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Frontiers in Physiology 2014CLC channels and transporters are expressed in most tissues and fulfill diverse functions. There are four human CLC channels, ClC-1, ClC-2, ClC-Ka, and ClC-Kb, and five... (Review)
Review
CLC channels and transporters are expressed in most tissues and fulfill diverse functions. There are four human CLC channels, ClC-1, ClC-2, ClC-Ka, and ClC-Kb, and five CLC transporters, ClC-3 through -7. Some of the CLC channels additionally associate with accessory subunits. Whereas barttin is mandatory for the functional expression of ClC-K, GlialCam is a facultative subunit of ClC-2 which modifies gating and thus increases the functional variability within the CLC family. Isoform-specific ion conduction and gating properties optimize distinct CLC channels for their cellular tasks. ClC-1 preferentially conducts at negative voltages, and the resulting inward rectification provides a large resting chloride conductance without interference with the muscle action potential. Exclusive opening at voltages negative to the chloride reversal potential allows for ClC-2 to regulate intracellular chloride concentrations. ClC-Ka and ClC-Kb are equally suited for inward and outward currents to support transcellular chloride fluxes. Every human CLC channel gene has been linked to a genetic disease, and studying these mutations has provided much information about the physiological roles and the molecular basis of CLC channel function. Mutations in the gene encoding ClC-1 cause myotonia congenita, a disease characterized by sarcolemmal hyperexcitability and muscle stiffness. Loss-of-function of ClC-Kb/barttin channels impairs NaCl resorption in the limb of Henle and causes hyponatriaemia, hypovolemia and hypotension in patients suffering from Bartter syndrome. Mutations in CLCN2 were found in patients with CNS disorders but the functional role of this isoform is still not understood. Recent links between ClC-1 and epilepsy and ClC-Ka and heart failure suggested novel cellular functions of these proteins. This review aims to survey the knowledge about physiological and pathophysiological functions of human CLC channels in the light of recent discoveries from biophysical, physiological, and genetic studies.
PubMed: 25339907
DOI: 10.3389/fphys.2014.00378 -
Neuromuscular Disorders : NMD Feb 2014Over the past decade there have been major advances in defining the genetic basis of the majority of congenital myopathy subtypes. However the relationship between each...
Over the past decade there have been major advances in defining the genetic basis of the majority of congenital myopathy subtypes. However the relationship between each congenital myopathy, defined on histological grounds, and the genetic cause is complex. Many of the congenital myopathies are due to mutations in more than one gene, and mutations in the same gene can cause different muscle pathologies. The International Standard of Care Committee for Congenital Myopathies performed a literature review and consulted a group of experts in the field to develop a summary of (1) the key features common to all forms of congenital myopathy and (2) the specific features that help to discriminate between the different genetic subtypes. The consensus statement was refined by two rounds of on-line survey, and a three-day workshop. This consensus statement provides guidelines to the physician assessing the infant or child with hypotonia and weakness. We summarise the clinical features that are most suggestive of a congenital myopathy, the major differential diagnoses and the features on clinical examination, investigations, muscle pathology and muscle imaging that are suggestive of a specific genetic diagnosis to assist in prioritisation of genetic testing of known genes. As next generation sequencing becomes increasingly used as a diagnostic tool in clinical practise, these guidelines will assist in determining which sequence variations are likely to be pathogenic.
Topics: Biopsy; Diagnosis, Differential; Genotype; Humans; Magnetic Resonance Imaging; Muscles; Myotonia Congenita; Phenotype
PubMed: 24456932
DOI: 10.1016/j.nmd.2013.11.003 -
Frontiers in Neurology 2022Non-dystrophic myotonias (NDMs) are skeletal muscle ion channelopathies caused by or mutations. This study aimed to describe the clinical, myopathological, and genetic...
INTRODUCTION
Non-dystrophic myotonias (NDMs) are skeletal muscle ion channelopathies caused by or mutations. This study aimed to describe the clinical, myopathological, and genetic analysis of NDM in a large Chinese cohort.
METHODS
We reviewed the clinical manifestations, laboratory results, electrocardiogram, electromyography, muscle biopsy, genetic analysis, treatment, and follow-up of 20 patients (from 18 families) with NDM.
RESULTS
Cases included myotonia congenita (MC, 17/20) and paramyotonia congenita (PMC, 3/20). Muscle stiffness and hypertrophy, grip and percussion myotonia, and the warm-up phenomenon were frequently observed in MC and PMC patients. Facial stiffness, eye closure myotonia, and cold sensitivity were more common in PMC patients and could be accompanied by permanent weakness. Nine MC patients and two PMC patients had cardiac abnormalities, mainly manifested as cardiac arrhythmia, and the father of one patient died of sudden cardiac arrest. Myotonic runs in electromyography were found in all patients, and seven MC patients had mild myopathic changes. There was no difference in muscle pathology between MC and PMC patients, most of whom had abnormal muscle fiber type distribution or selective muscle fiber atrophy. Nineteen variants were found in 17 MC patients, among which c.795T>G (p.D265E) was a new variant, and two variants were found in three PMC patients. The patients were treated with mexiletine and/or carbamazepine, and the symptoms of myotonia were partially improved.
CONCLUSIONS
MC and PMC have considerable phenotypic overlap. Genetic investigation contributes to identifying the subtype of NDM. The muscle pathology of NDM lacks specific changes.
PubMed: 35350395
DOI: 10.3389/fneur.2022.830707 -
Internal Medicine (Tokyo, Japan) Oct 2005Myotonia is repetitive firing of muscle action potentials causing prolonged muscle contractions even after mechanical stimulations to the muscles have ceased. Most... (Review)
Review
Myotonia is repetitive firing of muscle action potentials causing prolonged muscle contractions even after mechanical stimulations to the muscles have ceased. Most common myotonic disorder is myotonic dystrophy which is now termed DM1, myotonic dystrophy type 1. In Japan, proximal myotonic myopathy, which is now called DM2 has not been reported. Both DM1 and DM2 have Cl channel abnormality which causes myotonia. Less commonly we encounter Thomsen's disease, and autosomal recessive generalized myotonia (Becker type) which also have a Cl channel abnormality. There are other myotonic disorders related to Na channelopathy which include three disorders: paramyotonia congenita, adynamia episodica hereditaria, and myotonia fluctuans. Myotonia has been treated by various Na channel blockers, mexiletine, phenytoin, and carbamazepine, but they were originally developed for cardiac arrhythmia, or seizure disorders and they have undesirable side effects, weakness. Comprehensive treatment includes myotonia control without reducing the strength, and care for systemic manifestations of DM1.
Topics: Humans; Myotonic Disorders
PubMed: 16293911
DOI: 10.2169/internalmedicine.44.1027 -
The Turkish Journal of Pediatrics 2020Congenital Myotonia (CM) is a disease caused by mutations in the skeletal muscle chloride channel gene (CLCN1). Mutations can be transmitted as autosomal dominant... (Review)
Review
BACKGROUND AND OBJECTIVES
Congenital Myotonia (CM) is a disease caused by mutations in the skeletal muscle chloride channel gene (CLCN1). Mutations can be transmitted as autosomal dominant (Thomsen's disease) or recessive (Becker's disease). CM is more common in men and Becker myotonia may be 10 times more common than Thomsen myotonia. Genotypic and phenotypic characteristics of CM may vary according to geographical region and ethnicity.
METHOD
In this study, we present the genotypic and phenotypic characteristics of 20 Turkish CM patients all diagnosed by molecular genetic testing. The clinical and laboratory features of the patients with mutation in CLCN1 gene were retrospectively analyzed.
RESULTS
Eleven of the patients were female. c.1064+1G > A splice-site change, p.Arg338X (c.1012 C > T) stop codon, p.Gly190Ser (c.568_569delinsTC) missense mutations were detected. Eight of the 20 patients were found to be compatible with Becker type and 12 with Thomsen type, based on mode of inheritance, neurological examination findings and genetic test results.
CONCLUSION
The c.1064+1G > A splice-site change mutation, defined for the first time in this study, expands the spectrum of mutations in the CLCN1 gene. Thomsen type and female gender were observed to be more frequent in this series of patients from Turkey.
Topics: Chloride Channels; Female; Humans; Male; Mutation; Mutation, Missense; Myotonia Congenita; Pedigree; Retrospective Studies
PubMed: 32558419
DOI: 10.24953/turkjped.2020.03.012 -
The Korean Journal of Physiology &... Jul 2017Myotonia congenita (MC) is a genetic disease that displays impaired relaxation of skeletal muscle and muscle hypertrophy. This disease is mainly caused by mutations of...
Myotonia congenita (MC) is a genetic disease that displays impaired relaxation of skeletal muscle and muscle hypertrophy. This disease is mainly caused by mutations of that encodes human skeletal muscle chloride channel (CLC-1). CLC-1 is a voltage gated chloride channel that activates upon depolarizing potentials and play a major role in stabilization of resting membrane potentials in skeletal muscle. In this study, we report 4 unrelated Korean patients diagnosed with myotonia congenita and their clinical features. Sequence analysis of all coding regions of the patients was performed and mutation, R47W and A298T, was commonly identified. The patients commonly displayed transient muscle weakness and only one patient was diagnosed with autosomal dominant type of myotonia congenita. To investigate the pathological role of the mutation, electrophysiological analysis was also performed in HEK 293 cells transiently expressing homo- or heterodimeric mutant channels. The mutant channels displayed reduced chloride current density and altered channel gating. However, the effect of A298T on channel gating was reduced with the presence of R47W in the same allele. This analysis suggests that impaired CLC-1 channel function can cause myotonia congenita and that R47W has a protective effect on A298T in relation to channel gating. Our results provide clinical features of Korean myotonia congenita patients who have the heterozygous mutation and reveal underlying pathophyological consequences of the mutants by taking electrophysiological approach.
PubMed: 28706458
DOI: 10.4196/kjpp.2017.21.4.439 -
Frontiers in Cellular Neuroscience 2015The voltage-dependent ClC-1 chloride channel belongs to the CLC channel/transporter family. It is a homodimer comprising two individual pores which can operate... (Review)
Review
The voltage-dependent ClC-1 chloride channel belongs to the CLC channel/transporter family. It is a homodimer comprising two individual pores which can operate independently or simultaneously according to two gating modes, the fast and the slow gate of the channel. ClC-1 is preferentially expressed in the skeletal muscle fibers where the presence of an efficient Cl(-) homeostasis is crucial for the correct membrane repolarization and propagation of action potential. As a consequence, mutations in the CLCN1 gene cause dominant and recessive forms of myotonia congenita (MC), a rare skeletal muscle channelopathy caused by abnormal membrane excitation, and clinically characterized by muscle stiffness and various degrees of transitory weakness. Elucidation of the mechanistic link between the genetic defects and the disease pathogenesis is still incomplete and, at this time, there is no specific treatment for MC. Still controversial is the subcellular localization pattern of ClC-1 channels in skeletal muscle as well as its modulation by some intracellular factors. The expression of ClC-1 in other tissues such as in brain and heart and the possible assembly of ClC-1/ClC-2 heterodimers further expand the physiological properties of ClC-1 and its involvement in diseases. A recent de novo CLCN1 truncation mutation in a patient with generalized epilepsy indeed postulates an unexpected role of this channel in the control of neuronal network excitability. This review summarizes the most relevant and state-of-the-art research on ClC-1 chloride channels physiology and associated diseases.
PubMed: 25964741
DOI: 10.3389/fncel.2015.00156 -
Journal of Electromyography and... Dec 2019Myotonia congenita (MC) is caused by pathogenic variants in the CLCN1 gene coding the chloride channel protein.
INTRODUCTION
Myotonia congenita (MC) is caused by pathogenic variants in the CLCN1 gene coding the chloride channel protein.
METHODS
To test the hypothesis that needle EMG could be helpful in distinguishing between the recessive and dominant MC, we performed EMG examination in 36 patients (23 men) aged 4-61 years with genetically proven MC: in 30 patients with autosomal recessive MC (Becker MC) and in 6 with autosomal dominant MC (Thomsen MC).
RESULTS
Myotonic discharges were recorded in 95.8% of examined muscles. For the whole MC group we observed a significant positive correlation between parameters of motor unit activity potentials (MUAPs) in vastus lateralis and tibialis anterior muscles and the duration of the disease. Similar correlation for biceps brachii also was found in Becker MC subgroup only.
DISCUSSION
EMG could still be helpful in diagnosis of MC and together with provocative tests might be useful in differentiation between recessive and autosomal MC.
Topics: Adolescent; Adult; Child; Child, Preschool; Diagnosis, Differential; Electromyography; Evoked Potentials, Motor; Female; Genes, Dominant; Genes, Recessive; Humans; Male; Middle Aged; Muscle, Skeletal; Mutation; Myotonia Congenita
PubMed: 31610484
DOI: 10.1016/j.jelekin.2019.102362 -
Biomedicines Sep 2023Myotonia congenita is a hereditary muscle disease mainly characterized by muscle hyperexcitability, which leads to a sustained burst of discharges that correlates with... (Review)
Review
Myotonia congenita is a hereditary muscle disease mainly characterized by muscle hyperexcitability, which leads to a sustained burst of discharges that correlates with the magnitude and duration of involuntary aftercontractions, muscle stiffness, and hypertrophy. Mutations in the chloride voltage-gated channel 1 () gene that encodes the skeletal muscle chloride channel (ClC-1) are responsible for this disease, which is commonly known as myotonic chloride channelopathy. The biophysical properties of the mutated channel have been explored and analyzed through in vitro approaches, providing important clues to the general function/dysfunction of the wild-type and mutated channels. After an exhaustive search for mutations, we report in this review more than 350 different mutations identified in the literature. We start discussing the physiological role of the ClC-1 channel in skeletal muscle functioning. Then, using the reported functional effects of the naturally occurring mutations, we describe the biophysical and structural characteristics of the ClC-1 channel to update the knowledge of the function of each of the ClC-1 helices, and finally, we attempt to point out some patterns regarding the effects of mutations in the different helices and loops of the protein.
PubMed: 37892996
DOI: 10.3390/biomedicines11102622 -
Frontiers in Neurology 2020Four main clinical phenotypes have been traditionally described in patients mutated in SCN4A, including sodium-channel myotonia (SCM), paramyotonia congenita (PMC),...
Four main clinical phenotypes have been traditionally described in patients mutated in SCN4A, including sodium-channel myotonia (SCM), paramyotonia congenita (PMC), Hypokaliemic type II (HypoPP2), and Hyperkaliemic/Normokaliemic periodic paralysis (HyperPP/NormoPP); in addition, rare phenotypes associated with mutations in SCN4A are congenital myasthenic syndrome and congenital myopathy. However, only scarce data have been reported in literature on large patient cohorts including phenotypes characterized by myotonia and episodes of paralysis. We retrospectively investigated clinical and molecular features of 80 patients fulfilling the following criteria: (1) clinical and neurophysiological diagnosis of myotonia, or clinical diagnosis of PP, and (2) presence of a pathogenic SCN4A gene variant. Patients presenting at birth with episodic laryngospasm or congenital myopathy-like phenotype with later onset of myotonia were considered as neonatal SCN4A. PMC was observed in 36 (45%) patients, SCM in 30 (37.5%), Hyper/NormoPP in 7 (8.7%), HypoPP2 in 3 (3.7%), and neonatal SCN4A in 4 (5%). The median age at onset was significantly earlier in PMC than in SCM ( < 0.01) and in Hyper/NormoPP than in HypoPP2 ( = 0.02). Cold-induced myotonia was more frequently observed in PMC ( = 34) than in SCM ( = 23) ( = 0.04). No significant difference was found in age at onset of episodes of paralysis among PMC and PP or in frequency of permanent weakness between PP ( = 4), SCM ( = 5), and PMC ( = 10). PP was more frequently associated with mutations in the S4 region of the NaV1.4 channel protein compared to SCM and PMC ( < 0.01); mutations causing PMC were concentrated in the C-terminal region of the protein, while SCM-associated mutations were detected in all the protein domains. Our data suggest that skeletal muscle channelopathies associated with mutations in SCN4A represent a continuum in the clinical spectrum.
PubMed: 32849172
DOI: 10.3389/fneur.2020.00646