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Olave-Rodriguez JA, Bonilla-Escobar FJ, Candelo E, Rodriguez-Rojas LX. First Two Case Reports of Becker's Type Myotonia Congenita in Colombia: Clinical and Genetic Features. Appl Clin Genet 2021; 14:473-479. [PMID: 34938096 PMCID: PMC8687676 DOI: 10.2147/tacg.s323559] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2021] [Accepted: 10/26/2021] [Indexed: 11/23/2022] Open
Abstract
Background Becker's type myotonia congenita is an autosomal recessive nondystrophic skeletal muscle disorder characterized by muscle stiffness and the inability of muscle relaxation after voluntary contraction. It is caused by mutations in the CLCN1 gene, which encodes for a chloride channel mainly expressed in the striated muscle. Most cases have been reported in the European population, and only mexiletine has demonstrated a randomized placebo-controlled, double-blinded effectiveness. Case Presentation We present two male siblings from Colombia with Latino ancestry, without parental consanguinity, with myotonia during voluntary movements, muscle hypertrophy of lower extremities, transient weakness, and severe muscle fatigue after exercise from three years of age. A genetic panel for dystrophic muscle disorders and a muscle biopsy were both negative. Genetic testing was performed in their second decade of life. Both patients' exomic sequencing test reported the mutation c.1129C >T (p.Arg377*) affecting exon 10 of the CLCN1, generating a premature stop codon. This mutation was described as pathogenic and observed in only one other patient in the United Kingdom. Conclusion To our knowledge, these are the first cases of Becker's type myotonia congenita reported in Colombia. Increasing awareness of healthcare providers for this type of disease in the region could lead to the identification of undiagnosed patients. Limited availability of medical geneticists as well as genetic testing may be the cause of the lack of previous description of cases, in addition to the delay in the diagnosis of the patients. Further epidemiological studies can reveal underdiagnosed myotonias in the country and in the Latin-American region.
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Affiliation(s)
| | - Francisco Javier Bonilla-Escobar
- Somos Ciencia al Servicio de la Comunidad, Fundación SCISCO/Science to Serve the Community, SCISCO Foundation, Cali, Colombia.,Universidad del Valle, Cali, Colombia.,Institute for Clinical Research Education, University of Pittsburgh, Pittsburgh, PA, USA
| | - Estephania Candelo
- Centro de Investigaciones Clínicas, Fundación Valle del Lili, Cali, Colombia.,Centro enfermedades raras y malformaciones congenitas (CIACER), Universidad Icesi, Cali, Colombia
| | - Lisa Ximena Rodriguez-Rojas
- Universidad Icesi, Faculty of Health Sciences, Cali, Colombia.,Human Genetics Department, Fundación Valle del Lili, Cali, Colombia
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Morales F, Pusch M. An Up-to-Date Overview of the Complexity of Genotype-Phenotype Relationships in Myotonic Channelopathies. Front Neurol 2020; 10:1404. [PMID: 32010054 PMCID: PMC6978732 DOI: 10.3389/fneur.2019.01404] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Accepted: 12/23/2019] [Indexed: 12/11/2022] Open
Abstract
Myotonic disorders are inherited neuromuscular diseases divided into dystrophic myotonias and non-dystrophic myotonias (NDM). The latter is a group of dominant or recessive diseases caused by mutations in genes encoding ion channels that participate in the generation and control of the skeletal muscle action potential. Their altered function causes hyperexcitability of the muscle membrane, thereby triggering myotonia, the main sign in NDM. Mutations in the genes encoding voltage-gated Cl− and Na+ channels (respectively, CLCN1 and SCN4A) produce a wide spectrum of phenotypes, which differ in age of onset, affected muscles, severity of myotonia, degree of hypertrophy, and muscle weakness, disease progression, among others. More than 200 CLCN1 and 65 SCN4A mutations have been identified and described, but just about half of them have been functionally characterized, an approach that is likely extremely helpful to contribute to improving the so-far rather poor clinical correlations present in NDM. The observed poor correlations may be due to: (1) the wide spectrum of symptoms and overlapping phenotypes present in both groups (Cl− and Na+ myotonic channelopathies) and (2) both genes present high genotypic variability. On the one hand, several mutations cause a unique and reproducible phenotype in most patients. On the other hand, some mutations can have different inheritance pattern and clinical phenotypes in different families. Conversely, different mutations can be translated into very similar phenotypes. For these reasons, the genotype-phenotype relationships in myotonic channelopathies are considered complex. Although the molecular bases for the clinical variability present in myotonic channelopathies remain obscure, several hypotheses have been put forward to explain the variability, which include: (a) differential allelic expression; (b) trans-acting genetic modifiers; (c) epigenetic, hormonal, or environmental factors; and (d) dominance with low penetrance. Improvements in clinical tests, the recognition of the different phenotypes that result from particular mutations and the understanding of how a mutation affects the structure and function of the ion channel, together with genetic screening, is expected to improve clinical correlation in NDMs.
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Affiliation(s)
- Fernando Morales
- Instituto de Investigaciones en Salud, Universidad de Costa, San José, Costa Rica
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3
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A large intragenic deletion in the CLCN1 gene causes Hereditary Myotonia in pigs. Sci Rep 2019; 9:15632. [PMID: 31666547 PMCID: PMC6821760 DOI: 10.1038/s41598-019-51286-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Accepted: 09/11/2019] [Indexed: 12/14/2022] Open
Abstract
Mutations in the CLCN1 gene are the primary cause of non-dystrophic Hereditary Myotonia in several animal species. However, there are no reports of Hereditary Myotonia in pigs to date. Therefore, the objective of the present study was to characterize the clinical and molecular findings of Hereditary Myotonia in an inbred pedigree. The clinical, electromyographic, histopathological, and molecular findings were evaluated. Clinically affected pigs presented non-dystrophic recessive Hereditary Myotonia. Nucleotide sequence analysis of the entire coding region of the CLCN1 gene revealed the absence of the exons 15 and 16 in myotonic animals. Analysis of the genomic region flanking the deletion unveiled a large intragenic deletion of 4,165 nucleotides. Interestingly, non-related, non-myotonic pigs expressed transcriptional levels of an alternate transcript (i.e., X2) that was identical to the deleted X1 transcript of myotonic pigs. All myotonic pigs and their progenitors were homozygous recessive and heterozygous, respectively, for the 4,165-nucleotide deletion. This is the first study reporting Hereditary Myotonia in pigs and characterizing its clinical and molecular findings. Moreover, to the best of our knowledge, Hereditary Myotonia has never been associated with a genomic deletion in the CLCN1 gene in any other species.
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Imbrici P, Altamura C, Pessia M, Mantegazza R, Desaphy JF, Camerino DC. ClC-1 chloride channels: state-of-the-art research and future challenges. Front Cell Neurosci 2015; 9:156. [PMID: 25964741 PMCID: PMC4410605 DOI: 10.3389/fncel.2015.00156] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Accepted: 04/08/2015] [Indexed: 01/06/2023] Open
Abstract
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.
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Affiliation(s)
- Paola Imbrici
- Department of Pharmacy - Drug Sciences, University of Bari “Aldo Moro”,Bari, Italy
| | - Concetta Altamura
- Department of Pharmacy - Drug Sciences, University of Bari “Aldo Moro”,Bari, Italy
| | - Mauro Pessia
- Department of Pharmacy - Drug Sciences, University of Bari “Aldo Moro”,Bari, Italy
| | - Renato Mantegazza
- Department of Pharmacy - Drug Sciences, University of Bari “Aldo Moro”,Bari, Italy
| | | | - Diana Conte Camerino
- Department of Pharmacy - Drug Sciences, University of Bari “Aldo Moro”,Bari, Italy
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5
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A large cohort of myotonia congenita probands: novel mutations and a high-frequency mutation region in exons 4 and 5 of the CLCN1 gene. J Hum Genet 2013; 58:581-7. [DOI: 10.1038/jhg.2013.58] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2013] [Revised: 04/30/2013] [Accepted: 05/01/2013] [Indexed: 11/08/2022]
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Ivanova EA, Dadali EL, Fedotov VP, Kurbatov SA, Rudenskaya GE, Proskokova TN, Polyakov AV. The spectrum of CLCN1 gene mutations in patients with nondystrophic Thomsen’s and Becker’s myotonias. RUSS J GENET+ 2012. [DOI: 10.1134/s1022795412090049] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Mazón MJ, Barros F, De la Peña P, Quesada JF, Escudero A, Cobo AM, Pascual-Pascual SI, Gutiérrez-Rivas E, Guillén E, Arpa J, Eraso P, Portillo F, Molano J. Screening for mutations in Spanish families with myotonia. Functional analysis of novel mutations in CLCN1 gene. Neuromuscul Disord 2012; 22:231-43. [DOI: 10.1016/j.nmd.2011.10.013] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2011] [Revised: 10/09/2011] [Accepted: 10/13/2011] [Indexed: 11/28/2022]
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Abstract
Myotonia is a symptom of many different acquired and genetic muscular conditions that impair the relaxation phase of muscular contraction. Myotonia congenita is a specific inherited disorder of muscle membrane hyperexcitability caused by reduced sarcolemmal chloride conductance due to mutations in CLCN1, the gene coding for the main skeletal muscle chloride channel ClC-1. The disorder may be transmitted as either an autosomal-dominant or recessive trait with close to 130 currently known mutations. Although this is a rare disorder, elucidation of the pathophysiology underlying myotonia congenita established the importance of sarcolemmal chloride conductance in the control of muscle excitability and demonstrated the first example of human disease associated with the ClC family of chloride transporting proteins.
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Affiliation(s)
- Christoph Lossin
- Department of Neurology, UC Davis School of Medicine, Sacramento, California 95817
| | - Alfred L George
- Departments of Medicine and Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232
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9
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Lin MJ, You TH, Pan H, Hsiao KM. Functional characterization of CLCN1 mutations in Taiwanese patients with myotonia congenita via heterologous expression. Biochem Biophys Res Commun 2006; 351:1043-7. [PMID: 17097617 DOI: 10.1016/j.bbrc.2006.10.158] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2006] [Accepted: 10/27/2006] [Indexed: 11/16/2022]
Abstract
Mutations in the CLCN1 gene frequently associate with myotonia congenita (MC). We have recently reported several CLCN1 mutants in Taiwanese patients. To further elucidate the correlation between the genotypes and phenotypes, in this study, we used Xenopus oocyte as a system to investigate the functional effects of these mutants. The fs793X and G482R mutants, which were suggested to have a dual inheritance pattern, were found to cause a functional loss of CLCN1 channels. While co-expression of fs793X and wild-type (WT) showed a reduction of chloride conductance by about half of WT channels, the activation curve of voltage-dependence was not shifted. A compound heterozygous mutant, P575S/D644G, was found in a patient. When both mutants were co-expressed in oocytes, they caused a shift of the voltage-dependence of activation curve to more positive values than individual mutant. This indicates that both P575S and D644G mutants may contribute cooperatively to change the gating property of CLCN1 channel. Interestingly, the S471F mutant did not cause significant alternation of functional properties. Consistent with the fact that T631I mutant was found in three asymptomatic individuals, the electrophysiological parameters of T631I were similar to those of WT CLCN1 channels, suggesting that T631I is a neutral mutation. These results further clarify the correlation between the mutations and their functional implications of CLCN1 channels.
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Affiliation(s)
- Min-Jon Lin
- Department of Biomedical Sciences, Chung Shan Medical University, Taichung, Taiwan, ROC
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10
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Kuo HC, Hsiao KM, Chang LI, You TH, Yeh TH, Huang CC. Novel mutations at carboxyl terminus of CIC-1 channel in myotonia congenita. Acta Neurol Scand 2006; 113:342-6. [PMID: 16629771 DOI: 10.1111/j.1600-0404.2006.00589.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
OBJECTIVES Myotonia congenita (MC), caused by mutations in the muscle chloride channel (CLCN1) gene, can be inherited dominantly or recessively. The mutations at the carboxyl terminus of the CLCN1 gene have been identified in MC patients, but the functional implication of these mutations is unknown. MATERIAL AND METHODS Direct sequencing of polymerase chain reaction products covering the whole coding region of the CLCN1 gene was performed in a MC family. This study was designed to investigate the clinical manifestations and genetic analysis of the CLCN1 gene. RESULTS We identified two novel mutations, 2330delG and 1892C>T, from a genetic screening of the CLCN1 gene in the MC family. The 2330delG mutant allele producing a fs793X truncated protein was identified in a heterozygous state in all the patients. The 1892C>T nucleotide change induced a missense mutation (T631I) found in several asymptomatic individuals, indicating that it may not be associated with MC. Intriguingly, the 2330delG mutation was also found in an asymptomatic subject who also carried the 1892C>T mutation. CONCLUSION The data indicate that the fs793X mutant protein causes dominantly inherited MC. Because the mutation has been found in a recessive pedigree, the fs793X mutation may have a dual inheritance pattern.
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Affiliation(s)
- H-C Kuo
- Department of Neurology, Chang Gung Memorial Hospital and University, Taipei, Taiwan
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11
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Abstract
Myotonia congenita is a hereditary chloride channel disorder characterized by delayed relaxation of skeletal muscle (myotonia). It is caused by mutations in the skeletal muscle chloride channel gene CLCN1 on chromosome 7. The phenotypic spectrum of myotonia congenita ranges from mild myotonia disclosed only by clinical examination to severe and disabling myotonia with transient weakness and myopathy. The most severe phenotypes are seen in patients with two mutated alleles. Heterozygotes are often asymptomatic but for some mutations heterozygosity is sufficient to cause pronounced myotonia, although without weakness and myopathy. Thus, the phenotype depends on the mutation type to some extent, but this does not explain the fact that severity varies greatly between heterozygous family members and may even vary with time in the individual patient. In this review, existing knowledge about phenotypic variability is summarized, and the possible contributing factors are discussed.
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Affiliation(s)
- Eskild Colding-Jørgensen
- Department of Clinical Neurophysiology 19, Glostrup Hospital, University of Copenhagen DK-2600 Glostrup, Denmark.
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Lassaletta Atienza A, Cebrero García M, González Santiago MP, García Frías E. Incapacidad para iniciar la deambulación tras el reposo prolongado en una adolescente. An Pediatr (Barc) 2004; 60:278-9. [PMID: 14987522 DOI: 10.1016/s1695-4033(04)78265-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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13
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Grunnet M, Jespersen T, Colding-Jørgensen E, Schwartz M, Klaerke DA, Vissing J, Olesen SP, Dunø M. Characterization of two new dominant ClC-1 channel mutations associated with myotonia. Muscle Nerve 2003; 28:722-32. [PMID: 14639587 DOI: 10.1002/mus.10501] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Voltage-gated ClC-1 chloride channels encoded by the CLCN1 gene have a major role in setting the membrane potential in skeletal muscle. More than 60 CLCN1 mutations have been associated with myotonia congenita. These mutations are traditionally classified as recessive (Becker's disease) or dominant (Thomsen's disease). In this study, we have electrophysiologically characterized two new dominant ClC-1 mutations, thereby elucidating the observed phenotype in patients. The two ClC-1 mutants M128V and E193K were identified, and the DNA was isolated from patients and subsequently expressed in Xenopus laevis oocytes for electrophysiological characterization. Both ClC-1 mutants, M128V and E193K, showed a large rightward shift in the current-voltage relationship. In addition, the activation kinetics were slowed in the ClC-1 M128V mutant, as compared to the wild-type ClC-1. Interestingly, ClC-1 E193K revealed a change in reversal potential compared to wild-type channels. This finding supports the notion that the E193 amino acid is an important determinant in the selectivity filter of the human ClC-1 channel. The electrophysiological behavior of both mutants demonstrates a severe reduction in ClC-1 channel conductance under physiologically relevant membrane potentials. These studies thereby explain the molecular background for the observed myotonia in patients.
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Affiliation(s)
- Morten Grunnet
- Department of Medical Physiology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark.
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Abstract
Ion channels are complex proteins that span the lipid bilayer of the cell membrane, where they orchestrate the electrical signals necessary for normal function of the central nervous system, peripheral nerve, and both skeletal and cardiac muscle. The role of ion channel defects in the pathogenesis of numerous disorders, many of them neuromuscular, has become increasingly apparent over the last decade. Progress in molecular biology has allowed cloning and expression of genes that encode channel proteins, while comparable advances in biophysics, including patch-clamp electrophysiology and related techniques, have made the study of expressed proteins at the level of single channel molecules possible. Understanding the molecular basis of ion channel function and dysfunction will facilitate both the accurate classification of these disorders and the rational development of specific therapeutic interventions. This review encompasses clinical, genetic, and pathophysiological aspects of ion channels disorders, focusing mainly on those with neuromuscular manifestations.
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Affiliation(s)
- Kleopas A Kleopa
- Department of Neurology, University of Pennsylvania School of Medicine, 122 College Hall, Philadelphia, PA 19104, USA
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Abstract
Pure non-syndromic, non-dystrophic myotonia in humans is caused by mutations in the genes coding for the skeletal muscle sodium channel (SCN5A) or the skeletal muscle chloride channel (CLCN1) with similar phenotypes. Chloride-channel myotonia can be dominant (Thomsen-type myotonia) or recessive (Becker-type myotonia). More than 60 myotonia-causing mutations in the CLCN1 gene have been identified, with only a few of them being dominant. A common phenotype of dominant mutations is a dominant negative effect of mutant subunits in mutant-WT heterodimers, causing a large shift of the steady-state open probability voltage-dependence towards more positive, unphysiological voltages. The study of the properties of disease causing mutations has helped in understanding the functional properties of the CLC-1 channel that is part of a nine-member gene family of chloride channels. The large body of knowledge obtained for CLC-1 may also help to better understand the other CLC channels, three of which are also involved in genetic diseases.
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Affiliation(s)
- Michael Pusch
- Istituto di Cibernetica e Biofisica, CNR, Genova, Italy.
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Jentsch TJ, Stein V, Weinreich F, Zdebik AA. Molecular structure and physiological function of chloride channels. Physiol Rev 2002; 82:503-68. [PMID: 11917096 DOI: 10.1152/physrev.00029.2001] [Citation(s) in RCA: 925] [Impact Index Per Article: 42.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cl- channels reside both in the plasma membrane and in intracellular organelles. Their functions range from ion homeostasis to cell volume regulation, transepithelial transport, and regulation of electrical excitability. Their physiological roles are impressively illustrated by various inherited diseases and knock-out mouse models. Thus the loss of distinct Cl- channels leads to an impairment of transepithelial transport in cystic fibrosis and Bartter's syndrome, to increased muscle excitability in myotonia congenita, to reduced endosomal acidification and impaired endocytosis in Dent's disease, and to impaired extracellular acidification by osteoclasts and osteopetrosis. The disruption of several Cl- channels in mice results in blindness. Several classes of Cl- channels have not yet been identified at the molecular level. Three molecularly distinct Cl- channel families (CLC, CFTR, and ligand-gated GABA and glycine receptors) are well established. Mutagenesis and functional studies have yielded considerable insights into their structure and function. Recently, the detailed structure of bacterial CLC proteins was determined by X-ray analysis of three-dimensional crystals. Nonetheless, they are less well understood than cation channels and show remarkably different biophysical and structural properties. Other gene families (CLIC or CLCA) were also reported to encode Cl- channels but are less well characterized. This review focuses on molecularly identified Cl- channels and their physiological roles.
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Affiliation(s)
- Thomas J Jentsch
- Zentrum für Molekulare Neurobiologie Hamburg, Universität Hamburg, Hamburg, Germany.
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Davies NP, Hanna MG. The skeletal muscle channelopathies: basic science, clinical genetics and treatment. Curr Opin Neurol 2001; 14:539-51. [PMID: 11562564 DOI: 10.1097/00019052-200110000-00001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The human neurological channelopathies are a rapidly expanding group of mainly genetic conditions that are characterized by dysfunction of membrane-bound glycoproteins (ion channels). The skeletal muscle channelopathies were the first to be characterized in this group. In recent years significant progress has been made in our understanding of the molecular genetic and cellular electrophysiological bases of these disorders. DNA-based diagnosis is now a reality for many of the channelopathies. The advances made have implications for both genetic counselling and for tailoring treatment to specific channelopathies.
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Sasaki R, Ito N, Shimamura M, Murakami T, Kuzuhara S, Uchino M, Uyama E. A novelCLCN1 mutation: P480T in a Japanese family with Thomsen's myotonia congenita. Muscle Nerve 2001; 24:357-63. [PMID: 11353420 DOI: 10.1002/1097-4598(200103)24:3<357::aid-mus1006>3.0.co;2-e] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
At least 50 disease-causing mutations in the skeletal muscle voltage-gated chloride channel gene (CLCN1), almost all of which originate from Caucasian families, have been identified. We investigated a Japanese family with Thomsen's myotonia congenita that included 16 affected individuals (8 men and 8 women) through five generations. Polymerase chain reaction (PCR)-single-strand conformation polymorphism (SSCP) screening of 11 members showed an aberrant conformer in exon 13 of CLCN1 complementary DNA (cDNA) in 8 affected and 1 unaffected members. By sequence analysis, we identified a C-to-A transition at nucleotide position 1438, resulting in a substitution of proline for threonine at amino acid position 480 (P480T), the same position of the original mutation (P480L) in Thomsen's disease. The P480T mutation was novel and absent in 100 normal controls. Seven of the 8 affected individuals were heterozygous; another, from affected parents, was homozygous. Clinically, myotonia in the homozygous patient was more severe than that in heterozygous patients, probably due to the gene dosage effect. On a long-train nerve-stimulation test at a rate of 3 Hz, M-wave responses in the homozygous patient showed marked decrement followed by recovery. In contrast, the heterozygous patients showed just a slight decrement or no changes, and none of 2 patients with myotonic muscular dystrophy or 2 normal controls revealed any decrement. Thus, the long-train nerve-stimulation test at a low stimulus frequency may be a useful tool to assess the disease-severity/genotype relationship in myotonia congenita.
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Affiliation(s)
- R Sasaki
- Department of Neurology, Mie University School of Medicine, Mie, Japan
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