Nemaline Myopathy Research Articles

In a cohort of 961 clinically suspected Duchenne muscular dystrophy patients, 105 were diagnosed to have other muscular dystrophies (OMDs), with LGMD2E (variant SGCB c.544A>C) being the most common.

Targeted next generation sequence analyses in a cohort of 961 previously described patients with clinically suspected Duchene muscular dystrophy (DMD) revealed that 145/961 (15%) had variants in genes associated with other muscular dystrophies (OMDs). NGS was carried out in DMD negative patients after deletion/duplication analysis followed by WES for No variant cases. The majority of patients with OMDs had autosomal recessive diseases that included Limb-Girdle Muscular Dystrophies (LGMDs), Bethlem, Ullrich congenital Myopathies and Emery-Driefuss muscular dystrophy. 3.5% of patients were identified with other disorders like Charcot-Marie Tooth and Nemaline myopathy. A small percentage of patients, 0.6% remain undiagnosed. Of a total of 78 genetic variants identified, 44 were found to be novel. Interestingly, a third of patients with OMDs were found to have LGMD2E/R4, a severe form of LGMD that afflicts young children with clinical symptoms similar to DMD. Almost one third of the unrelated LGMD2E/R4 patients had the same point mutation (c.544A>C) in the SGCB gene, suggestive of a founder effect, described here for the first time in India. This study underscores the need for a complete genetic work up to precisely diagnose patients and to initiate appropriate counseling programs, disease management and prevention strategies.

Late-onset primary muscle diseases mimicking sarcopenia.

Sarcopenia is an age-related loss of skeletal muscle mass, strength, and function that causes various health problems. In contrast, late-onset primary myopathies, which occur in the older population, are caused by a variety of factors, including genetic mutations, autoimmune processes, and metabolic abnormalities. Although sarcopenia and primary myopathy are two distinct disease processes, their symptoms can overlap, making differentiation challenging. The diagnostic criteria for sarcopenia have evolved over time, and various criteria have been proposed by expert groups. Late-onset primary muscle diseases such as inclusion body myositis, sporadic late-onset nemaline myopathy, muscular dystrophies, distal myopathies, myofibrillar myopathies, metabolic myopathies, and mitochondrial myopathies share common pathogenic mechanisms with sarcopenia, further complicating the diagnostic process. Appropriate clinical evaluation, including detailed history-taking, physical examination, and diagnostic testing, is essential for accurate diagnosis and management. Treatment approaches, including exercise, nutritional support, and disease-specific therapies, must be tailored to the characteristics of each disease. Despite these differences, sarcopenia and primary myopathies require careful consideration in the clinical setting for proper diagnosis and management. This review outlines the evolution of diagnostic criteria and diagnostic items for sarcopenia, late-onset primary myopathies that should be differentiated from sarcopenia, common pathomechanisms, and diagnostic algorithms to properly differentiate primary myopathies. Geriatr Gerontol Int 2024; ••: ••-••.

Tuning the idling molecular motor in muscle to treat nemaline myopathy.

Tuning the idling molecular motor in muscle to treat nemaline myopathy.

31P Nutritional status of patients with nemaline myopathy and related congenital myopathies in Finland

31P Nutritional status of patients with nemaline myopathy and related congenital myopathies in Finland

21P Tongue ultrasound assessment in patients with nemaline myopathy

21P Tongue ultrasound assessment in patients with nemaline myopathy

A Case Study on Anesthesia for Percutaneous Closure of Large Secundum ASD in a Patient with Nemaline Myopathy Type

A Case Study on Anesthesia for Percutaneous Closure of Large Secundum ASD in a Patient with Nemaline Myopathy Type

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes with coexisting nemaline myopathy: a case report

BackgroundMitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes and nemaline myopathy are two rare genetic conditions. We report the first case reported in world literature with coexistence of both these rare disorders.Case presentationA 11-year-old previously healthy Sri Lankan male child, product of a nonconsanguineous marriage with normal development presented with acute onset short lasting recurring episodes of right-sided eye deviation with impaired consciousness. In between episodes he regained consciousness. Family history revealed a similar presentation in the mother at 36 years of age. Examination was significant for short stature and proximal upper and lower limb weakness. His plasma and cerebrospinal fluid lactate were elevated. Magnetic resonance imaging brain had evidence of an acute infarction in the right occipital territory. Sanger sequencing for common mitochondrial variants of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes confirmed this diagnosis. Whole exome sequencing revealed pathogenic compound heterozygous variants in NEB gene implicating in coexisting nemaline myopathy. Acute presentation was managed with supportive care, antiepileptics, and mitochondrial supplementation. Currently he is stable on daily supplementation of arginine and limb-strengthening physiotherapy. He is being monitored closely clinically and with serum lactate level.ConclusionGenetic diseases are rare. Coexistence of two genetic conditions is even rarer. Genetic confirmation of diagnosis is imperative for prediction of complications, accurate management, and genetic counseling.

Myosin ATPase inhibition fails to rescue the metabolically dysregulated proteome of nebulin-deficient muscle.

Nemaline myopathy (NM) is a genetic muscle disease, primarily caused by mutations in the NEB gene (NEB-NM) and with muscle myosin dysfunction as a major molecular pathogenic mechanism. Recently, we have observed that the myosin biochemical super-relaxed state was significantly impaired in NEB-NM, inducing an aberrant increase in ATP consumption and remodelling of the energy proteome in diseased muscle fibres. Because the small-molecule Mavacamten is known to promote the myosin super-relaxed state and reduce the ATP demand, we tested its potency in the context of NEB-NM. We first conducted in vitro experiments in isolated single myofibres from patients and found that Mavacamten successfully reversed the myosin ATP overconsumption. Following this, we assessed its short-term in vivo effects using the conditional nebulin knockout (cNeb KO) mouse model and subsequently performing global proteomics profiling in dissected soleus myofibres. After a 4week treatment period, we observed a remodelling of a large number of proteins in both cNeb KO mice and their wild-type siblings. Nevertheless, these changes were not related to the energy proteome, indicating that short-term Mavacamten treatment is not sufficient to properly counterbalance the metabolically dysregulated proteome of cNeb KO mice. Taken together, our findings emphasize Mavacamten potency in vitro but challenge its short-term efficacy in vivo. KEY POINTS: No cure exists for nemaline myopathy, a type of genetic skeletal muscle disease mainly derived from mutations in genes encoding myofilament proteins. Applying Mavacamten, a small molecule directly targeting the myofilaments, to isolated membrane-permeabilized muscle fibres from human patients restored myosin energetic disturbances. Treating a mouse model of nemaline myopathy in vivo with Mavacamten for 4weeks, remodelled the skeletal muscle fibre proteome without any noticeable effects on energetic proteins. Short-term Mavacamten treatment may not be sufficient to reverse the muscle phenotype in nemaline myopathy.

Rare abnormality of pyramidal tract and oligospermia as a presenting sign of nemaline myopathies: A case report

Nemaline myopathies constitute a significant portion of congenital or structural myopathies. It is characterized by typically non-progressive or slowly progressive generalized muscle weakness. However, abnormalities of the pyramidal tract are uncommon. To investigate the relevant clinical, pathological, and genetic characteristics, we gathered clinical data from a patient with nemaline myopathy with motor neuron disease and oligospermia, which were confirmed by muscle pathology examination and gene sequencing. This report describes a 35-year-old Chinese male who had been experiencing limb weakness, primarily in the lower limbs, since childhood. He occasionally stumbled while walking, faced difficulties climbing stairs and mountains, exhibited poorer walking and running abilities compared to his peers, and easily felt fatigued, though relieved after resting. Oligospermia was diagnosed in adulthood. He was initially diagnosed with motor neuron disease, most likely Kennedy disease. Nemaline myopathy was definitively diagnosed through muscle pathology examination and gene sequencing conducted at our institution. This case report underscores the importance of considering a diagnosis of nemaline myopathy in cases where pyramidal tract damage and oligospermia, though exceedingly rare, coexist.

A cross-sectional study in 18 patients with typical and mild forms of nemaline myopathy in the Netherlands

Nemaline myopathy (NM) is a congenital myopathy with generalised muscle weakness, most pronounced in neck flexor, bulbar and respiratory muscles. The aim of this cross-sectional study was to assess the Dutch NM patient cohort. We assessed medical history, physical examination, quality of life (QoL), fatigue severity, motor function (MFM), and respiratory muscle function. We included 18 of the 28 identified patients (13 females (11–67 years old); five males (31–74 years old)) with typical or mild NM and eight different genotypes. Nine patients (50 %) used a wheelchair, eight patients (44 %) used mechanical ventilation, and four patients (22 %) were on tube feeding. Spinal deformities were found in 14 patients (78 %). The median Medical Research Council (MRC) sum score was 38/60 [interquartile range 32–51] in typical and 48/60 [44–50] in mild NM. The experienced QoL was lower and fatigue severity was higher than reference values of the healthy population. The total MFM score was 55 % [49–94] in typical and 88 % [72–93] in mild NM. Most of the patients who performed spirometry had a restrictive lung function pattern (11/15). This identification and characterisation of the Dutch NM patient cohort is important for international collaboration and can guide the design of future clinical trials.

Muscle cofilin alters neuromuscular junction postsynaptic development to strengthen functional neurotransmission.

Cofilin, an actin-severing protein, plays key roles in muscle sarcomere addition and maintenance. Our previous work found that Drosophila cofilin (DmCFL) knockdown in muscle causes progressive deterioration of muscle structure and function and produces features seen in nemaline myopathy caused by cofilin mutations. We hypothesized that disruption of actin cytoskeleton dynamics by DmCFL knockdown would impact other aspects of muscle development, and, thus, conducted an RNA-sequencing analysis that unexpectedly revealed upregulated expression of numerous neuromuscular junction (NMJ) genes. We found that DmCFL is enriched in the muscle postsynaptic compartment and that DmCFL muscle knockdown causes F-actin disorganization in this subcellular domain prior to the sarcomere defects observed later in development. Despite NMJ gene expression changes, we found no significant changes in gross presynaptic Bruchpilot active zones or total postsynaptic glutamate receptor levels. However, DmCFL knockdown resulted in mislocalization of GluRIIA class glutamate receptors in more deteriorated muscles and strongly impaired NMJ transmission strength. These findings expand our understanding of the roles of cofilin in muscle to include NMJ structural development and suggest that NMJ defects may contribute to the pathophysiology of nemaline myopathy.

Kbtbd13R408C-knockin mouse model reveals impaired relaxation kinetics as novel pathomechanism for NEM6 cardiomyopathy

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): VENI-Nederlandse organisatie voor Wetenschappelijk Onderzoek (NWO) We identified a novel cardiomyopathy gene: KBTBD13 encoding kelch repeat and BTB (POZ) domain containing 13. The Dutch founder variant KBTBD13R408C not only affects skeletal muscle function resulting in nemaline myopathy type 6 (NEM6), but also affects the heart. In the Dutch NEM6 cohort, various cardiac abnormalities were observed, including systolic dysfunction, diastolic dysfunction, atrial fibrillation, ventricular tachycardia and three patients died of sudden cardiac death. The majority of NEM6 patients harbors the Dutch founder variant, c.1222C>T, p.Arg408Cys (KBTBD13R408C). To provide insight in the mechanism underlying cardiac dysfunction in NEM6, here we assessed cardiac structure and function in Kbtbd13R408C-knockin mice, which closely recapitulate the well characterized skeletal muscle phenotype, i.e. impaired relaxation kinetics and mitochondrial dysfunction. Pressure-volume loop analyses showed that the end-diastolic pressure-volume relation was steeper in Kbtbd13R408C-knockin mice, indicating diastolic dysfunction. Histological evaluation of cardiac structure revealed no increase in fibrosis in Kbtbd13R408C-knockin mice. Also, no alterations in titin isoform composition or myosin heavy chain composition were observed that could account for the increased diastolic stiffness. Next, we studied the contraction and relaxation kinetics in wild type (WT) and Kbtbd13R408C-knockin mice at the intact single cardiomyocyte level by a high-throughput contractility set-up. Our data showed a prolonged relaxation time in Kbtbd13R408C-knockin mice compared to WT mice, indicating impaired relaxation kinetics. No differences in the magnitude of contraction (percentage of shortening) was found between cardiomyocytes of Kbtbd13R408C-knockin and WT mice. In parallel, calcium-handling was assessed by calcium indicator Fura-2AM. These studies reveal that calcium-release is not affected, but calcium-reuptake is slower in Kbtbd13R408C-knockin mice, which might contribute to the impaired relaxation kinetics. Current studies focus on how KBTBD13R408C affects calcium-reuptake kinetics and sarcomere kinetics in NEM6 cardiomyocytes. Hence, our studies provide the first insights in the pathomechanism underlying cardiac dysfunction in NEM6.

Establishment of an induced pluripotent stem cell (iPSC) line (INNDSUi004-A) from a patient with Congenital Nemaline Myopathy

We used a non-integrated reprogramming approach to establish a human induced pluripotent stem cell (hiPSC) line (INNDSUi004-A) from the skin fibroblasts of a 13-year-old female individual with Congenital Nemaline Myopath. The cells obtained have typical characteristics of embryonic stem cells, show expression of specific pluripotency markers, and can differentiate into three germ layers in vitro. This iPSC cell line has the genetic information of the patient and is a good model for studying disease mechanisms and developing novel therapies.

Characterization of NEB pathogenic variants in patients reveals novel nemaline myopathy disease mechanisms and omecamtiv mecarbil force effects.

Nebulin, a critical protein of the skeletal muscle thin filament, plays important roles in physiological processes such as regulating thin filament length (TFL), cross-bridge cycling, and myofibril alignment. Pathogenic variants in the nebulin gene (NEB) cause NEB-based nemaline myopathy (NEM2), a genetically heterogeneous disorder characterized by hypotonia and muscle weakness, currently lacking curative therapies. In this study, we examined a cohort of ten NEM2 patients, each with unique pathogenic variants, aiming to understand their impact on mRNA, protein, and functional levels. Results show that pathogenic truncation variants affect NEB mRNA stability and lead to nonsense-mediated decay of the mutated transcript. Moreover, a high incidence of cryptic splice site activation was found in patients with pathogenic splicing variants that are expected to disrupt the actin-binding sites of nebulin. Determination of protein levels revealed patients with either relatively normal or markedly reduced nebulin. We observed a positive relation between the reduction in nebulin and a reduction in TFL, or reduction in tension (both maximal and submaximal tension). Interestingly, our study revealed a pathogenic duplication variant in nebulin that resulted in a four-copy gain in the triplicate region of NEB and a much larger nebulin protein and longer TFL. Additionally, we investigated the effect of Omecamtiv mecarbil (OM), a small-molecule activator of cardiac myosin, on force production of type 1 muscle fibers of NEM2 patients. OM treatment substantially increased submaximal tension across all NEM2 patients ranging from 87 to 318%, with the largest effects in patients with the lowest level of nebulin. In summary, this study indicates that post-transcriptional or post-translational mechanisms regulate nebulin expression. Moreover, we propose that the pathomechanism of NEM2 involves not only shortened but also elongated thin filaments, along with the disruption of actin-binding sites resulting from pathogenic splicing variants. Significantly, our findings highlight the potential of OM treatment to improve skeletal muscle function in NEM2 patients, especially those with large reductions in nebulin levels.

Comprehensive phenotypic characterization of an allelic series of zebrafish models of NEB-related nemaline myopathy.

Nemaline myopathy (NM) is a rare congenital neuromuscular disorder characterized by muscle weakness and hypotonia, slow gross motor development, and decreased respiratory function. Mutations in at least twelve genes, all of each encode proteins that are either components of the muscle thin filament or regulate its length and stability, have been associated with NM. Mutations in Nebulin (NEB), a giant filamentous protein localized in the sarcomere, account for more than 50% of NM cases. At present, there remains a lack of understanding of whether NEB genotype influences nebulin function and NM-patient phenotypes. In addition, there is a lack of therapeutically tractable models that can enable drug discovery and address the current unmet treatment needs of patients. To begin to address these gaps, here we have characterized five new zebrafish models of NEB-related NM. These mutants recapitulate most aspects of NEB-based NM, showing drastically reduced survival, defective muscle structure, reduced contraction force, shorter thin filaments, presence of electron-dense structures in myofibers, and thickening of the Z-disks. This study represents the first extensive investigation of an allelic series of nebulin mutants, and thus provides an initial examination in pre-clinical models of potential genotype-phenotype correlations in human NEB patients. It also represents the first utilization of a set of comprehensive outcome measures in zebrafish, including correlation between molecular analyses, structural and biophysical investigations, and phenotypic outcomes. Therefore, it provides a rich source of data for future studies exploring the NM pathomechanisms, and an ideal springboard for therapy identification and development for NEB-related NM.

Metastasis-associated 1 localizes to the sarcomeric Z-disc and is implicated in skeletal muscle pathology.

Metastasis-associated 1 (MTA1), a subunit of the nucleosome remodeling and histone deacetylation (NuRD) corepressor complex, was reported to be expressed in the cytoplasm of skeletal muscles. However, the exact subcellular localization and the functional implications of MTA1 in skeletal muscles have not been examined. This study aims to demonstrate the subcellular localization of MTA1 in skeletal muscles and reveal its possible roles in skeletal muscle pathogenesis. Striated muscles (skeletal and cardiac) from C57BL/6 mice of 4-5 weeks were collected to examine the expression of MTA1 by Western blotting and immunohistochemistry. Immunofluorescence and immunoelectron microscopy were performed for MTA1, α-actinin (a Z-disc marker protein), and SMN (survival of motor neuron) proteins. Gene Expression Omnibus (GEO) data sets were analyzed using the GEO2R online tool to explore the functional implications of MTA1 in skeletal muscles. MTA1 expression was detected by Western blotting and immunohistochemistry in skeletal and cardiac muscles. Subcellular localization of MTA1 was found in the Z-disc of sarcomeres, where α-actinin and SMN were expressed. Data mining of GEO profiles suggested that MTA1 dysregulation is associated with multiple skeletal muscle defects, such as Duchenne muscular dystrophy, Emery-Dreifuss muscular dystrophy, nemaline myopathy, and dermatomyositis. The GEO analysis also showed that MTA1 expression gradually decreased with age in mouse skeletal muscle precursor cells. The subcellular localization of MTA1 in sarcomeres of skeletal muscles implies its biological roles in sarcomere structures and its possible contribution to skeletal muscle pathology.

Haplotype information of large neuromuscular disease genes provided by linked-read sequencing has a potential to increase diagnostic yield.

Rare or novel missense variants in large genes such as TTN and NEB are frequent in the general population, which hampers the interpretation of putative disease-causing biallelic variants in patients with sporadic neuromuscular disorders. Often, when the first initial genetic analysis is performed, the reconstructed haplotype, i.e. phasing information of the variants is missing. Segregation analysis increases the diagnostic turnaround time and is not always possible if samples from family members are lacking. To overcome this difficulty, we investigated how well the linked-read technology succeeded to phase variants in these large genes, and whether it improved the identification of structural variants. Linked-read sequencing data of nemaline myopathy, distal myopathy, and proximal myopathy patients were analyzed for phasing, single nucleotide variants, and structural variants. Variant phasing was successful in the large muscle genes studied. The longest continuous phase blocks were gained using high-quality DNA samples with long DNA fragments. Homozygosity increased the number of phase blocks, especially in exome sequencing samples lacking intronic variation. In our cohort, linked-read sequencing added more information about the structural variation but did not lead to a molecular genetic diagnosis. The linked-read technology can support the clinical diagnosis of neuromuscular and other genetic disorders.

Tirasemtiv enhances submaximal muscle tension in an Acta1:p.Asp286Gly mouse model of nemaline myopathy.

Nemaline myopathies are the most common form of congenital myopathies. Variants in ACTA1 (NEM3) comprise 15-25% of all nemaline myopathy cases. Patients harboring variants in ACTA1 present with a heterogeneous disease course characterized by stable or progressive muscle weakness and, in severe cases, respiratory failure and death. To date, no specific treatments are available. Since NEM3 is an actin-based thin filament disease, we tested the ability of tirasemtiv, a fast skeletal muscle troponin activator, to improve skeletal muscle function in a mouse model of NEM3, harboring the patient-based p.Asp286Gly variant in Acta1. Acute and long-term tirasemtiv treatment significantly increased muscle contractile capacity at submaximal stimulation frequencies in both fast-twitch extensor digitorum longus and gastrocnemius muscle, and intermediate-twitch diaphragm muscle in vitro and in vivo. Additionally, long-term tirasemtiv treatment in NEM3 mice resulted in a decreased respiratory rate with preserved minute volume, suggesting more efficient respiration. Altogether, our data support the therapeutic potential of fast skeletal muscle troponin activators in alleviating skeletal muscle weakness in a mouse model of NEM3 caused by the Acta1:p.Asp286Gly variant.

Scoliosis in a patient with nemaline myopathy: a case report and narrative review

Introduction: Nemaline myopathy, described in 1950, is a rare syndrome, and among the possible alterations, scoliosis is a frequent alteration. This article describes the case of a 13-year-old patient with nemaline myopathy and scoliosis treated surgically. During the procedure, several unexpected surgical difficulties were encountered, such as fusion of posterior elements, difficulty in passing screws and liquor leaked out. Therefore, more studies are necessary and the presence of an experimental operation to help with surgical complications are prudent.

Peripheral thickening of the sarcomeres and pointed end elongation of the thin filaments are both promoted by SALS and its formin interaction partners.

During striated muscle development the first periodically repeated units appear in the premyofibrils, consisting of immature sarcomeres that must undergo a substantial growth both in length and width, to reach their final size. Here we report that, beyond its well established role in sarcomere elongation, the Sarcomere length short (SALS) protein is involved in Z-disc formation and peripheral growth of the sarcomeres. Our protein localization data and loss-of-function studies in the Drosophila indirect flight muscle strongly suggest that radial growth of the sarcomeres is initiated at the Z-disc. As to thin filament elongation, we used a powerful nanoscopy approach to reveal that SALS is subject to a major conformational change during sarcomere development, which might be critical to stop pointed end elongation in the adult muscles. In addition, we demonstrate that the roles of SALS in sarcomere elongation and radial growth are both dependent on formin type of actin assembly factors. Unexpectedly, when SALS is present in excess amounts, it promotes the formation of actin aggregates highly resembling the ones described in nemaline myopathy patients. Collectively, these findings helped to shed light on the complex mechanisms of SALS during the coordinated elongation and thickening of the sarcomeres, and resulted in the discovery of a potential nemaline myopathy model, suitable for the identification of genetic and small molecule inhibitors.