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ELife Aug 2022Dystonin (), which encodes cytoskeletal linker proteins, expresses three tissue-selective isoforms: neural DST-a, muscular DST-b, and epithelial DST-e. mutations cause...
Dystonin (), which encodes cytoskeletal linker proteins, expresses three tissue-selective isoforms: neural DST-a, muscular DST-b, and epithelial DST-e. mutations cause different disorders, including hereditary sensory and autonomic neuropathy 6 (HSAN-VI) and epidermolysis bullosa simplex; however, etiology of the muscle phenotype in -related diseases has been unclear. Because contains all of the -encoding exons, known HSAN-VI mutations could affect both DST-a and DST-b isoforms. To investigate the specific function of DST-b in striated muscles, we generated a -specific mutant mouse model harboring a nonsense mutation. mutant mice exhibited late-onset protein aggregate myopathy and cardiomyopathy without neuropathy. We observed desmin aggregation, focal myofibrillar dissolution, and mitochondrial accumulation in striated muscles, which are common characteristics of myofibrillar myopathy. We also found nuclear inclusions containing p62, ubiquitin, and SUMO proteins with nuclear envelope invaginations as a unique pathological hallmark in mutation-induced cardiomyopathy. RNA-sequencing analysis revealed changes in expression of genes responsible for cardiovascular functions. In silico analysis identified alleles with nonsense mutations in populations worldwide, suggesting that some unidentified hereditary myopathy and cardiomyopathy are caused by mutations. Here, we demonstrate that the Dst-b isoform is essential for long-term maintenance of striated muscles.
Topics: Animals; Cardiomyopathies; Dystonin; Hereditary Sensory and Autonomic Neuropathies; Mice; Muscular Diseases; Mutation; Protein Aggregates; Protein Isoforms
PubMed: 35942699
DOI: 10.7554/eLife.78419 -
Journal of Clinical Medicine Feb 2021Myofibrillar myopathies (MFM) are heterogeneous hereditary muscle diseases with characteristic myopathological features of Z-disk dissolution and aggregates of its...
Myofibrillar myopathies (MFM) are heterogeneous hereditary muscle diseases with characteristic myopathological features of Z-disk dissolution and aggregates of its degradation products. The onset and progression of the disease are variable, with an elusive genetic background, and around half of the cases lacking molecular diagnosis. Here, we attempted to establish possible genetic foundations of MFM by performing whole exome sequencing (WES) in eleven unrelated families of 13 patients clinically diagnosed as MFM spectrum. A filtering strategy aimed at identification of variants related to the disease was used and included integrative analysis of WES data and human phenotype ontology (HPO) terms, analysis of muscle-expressed genes, and analysis of the disease-associated interactome. Genetic diagnosis was possible in eight out of eleven cases. Putative causative mutations were found in the (two cases), , , and (four cases) genes, the latter typically presenting with a rigid spine syndrome. Moreover, a variety of additional, possibly phenotype-affecting variants were found. These findings indicate a markedly heterogeneous genetic background of MFM and show the usefulness of next generation sequencing in the identification of disease-associated mutations. Finally, we discuss the emerging concept of variant load as the basis of phenotypic heterogeneity.
PubMed: 33652732
DOI: 10.3390/jcm10050914 -
Neuromuscular Disorders : NMD Feb 2020Dropped head syndrome can be the presenting feature of a wide spectrum of neurological conditions. In this study, we aimed to define the clinical characteristics and...
Dropped head syndrome can be the presenting feature of a wide spectrum of neurological conditions. In this study, we aimed to define the clinical characteristics and treatment outcomes of 107 patients, where head drop was the presenting or predominant clinical feature of a myopathy. Median age at presentation was 68 years (range 42-88). A specific diagnosis was reached in 53% of patients: Inflammatory myopathy (n = 16), myopathy with rimmed vacuoles (n = 10), radiation-induced myopathy (n = 8), sporadic late-onset nemaline myopathy (n = 7), myofibrillar myopathy (n = 4), facioscapulohumeral dystrophy (n = 3), inclusion body myositis (n = 2), mitochondrial myopathy (n = 2), scleroderma-associated myopathy (n = 2), and single cases of necrotizing autoimmune myopathy, drug-induced myopathy, and B-cell chronic lymphocytic leukemia-myopathy. Splenius capitis had the highest diagnostic yield for a muscle biopsy (67%). When tested, 31/35 (89%) of patients had abnormal pulmonary function tests, 15/30 (50%) abnormal swallow evaluation, 24/65 (37%) abnormal electrocardiogram and 5/38 (13%) abnormal transthoracic echocardiogram. 23/43 (53%) treated patients responded to treatment. Patient-reported limb weakness and neck flexion weakness on physical examination were associated with good response to treatment. A wide spectrum of acquired and hereditary myopathies can present with head drop, some of which are potentially treatable. Establishing a diagnosis is crucial for timely treatment administration, screening for swallowing and cardiorespiratory involvement, and counseling regarding prognosis.
Topics: Adult; Aged; Aged, 80 and over; Female; Head; Humans; Male; Middle Aged; Muscular Diseases; Neck Muscles; Paraspinal Muscles; Pharyngeal Muscles; Respiratory Muscles
PubMed: 32005492
DOI: 10.1016/j.nmd.2019.12.001 -
Muscle & Nerve Dec 2021Immune-mediated necrotizing myopathy (IMNM) is an immune-mediated myopathy typically presenting with progressive subacute weakness and characteristic, but nonspecific,...
INTRODUCTION/AIMS
Immune-mediated necrotizing myopathy (IMNM) is an immune-mediated myopathy typically presenting with progressive subacute weakness and characteristic, but nonspecific, myopathological findings. Atypical cases however can mimic other inherited or acquired myopathies, depriving patients of treatment. We describe a cohort of such patients.
METHODS
We retrospectively identified IMNM patients who either previously carried a diagnosis of an inherited myopathy established on clinicopathological grounds or whose muscle biopsies displayed atypical features suggestive of a different myopathy.
RESULTS
Among 131 IMNM patients, seven previously unreported patients (5%) met one of the above criteria. Three patients were diagnosed with limb-girdle muscular dystrophy on the basis of a chronic progressive course of weakness and family history of myopathy or cardiomyopathy. The other four patients displayed atypical histological features (two prominent mitochondrial abnormalities, one myofibrillar pathology, and one granulomatous inflammation). Immunostaining of biopsies from 12 additional IMNM patients did not identify myofibrillar pathology. The patient with granulomatous inflammation was known to have pulmonary sarcoidosis. Genetic testing for inherited myopathies was unrevealing. Antibodies against 3-hydroxy-3-methylglutaryl-CoA reductase or signal recognition particle were identified in 5 and 1 patients, respectively. Four patients presented with slowly progressive weakness over 3-13 y, while weakness was subacute over ≤6 mo in three patients. All patients responded to immunomodulatory therapy.
DISCUSSION
Atypical clinical and histological features can occur in IMNM patients, causing delays in diagnosis and treatment. Clinicians should, therefore, consider IMNM in the differential diagnosis of unexplained proximal myopathies in spite of atypical clinical and myopathological findings.
Topics: Autoantibodies; Autoimmune Diseases; Humans; Muscle, Skeletal; Muscular Diseases; Myositis; Necrosis; Retrospective Studies
PubMed: 34617293
DOI: 10.1002/mus.27435 -
Frontiers in Neurology 2020Myofibrillar myopathy is a group of hereditary neuromuscular disorders characterized by dissolution of myofibrils and abnormal intracellular accumulation of Z...
Myofibrillar myopathy is a group of hereditary neuromuscular disorders characterized by dissolution of myofibrils and abnormal intracellular accumulation of Z disc-related proteins. We aimed to characterize the clinical, physiological, pathohistological, and genetic features of Chinese myofibrillar myopathy patients from a single neuromuscular center. A total of 18 patients were enrolled. Demographic and clinical data were collected. Laboratory investigations, electromyography, and cardiac evaluation was performed. Routine and immunohistochemistry stainings against desmin, αB-crystallin, and BAG3 of muscle specimen were carried out. Finally, next-generation sequencing panel array for genes associated with hereditary neuromuscular disorders were performed. Twelve pathogenic variants in , and were identified, of which seven were novel mutations. The novel c.1256C>T substitution is a high frequency mutation. The combined recessively/dominantly transmitted c.19993G>T and c.107545delG mutations in gene cause a limb girdle muscular dystrophy phenotype with the classical myofibrillar myopathy histological changes. We report for the first time that hereditary myopathy with early respiratory failure patient can have peripheral nerve and severe spine involvement. The mutation in Ig-like domain 16 of is associated with the limb girdle type of filaminopathy, and the mutation in Ig-like domain 18 with distal myopathy type. These findings expand the phenotypic and genotypic correlation spectrum of myofibrillar myopathy.
PubMed: 33041974
DOI: 10.3389/fneur.2020.01014 -
Journal of Clinical Neuromuscular... Dec 2020We report a case of 2 sisters in their 20s with genetically confirmed UDP-N-acetylglucoasmine 2-epimerase/N-acetylmannosamine kinase myopathy along with muscle biopsy...
We report a case of 2 sisters in their 20s with genetically confirmed UDP-N-acetylglucoasmine 2-epimerase/N-acetylmannosamine kinase myopathy along with muscle biopsy findings. Both patients described slowly progressive signs of distal-predominant weakness since adolescence that had been dismissed as "clumsiness." Exam and electrodiagnostic testing suggested a predominately distal myopathy. Muscle biopsy of the left tibialis anterior revealed rimmed vacuoles and, interestingly, also had characteristic features of a myofibrillar myopathy. Genetic testing confirmed a diagnosis of autosomal recessive GNE myopathy in both patients. GNE myopathy has not typically been considered a myofibrillar myopathy, but this case raises possibilities worthy of further exploration. It is possible that the unique combination of pathogenic alleles in GNE reported here has led to a novel form of GNE myopathy with muscle biopsy showing characteristic features of GNE myopathy and myofibrillar myopathy. The other possibility is that myofibrillar myopathy may be a more common feature of GNE myopathies than classically described.
Topics: Adult; Biopsy; Distal Myopathies; Female; Humans; Muscle, Skeletal; Mutation; Myopathies, Structural, Congenital
PubMed: 33214394
DOI: 10.1097/CND.0000000000000317 -
Journal of Clinical Medicine Feb 2021Over the past decades, there has been tremendous progress in understanding genetic alterations that can result in different phenotypes of human cardiomyopathies. More... (Review)
Review
Over the past decades, there has been tremendous progress in understanding genetic alterations that can result in different phenotypes of human cardiomyopathies. More than a thousand mutations in various genes have been identified, indicating that distinct genetic alterations, or combinations of genetic alterations, can cause either hypertrophic (HCM), dilated (DCM), restrictive (RCM), or arrhythmogenic cardiomyopathies (ARVC). Translation of these results from "bench to bedside" can potentially group affected patients according to their molecular etiology and identify subclinical individuals at high risk for developing cardiomyopathy or patients with overt phenotypes at high risk for cardiac deterioration or sudden cardiac death. These advances provide not only mechanistic insights into the earliest manifestations of cardiomyopathy, but such efforts also hold the promise that mutation-specific pathophysiology might result in novel "personalized" therapeutic possibilities. Recently, the FLNC gene encoding the sarcomeric protein filamin C has gained special interest since FLNC mutations were found in several distinct and possibly overlapping cardiomyopathy phenotypes. Specifically, mutations in FLNC were initially only linked to myofibrillar myopathy (MFM), but are now increasingly found in various forms of human cardiomyopathy. FLNC thereby represents another example for the complex genetic and phenotypic continuum of these diseases.
PubMed: 33557094
DOI: 10.3390/jcm10040577 -
Acta Neuropathologica Communications Sep 2020Filamin C (FLNc) is mainly expressed in striated muscle cells where it localizes to Z-discs, myotendinous junctions and intercalated discs. Recent studies have revealed...
Filamin C (FLNc) is mainly expressed in striated muscle cells where it localizes to Z-discs, myotendinous junctions and intercalated discs. Recent studies have revealed numerous mutations in the FLNC gene causing familial and sporadic myopathies and cardiomyopathies with marked clinical variability. The most frequent myopathic mutation, p.W2710X, which is associated with myofibrillar myopathy, deletes the carboxy-terminal 16 amino acids from FLNc and abolishes the dimerization property of Ig-like domain 24. We previously characterized "knock-in" mice heterozygous for this mutation (p.W2711X), and have now investigated homozygous mice using protein and mRNA expression analyses, mass spectrometry, and extensive immunolocalization and ultrastructural studies. Although the latter mice display a relatively mild myopathy under normal conditions, our analyses identified major mechanisms causing the pathophysiology of this disease: in comparison to wildtype animals (i) the expression level of FLNc protein is drastically reduced; (ii) mutant FLNc is relocalized from Z-discs to particularly mechanically strained parts of muscle cells, i.e. myotendinous junctions and myofibrillar lesions; (iii) the number of lesions is greatly increased and these lesions lack Bcl2-associated athanogene 3 (BAG3) protein; (iv) the expression of heat shock protein beta-7 (HSPB7) is almost completely abolished. These findings indicate grave disturbances of BAG3-dependent and -independent autophagy pathways that are required for efficient lesion repair. In addition, our studies reveal general mechanisms of lesion formation and demonstrate that defective FLNc dimerization via its carboxy-terminal domain does not disturb assembly and basic function of myofibrils. An alternative, more amino-terminally located dimerization site might compensate for that loss. Since filamins function as stress sensors, our data further substantiate that FLNc is important for mechanosensing in the context of Z-disc stabilization and maintenance.
Topics: Animals; Filamins; Gene Knock-In Techniques; Homozygote; Mice; Mutation; Myopathies, Structural, Congenital; Sarcomeres
PubMed: 32887649
DOI: 10.1186/s40478-020-01001-9 -
Muscle & Nerve May 2023
Topics: Humans; Myositis, Inclusion Body; Muscle, Skeletal; Myopathies, Structural, Congenital; Phenotype; Myositis
PubMed: 36815757
DOI: 10.1002/mus.27806 -
MedRxiv : the Preprint Server For... Feb 2024Myofibrillar myopathy 6 (MFM6) is a rare childhood-onset myopathy characterized by myofibrillar disintegration, muscle weakness, and cardiomyopathy. The genetic cause of...
Myofibrillar myopathy 6 (MFM6) is a rare childhood-onset myopathy characterized by myofibrillar disintegration, muscle weakness, and cardiomyopathy. The genetic cause of MFM6 is p.Pro209Leu mutation (rs121918312-T) in the gene, which generates the disease outcomes in a dominant fashion. Since the consequences of the mutation are strong and rapidly progressing, most MFM6 patients are due to mutation. There are no effective treatments for MFM6 despite its well-known genetic cause. Given p.Pro209Leu mutation is dominant, regenerative medicine approaches employing orthologous stem cells in which mutant is inactivated offer a promising avenue. Here, we developed personalized allele-specific CRISPR-Cas9 strategies capitalizing on PAM-altering SNP and PAM-proximal SNP. In order to identify the disease chromosome carrying the mutation in our two affected individuals, haplotype phasing through cloning-sequencing was performed. Based on the sequence differences between mutant and normal , we developed personalized allele-specific CRISPR-Cas9 strategies to selectively inactivate the mutant allele 1) by preventing the transcription of the mutant and 2) by inducing nonsense-mediated decay (NMD) of mutant mRNA. Subsequent experimental validation in patient-derived induced pluripotent stem cell (iPSC) lines showed complete allele specificities of our CRISPR-Cas9 strategies and molecular consequences attributable to inactivated mutant . In addition, mutant allele-specific CRISPR-Cas9 targeting did not alter the characteristics of iPSC or the capacity to differentiate into cardiomyocytes. Together, our data demonstrate the feasibility and potential of personalized allele-specific CRISPR-Cas9 approaches to selectively inactivate the mutant to generate cell resources for regenerative medicine approaches for MFM6.
PubMed: 38352343
DOI: 10.1101/2024.02.03.24302252