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Neuromuscular Disorders : NMD Aug 2022The diagnosis of adult-onset genetic muscle diseases is challenging because of the diversity of clinical phenotypes, findings on muscle biopsy that may be nonspecific,...
The diagnosis of adult-onset genetic muscle diseases is challenging because of the diversity of clinical phenotypes, findings on muscle biopsy that may be nonspecific, and the large number of genetic causes. Even with thorough investigation, the diagnostic yield for genetic testing in these populations is very low, and the distinction from acquired conditions such as sporadic inclusion body myositis [sIBM] can also prove difficult. In this study, we analysed whole transcriptome data generated from RNA isolated from muscle biopsy tissues, from a cohort of 16 participants with sIBM and other histologic diagnoses. Our objective was to identify candidate RNA biomarkers that could be an adjunctive tool in differentiating these conditions. Principal component analysis was able to delineate the groups based on their histologic diagnoses. Gene ontology and pathway analyses demonstrated dysregulation of immune pathways in sIBM. In mitochondrial myopathy we observed upregulation of FGF21, GDF15, ASNS and TRIB3, which are known candidate biomarkers for mitochondrial myopathy. Novel findings included the identification of transcripts of unknown function that were dysregulated in myofibrillar myopathy [JPX], dystrophic changes [MEG3], and mitochondrial myopathy [GAS5]. We suggest future investigations with larger cohorts of participants to confirm the findings of this study, with further directed experiments to determine the role of novel transcripts in disease pathogenesis.
Topics: Biomarkers; Biopsy; Gene Expression Profiling; Humans; Muscle, Skeletal; Myositis, Inclusion Body; RNA
PubMed: 35850946
DOI: 10.1016/j.nmd.2022.04.009 -
Clinica Chimica Acta; International... Jun 2022Myofibrillar myopathy (MFM) is characterized by phenotypic heterogeneity; decreased function of the myosin-directed chaperone, UNC-45B protein, leads to MFM II, which is...
Myofibrillar myopathy (MFM) is characterized by phenotypic heterogeneity; decreased function of the myosin-directed chaperone, UNC-45B protein, leads to MFM II, which is characterized by slow progressive proximal myasthenia. Currently, only two studies have reported 11 cases worldwide. This study aimed to conduct genetic research and etiological analysis of a neonatal case of perinatal myasthenia who eventually died due to autonomic dyspnea. The case involved a newborn female admitted for weak cries and groaning. Physical examination revealed shallow and irregular spontaneous breathing, difficulty feeding, hip flexion and knee flexion in both lower limbs, hypotonia (level 1), less translation action, and inability to resist gravity. The child died at 23 days after birth. Gene testing, mutation analysis, and crystal structure analysis were conducted. Cell culture and plasmid construction were conducted, followed by western blot analysis. Pathological changes, including Z-line breakage, were observed in the muscle biopsies of different tissues. Gene testing showed that UNC-45B had a novel compound heterozygous mutation (c.2357T>A/p.Met786Lys, c.2591A>C/p.His864Pro), and in vitro functional experiments showed that the variants could lead to a decrease in protein expression. This study expands the UNC-45B mutation and phenotype spectrum by reporting an MFM II case in a Chinese patient for the first time.
Topics: Female; Humans; Muscle Weakness; Muscle, Skeletal; Mutation; Myopathies, Structural, Congenital; Phenotype
PubMed: 35292251
DOI: 10.1016/j.cca.2022.03.002 -
Journal of Clinical Neuromuscular... Sep 2022Myofibrillar myopathy is a clinically and genetically heterogeneous group of muscle disorders characterized by myofibrillar degeneration. Bcl-2-associated athanogene 3... (Review)
Review
Myofibrillar myopathy is a clinically and genetically heterogeneous group of muscle disorders characterized by myofibrillar degeneration. Bcl-2-associated athanogene 3 (BAG3)-related myopathy is the rarest form of myofibrillar myopathy. Patients with BAG3-related myopathy present with early-onset and progressive muscle weakness, rigid spine, respiratory insufficiency, and cardiomyopathy. Notably, the heterozygous mutation (Pro209Leu) in BAG3 is commonly associated with rapidly progressive cardiomyopathy in childhood. We describe a male patient with the BAG3 (Pro209Leu) mutation. The patient presented at age 7 years with muscle weakness predominantly in the proximal lower limbs. Histologic findings revealed a mixture of severe neurogenic and myogenic changes. His motor symptoms progressed rapidly in the next decade, becoming wheelchair-dependent by age 17 years; however, at the age of 19 years, cardiomyopathy was not evident. This study reports a case of BAG3-related myopathy without cardiac involvement and further confirmed the wide phenotypic spectrum of BAG3-related myopathy.
Topics: Adaptor Proteins, Signal Transducing; Apoptosis Regulatory Proteins; Cardiomyopathies; Humans; Male; Muscle Weakness; Mutation; Myopathies, Structural, Congenital; Phenotype
PubMed: 36005473
DOI: 10.1097/CND.0000000000000392 -
Communications Biology Mar 2021Mechanical stress induced by contractions constantly threatens the integrity of muscle Z-disc, a crucial force-bearing structure in striated muscle. The PDZ-LIM proteins...
Mechanical stress induced by contractions constantly threatens the integrity of muscle Z-disc, a crucial force-bearing structure in striated muscle. The PDZ-LIM proteins have been proposed to function as adaptors in transducing mechanical signals to preserve the Z-disc structure, however the underlying mechanisms remain poorly understood. Here, we show that LDB3, a well-characterized striated muscle PDZ-LIM protein, modulates mechanical stress signaling through interactions with the mechanosensing domain in filamin C, its chaperone HSPA8, and PKCα in the Z-disc of skeletal muscle. Studies of Ldb3 mice indicate that the myopathy-associated LDB3 p.Ala165Val mutation triggers early aggregation of filamin C and its chaperones at muscle Z-disc before aggregation of the mutant protein. The mutation causes protein aggregation and eventually Z-disc myofibrillar disruption by impairing PKCα and TSC2-mTOR, two important signaling pathways regulating protein stability and disposal of damaged cytoskeletal components at a major mechanosensor hub in the Z-disc of skeletal muscle.
Topics: Adaptor Proteins, Signal Transducing; Animals; Autophagy; Disease Models, Animal; Down-Regulation; Filamins; HSC70 Heat-Shock Proteins; LIM Domain Proteins; Mechanotransduction, Cellular; Mice, Inbred C57BL; Mice, Transgenic; Muscle Contraction; Muscle Strength; Muscle, Skeletal; Myopathies, Structural, Congenital; Point Mutation; Protein Aggregates; Protein Aggregation, Pathological; Protein Kinase C-alpha; TOR Serine-Threonine Kinases; Tuberous Sclerosis Complex 2 Protein; Mice
PubMed: 33742095
DOI: 10.1038/s42003-021-01864-1 -
Acta Neuropathologica Jan 2023DNAJ/HSP40 co-chaperones are integral to the chaperone network, bind client proteins and recruit them to HSP70 for folding. We performed exome sequencing on patients...
DNAJ/HSP40 co-chaperones are integral to the chaperone network, bind client proteins and recruit them to HSP70 for folding. We performed exome sequencing on patients with a presumed hereditary muscle disease and no genetic diagnosis. This identified four individuals from three unrelated families carrying an unreported homozygous stop gain (c.856A > T; p.Lys286Ter), or homozygous missense variants (c.74G > A; p.Arg25Gln and c.785 T > C; p.Leu262Ser) in DNAJB4. Affected patients presented with axial rigidity and early respiratory failure requiring ventilator support between the 1st and 4th decade of life. Selective involvement of the semitendinosus and biceps femoris muscles was seen on MRI scans of the thigh. On biopsy, muscle was myopathic with angular fibers, protein inclusions and occasional rimmed vacuoles. DNAJB4 normally localizes to the Z-disc and was absent from muscle and fibroblasts of affected patients supporting a loss of function. Functional studies confirmed that the p.Lys286Ter and p.Leu262Ser mutant proteins are rapidly degraded in cells. In contrast, the p.Arg25Gln mutant protein is stable but failed to complement for DNAJB function in yeast, disaggregate client proteins or protect from heat shock-induced cell death consistent with its loss of function. DNAJB4 knockout mice had muscle weakness and fiber atrophy with prominent diaphragm involvement and kyphosis. DNAJB4 knockout muscle and myotubes had myofibrillar disorganization and accumulated Z-disc proteins and protein chaperones. These data demonstrate a novel chaperonopathy associated with DNAJB4 causing a myopathy with early respiratory failure. DNAJB4 loss of function variants may lead to the accumulation of DNAJB4 client proteins resulting in muscle dysfunction and degeneration.
Topics: Animals; Mice; Mutation; Muscular Diseases; Molecular Chaperones; Mutation, Missense; Respiratory Insufficiency; Muscle, Skeletal
PubMed: 36264506
DOI: 10.1007/s00401-022-02510-8 -
Human Molecular Genetics Dec 2023
PubMed: 37788121
DOI: 10.1093/hmg/ddad168 -
Neuromuscular Disorders : NMD Dec 2021We report a case of a patient presenting with arrhythmogenic cardiomyopathy, myofibrillar myopathy, and multiorgan tumors. A 41-year-old woman with a history of...
We report a case of a patient presenting with arrhythmogenic cardiomyopathy, myofibrillar myopathy, and multiorgan tumors. A 41-year-old woman with a history of hypertrophic cardiomyopathy, diagnosed at 6 years of age, developed scoliosis after puberty. Following spinal surgery to address the scoliosis, she developed recurrent severe arrhythmia and heart failure. She developed hypoventilation at age 29 years. Proximal dominant weakness and mild elevation of serum creatine kinase indicated possible myopathy. Myofibrillar myopathy was diagnosed by muscle biopsy at age 30 year. Acute abdomen was repeatedly reported from age 33 years, eventually leading to a diagnosis of gastric polyp and erosive ulcer. A urinary bladder tumor was found at age 35 years, and breast cancer was diagnosed at age 40 years. Whole exome sequencing detected a heterozygous missense mutation in Filamin C. Recent evidences suggest that filamins are associated with tumors, and this case further highlights the clinical spectrum of filaminopathy.
Topics: Adult; Breast Neoplasms; Cardiomyopathy, Hypertrophic; Female; Humans; Muscular Dystrophies; Myopathies, Structural, Congenital; Urinary Bladder Neoplasms
PubMed: 34857437
DOI: 10.1016/j.nmd.2021.10.002 -
Stem Cell Research & Therapy Jan 2024Beyond the observed alterations in cellular structure and mitochondria, the mechanisms linking rare genetic mutations to the development of heart failure in patients...
BACKGROUND
Beyond the observed alterations in cellular structure and mitochondria, the mechanisms linking rare genetic mutations to the development of heart failure in patients affected by desmin mutations remain unclear due in part, to the lack of relevant human cardiomyocyte models.
METHODS
To shed light on the role of mitochondria in these mechanisms, we investigated cardiomyocytes derived from human induced pluripotent stem cells carrying the heterozygous DES mutation that were either isolated from a patient or generated by gene editing. To increase physiological relevance, cardiomyocytes were either cultured on an anisotropic micropatterned surface to obtain elongated and aligned cardiomyocytes, or as a cardiac spheroid to create a micro-tissue. Moreover, when applicable, results from cardiomyocytes were confirmed with heart biopsies of suddenly died patient of the same family harboring DES mutation, and post-mortem heart samples from five control healthy donors.
RESULTS
The heterozygous DES mutation leads to dramatic changes in the overall cytoarchitecture of cardiomyocytes, including cell size and morphology. Most importantly, mutant cardiomyocytes display altered mitochondrial architecture, mitochondrial respiratory capacity and metabolic activity reminiscent of defects observed in patient's heart tissue. Finally, to challenge the pathological mechanism, we transferred normal mitochondria inside the mutant cardiomyocytes and demonstrated that this treatment was able to restore mitochondrial and contractile functions of cardiomyocytes.
CONCLUSIONS
This work highlights the deleterious effects of DES mutation, demonstrates the crucial role of mitochondrial abnormalities in the pathophysiology of desmin-related cardiomyopathy, and opens up new potential therapeutic perspectives for this disease.
Topics: Humans; Desmin; Induced Pluripotent Stem Cells; Cardiomyopathies; Mutation; Myocytes, Cardiac; Mitochondria
PubMed: 38167524
DOI: 10.1186/s13287-023-03619-7 -
PLoS Genetics Nov 2020Mutations in the molecular co-chaperone Bcl2-associated athanogene 3 (BAG3) are found to cause dilated cardiomyopathy (DCM), resulting in systolic dysfunction and heart...
Mutations in the molecular co-chaperone Bcl2-associated athanogene 3 (BAG3) are found to cause dilated cardiomyopathy (DCM), resulting in systolic dysfunction and heart failure, as well as myofibrillar myopathy (MFM), which is characterized by protein aggregation and myofibrillar disintegration in skeletal muscle cells. Here, we generated a CRISPR/Cas9-induced Bag3 knockout zebrafish line and found the complete preservation of heart and skeletal muscle structure and function during embryonic development, in contrast to morpholino-mediated knockdown of Bag3. Intriguingly, genetic compensation, a process of transcriptional adaptation which acts independent of protein feedback loops, was found to prevent heart and skeletal muscle damage in our Bag3 knockout model. Proteomic profiling and quantitative real-time PCR analyses identified Bag2, another member of the Bag protein family, significantly upregulated on a transcript and protein level in bag3-/- mutants. This implied that the decay of bag3 mutant mRNA in homozygous bag3-/- embryos caused the transcriptional upregulation of bag2 expression. We further demonstrated that morpholino-mediated knockdown of Bag2 in bag3-/- embryos evoked severe functional and structural heart and skeletal muscle defects, which are similar to Bag3 morphants. However, Bag2 knockdown in bag3+/+ or bag3+/- embryos did not result in (cardio-)myopathy. Finally, we found that inhibition of the nonsense-mediated mRNA decay (NMD) machinery by knockdown of upf1, an essential NMD factor, caused severe heart and skeletal muscle defects in bag3-/- mutants due to the blockade of transcriptional adaptation of bag2 expression. Our findings provide evidence that genetic compensation might vitally influence the penetrance of disease-causing bag3 mutations in vivo.
Topics: Adaptor Proteins, Signal Transducing; Animals; Apoptosis; Apoptosis Regulatory Proteins; Cardiomyopathies; Cardiomyopathy, Dilated; Disease Models, Animal; Heart Failure; Molecular Chaperones; Muscle Fibers, Skeletal; Muscular Diseases; Mutation; Myocardium; Myopathies, Structural, Congenital; Phenotype; Proteomics; Zebrafish; Zebrafish Proteins
PubMed: 33137814
DOI: 10.1371/journal.pgen.1009088 -
European Journal of Human Genetics :... Jan 2023Autosomal dominant variants in LDB3 (also known as ZASP), encoding the PDZ-LIM domain-binding factor, have been linked to a late onset phenotype of cardiomyopathy and...
Autosomal dominant variants in LDB3 (also known as ZASP), encoding the PDZ-LIM domain-binding factor, have been linked to a late onset phenotype of cardiomyopathy and myofibrillar myopathy in humans. However, despite knockout mice displaying a much more severe phenotype with premature death, bi-allelic variants in LDB3 have not yet been reported. Here we identify biallelic loss-of-function variants in five unrelated cardiomyopathy families by next-generation sequencing. In the first family, we identified compound heterozygous LOF variants in LDB3 in a fetus with bilateral talipes and mild left cardiac ventricular enlargement. Ultra-structural examination revealed highly irregular Z-disc formation, and RNA analysis demonstrated little/no expression of LDB3 protein with a functional C-terminal LIM domain in muscle tissue from the affected fetus. In a second family, a homozygous LDB3 nonsense variant was identified in a young girl with severe early-onset dilated cardiomyopathy with left ventricular non-compaction; the same homozygous nonsense variant was identified in a third unrelated female infant with dilated cardiomyopathy. We further identified homozygous LDB3 frameshift variants in two unrelated probands diagnosed with cardiomegaly and severely reduced left ventricular ejection fraction. Our findings demonstrate that recessive LDB3 variants can lead to an early-onset severe human phenotype of cardiomyopathy and myopathy, reminiscent of the knockout mouse phenotype, and supporting a loss of function mechanism.
Topics: Infant; Mice; Animals; Humans; Child; Female; Cardiomyopathy, Dilated; Stroke Volume; Adaptor Proteins, Signal Transducing; LIM Domain Proteins; Ventricular Function, Left; Cardiomyopathies
PubMed: 36253531
DOI: 10.1038/s41431-022-01204-9