-RM phenotype. Finally, these results point out to an unrecognized interplay between mitochondrial bioenergetics and ER homeostasis in skeletal muscle. They could therefore pave the way to the identification of biomarkers and therapeutic drugs for SEPN1-RM and for other disorders in which muscle ER-mitochondria cross-talk are impaired.

Evidence of diaphragmatic dysfunction with severe alveolar hypoventilation syndrome in mitochondrial respiratory chain deficiency

Diaphragmatic dysfunction has been reported in congenital myopathies, muscular dystrophies, and occasionally, mitochondrial respiratory chain deficiency. Using a minimally invasive procedure in 3 young girls, 1 with a heteroplasmic MT-CYB mutation and 2 with biallelic pathogenic TK2 variants, we provided functional evidence of diaphragmatic dysfunction with global respiratory muscle weakness in mitochondrial respiratory chain deficiency. Analysis of respiratory muscle performance using esogastric pressures revealed paradoxical breathing and severe global inspiratory and expiratory muscle weakness with a sniff esophageal inspiratory pressure and a gastric pressure during cough averaging 50% and 40% of predicted values, respectively. This diaphragmatic dysfunction was responsible for severe undiagnosed nocturnal hypoventilation, requiring noninvasive ventilation. Our results underline the interest of this minimally invasive procedure for the evaluation of respiratory muscle performance and its potential value for the monitoring of future clinical trials in respiratory chain deficiency.

Update on Congenital Myopathies in Adulthood

Congenital myopathies (CMs) constitute a group of heterogenous rare inherited muscle diseases with different incidences. They are traditionally grouped based on characteristic histopathological findings revealed on muscle biopsy. In recent decades, the ever-increasing application of modern genetic technologies has not just improved our understanding of their pathophysiology, but also expanded their phenotypic spectrum and contributed to a more genetically based approach for their classification. Later onset forms of CMs are increasingly recognised. They are often considered milder with slower progression, variable clinical presentations and different modes of inheritance. We reviewed the key features and genetic basis of late onset CMs with a special emphasis on those forms that may first manifest in adulthood.

Physical and Functional Cross Talk Between Endo-Sarcoplasmic Reticulum and Mitochondria in Skeletal Muscle

Significance: The physiological relevance of contacts between the sarcoplasmic reticulum (SR), a specialized domain of the endoplasmic reticulum (ER) in skeletal muscle, and mitochondria is still not clear. Recent Advances: An extensive close proximity of these two organelles is a late developmental event, which suggests that it does not have an essential function. Critical Issues: The intimate association of SR/mitochondria develops during murine postnatal differentiation and the recovery of denervated atrophic muscle, which suggests that this is a highly regulated process with a specific function. Analyses of mouse models for muscle diseases suggest that impaired ER/SR-mitochondrial contacts may be due to ER stress and lead to defective bioenergetics and insulin signaling. Future Directions: Future studies are necessary to identify the molecular determinants weakening insulin signaling upon impairment of ER/mitochondrial contacts in skeletal muscles as well as to analyze the distance between SR/ER and mitochondria in muscle diseases associated with ER stress.

Protein-protein interactions of ER-resident selenoproteins with their physiological partners

ER is a highly specialized complex of branched microtubules enclosed in a membrane and communicating with each other, its functions in the cell are important and very diverse: lipid and phospholipid synthesis, calcium storage, hormone synthesis, protein synthesis and maturation, membrane production, toxin neutralization, etc. The high concentration of calcium ions and the oxidizing properties of the contents of the ER cavities contribute to the proper synthesis and folding of proteins designed for secretion or exposure on the surface of the cell membrane. However, disturbance of redox regulation can lead to the accumulation of improperly folded proteins in the ER, disruption of calcium regulation, which can cause ER-stress. This review is devoted to the role of ER-resident selenoproteins in the processes occurring in this organelle of a cell. The main emphasis is placed on the study of protein-protein interactions of selenoproteins with their physiological partners; this will facilitate understanding of their functional purpose in this organelle. Currently, 7 selenoproteins are known that are localized in the ER, but the functions of most of them are not at all clear, for some, physiological partners have been identified. It is known that selenoproteins are oxidoreductases with antioxidant properties, this is extremely important for the normal functioning of ER. Therefore, this review can be very useful for understanding the full picture of the functions of ER-resident selenoproteins obtained on the basis of recent data.

Non-invasive Ventilation in Children With Neuromuscular Disease

The respiratory muscles are rarely spared in children with neuromuscular diseases (NMD) which puts them at risk of alveolar hypoventilation. The role of non-invasive ventilation (NIV) is then to assist or "replace" the weakened respiratory muscles in order to correct alveolar hypoventilation by maintaining a sufficient tidal volume and minute ventilation. As breathing is physiologically less efficient during sleep, NIV will be initially used at night but, with the progression of respiratory muscle weakness, NIV can be extended during daytime, preferentially by means of a mouthpiece in order to allow speech and eating. Although children with NMD represent the largest group of children requiring long term NIV, there is a lack of validated criteria to start NIV. There is an agreement to start long term NIV in case of isolated nocturnal hypoventilation, before the appearance of daytime hypercapnia, and/or in case of acute respiratory failure requiring any type of ventilatory support. NIV is associated with a correction in night- and daytime gas exchange, an increase in sleep efficiency and an increase in survival. NIV and/or intermittent positive pressure breathing (IPPB) have been shown to prevent thoracic deformities and consequent thoracic and lung hypoplasia in young children with NMD. NIV should be performed with a life support ventilator appropriate for the child's weight, with adequate alarms, and an integrated (±additional) battery. Humidification is recommended to improve respiratory comfort and prevent drying of bronchial secretions. A nasal interface (or nasal canula) is the preferred interface, a nasobuccal interface can be used with caution in case of mouth breathing. The efficacy of NIV should be assessed on the correction of alveolar ventilation. Patient ventilator synchrony and the absence of leaks can be assessed on a sleep study with NIV or on the analysis of the ventilator's in-built software. The ventilator settings and the interface should be adapted to the child's growth and progression of respiratory muscle weakness. NIV should be associated with an efficient clearance of bronchial secretions by a specific program on the ventilator, IPPB, or mechanical insufflation-exsufflation. Finally, these children should be managed by an expert pediatric multi-disciplinary team.

Daytime noninvasive ventilatory support for patients with ventilatory pump failure: a narrative review

Over the past three decades, the use of noninvasive ventilation or "NIV" to assuage symptoms of hypoventilation for patients with early onset or mild ventilatory pump failure has been extended to up to the use of continuous noninvasive ventilatory support (CNVS) at full ventilatory support settings as a definitive alternative to tracheostomy mechanical ventilation. NVS, along with mechanical insufflation-exsufflation, now provides a noninvasive option for the management of both chronic and acute respiratory failure for these patients. The most common diagnoses for which these methods are useful include chest wall deformities, neuromuscular diseases, morbid obesity, high level spinal cord injury and idiopathic, primary or secondary disorders of the ventilatory control. Thus, NVS is being used in diverse settings: critical care units, medical wards, at home, and in extended care. The aim of this review is to examine the techniques used for daytime support.

Signs and Symptoms in Congenital Myopathies

Congenital myopathies (CM) represent a continuously growing group of disorders with a wide range of clinical and histopathologic presentations. The refinement and application of new technologies for genetic diagnosis have broadened our understanding of the genetic causes of CM. Our growing knowledge has revealed that there are no clear limits between each subgroup of CM, and thus the clinical overlap between genes has become more evident. The implementation of next generation sequencing has produced vast amounts of genomic data that may be difficult to interpret. With an increasing number of reports revealing variants of unknown significance, it is essential to support the genetic diagnosis with a well characterized clinical description of the patient. Phenotype-genotype correlation should be a priority at the moment of disclosing the genetic results. Thus, a detailed physical examination can provide us with subtle differences that are not only key in order to arrive at a correct diagnosis, but also in the characterization of new myopathies and candidate genes.

A maladaptive ER stress response triggers dysfunction in highly active muscles of mice with SELENON loss

Selenoprotein N (SELENON) is an endoplasmic reticulum (ER) protein whose loss of function leads to human SELENON-related myopathies. SelenoN knockout (KO) mouse limb muscles, however, are protected from the disease, and display no major alterations in muscle histology or contractile properties. Interestingly, we find that the highly active diaphragm muscle shows impaired force production, in line with the human phenotype. In addition, after repeated stimulation with a protocol which induces muscle fatigue, also hind limb muscles show altered relaxation times. Mechanistically, muscle SELENON loss alters activity-dependent calcium handling selectively impinging on the Ca²⁺ uptake of the sarcoplasmic reticulum and elicits an ER stress response, including the expression of the maladaptive CHOP-induced ERO1. In SELENON-devoid models, ERO1 shifts ER redox to a more oxidised poise, and further affects Ca²⁺ uptake. Importantly, CHOP ablation in SelenoN KO mice completely prevents diaphragm dysfunction, the prolonged limb muscle relaxation after fatigue, and restores Ca²⁺ uptake by attenuating the induction of ERO1. These findings suggest that SELENON is part of an ER stress-dependent antioxidant response and that the CHOP/ERO1 branch of the ER stress response is a novel pathogenic mechanism underlying SELENON-related myopathies.