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

Utility of exome sequencing for the diagnosis of pediatric-onset neuromuscular diseases beyond diagnostic yield: a narrative review

Diagnosis of neuromuscular diseases (NMD) can be challenging because of the heterogeneity of this group of diseases. This review aimed to describe the diagnostic yield of whole exome sequencing (WES) for pediatric-onset neuromuscular disease diagnosis, as well as other benefits of this approach in patient management since WES can contribute to appropriate treatment selection in NMD patients. WES increases the possibility of reaching a conclusive genetic diagnosis when other technologies have failed and even exploring new genes not previously associated with a specific NMD. Moreover, this strategy can be useful when a dual diagnosis is suspected in complex congenital anomalies and undiagnosed cases.

An evaluation of clinical presentation and genetic testing approaches for patients with neuromuscular disorders

Inherited neuromuscular disorders (NMDs) are a large group of genetic conditions characterized by impaired peripheral nerve, motor neuron, neuromuscular junction, or skeletal muscle function. These conditions are also known to have clinical and genetic heterogeneity and variable ages of onset. Clinical evaluation for NMDs has increasingly incorporated molecular genetics. However, genetic testing is complicated by the variety of testing options and the ambiguity of NMD phenotypes. Examining test selection and yield may elucidate testing recommendations and improve the diagnostic journey for these patients. This retrospective chart review evaluated the clinical presentations, genetic testing approaches, and diagnostic outcomes of 155 patients with suspected NMDs at Cincinnati Children's Hospital Medical Center. A total of 262 individual tests were ordered, averaging 1.7 tests per patient. The clinic utilized 26 separate genetic tests, with test yields ranging from 0% to 66%. Overall, 21% of patients received a genetic diagnosis. Of all the clinical findings evaluated, elevated CPK levels with or without muscle weakness were the most informative symptoms correlated with a diagnostic result. This study highlights several genetic testing considerations for NMDs, including the variability of diagnostic outcomes. This knowledge is relevant to clinicians and patients, especially during the pretest counseling and consenting process.

An early onset benign myopathy with glycogen storage caused by a de novo 1.4 Mb-deletion of chromosome 14

Early onset myopathies are a clinically and histologically heterogeneous monogenic diseases linked to approximately 90 genes. Molecular diagnosis is challenging, especially in patients with a mild phenotype. We describe a 26-year-old man with neonatal hypotonia, motor delay and seizures during infancy, and non-progressive, mild muscular weakness in adulthood. Serum Creatine kinase level was normal. Whole-body muscle MRI showed thin muscles, and brain MRI was unremarkable. A deltoid muscle biopsy showed glycogen storage. WGS revealed a de novo 1.4 Mb-deletion of chromosome 14, confirmed by Array-CGH. This microdeletion causes the loss of ten genes including RALGAPA1, encoding for RalA, a regulator of glucose transporter 4 (GLUT4) expression at the membrane of myofibers. GLUT4 was overexpressed in patient's muscle. Here we highlight the importance to search for chromosomal alterations in the diagnostic workup of early onset myopathies.

[Genomics and proteomics in the research of neuromuscular diseases]

Neurological diseases affect 3-5% of children and, apart from cardiovascular diseases and cancer, represent the most prominent cause of morbidity and mortality in adults and particularly in the aged population of western Europe. Neuromuscular disorders are a subgroup of neurological diseases and often have a genetic origin, which leads to familial clustering. Despite the enormous progress in the analysis of the genome, such as by sequence analysis of coding regions of deoxyribonucleic acid or even the entire deoxyribonucleic acid sequence, in approximately 50% of the patients suffering from rare forms of neurological diseases the genetic cause remains unsolved. The reasons for this limited detection rate are presented in this article. If a treatment concept is available, under certain conditions this can have an impact on the adequate and early treatment of these patients. Considering neuromuscular disorders as a paradigm, this article reports on the advantages of the inclusion of next generation sequencing analysis-based DNA investigations as an omics technology (genomics) and the advantage of the integration with protein analyses (proteomics). A special focus is on the combination of genomics and proteomics in the sense of a proteogenomic approach in the diagnostics and research of these diseases. Along this line, this article presents a proteogenomic approach in the context of a multidisciplinary project aiming towards improved diagnostic work-up and future treatment of patients with neuromuscular diseases; "NMD-GPS: gene and protein signatures as a global positioning system in patients suffering from neuromuscular diseases".

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.

Spectrum of Clinical Features in X-Linked Myotubular Myopathy Carriers: An International Questionnaire Study

OBJECTIVE

To characterize the spectrum of clinical features in a cohort of X-linked myotubular myopathy (XL-MTM) carriers, including prevalence, genetic features, clinical symptoms, and signs, as well as associated disease burden.

METHODS

We performed a cross-sectional online questionnaire study among XL-MTM carriers. Participants were recruited from patient associations, medical centers, and registries in the United Kingdom, Germany, and the Netherlands. We used a custom-made questionnaire, the Checklist Individual Strength (CIS), the Frenchay Activities Index (FAI), the Short Form 12 (SF-12) health survey, and the McGill Pain Questionnaire. Carriers were classified as manifesting or nonmanifesting on the basis of self-reported ambulation and muscle weakness.

RESULTS

The prevalence of manifesting carriers in this study population (n = 76) was 51%, subdivided into mild (independent ambulation, 39%), moderate (assisted ambulation, 9%), and severe (wheelchair dependent, 3%) phenotypes. In addition to muscle weakness, manifesting carriers frequently reported fatigue (70%) and exercise intolerance (49%). Manifesting carriers scored higher on the overall CIS (p = 0.001), the fatigue subscale (p < 0.001), and least severe pain subscale (p = 0.005) than nonmanifesting carriers. They scored lower on the FAI (p = 0.005) and the physical component of the SF-12 health survey (p < 0.001).

CONCLUSIONS

The prevalence of manifesting XL-MTM carriers may be higher than currently assumed, most having a mild phenotype and a wide variety of symptoms. Manifesting carriers are particularly affected by fatigue, limitations of daily activities, pain, and reduced quality of life. Our findings should increase awareness and provide useful information for health care providers and future clinical trials.

The Role of Z-disc Proteins in Myopathy and Cardiomyopathy

The Z-disc acts as a protein-rich structure to tether thin filament in the contractile units, the sarcomeres, of striated muscle cells. Proteins found in the Z-disc are integral for maintaining the architecture of the sarcomere. They also enable it to function as a (bio-mechanical) signalling hub. Numerous proteins interact in the Z-disc to facilitate force transduction and intracellular signalling in both cardiac and skeletal muscle. This review will focus on six key Z-disc proteins: α-actinin 2, filamin C, myopalladin, myotilin, telethonin and Z-disc alternatively spliced PDZ-motif (ZASP), which have all been linked to myopathies and cardiomyopathies. We will summarise pathogenic variants identified in the six genes coding for these proteins and look at their involvement in myopathy and cardiomyopathy. Listing the Minor Allele Frequency (MAF) of these variants in the Genome Aggregation Database (GnomAD) version 3.1 will help to critically re-evaluate pathogenicity based on variant frequency in normal population cohorts.

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.

Advances in the diagnosis of inherited neuromuscular diseases and implications for therapy development

Advances in DNA sequencing technologies have resulted in a near doubling, in under 10 years, of the number of causal genes identified for inherited neuromuscular disorders. However, around half of patients, whether children or adults, do not receive a molecular diagnosis after initial diagnostic workup. Massively parallel technologies targeting RNA, proteins, and metabolites are being increasingly used to diagnose these unsolved cases. The use of these technologies to delineate pathways, biomarkers, and therapeutic targets has led to new approaches entering the drug development pipeline. However, these technologies might give rise to misleading conclusions if used in isolation, and traditional techniques including comprehensive neurological evaluation, histopathology, and biochemistry continue to have a crucial role in diagnostics. For optimal diagnosis, prognosis, and precision medicine, no single ruling technology exists. Instead, an interdisciplinary approach combining novel and traditional neurological techniques with computer-aided analysis and international data sharing is needed to advance the diagnosis and treatment of neuromuscular disorders.

The spectrum of muscle pathologies: Three decades of experience from a reference laboratory in Saudi Arabia

BACKGROUND

When investigating patients with a suspected neuromuscular disorder, a muscle biopsy is considered an instrumental tool to reach a definitive diagnosis. There is a paucity of publications that assess the diagnostic utilization and yield of muscle biopsies. We intend to present our experience in this regard over an extended period of more than three decades.

METHODS

This is an observational retrospective cohort study in which we collected pathology reports for muscle biopsies diagnosed at our reference lab between 1986 and 2017.

RESULTS

We identified a total of 461 cases of muscle biopsy performed, which fulfilled the inclusion criteria. Pediatric cases defined as ≤14 years of age constituted a significant proportion of cases (n = 275, 60%). Normal biopsies were reported in 27% of cases (n = 124), and in 4%, the biopsies were non-diagnostic. The most common pathologies reported were non-specific myopathy (n = 72, 16%), dystrophy (n = 71, 15%), and neurogenic disorders (n = 60, 13%).

CONCLUSION

In conclusion, the muscle biopsy will continue to play a crucial role, as a gold standard or as a complementary investigation, in the diagnosis of certain neuromuscular disorders. Increasing the yield and accuracy of muscle pathology should be the main concern and priority to neuropathologists reporting muscle biopsies. In addition, utilizing next-generation sequencing and other molecular techniques have changed the location of muscle biopsy in the algorithm of the diagnosis of neuromuscular disorders. This paper is an urgent call to establish the Saudi Neuropathology Society and the muscle pathology and neuromuscular disorders registry.

A mutation update for the FLNC gene in myopathies and cardiomyopathies

Filamin C (FLNC) variants are associated with cardiac and muscular phenotypes. Originally, FLNC variants were described in myofibrillar myopathy (MFM) patients. Later, high‐throughput screening in cardiomyopathy cohorts determined a prominent role for FLNC in isolated hypertrophic and dilated cardiomyopathies (HCM and DCM). FLNC variants are now among the more prevalent causes of genetic DCM. FLNC‐associated DCM is associated with a malignant clinical course and a high risk of sudden cardiac death. The clinical spectrum of FLNC suggests different pathomechanisms related to variant types and their location in the gene. The appropriate functioning of FLNC is crucial for structural integrity and cell signaling of the sarcomere. The secondary protein structure of FLNC is critical to ensure this function. Truncating variants with subsequent haploinsufficiency are associated with DCM and cardiac arrhythmias. Interference with the dimerization and folding of the protein leads to aggregate formation detrimental for muscle function, as found in HCM and MFM. Variants associated with HCM are predominantly missense variants, which cluster in the ROD2 domain. This domain is important for binding to the sarcomere and to ensure appropriate cell signaling. We here review FLNC genotype–phenotype correlations based on available evidence.

Clinical exome sequencing in neuromuscular diseases: an experience from Turkey

Neuromuscular diseases (NMDs) encompass a variety of ailments from muscular dystrophies to ataxias, in the course of which the functioning of the muscles is eventually either directly or indirectly impaired. The clinical diagnosis of a particular NMD is not always straightforward due to the clinical and genetic heterogeneity of the disorders under investigation. Traditional diagnostic tools such as electrophysiological tests and muscle biopsies are both invasive and painful methods, causing the patients to be reluctant. Next-generation sequencing, on the other hand, emerged as an alternative method for the diagnosis of NMDs, both with its minimally invasive nature and fast processing period. In this study, clinical exome sequencing (CES) was applied to a cohort of 70 probands in Turkey, 44 of whom received a final diagnosis, representing a diagnostic rate of 62.9%. Out of the 50 mutations identified to be causal, 26 were novel in the known 27 NMD genes. Two probands had complex/blended phenotypes. Molecular confirmation of clinical diagnosis of NMDs has a major prognostic impact and is crucial for the management and the possibility of alternative reproductive options. CES, which has been increasingly adopted to diagnose single-gene disorders, is also a powerful tool for revealing the etiopathogenesis in complex/blended phenotypes, as observed in two probands of the cohort.