Spectrum of metabolic myopathies

miR-1 sustains muscle physiology by controlling V-ATPase complex assembly

Muscle function requires unique structural and metabolic adaptations that can render muscle cells selectively vulnerable, with mutations in some ubiquitously expressed genes causing myopathies but sparing other tissues. We uncovered a muscle cell vulnerability by studying miR-1, a deeply conserved, muscle-specific microRNA whose ablation causes various muscle defects. Using Caenorhabditis elegans, we found that miR-1 represses multiple subunits of the ubiquitous vacuolar adenosine triphosphatase (V-ATPase) complex, which is essential for internal compartment acidification and metabolic signaling. V-ATPase subunits are predicted miR-1 targets in animals ranging from C. elegans to humans, and we experimentally validated this in Drosophila. Unexpectedly, up-regulation of V-ATPase subunits upon miR-1 deletion causes reduced V-ATPase function due to defects in complex assembly. These results reveal V-ATPase assembly as a conserved muscle cell vulnerability and support a previously unknown role for microRNAs in the regulation of protein complexes.

Early Findings in Neonatal Cases of RYR1-Related Congenital Myopathies

Ryanodine receptor type 1-related congenital myopathies are the most represented subgroup among congenital myopathies (CMs), typically presenting a central core or multiminicore muscle histopathology and high clinical heterogeneity. We evaluated a cohort of patients affected with Ryanodine receptor type 1-related congenital myopathy (RYR1-RCM), focusing on four patients who showed a severe congenital phenotype and underwent a comprehensive characterization at few months of life. To date there are few reports on precocious instrumental assessment. In two out of the four patients, a muscle biopsy was performed in the first days of life (day 5 and 37, respectively) and electron microscopy was carried out in two patients detecting typical features of congenital myopathy. Two patients underwent brain MRI in the first months of life (15 days and 2 months, respectively), one also a fetal brain MRI. In three children electromyography was performed in the first week of life and neurogenic signs were excluded. Muscle MRI obtained within the first years of life showed a typical pattern of RYR1-CM. The diagnosis was confirmed through genetic analysis in three out of four cases using Next Generation Sequencing (NGS) panels. The development of a correct and rapid diagnosis is a priority and may lead to prompt medical management and helps optimize inclusion in future clinical trials.

Skin damage in a patient with lipid storage myopathy with a novel ETFDH mutation responsive to riboflavin

Background: Recessive mutations in ETFDH gene have been associated with Multiple Acyl-CoA dehydrogenase deficiency (MADD). The late-onset MADD is often muscle involved, presenting with lipid storage myopathy (LSM). The symptoms of LSM were heterogeneous and definite diagnosis of this disease depends on the pathology and gene test.Methods: Neurological examination, muscle biopsy, and MRI examinations were performed in a patient with a novel missense ETFDH mutation.Results: We describe a patient with lipid storage myopathy complicated with skin damage. In addition, the next generation revealed a novel missense mutation (c.970G > T, p.Val324Leu) in exon 8, which was predicted to be a disease-causing mutation by Mutation-taster, and destroy the function of the protein by Sift.Conclusion: These findings expand the known mutational spectrum of ETFDH and phenotype of MADD.

Mobility assessment using wearable technology in patients with late-onset Pompe disease

Late-onset Pompe disease (LOPD) is a rare genetic disorder due to the absence or deficiency of acid alpha-glucosidase enzyme resulting in slowly progressing reduction of muscle strength, causing difficulties with mobility and respiration. Wearable technologies offer novel options to evaluate mobility in a real-world setting. LOPD patients self-reporting LOPD, ≥18 years, US residents, walking (with or without aid), and not on invasive ventilation were recruited for a 6- to 8-week wearable study via patient organizations. Eligible patients were shipped a wearable tracker (Fitbit One™) and completed self-assessment questionnaires. Mobility outcome measures were median step count and peak 1-min activity. In the analyses cohort (N = 29), engagement in data sharing was high (94% of patients uploaded data for more than half the study days). Mean age was 43 years, 90% were females, and 93% were diagnosed in adulthood. Mean delay in diagnosis was 10 years; most had disease onset for ≥10 years (55%); some required walking aid (17%) and breathing assistance (38%). Mean step count differed by age (20-39 years: 4071 vs. 40-69 years: 2394, p < 0.01), diagnostic delay (<10 years: 3584 vs. ≥10 years: 2232, p < 0.05), disease duration (<10 years: 4219 vs. ≥10 years: 2462, p < 0.05), and ambulatory status (aided: 1883 vs. unaided: 3408, p < 0.05). Patient-reported "fatigue and pain" score was inversely correlated with step count (Pearson's r = -0.42, p < 0.05) and peak 1-min activity (Pearson's r = -0.49, p < 0.01). This study illustrates a new approach to measure mobility in LOPD patients and establishes a framework for future outcomes data collection.

A pattern-based approach to the interpretation of skeletal muscle biopsies

The interpretation of muscle biopsies is complex and provides the most useful information when integrated with the clinical presentation of the patient. These biopsies are performed for workup of a wide range of diseases including dystrophies, metabolic diseases, and inflammatory processes. Recent insights have led to changes in the classification of inflammatory myopathies and have changed the role that muscle biopsies have in the workup of inherited diseases. These changes will be reviewed. This review follows a morphology-driven approach by discussing diseases of skeletal muscle based on a few basic patterns that include cases with (1) active myopathic damage and inflammation, (2) active myopathic damage without associated inflammation, (3) chronic myopathic changes, (4) myopathies with distinctive inclusions or vacuoles, (5) biopsies mainly showing atrophic changes, and (6) biopsies that appear normal on routine preparations. Each of these categories goes along with certain diagnostic considerations and pitfalls. Individual biopsy features are only rarely pathognomonic. Establishing a firm diagnosis therefore typically requires integration of all of the biopsy findings and relevant clinical information. With this approach, a muscle biopsy can often provide helpful information in the diagnostic workup of patients presenting with neuromuscular problems.

Myo-Glyco disease Biology: Genetic Myopathies Caused by Abnormal Glycan Synthesis and Degradation

Glycosylation is a major form of post-translational modification and plays various important roles in organisms by modifying proteins or lipids, which generates functional variability and can increase their stability. Because of the physiological importance of glycosylation, defects in genes encoding proteins involved in glycosylation or glycan degradation are sometimes associated with human diseases. A number of genetic neuromuscular diseases are caused by abnormal glycan modification or degeneration. Heterogeneous and complex modification machinery, and difficulties in structural and functional analysis of glycans have impeded the understanding of how glycosylation contributes to pathology. However, recent rapid advances in glycan and genetic analyses, as well as accumulating genetic and clinical information have greatly contributed to identifying glycan structures and modification enzymes, which has led to breakthroughs in the understanding of the molecular pathogenesis of various diseases and the possible development of therapeutic strategies. For example, studies on the relationship between glycosylation and muscular dystrophy in the last two decades have significantly impacted the fields of glycobiology and neuromyology. In this review, the basis of glycan structure and biosynthesis will be briefly explained, and then molecular pathogenesis and therapeutic concepts related to neuromuscular diseases will be introduced from the point of view of the life cycle of a glycan molecule.

Role of autophagy in inherited metabolic and endocrine myopathies

The prevalence of cardiometabolic disease has reached an exponential rate of rise over the last decades owing to high fat/high caloric diet intake and satiety life style. Although the presence of dyslipidemia, insulin resistance, hypertension and obesity mainly contributes to the increased incidence of cardiometabolic diseases, population-based, clinical and genetic studies have revealed a rather important role for inherited myopathies and endocrine disorders in the ever-rising metabolic anomalies. Inherited metabolic and endocrine diseases such as glycogen storage and lysosomal disorders have greatly contributed to the overall prevalence of cardiometabolic diseases. Recent evidence has demonstrated an essential role for proteotoxicity due to autophagy failure and/or dysregulation in the onset of inherited metabolic and endocrine disorders. Given the key role for autophagy in the degradation and removal of long-lived or injured proteins and organelles for the maintenance of cellular and organismal homeostasis, this mini-review will discuss the potential contribution of autophagy dysregulation in the pathogenesis of inherited myopathies and endocrine disorders, which greatly contribute to an overall rise in prevalence of cardiometabolic disorders. Molecular, clinical, and epidemiological aspects will be covered as well as the potential link between autophagy and metabolic anomalies thus target therapy may be engaged for these comorbidities.

Testing for Inborn Errors of Metabolism

PURPOSE OF REVIEW

This article provides an overview of genetic metabolic disorders that can be identified by metabolic tests readily available to neurologists, such as tests for ammonia, plasma amino acids, and urine organic acids. The limitations of these tests are also discussed, as they only screen for a subset of the many inborn errors of metabolism that exist.

RECENT FINDINGS

Advances in next-generation sequencing and the emerging use of advanced metabolomic screening have made it possible to diagnose treatable inborn errors of metabolism that are not included in current newborn screening programs. Some of these inborn errors of metabolism are especially likely to present with nonspecific neurologic phenotypes, such as epilepsy, ataxia, or intellectual disability. However, cost may be a barrier to obtaining these newer tests. It is important to keep in mind that common metabolic testing may lead to treatable diagnoses. Resources are available to guide neurologists in diagnosing genetic metabolic conditions.

SUMMARY

This article introduces the clinical presentations of treatable inborn errors of metabolism that are important for neurologists to consider in patients of all ages. Inborn errors of metabolism are rare, but they can present with neurologic symptoms. Newborns are now screened for many treatable metabolic disorders, but these screening tests may miss milder presentations of treatable inborn errors of metabolism that present later in life. These patients may present to adult neurologists who may be less likely to consider metabolic genetic testing.

Pulmonary functions and sleep-related breathing disorders in lipid storage disease

PURPOSE

Pulmonary function abnormalities and sleep-related breathing disorders (SRBD) are frequent in subjects with several neuromuscular diseases but there is no data about lipid storage diseases (LSD). Therefore, we aimed to evaluate pulmonary functions and SRBD in adults with LSD.

METHODS

Pulmonary functions (forced expiratory volume (FEV₁), forced vital capacity (FVC), supine FVC, upright-supine FVC% change, maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), peak cough flow (PCF)), arterial blood gases, and polysomnographic data of all subjects were evaluated.

RESULTS

Twenty-five subjects with LSD were evaluated [17 males, 8 females; age 34.9 ± 15 years; BMI 26.5 ± 3.4 kg/m²]. MIP was - 72.2 ± 32.7 cmH₂O (< - 80 cmH₂O in 13 subjects), MEP was 80.9 ± 39.1 cmH₂O (< 80 cmH₂O in 9 subjects, < 40 cmH₂O in 6 subjects), and PCF was 441.3 ± 190.9 L/min (< 360 L/min in 11 subjects). FVC was 87.8% ± 25.7 and 6 subjects had FVC < 80%. Seven subjects had diaphragm dysfunction (four upright-supine FVC% ≥ 15, three dyspnea in supine position with paradoxical abdominal respiration). Five subjects had hypoxemia (PaO₂ < 80 mmHg) and 8 subjects had hypercapnia (PaCO₂ > 45 mmHg). REM sleep had decreased in all subjects (10.2% ± 6.1). Obstructive sleep apnea (OSA) was found in 80% of the subjects (n = 20; 9 mild, 9 moderate, 2 severe). For subjects with OSA, apnea-hypopnea index (AHI) was 20.8 ± 15.9/h, oxygen desaturation index (ODI) was 11.9 ± 15.4/h, AHI_REM was 30.6 ± 19.7/h, AHI_NREM was 19.7 ± 16.6/h, ODI_REM was 27.2 ± 26.1/h, and ODI_NREM was 11.4 ± 15/h. Five subjects (20%) diagnosed as REM-related OSA. Nocturnal mean SpO₂ was 94.9% ± 1.7, lowest SpO₂ was 73.3% ± 13.9, and time spent with SpO₂ < 90% was 2.4% ± 7.2.

CONCLUSION

In subjects with LSD, pulmonary function impairment, daytime hypercapnia and hypoxemia, and OSA, especially REM-related OSA, are frequent. Therefore, pulmonary functions and polysomnography should be performed routinely.

Phenotype, disease severity and pain are major determinants of quality of life in Fabry disease: results from a large multicenter cohort study

Quality of life (QoL) is decreased in patients with Fabry disease (FD). To improve QoL, it is important to understand the influence of FD related characteristics, symptoms, and complications. In this retrospective cohort study we explored the effect of pain (measured by the Brief Pain Inventory), phenotype, treatment, and FD-related complications on QoL. QoL data of Fabry patients as assessed by the EuroQol five dimension questionnaire (EQ-5D) from two international centers of excellence were collected. The aim of this study was to evaluate the effect of sex, phenotype, age, different states of disease severity, pain, and ERT on EQ-5D utilities. For 286 adult FD patients (mean age 42.5 years, 40% men, 60% classical phenotype) 2240 EQ-5Ds were available. QoL is decreased in men as well as women with FD, especially in older men with a classical phenotype. At age 50, utility was lower in men with classical FD compared to those with non-classical disease (β = -0.12, 95% CI: -0.23 - 0.01, p = 0.037) with further difference in the years thereafter. Cardiovascular complications, stroke or transient ischemic attacks, multiple FD-related complications and pain were also associated with decreased utilities. Overall, no change in utility was seen in patients on ERT over a mean follow-up of 6.1 years. FD leads to a decreased QoL compared to the general population. Disease complications and pain both negatively influence QoL. Adequate assessment and treatment of pain as well as improved strategies to prevent disease complications are needed to improve QoL in the FD population.

Treatment of muscle weakness in neuromuscular disorders

INTRODUCTION

Weakness is one of the predominant clinical manifestations of neuromuscular disorders (NMDs), which strongly influences daily life, prognosis, and outcome of affected patients. One of the major therapeutic goals in NMD-patients is to completely resolve muscle weakness. Various treatment options are available and include physical therapy, electrotherapy, diet, drugs, avoidance or withdrawal of muscle-toxic and weakness-inducing agents, detoxification, stem-cell-therapy, plasma-exchange, respiratory therapy, or surgery. Most accessible to treatment is weakness from immune-mediated neuropathies, immune-mediated transmission-disorders, and idiopathic immune myopathies. Areas covered: This manuscript aims to summarize and discuss recent findings and future perspectives concerning the treatment of muscle weakness in NMDs. Data were obtained by a literature search in databases such as PubMed and Current-Contents. Expert commentary: Weakness is most easily treatable in acquired NMDs and in hereditary myopathies and neuropathies beneficial treatment options are also available. Research needs to be encouraged and intensified to further expand the spectrum of treatment options for weakness.

Neuromuscular disease. Diagnosis and discovery in limb-girdle muscular dystrophy

Whole-exome sequencing is a new tool for neuromuscular clinicians, and recent findings show that it improves the diagnosis of limb-girdle muscular dystrophy. The technique has a dual role as a tool for diagnosis and discovery in genetically heterogeneous neuromuscular diseases.

Rhabdomyolysis: a genetic perspective

Rhabdomyolysis (RM) is a clinical emergency characterized by fulminant skeletal muscle damage and release of intracellular muscle components into the blood stream leading to myoglobinuria and, in severe cases, acute renal failure. Apart from trauma, a wide range of causes have been reported including drug abuse and infections. Underlying genetic disorders are also a cause of RM and can often pose a diagnostic challenge, considering their marked heterogeneity and comparative rarity.

In this paper we review the range of rare genetic defects known to be associated with RM. Each gene has been reviewed for the following: clinical phenotype, typical triggers for RM and recommended diagnostic approach. The purpose of this review is to highlight the most important features associated with specific genetic defects in order to aid the diagnosis of patients presenting with hereditary causes of recurrent RM.

The sarcomeric M-region: a molecular command center for diverse cellular processes

The sarcomeric M-region anchors thick filaments and withstands the mechanical stress of contractions by deformation, thus enabling distribution of physiological forces along the length of thick filaments. While the role of the M-region in supporting myofibrillar structure and contractility is well established, its role in mediating additional cellular processes has only recently started to emerge. As such, M-region is the hub of key protein players contributing to cytoskeletal remodeling, signal transduction, mechanosensing, metabolism, and proteasomal degradation. Mutations in genes encoding M-region related proteins lead to development of severe and lethal cardiac and skeletal myopathies affecting mankind. Herein, we describe the main cellular processes taking place at the M-region, other than thick filament assembly, and discuss human myopathies associated with mutant or truncated M-region proteins.