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FASEB Journal : Official Publication of... Oct 2016Myotonia congenita is an inherited disease that is characterized by impaired muscle relaxation after contraction caused by loss-of-function mutations in the skeletal...
Myotonia congenita is an inherited disease that is characterized by impaired muscle relaxation after contraction caused by loss-of-function mutations in the skeletal muscle ClC-1 channel. We report a novel ClC-1 mutation, T335N, that is associated with a mild phenotype in 1 patient, located in the extracellular I-J loop. The purpose of this study was to provide a solid correlation between T335N dysfunction and clinical symptoms in the affected patient as well as to offer hints for drug development. Our multidisciplinary approach includes patch-clamp electrophysiology on T335N and ClC-1 wild-type channels expressed in tsA201 cells, Western blot and quantitative PCR analyses on muscle biopsies from patient and unaffected individuals, and molecular dynamics simulations using a homology model of the ClC-1 dimer. T335N channels display reduced chloride currents as a result of gating alterations rather than altered surface expression. Molecular dynamics simulations suggest that the I-J loop might be involved in conformational changes that occur at the dimer interface, thus affecting gating. Finally, the gene expression profile of T335N carrier showed a diverse expression of K channel genes, compared with control individuals, as potentially contributing to the phenotype. This experimental paradigm satisfactorily explained myotonia in the patient. Furthermore, it could be relevant to the study and therapy of any channelopathy.-Imbrici, P., Altamura, C., Camerino, G. M., Mangiatordi, G. F., Conte, E., Maggi, L., Brugnoni, R., Musaraj, K., Caloiero, R., Alberga, D., Marsano, R. M., Ricci, G., Siciliano, G., Nicolotti, O., Mora, M., Bernasconi, P., Desaphy, J.-F., Mantegazza, R., Camerino, D. C. Multidisciplinary study of a new ClC-1 mutation causing myotonia congenita: a paradigm to understand and treat ion channelopathies.
Topics: Channelopathies; Chloride Channels; Electrophysiological Phenomena; Humans; Ion Channel Gating; Muscle, Skeletal; Mutation; Myotonia Congenita; Patch-Clamp Techniques; Phenotype
PubMed: 27324117
DOI: 10.1096/fj.201500079R -
International Journal of Molecular... Oct 2022Nemaline myopathy (NM), a structural congenital myopathy, presents a significant clinical and genetic heterogeneity. Here, we compiled molecular and clinical data of 30...
Nemaline myopathy (NM), a structural congenital myopathy, presents a significant clinical and genetic heterogeneity. Here, we compiled molecular and clinical data of 30 Brazilian patients from 25 unrelated families. Next-generation sequencing was able to genetically classify all patients: sixteen families (64%) with mutation in NEB, five (20%) in ACTA1, two (8%) in KLHL40, and one in TPM2 (4%) and TPM3 (4%). In the NEB-related families, 25 different variants, 11 of them novel, were identified; splice site (10/25) and frame shift (9/25) mutations were the most common. Mutation c.24579 G>C was recurrent in three unrelated patients from the same region, suggesting a common ancestor. Clinically, the “typical” form was the more frequent and caused by mutations in the different NM genes. Phenotypic heterogeneity was observed among patients with mutations in the same gene. Respiratory involvement was very common and often out of proportion with limb weakness. Muscle MRI patterns showed variability within the forms and genes, which was related to the severity of the weakness. Considering the high frequency of NEB mutations and the complexity of this gene, NGS tools should be combined with CNV identification, especially in patients with a likely non-identified second mutation.
Topics: Brazil; Humans; Muscle Proteins; Muscle, Skeletal; Mutation; Myopathies, Nemaline; Myotonia Congenita
PubMed: 36233295
DOI: 10.3390/ijms231911995 -
Muscle & Nerve Feb 2019Paramyotonia congenita (PMC) is a nondystrophic myotonic disorder that is believed to be caused by a defect in Na 1.4 sodium channel inactivation. Ranolazine, which acts...
INTRODUCTION
Paramyotonia congenita (PMC) is a nondystrophic myotonic disorder that is believed to be caused by a defect in Na 1.4 sodium channel inactivation. Ranolazine, which acts by enhancing slow inactivation of sodium channels, has been proposed as a therapeutic option, but in vivo studies are lacking.
METHODS
We conducted an open-label, single-center trial of ranolazine to evaluate efficacy and tolerability in patients with PMC. Subjective symptoms of stiffness, weakness, and pain as well as clinical and electrical myotonia were evaluated. Baseline measures were compared with those after 4 weeks of treatment with ranolazine.
RESULTS
Ranolazine was tolerated well without any serious adverse events. Both subjective symptoms and clinical myotonia were significantly improved. Duration of myotonia was reduced according to electromyography, but this change was not statistically significant in all tested muscles.
DISCUSSION
Our findings support the use of ranolazine as a treatment for myotonia in PMC and suggest that a randomized, placebo-controlled trial is warranted. Muscle Nerve 59:240-243, 2019.
Topics: Adult; Electromyography; Female; Hand Strength; Humans; Male; Middle Aged; Muscle Weakness; Myotonic Disorders; Pain; Ranolazine; Severity of Illness Index; Sodium Channel Blockers; Stiff-Person Syndrome
PubMed: 30390395
DOI: 10.1002/mus.26372 -
Frontiers in Neuroscience 2022Optically pumped magnetometers (OPM) are quantum sensors that enable the contactless, non-invasive measurement of biomagnetic muscle signals, i.e., magnetomyography...
Optically pumped magnetometers (OPM) are quantum sensors that enable the contactless, non-invasive measurement of biomagnetic muscle signals, i.e., magnetomyography (MMG). Due to the contactless recording, OPM-MMG might be preferable to standard electromyography (EMG) for patients with neuromuscular diseases, particularly when repetitive recordings for diagnostic and therapeutic monitoring are mandatory. OPM-MMG studies have focused on recording physiological muscle activity in healthy individuals, whereas research on neuromuscular patients with pathological altered muscle activity is non-existent. Here, we report a proof-of-principle study on the application of OPM-MMG in patients with neuromuscular diseases. Specifically, we compare the muscular activity during maximal isometric contraction of the left rectus femoris muscle in three neuromuscular patients with severe (Transthyretin Amyloidosis in combination with Pompe's disease), mild (Charcot-Marie-Tooth disease, type 2), and without neurogenic, but myogenic, damage (Myotonia Congenita). Seven healthy young participants served as the control group. As expected, and confirmed by using simultaneous surface electromyography (sEMG), a time-series analysis revealed a dispersed interference pattern during maximal contraction with high amplitudes. Furthermore, both patients with neurogenic damage (ATTR and CMT2) showed a reduced variability of the MMG signal, quantified as the signal standard deviation of the main component of the frequency spectrum, highlighting the reduced possibility of motor unit recruitment due to the loss of motor neurons. Our results show that recording pathologically altered voluntary muscle activity with OPM-MMG is possible, paving the way for the potential use of OPM-MMG in larger studies to explore the potential benefits in clinical neurophysiology.
PubMed: 36523432
DOI: 10.3389/fnins.2022.1010242 -
The Journal of Physiology Nov 2017Paramyotonia congenita is a hereditary channelopathy caused by missense mutations in the SCN4A gene, which encodes the α subunit of the human skeletal muscle...
KEY POINTS
Paramyotonia congenita is a hereditary channelopathy caused by missense mutations in the SCN4A gene, which encodes the α subunit of the human skeletal muscle voltage-gated sodium channel NaV1.4. Affected individuals suffered from myotonia and paralysis of muscles, which were aggravated by exposure to cold. We report a three-generation Chinese family with patients presenting paramyotonia congenita and identify a novel N1366S mutation of NaV1.4. Whole-cell electrophysiological recordings of the N1366S channel reveal a gain-of-function change of gating in response to cold. Modelling and molecular dynamic simulation data suggest that an arginine-to-serine substitution at position 1366 increases the distance from N1366 to R1454 and disrupts the hydrogen bond formed between them at low temperature. We demonstrate that N1366S is a disease-causing mutation and that the temperature-sensitive alteration of N1366S channel activity may be responsible for the pronounced paramyotonia congenita symptoms of these patients.
ABSTRACT
Paramyotonia congenita is an autosomal dominant skeletal muscle channelopathy caused by missense mutations in SCN4A, the gene encoding the α subunit of the human skeletal muscle voltage-gated sodium channel NaV1.4. We report a three-generation family in which six members present clinical symptoms of paramyotonia congenita characterized by a marked worsening of myotonia by cold and by the presence of clear episodes of paralysis. We identified a novel mutation in SCN4A (Asn1366Ser, N1366S) in all patients in the family but not in healthy relatives or in 500 normal control subjects. Functional analysis of the channel protein expressed in HEK293 cells by whole-cell patch clamp recording revealed that the N1366S mutation led to significant alterations in the gating process of the NaV1.4 channel. The N1366S mutant displayed a cold-induced hyperpolarizing shift in the voltage dependence of activation and a depolarizing shift in fast inactivation, as well as a reduced rate of fast inactivation and accelerated recovery from fast inactivation. In addition, homology modelling and molecular dynamic simulation of N1366S and wild-type NaV1.4 channels indicated that the arginine-to-serine substitution disrupted the hydrogen bond formed between N1366 and R1454. Together, our results suggest that N1366S is a gain-of-function mutation of NaV1.4 at low temperature and the mutation may be responsible for the clinical symptoms of paramyotonia congenita in the affected family and constitute a basis for studies into its pathogenesis.
Topics: Adult; Aged; Cold Temperature; Female; Gain of Function Mutation; HEK293 Cells; Humans; Ion Channel Gating; Male; Middle Aged; Molecular Dynamics Simulation; Myotonic Disorders; NAV1.4 Voltage-Gated Sodium Channel
PubMed: 28940424
DOI: 10.1113/JP274877 -
Neurophysiologie Clinique = Clinical... Jun 2017To investigate the cause of transient weakness in myotonia congenita (MC) and the mechanism of action of mexiletine in reducing weakness.
OBJECTIVE
To investigate the cause of transient weakness in myotonia congenita (MC) and the mechanism of action of mexiletine in reducing weakness.
METHODS
The changes in neuromuscular excitability produced by 1min of maximal voluntary contractions (MVC) were measured on the amplitude of compound muscle action potentials (CMAP) in two patients with either recessive or dominant MC, compared to control values obtained in 20 healthy subjects. Measurements were performed again in MC patients after mexiletine therapy.
RESULTS
Transient reduction in maximal CMAP amplitude lasting several minutes after MVC was evident in MC patients, whereas no change was observed in controls. Mexiletine efficiently reduced this transient CMAP depression in both patients.
DISCUSSION
Transient CMAP depression following sustained MVC may represent the electrophysiological correlate of the weakness clinically experienced by the patients. In MC, the low chloride conductance could induce self-sustaining action potentials after MVC, determining progressive membrane depolarization and a loss of excitability of muscle fibers, thus resulting in transient paresis. Mexiletine may prevent conduction block due to excessive membrane depolarization, thus reducing the transient CMAP depression following sustained MVC.
Topics: Action Potentials; Adult; Electromyography; Female; Humans; Male; Mexiletine; Muscle Contraction; Muscle Weakness; Muscle, Skeletal; Myotonia Congenita; Transcutaneous Electric Nerve Stimulation; Treatment Outcome
PubMed: 28153715
DOI: 10.1016/j.neucli.2017.01.003 -
Frontiers in Pharmacology 2022Myotonia congenita (MC) is an inherited rare disease characterized by impaired muscle relaxation after contraction, resulting in muscle stiffness. It is caused by...
Myotonia congenita (MC) is an inherited rare disease characterized by impaired muscle relaxation after contraction, resulting in muscle stiffness. It is caused by loss-of-function mutations in the skeletal muscle chloride channel ClC-1, important for the stabilization of resting membrane potential and for the repolarization phase of action potentials. Thanks to functional studies, the molecular mechanisms by which ClC-1 mutations alter chloride ion influx into the cell have been in part clarified, classifying them in "gating-defective" or "expression-defective" mutations. To date, the treatment of MC is only palliative because no direct ClC-1 activator is available. An ideal drug should be one which is able to correct biophysical defects of ClC-1 in the case of gating-defective mutations or a drug capable to recover ClC-1 protein expression on the plasma membrane for trafficking-defective ones. In this study, we tested the ability of niflumic acid (NFA), a commercial nonsteroidal anti-inflammatory drug, to act as a pharmacological chaperone on trafficking-defective MC mutants (A531V, V947E). Wild-type (WT) or MC mutant ClC-1 channels were expressed in HEK293 cells and whole-cell chloride currents were recorded with the patch-clamp technique before and after NFA incubation. Membrane biotinylation assays and western blot were performed to support electrophysiological results. A531V and V947E mutations caused a decrease in chloride current density due to a reduction of ClC-1 total protein level and channel expression on the plasma membrane. The treatment of A531V and V947E-transfected cells with 50 µM NFA restored chloride currents, reaching levels similar to those of WT. Furthermore, no significant difference was observed in voltage dependence, suggesting that NFA increased protein membrane expression without altering the function of ClC-1. Indeed, biochemical experiments confirmed that V947E total protein expression and its plasma membrane distribution were recovered after NFA incubation, reaching protein levels similar to WT. Thus, the use of NFA as a pharmacological chaperone in trafficking defective ClC-1 channel mutations could represent a good strategy in the treatment of MC. Because of the favorable safety profile of this drug, our study may easily open the way for confirmatory human pilot studies aimed at verifying the antimyotonic activity of NFA in selected patients carrying specific ClC-1 channel mutations.
PubMed: 36034862
DOI: 10.3389/fphar.2022.958196 -
Revista de Neurologia Feb 2023Myotonia congenita is the most common form of genetic myotonia and is caused by mutations in the CLCN1 gene. It can be inherited in an autosomal dominant or recessive...
INTRODUCTION
Myotonia congenita is the most common form of genetic myotonia and is caused by mutations in the CLCN1 gene. It can be inherited in an autosomal dominant or recessive manner. We present a series of cases to update its incidence in our environment, to describe its phenotype in relation to the genotype found, and we also review the mutations found, among which we provide a new, undescribed alteration.
CASES REPORT
The medical records of patients with a diagnosis of congenital myotonia studied and followed up in the pediatric neurology section in a tertiary hospital between the years 2015-2020 were reviewed. Demographic variables (age, sex), disease course (age of onset, symptoms and signs, time elapsed until diagnosis, clinical evolution), family history and evaluation of response to treatment were collected. Five cases with a clinical diagnosis of myotonia congenita were identified (three with Becker's disease and two with Thomsen's disease). The incidence in relation to the number of births is estimated at 1:15,000 newborns for cases with the Becker phenotype and 1:21,000 newborns for the Thomsen phenotypes. We found a probably pathogenic mutation not previously described (CLCN1: c.824T> C).
CONCLUSIONS
the approximate incidence in our environment was higher than previously known and we describe a new, undescribed mutation: c.824T> C with pathogenicity predictors that behaved like a Becker recessive phenotype but with an earlier debut.
Topics: Humans; Myotonia Congenita; Incidence; Chloride Channels; Mutation; Muscular Dystrophy, Duchenne; Pedigree
PubMed: 36782350
DOI: 10.33588/rn.7604.2021357 -
Neuromuscular Disorders : NMD Jul 2018An eight week old Labrador Retriever puppy presented with stiff-legged robotic gait. Abnormal gait was most evident after rest and improved with prolonged activity. On...
An eight week old Labrador Retriever puppy presented with stiff-legged robotic gait. Abnormal gait was most evident after rest and improved with prolonged activity. On occasions, initiation of sudden movements would result in collapse with rigidity of the trunk and stiff extended limbs for several seconds. Other clinical signs were excitement-induced upper airway stridor and oropharyngeal dysphagia. Myotonia congenita was diagnosed based on clinical signs, abundant myotonic discharges on electromyography and exclusion of structural myopathies on histology. Whole exome sequencing revealed a case-specific homozygous variant in CLCN1, c.2275A > T resulting in a premature stop codon, p.R759X. The CLCN1 variant was absent from the genomes of 127 Labrador Retriever controls and 474 control dogs from other breeds. This study expands the spectrum of identified canine CLCN1 mutations and the list of affected breeds in myotonia congenita and highlights the potential value of dogs as translational large animal models of human genetic diseases.
Topics: Animals; Chloride Channels; Dog Diseases; Dogs; Electromyography; Mutation; Myotonia Congenita; Exome Sequencing
PubMed: 29934119
DOI: 10.1016/j.nmd.2018.05.002 -
Frontiers in Physiology 2020Reduced Cl conductance causes inhibited muscle relaxation after forceful voluntary contraction due to muscle membrane hyperexcitability. This represents the...
Reduced Cl conductance causes inhibited muscle relaxation after forceful voluntary contraction due to muscle membrane hyperexcitability. This represents the pathomechanism of myotonia congenita. Due to the prevailing data suggesting that an increased potassium level is a main contributor, we studied the effect of a modulator of a big conductance Ca- and voltage-activated K channels (BK) modulator on contraction and relaxation of slow- and high-twitch muscle specimen before and after the pharmacological induction of myotonia. Human and murine muscle specimens (wild-type and BK) were exposed to anthracene-9-carboxylic acid (9-AC) to inhibit CLC-1 chloride channels and to induce myotonia . Functional effects of BK-channel activation and blockade were investigated by exposing slow-twitch (soleus) and fast-twitch (extensor digitorum longus) murine muscle specimens or human musculus vastus lateralis to an activator (NS1608) and a blocker (Paxilline), respectively. Muscle-twitch force and relaxation times (T) were monitored. Compared to wild type, fast-twitch muscle specimen of BK mice resulted in a significantly decreased T in presence of 9-AC. Paxilline significantly shortened T of murine slow- and fast-twitch muscles as well as human vastus lateralis muscle. Moreover, twitch force was significantly reduced after application of Paxilline in myotonic muscle. NS1608 had opposite effects to Paxilline and aggravated the onset of myotonic activity by prolongation of T. The currently used standard therapy for myotonia is, in some individuals, not very effective. This study demonstrated that a BK channel blocker lowers myotonic stiffness and thus highlights its potential therapeutic option in myotonia congenital (MC).
PubMed: 33329012
DOI: 10.3389/fphys.2020.533946