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Marinakis NM, Svingou M, Papadimas GK, Papadopoulos C, Chroni E, Pons R, Pavlou E, Sarmas I, Kosma K, Apostolou P, Sofocleous C, Traeger-Synodinos J, Kekou K. Myotonia congenita in a Greek cohort: Genotype spectrum and impact of the CLCN1:c.501C > G variant as a genetic modifier. Muscle Nerve 2024. [PMID: 38855810 DOI: 10.1002/mus.28180] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Revised: 05/18/2024] [Accepted: 05/24/2024] [Indexed: 06/11/2024]
Abstract
INTRODUCTION/AIMS Myotonia congenita (MC) is the most common hereditary channelopathy in humans. Characterized by muscle stiffness, MC may be transmitted as either an autosomal dominant (Thomsen) or a recessive (Becker) disorder. MC is caused by variants in the voltage-gated chloride channel 1 (CLCN1) gene, important for the normal repolarization of the muscle action potential. More than 250 disease-causing variants in the CLCN1 gene have been reported. This study provides an MC genotype-phenotype spectrum in a large cohort of Greek patients and focuses on novel variants and disease epidemiology, including additional insights for the variant CLCN1:c.501C > G. METHODS Sanger sequencing for the entire coding region of the CLCN1 gene was performed. Targeted segregation analysis of likely candidate variants in additional family members was performed. Variant classification was based on American College of Medical Genetics (ACMG) guidelines. RESULTS Sixty-one patients from 47 unrelated families were identified, consisting of 51 probands with Becker MC (84%) and 10 with Thomsen MC (16%). Among the different variants detected, 11 were novel and 16 were previously reported. The three most prevalent variants were c.501C > G, c.2680C > T, and c.1649C > G. Additionally, c.501C > G was detected in seven Becker cases in-cis with the c.1649C > G. DISCUSSION The large number of patients in whom a diagnosis was established allowed the characterization of genotype-phenotype correlations with respect to both previously reported and novel findings. For the c.501C > G (p.Phe167Leu) variant a likely nonpathogenic property is suggested, as it only seems to act as an aggravating modifying factor in cases in which a pathogenic variant triggers phenotypic expression.
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Affiliation(s)
- Nikolaos M Marinakis
- Laboratory of Medical Genetics, Medical School, St. Sophia's Children's Hospital, National and Kapodistrian University of Athens, Athens, Greece
- Research University Institute for the Study and Prevention of Genetic and Malignant Disease of Childhood, St. Sophia's Children's Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Maria Svingou
- Laboratory of Medical Genetics, Medical School, St. Sophia's Children's Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Giorgos-Konstantinos Papadimas
- Department of Neurology, Eginition Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece
| | - Constantinos Papadopoulos
- Department of Neurology, Eginition Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece
| | - Elisabeth Chroni
- Department of Neurology, School of Medicine, University of Patras, Rio-Patras, Greece
| | - Roser Pons
- First Department of Pediatrics, Medical School, St. Sophia's Children's Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Evangelos Pavlou
- Department of Pediatrics, School of Medicine, Aristotle University of Thessaloniki, University General Hospital AHEPA, Thessaloniki, Greece
| | - Ioannis Sarmas
- Department of Neurology, Faculty of Medicine, University of Ioannina, Ioannina, Greece
| | - Konstantina Kosma
- Laboratory of Medical Genetics, Medical School, St. Sophia's Children's Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Paraskevi Apostolou
- Human Molecular Genetics Laboratory, INRaSTES, National Center for Scientific Research "Demokritos", Athens, Greece
| | - Christalena Sofocleous
- Laboratory of Medical Genetics, Medical School, St. Sophia's Children's Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Joanne Traeger-Synodinos
- Laboratory of Medical Genetics, Medical School, St. Sophia's Children's Hospital, National and Kapodistrian University of Athens, Athens, Greece
| | - Kyriaki Kekou
- Laboratory of Medical Genetics, Medical School, St. Sophia's Children's Hospital, National and Kapodistrian University of Athens, Athens, Greece
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Vicino A, Brugnoni R, Maggi L. Diagnostics in skeletal muscle channelopathies. Expert Rev Mol Diagn 2023; 23:1175-1193. [PMID: 38009256 DOI: 10.1080/14737159.2023.2288258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Accepted: 11/22/2023] [Indexed: 11/28/2023]
Abstract
INTRODUCTION Skeletal muscle channelopathies (SMCs) are a heterogenous group of disorders, caused by mutations in skeletal ion channels leading to abnormal muscle excitability, resulting in either delayed muscle relaxation (myotonia) which characterizes non-dystrophic myotonias (NDMs), or membrane transient inactivation, causing episodic weakness, typical of periodic paralyses (PPs). AREAS COVERED SMCs include myotonia congenita, paramyotonia congenita, and sodium-channel myotonia among NDMs, and hyper-normokalemic, hypokalemic, or late-onset periodic paralyses among PPs. When suspecting an SMC, a structured diagnostic approach is required. Detailed personal and family history and clinical examination are essential, while neurophysiological tests should confirm myotonia and rule out alternative diagnosis. Moreover, specific electrodiagnostic studies are important to further define the phenotype of de novo cases and drive molecular analyses together with clinical data. Definite diagnosis is achieved through genetic testing, either with Sanger sequencing or multigene next-generation sequencing panel. In still unsolved patients, more advanced techniques, as exome-variant sequencing or whole-genome sequencing, may be considered in expert centers. EXPERT OPINION The diagnostic approach to SMC is still mainly based on clinical data; moreover, definite diagnosis is sometimes complicated by the difficulty to establish a proper genotype-phenotype correlation. Lastly, further studies are needed to allow the genetic characterization of unsolved patients.
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Affiliation(s)
- Alex Vicino
- Neurology IV Unit, Neuroimmunology and Neuromuscular Diseases, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
- Nerve-Muscle Unit, Neurology Service, Department of Clinical Neurosciences, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland
| | - Raffaella Brugnoni
- Neurology IV Unit, Neuroimmunology and Neuromuscular Diseases, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Lorenzo Maggi
- Neurology IV Unit, Neuroimmunology and Neuromuscular Diseases, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
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Musa NH, Thilakavathy K, Mohamad NA, Kennerson ML, Inche Mat LN, Loh WC, Abdul Rashid AM, Baharin J, Ibrahim A, Wan Sulaiman WA, Hoo FK, Basri H, Yusof Khan AHK. Case report: Incomplete penetrance of autosomal dominant myotonia congenita caused by a rare CLCN1 variant c.1667T>A (p.I556N) in a Malaysian family. Front Genet 2023; 13:972007. [PMID: 36659963 PMCID: PMC9842662 DOI: 10.3389/fgene.2022.972007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Accepted: 09/23/2022] [Indexed: 01/04/2023] Open
Abstract
Myotonia congenita (MC) is a rare neuromuscular disease caused by mutations within the CLCN1 gene encoding skeletal muscle chloride channels. MC is characterized by delayed muscle relaxation during contraction, resulting in muscle stiffness. There is a lack of MC case reports and data on the prevalence among Malaysians. We report a clinical case of a 50-year-old woman presents with muscle stiffness and cramp episodes that started in early childhood. She had difficulty initiating muscle movement and presented with transient muscle weakness after rest, which usually improved after repeated contraction (warm-up phenomenon). She was diagnosed with MC after myotonic discharge on electromyography (EMG). Her brother had similar symptoms; however, no additional family members showed MC symptoms. Serum creatine kinase levels were elevated in both the proband and her brother with 447 U/L and 228 U/L recorded, respectively. Genetic analysis by whole-exome sequencing (WES) revealed a previously reported pathogenic CLCN1 gene variant c.1667T>A (p.I556N). Genetic screening of all family members revealed that the same variant was observed in the children of both the proband and her brother; however, the children did not present with either clinical or electrophysiological MC symptoms. The multiplex ligation-dependent probe amplification (MLPA) analysis conducted identified neither exon deletion nor duplication in CLCN1. In conclusion, this report describes the first case of MC in Malaysia in which incomplete penetrance observed in this family is caused by a known pathogenic CLCN1 variant.
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Affiliation(s)
- Nurul Huda Musa
- Department of Biomedical Science, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia,Centre of Foundation Studies, Universiti Teknologi MARA, Cawangan Selangor, Kampus Dengkil, Dengkil, Selangor, Malaysia
| | - Karuppiah Thilakavathy
- Department of Biomedical Science, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia,Genetics and Regenerative Research Group, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia,*Correspondence: Abdul Hanif Khan Yusof Khan, ; Karuppiah Thilakavathy,
| | - Nur Afiqah Mohamad
- Department of Neurology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia,Center for Foundation Studies, Foundation in Science, Lincoln University College, Petaling Jaya, Malaysia
| | - Marina L. Kennerson
- Northcott Neuroscience Laboratory, ANZAC Research Institute, Sydney Local Health District, Faculty of Medicine and Health, University of Sydney, Sydney, NSW, Australia,Molecular Medicine Laboratory, Concord Hospital, Concord, NSW, Australia
| | - Liyana Najwa Inche Mat
- Department of Neurology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia
| | - Wei Chao Loh
- Department of Neurology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia
| | - Anna Misyail Abdul Rashid
- Department of Neurology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia
| | - Janudin Baharin
- Department of Neurology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia
| | - Azliza Ibrahim
- Department of Neurology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia
| | - Wan Aliaa Wan Sulaiman
- Department of Neurology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia
| | - Fan Kee Hoo
- Department of Neurology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia
| | - Hamidon Basri
- Department of Neurology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia
| | - Abdul Hanif Khan Yusof Khan
- Department of Neurology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Malaysia,*Correspondence: Abdul Hanif Khan Yusof Khan, ; Karuppiah Thilakavathy,
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Suetterlin K, Matthews E, Sud R, McCall S, Fialho D, Burge J, Jayaseelan D, Haworth A, Sweeney MG, Kullmann DM, Schorge S, Hanna MG, Männikkö R. Translating genetic and functional data into clinical practice: a series of 223 families with myotonia. Brain 2022; 145:607-620. [PMID: 34529042 PMCID: PMC9014745 DOI: 10.1093/brain/awab344] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Revised: 07/13/2021] [Accepted: 08/05/2021] [Indexed: 11/14/2022] Open
Abstract
High-throughput DNA sequencing is increasingly employed to diagnose single gene neurological and neuromuscular disorders. Large volumes of data present new challenges in data interpretation and its useful translation into clinical and genetic counselling for families. Even when a plausible gene is identified with confidence, interpretation of the clinical significance and inheritance pattern of variants can be challenging. We report our approach to evaluating variants in the skeletal muscle chloride channel ClC-1 identified in 223 probands with myotonia congenita as an example of these challenges. Sequencing of CLCN1, the gene that encodes CLC-1, is central to the diagnosis of myotonia congenita. However, interpreting the pathogenicity and inheritance pattern of novel variants is notoriously difficult as both dominant and recessive mutations are reported throughout the channel sequence, ClC-1 structure-function is poorly understood and significant intra- and interfamilial variability in phenotype is reported. Heterologous expression systems to study functional consequences of CIC-1 variants are widely reported to aid the assessment of pathogenicity and inheritance pattern. However, heterogeneity of reported analyses does not allow for the systematic correlation of available functional and genetic data. We report the systematic evaluation of 95 CIC-1 variants in 223 probands, the largest reported patient cohort, in which we apply standardized functional analyses and correlate this with clinical assessment and inheritance pattern. Such correlation is important to determine whether functional data improves the accuracy of variant interpretation and likely mode of inheritance. Our data provide an evidence-based approach that functional characterization of ClC-1 variants improves clinical interpretation of their pathogenicity and inheritance pattern, and serve as reference for 34 previously unreported and 28 previously uncharacterized CLCN1 variants. In addition, we identify novel pathogenic mechanisms and find that variants that alter voltage dependence of activation cluster in the first half of the transmembrane domains and variants that yield no currents cluster in the second half of the transmembrane domain. None of the variants in the intracellular domains were associated with dominant functional features or dominant inheritance pattern of myotonia congenita. Our data help provide an initial estimate of the anticipated inheritance pattern based on the location of a novel variant and shows that systematic functional characterization can significantly refine the assessment of risk of an associated inheritance pattern and consequently the clinical and genetic counselling.
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Affiliation(s)
- Karen Suetterlin
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
- AGE Research Group, NIHR Newcastle Biomedical Research Centre, Newcastle-upon-Tyne Hospitals NHS Foundation Trust and Newcastle University, Newcastle-upon-Tyne, UK
| | - Emma Matthews
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
- Atkinson Morley Neuromuscular Centre, Department of Neurology, St Georges University Hospitals NHS Foundation Trust, London, UK
| | - Richa Sud
- Neurogenetics Unit, UCL Queen Square Institute of Neurology, London, UK
| | - Samuel McCall
- Neurogenetics Unit, UCL Queen Square Institute of Neurology, London, UK
| | - Doreen Fialho
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
- Department of Clinical Neurophysiology, King’s College Hospital, London, UK
| | - James Burge
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
- Department of Clinical Neurophysiology, King’s College Hospital, London, UK
| | - Dipa Jayaseelan
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
| | - Andrea Haworth
- Neurogenetics Unit, UCL Queen Square Institute of Neurology, London, UK
| | - Mary G Sweeney
- Neurogenetics Unit, UCL Queen Square Institute of Neurology, London, UK
| | - Dimitri M Kullmann
- Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, London, UK
| | - Stephanie Schorge
- Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, London, UK
- Department of Pharmacology, UCL School of Pharmacy, London, UK
| | - Michael G Hanna
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
| | - Roope Männikkö
- MRC International Centre for Genomic Medicine in Neuromuscular Diseases, Department of Neuromuscular Disease, UCL Queen Square Institute of Neurology, London, UK
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5
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Wang Q, Zhao Z, Shen H, Bing Q, Li N, Hu J. The Clinical, Myopathological, and Genetic Analysis of 20 Patients With Non-dystrophic Myotonia. Front Neurol 2022; 13:830707. [PMID: 35350395 PMCID: PMC8957821 DOI: 10.3389/fneur.2022.830707] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 01/25/2022] [Indexed: 11/29/2022] Open
Abstract
Introduction Non-dystrophic myotonias (NDMs) are skeletal muscle ion channelopathies caused by CLCN1 or SCN4A 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 CLCN1 variants were found in 17 MC patients, among which c.795T>G (p.D265E) was a new variant, and two SCN4A 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.
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Affiliation(s)
- Quanquan Wang
- Department of Neuromuscular Disorders, The Third Hospital of Hebei Medical University, Shijiazhuang, China.,Department of Neurology, Qilu Hospital of Shandong University, Qingdao, China
| | - Zhe Zhao
- Department of Neuromuscular Disorders, The Third Hospital of Hebei Medical University, Shijiazhuang, China
| | - Hongrui Shen
- Department of Neuromuscular Disorders, The Third Hospital of Hebei Medical University, Shijiazhuang, China
| | - Qi Bing
- Department of Neuromuscular Disorders, The Third Hospital of Hebei Medical University, Shijiazhuang, China
| | - Nan Li
- Department of Neuromuscular Disorders, The Third Hospital of Hebei Medical University, Shijiazhuang, China
| | - Jing Hu
- Department of Neuromuscular Disorders, The Third Hospital of Hebei Medical University, Shijiazhuang, China
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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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Rios JJ, Denton K, Yu H, Manickam K, Garner S, Russell J, Ludwig S, Rosenfeld JA, Liu P, Munch J, Sucato DJ, Beutler B, Wise CA. Saturation mutagenesis defines novel mouse models of severe spine deformity. Dis Model Mech 2021; 14:269194. [PMID: 34142127 PMCID: PMC8246263 DOI: 10.1242/dmm.048901] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Accepted: 05/19/2021] [Indexed: 12/12/2022] Open
Abstract
Embryonic formation and patterning of the vertebrate spinal column requires coordination of many molecular cues. After birth, the integrity of the spine is impacted by developmental abnormalities of the skeletal, muscular and nervous systems, which may result in deformities, such as kyphosis and scoliosis. We sought to identify novel genetic mouse models of severe spine deformity by implementing in vivo skeletal radiography as part of a high-throughput saturation mutagenesis screen. We report selected examples of genetic mouse models following radiographic screening of 54,497 mice from 1275 pedigrees. An estimated 30.44% of autosomal genes harbored predicted damaging alleles examined twice or more in the homozygous state. Of the 1275 pedigrees screened, 7.4% presented with severe spine deformity developing in multiple mice, and of these, meiotic mapping implicated N-ethyl-N-nitrosourea alleles in 21% of pedigrees. Our study provides proof of concept that saturation mutagenesis is capable of discovering novel mouse models of human disease, including conditions with skeletal, neural and neuromuscular pathologies. Furthermore, we report a mouse model of skeletal disease, including severe spine deformity, caused by recessive mutation in Scube3. By integrating results with a human clinical exome database, we identified a patient with undiagnosed skeletal disease who harbored recessive mutations in SCUBE3, and we demonstrated that disease-associated mutations are associated with reduced transactivation of Smad signaling in vitro. All radiographic results and mouse models are made publicly available through the Mutagenetix online database with the goal of advancing understanding of spine development and discovering novel mouse models of human disease. Summary: We report selected mouse models of spine deformity following mutagenesis across 30% of autosomal genes, results of which are made publicly available to advance understanding of spine development and disease.
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Affiliation(s)
- Jonathan J Rios
- Center for Pediatric Bone Biology and Translational Research, Scottish Rite for Children, Dallas, TX 75219, USA.,Department of Pediatrics, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.,McDermott Center for Human Growth and Development, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.,Department of Orthopaedic Surgery, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.,Simmons Comprehensive Cancer Center, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Kristin Denton
- Center for Pediatric Bone Biology and Translational Research, Scottish Rite for Children, Dallas, TX 75219, USA
| | - Hao Yu
- Center for Pediatric Bone Biology and Translational Research, Scottish Rite for Children, Dallas, TX 75219, USA
| | - Kandamurugu Manickam
- Division of Genetic and Genomic Medicine, Nationwide Children's Hospital, Columbus, OH 43205, USA
| | - Shannon Garner
- Division of Genetic and Genomic Medicine, Nationwide Children's Hospital, Columbus, OH 43205, USA
| | - Jamie Russell
- Center for the Genetics of Host Defense, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Sara Ludwig
- Center for the Genetics of Host Defense, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Jill A Rosenfeld
- Department of Molecular & Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.,Baylor Genetics, Houston, TX 77021, USA
| | - Pengfei Liu
- Department of Molecular & Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.,Baylor Genetics, Houston, TX 77021, USA
| | - Jake Munch
- Center for Pediatric Bone Biology and Translational Research, Scottish Rite for Children, Dallas, TX 75219, USA
| | - Daniel J Sucato
- Department of Orthopaedics, Scottish Rite for Children, Dallas, TX 75219, USA
| | - Bruce Beutler
- Center for the Genetics of Host Defense, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Carol A Wise
- Center for Pediatric Bone Biology and Translational Research, Scottish Rite for Children, Dallas, TX 75219, USA.,Department of Pediatrics, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.,McDermott Center for Human Growth and Development, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.,Department of Orthopaedic Surgery, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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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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Wei Z, Huaxing M, Xiaomei W, Juan W, Xueli C, Jing Z, Junhong G. Identification of two novel compound heterozygous CLCN1 mutations associated with autosomal recessive myotonia congenita. Neurol Res 2019; 41:1069-1074. [PMID: 31566103 DOI: 10.1080/01616412.2019.1672392] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Objectives: Myotonia congenita (MC) is a rare genetic muscular disorder caused by CLCN1 mutations, which codes for skeletal muscle chloride channel CLC1. MC is characterized by impaired muscle relaxation after contraction resulting in muscle stiffness. This study aimed to identify the genetic etiology of a Chinese family affected with recessive MC. Methods: Whole exome sequencing was performed to identify the disease-associated variants. The candidate causal genes discovered by WES were then confirmed by Sanger sequencing and co-segregation analyses were also conducted. Results: Two novel compound heterozygous mutations in CLCN1 gene, p.D94Y (paternal allele) and p.Y206* (maternal allele), were successfully identified as the pathogenic mutations by whole-exome sequencing (WES). The mutations were confirmed with Sanger sequencing in the family members and cosegregated with the MC phenotype. The two mutations have not been reported in the HGMD, dbSNP, 1000 Genomes project, ClinVar database, ExAC, and gnomAD previously. Mutation p.D94Y is predicted to be deleterious by using in silico tools and p.Y206* is a nonsense mutation, causing protein synthesis termination. Conclusions: Molecular genetics analysis offers an accurate method for diagnosing MC. Our results expand the mutational spectrum of recessive MC.
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Affiliation(s)
- Zhang Wei
- Department of Neurology, First Hospital, Shanxi Medical University , Taiyuan , China
| | - Meng Huaxing
- Department of Neurology, First Hospital, Shanxi Medical University , Taiyuan , China
| | - Wang Xiaomei
- Department of Geological Engineering, Shanxi Institute of Enegy , Taiyuan , China
| | - Wang Juan
- Department of Neurology, First Hospital, Shanxi Medical University , Taiyuan , China
| | - Chang Xueli
- Department of Neurology, First Hospital, Shanxi Medical University , Taiyuan , China
| | - Zhang Jing
- Department of Neurology, First Hospital, Shanxi Medical University , Taiyuan , China
| | - Guo Junhong
- Department of Neurology, First Hospital, Shanxi Medical University , Taiyuan , China
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10
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Becker's myotonia: novel mutations and clinical variability in patients born to consanguineous parents. Acta Neurol Belg 2018; 118:567-572. [PMID: 29480456 DOI: 10.1007/s13760-018-0893-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Accepted: 02/05/2018] [Indexed: 01/30/2023]
Abstract
Myotonia congenita is an inherited muscle disease present from childhood that is characterized by impaired muscle relaxation after contraction resulting in muscle stiffness; moreover, skeletal striated muscle groups may be involved. Myotonia congenita occurs due to chloride (Cl) channel mutations that reduce the stabilizing Cl conductance, and it is caused by mutations in the CLCN1 gene. This paper describes four patients from two different healthy consanguineous Turkish families with muscle stiffness and easy fatigability. A genetic investigation was performed. Mutation analyses showed a homozygous p.Tyr150* (c.450C > A) mutation in patients 1, 2 and 3 and a homozygous p.Leu159Cysfs*11 (c.475delC) mutation in patient 4 in the CLCN1 gene. These mutations have never been reported before and in silico analyses showed that the mutations were disease causing. They may be predicted to cause nonsense-mediated mRNA decay. Our data expand the spectrum of CLCN1 mutations and provide insights for genotype-phenotype correlations of myotonia congenita.
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11
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Park E, MacKinnon R. Structure of the CLC-1 chloride channel from Homo sapiens. eLife 2018; 7:36629. [PMID: 29809153 PMCID: PMC6019066 DOI: 10.7554/elife.36629] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Accepted: 05/15/2018] [Indexed: 11/18/2022] Open
Abstract
CLC channels mediate passive Cl− conduction, while CLC transporters mediate active Cl− transport coupled to H+ transport in the opposite direction. The distinction between CLC-0/1/2 channels and CLC transporters seems undetectable by amino acid sequence. To understand why they are different functionally we determined the structure of the human CLC-1 channel. Its ‘glutamate gate’ residue, known to mediate proton transfer in CLC transporters, adopts a location in the structure that appears to preclude it from its transport function. Furthermore, smaller side chains produce a wider pore near the intracellular surface, potentially reducing a kinetic barrier for Cl− conduction. When the corresponding residues are mutated in a transporter, it is converted to a channel. Finally, Cl− at key sites in the pore appear to interact with reduced affinity compared to transporters. Thus, subtle differences in glutamate gate conformation, internal pore diameter and Cl− affinity distinguish CLC channels and transporters. Channels and transporters are two classes of proteins that transport molecules and ions – collectively referred to as “substrates” – across cell membranes. Channels form a pore in the membrane and the substrates diffuse through passively. Transporters, on the other hand, actively pump substrates across a membrane, consuming energy in the process. Thus, channels and transporters work in distinct ways. Channels and transporters most often have unrelated structures, but there are rare examples of both existing within the same family of structurally similar proteins. CLC proteins, for example, include both chloride ion channels and transporters that pump chloride ions in one direction by harnessing the energy from hydrogen ions flowing in the other direction. It remains unclear why some CLC proteins work as channels while others are transporters, especially since the two seem indistinguishable on the basis of the order of their amino acids – the building blocks of all proteins. The conservation of the amino acid sequences implies they are structurally very similar. How then can different members perform such energetically distinct processes? Park and MacKinnon now show that the answer to this question serves as a reminder of how subtle nature can be. Indeed, while the structure of a human CLC channel (called CLC-1) is indeed similar to those of CLC transporters, one amino acid adopts a unique shape that explains why the protein cannot act as a transporter. This specific amino acid, a glutamate, is central to the exchange of chloride and hydrogen ions in CLC transporters. Park and MacKinnon show that its conformation in the CLC-1 channel stops this exchange, while leaving the pore open for the passive transport of chloride ions. Also, two other amino acids along the ion diffusion pathway in the CLC channel are smaller than their counterparts in CLC transporters, and so allow chloride ions to diffuse through more quickly. Lastly, Park and MacKinnon also note that channels do not require a wide pore: instead ions can still flow rapidly through a narrow pore if the chemical environment inside permits it. CLC proteins perform a number of important roles in humans, and mutations in CLC-encoding genes underlie numerous heritable diseases. It remains too early to know how this mechanistic study may or may not impact treatments, yet the findings will likely interest scientists working on ion conduction mechanisms and the evolution of molecular function.
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Affiliation(s)
- Eunyong Park
- Laboratory of Molecular Neurobiology and Biophysics, Howard Hughes Medical Institute, The Rockefeller University, New York, United States
| | - Roderick MacKinnon
- Laboratory of Molecular Neurobiology and Biophysics, Howard Hughes Medical Institute, The Rockefeller University, New York, United States
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12
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Symonds JD, Zuberi SM. Genetics update: Monogenetics, polygene disorders and the quest for modifying genes. Neuropharmacology 2017; 132:3-19. [PMID: 29037745 DOI: 10.1016/j.neuropharm.2017.10.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Revised: 10/09/2017] [Accepted: 10/11/2017] [Indexed: 12/19/2022]
Abstract
The genetic channelopathies are a broad collection of diseases. Many ion channel genes demonstrate wide phenotypic pleiotropy, but nonetheless concerted efforts have been made to characterise genotype-phenotype relationships. In this review we give an overview of the factors that influence genotype-phenotype relationships across this group of diseases as a whole, using specific individual channelopathies as examples. We suggest reasons for the limitations observed in these relationships. We discuss the role of ion channel variation in polygenic disease and highlight research that has contributed to unravelling the complex aetiological nature of these conditions. We focus specifically on the quest for modifying genes in inherited channelopathies, using the voltage-gated sodium channels as an example. Epilepsy related to genetic channelopathy is one area in which precision medicine is showing promise. We will discuss the successes and limitations of precision medicine in these conditions. This article is part of the Special Issue entitled 'Channelopathies.'
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Affiliation(s)
- Joseph D Symonds
- The Paediatric Neurosciences Research Group, Royal Hospital for Children, Queen Elizabeth University Hospitals, Glasgow, UK; School of Medicine, University of Glasgow, Glasgow, UK
| | - Sameer M Zuberi
- The Paediatric Neurosciences Research Group, Royal Hospital for Children, Queen Elizabeth University Hospitals, Glasgow, UK; School of Medicine, University of Glasgow, Glasgow, UK.
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13
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Chin HJ, Kim CH, Ha K, Shin JH, Kim DS, So I. Electrophysiological characteristics of R47W and A298T mutations in CLC-1 of myotonia congenita patients and evaluation of clinical features. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2017; 21:439-447. [PMID: 28706458 PMCID: PMC5507783 DOI: 10.4196/kjpp.2017.21.4.439] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/13/2017] [Revised: 04/18/2017] [Accepted: 04/19/2017] [Indexed: 01/09/2023]
Abstract
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 CLCN1 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.
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Affiliation(s)
- Hyung Jin Chin
- Department of Physiology, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Chan Hyeong Kim
- Department of Physiology, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Kotdaji Ha
- Department of Physiology, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Jin Hong Shin
- Department of Neurology, Research Institute for Convergence of Biomedical Research and Technology, Pusan University Yangsan Hospital, Yangsan 50612, Korea
| | - Dae-Seong Kim
- Department of Neurology, Research Institute for Convergence of Biomedical Research and Technology, Pusan University Yangsan Hospital, Yangsan 50612, Korea
| | - Insuk So
- Department of Physiology, Seoul National University College of Medicine, Seoul 03080, Korea
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14
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Structure of a CLC chloride ion channel by cryo-electron microscopy. Nature 2016; 541:500-505. [PMID: 28002411 PMCID: PMC5576512 DOI: 10.1038/nature20812] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Accepted: 11/18/2016] [Indexed: 12/18/2022]
Abstract
CLC proteins transport chloride (Cl-) ions across cellular membranes to regulate muscle excitability, electrolyte movement across epithelia, and acidification of intracellular organelles. Some CLC proteins are channels that conduct Cl- ions passively, whereas others are secondary active transporters that exchange two Cl- ions for one H+. The structural basis underlying these distinctive transport mechanisms is puzzling because CLC channels and transporters are expected to share the same architecture on the basis of sequence homology. Here we determined the structure of a bovine CLC channel (CLC-K) using cryo-electron microscopy. A conserved loop in the Cl- transport pathway shows a structure markedly different from that of CLC transporters. Consequently, the cytosolic constriction for Cl- passage is widened in CLC-K such that the kinetic barrier previously postulated for Cl-/H+ transporter function would be reduced. Thus, reduction of a kinetic barrier in CLC channels enables fast flow of Cl- down its electrochemical gradient.
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15
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Miryounesi M, Ghafouri-Fard S, Fardaei M. A Novel Missense Mutation in CLCN1 Gene in a Family with Autosomal Recessive Congenital Myotonia. IRANIAN JOURNAL OF MEDICAL SCIENCES 2016; 41:456-8. [PMID: 27582597 PMCID: PMC4967492] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Congenital recessive myotonia is a rare genetic disorder caused by mutations in CLCN1, which codes for the main skeletal muscle chloride channel ClC-1. More than 120 mutations have been found in this gene. The main feature of this disorder is muscle membrane hyperexcitability. Here, we report a 59-year male patient suffering from congenital myotonia. He had transient generalized myotonia, which started in early childhood. We analyzed CLCN1 sequence in this patient and other members of his family. We found a new missense mutation in CLCN1 gene (c.1886T>C, p.Leu629Pro). Co-segregation of this mutation with the disease was demonstrated by direct sequencing of the fragment in affected as well as unaffected members of this family. In addition, in silico analyses predicted that this nucleotide change would impair the protein function. Thus, this new nucleotide variation can be used for prenatal diagnosis in this family.
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Affiliation(s)
- Mohammad Miryounesi
- Genomic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Soudeh Ghafouri-Fard
- Department of Medical Genetics, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Majid Fardaei
- Department of Medical Genetics, Shiraz University of Medical Sciences, Shiraz, Iran,Correspondence: Majid Fardaei, PhD; Department of Medical Genetics, Fakhrabad Street, Shiraz, Iran Tel/Fax: +98 71 32349610
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16
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Tincheva S, Georgieva B, Todorov T, Savov A, Tsaneva S, Litvinenko I, Mitev V, Todorova A. Myotonia congenita type Becker in Bulgaria: First genetically proven cases and mutation screening of two presumable endemic regions. Neuromuscul Disord 2016; 26:675-680. [PMID: 27614575 DOI: 10.1016/j.nmd.2016.08.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2016] [Revised: 08/03/2016] [Accepted: 08/04/2016] [Indexed: 11/30/2022]
Abstract
Myotonia congenita type Becker is an autosomal recessive nondystrophic skeletal muscle disorder, caused by mutations in the CLCN1 gene. The disease is characterized by muscle stiffness and an inability of the muscle to relax after voluntary contraction. Here we report the results from molecular genetic testing of 6 families, referred for sequencing of the CLCN1 gene. The disease causing mutations were detected in 5 of the cases, representing diverse type of nucleotide changes: nonsense (p.Arg894*), splice-site (c.1471+1G>A), missense (p.Val273Met; p.Tyr524Cys). Two additional changes were detected in an asymptomatic individual (c.2284+5C>T and p.Phe167Leu). Two of the detected mutations are interesting from population point of view. The novel missense mutation p.Tyr524Cys was found in a large Bulgarian family with affected individuals in both vertical and horizontal pedigree directions, all of them carrying the mutation in homozygous form. They populate a village located in the northwest part of the country. Endogamous marriages are very unusual for the Bulgarian population, supposing a high carrier frequency in this subpopulation. Screening of 154 residents of the corresponding region showed a significant carrier frequency for the p.Tyr524Cys mutation of about 0.65% (1/154). The second interesting region in the context of Myotonia congenita type Becker is the southwest part of the country, where we found a large family of Bulgarian Turkish origin. The disease causing missense mutation p.Val273Met was again present in homozygous state. Surprisingly, the genetic testing of newborns from southwest Bulgaria showed an even higher carrier status of about 2.6% (3/116), disproving our initial hypothesis of endogamous marriages (traditionally common in this subpopulation) being the cause of the disease in these patients. However the probability of consanguineous marriages being the cause for further exaggeration of the anyway very high carrier frequency cannot be excluded.
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Affiliation(s)
- Savina Tincheva
- Department of Medical Chemistry and Biochemistry, Medical University Sofia, 2 Zdrave Str., Sofia, Bulgaria; Genetic Medico-Diagnostic Laboratory "Genica", 90 Tsar Asen Str., Sofia, Bulgaria.
| | - Bilyana Georgieva
- Department of Medical Chemistry and Biochemistry, Medical University Sofia, 2 Zdrave Str., Sofia, Bulgaria
| | - Tihomir Todorov
- Genetic Medico-Diagnostic Laboratory "Genica", 90 Tsar Asen Str., Sofia, Bulgaria
| | - Alexey Savov
- Department of Obstetrics and Gynecology, Faculty of Medicine, National Genetic Laboratory, Medical University Sofia, 2 Zdrave Str., Sofia, Bulgaria
| | - Slavena Tsaneva
- Genetic Medico-Diagnostic Laboratory "Genica", 90 Tsar Asen Str., Sofia, Bulgaria
| | - Ivan Litvinenko
- Department of Neurology, University Pediatric Hospital, Medical University, 11 Acad. Ivan Evstatiev Geshov Str., Sofia, Bulgaria
| | - Vanyo Mitev
- Department of Medical Chemistry and Biochemistry, Medical University Sofia, 2 Zdrave Str., Sofia, Bulgaria
| | - Albena Todorova
- Department of Medical Chemistry and Biochemistry, Medical University Sofia, 2 Zdrave Str., Sofia, Bulgaria; Genetic Medico-Diagnostic Laboratory "Genica", 90 Tsar Asen Str., Sofia, Bulgaria
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17
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Abstract
Myotonia (muscle stiffness) is a symptom of several inherited diseases in humans and also in animals. It is due to muscle membrane hyperexcitability, which, in turn, can be caused by mutations in plasma membrane ion channels. The skeletal muscle chloride channel CLC-1 provides the major part of muscle membrane conductance and is important for keeping this membrane close to its resting voltage. Mutations in CLC-1 can cause both recessive (Becker) and dominant (Thomsen) forms of myotonia. Some of these mutations have been introduced into the functional cDNA and analyzed in the Xenopus oocyte expression system. From these studies, it was concluded that CLC-1 functions as a homooligomer with probably four subunits. Dominant mutant subunits are assumed to associate with wild-type ones, leading to their inactivation. The principle disease-causing mechanism of dominant mutations is a drastic alteration in the voltage dependence of CLC-1 gating. Some mutations in CLC-1 can be inherited either recessively or dominantly, probably depending on the genetic background. These studies point to the important role of CLC-1 in muscle physiology and provide interesting insights into the structure and function of this gene family of voltage-gated chloride channels. NEUROSCIENTIST 2:225-232, 1996
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Affiliation(s)
- Klaus Steinmeyer
- Institute for Molecular Neuropathobiology Center for
Molecular Neurobiology (ZMNH) Hamburg University Hamburg
| | - Thomas J. Jentsch
- Institute for Molecular Neuropathobiology Center for
Molecular Neurobiology (ZMNH) Hamburg University Hamburg
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18
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Abstract
Familial disorders of skeletal muscle excitability were initially described early in the last century and are now known to be caused by mutations of voltage-gated ion channels. The clinical manifestations are often striking, with an inability to relax after voluntary contraction (myotonia) or transient attacks of severe weakness (periodic paralysis). An essential feature of these disorders is fluctuation of symptoms that are strongly impacted by environmental triggers such as exercise, temperature, or serum K(+) levels. These phenomena have intrigued physiologists for decades, and in the past 25 years the molecular lesions underlying these disorders have been identified and mechanistic studies are providing insights for therapeutic strategies of disease modification. These familial disorders of muscle fiber excitability are "channelopathies" caused by mutations of a chloride channel (ClC-1), sodium channel (NaV1.4), calcium channel (CaV1.1), and several potassium channels (Kir2.1, Kir2.6, and Kir3.4). This review provides a synthesis of the mechanistic connections between functional defects of mutant ion channels, their impact on muscle excitability, how these changes cause clinical phenotypes, and approaches toward therapeutics.
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Affiliation(s)
- Stephen C Cannon
- Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, CA, USA
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19
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Vindas-Smith R, Fiore M, Vásquez M, Cuenca P, del Valle G, Lagostena L, Gaitán-Peñas H, Estevez R, Pusch M, Morales F. Identification and Functional Characterization ofCLCN1Mutations Found in Nondystrophic Myotonia Patients. Hum Mutat 2015; 37:74-83. [DOI: 10.1002/humu.22916] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Accepted: 09/25/2015] [Indexed: 10/22/2022]
Affiliation(s)
- Rebeca Vindas-Smith
- Instituto de Investigaciones en Salud (INISA); Universidad de Costa Rica; San José Costa Rica
| | - Michele Fiore
- Istituto di Biofisica; CNR; Via De Marini 6 Genova Italy
| | - Melissa Vásquez
- Instituto de Investigaciones en Salud (INISA); Universidad de Costa Rica; San José Costa Rica
- Centro de Investigación en Neurociencias (CIN); Universidad de Costa Rica; San José Costa Rica
| | - Patricia Cuenca
- Instituto de Investigaciones en Salud (INISA); Universidad de Costa Rica; San José Costa Rica
- Centro de Investigación en Neurociencias (CIN); Universidad de Costa Rica; San José Costa Rica
- Escuela de Medicina; Universidad de Costa Rica; Curridabat San José Costa Rica
| | - Gerardo del Valle
- Laboratorio de Neurofisiología (Neurolab); Curridabat San José Costa Rica
| | | | - Héctor Gaitán-Peñas
- Departament de Ciències Fisiològiques II; Unitat de Fisiologia; Universitat de Barcelona; Carrer Feixa Llarga s/n, L'Hospitalet de Llobregat Barcelona Spain
- U-750, Centro de Investigación en red de enfermedades raras (CIBERER); ISCIII; Barcelona Spain
| | - Raúl Estevez
- Departament de Ciències Fisiològiques II; Unitat de Fisiologia; Universitat de Barcelona; Carrer Feixa Llarga s/n, L'Hospitalet de Llobregat Barcelona Spain
- U-750, Centro de Investigación en red de enfermedades raras (CIBERER); ISCIII; Barcelona Spain
| | - Michael Pusch
- Istituto di Biofisica; CNR; Via De Marini 6 Genova Italy
| | - Fernando Morales
- Instituto de Investigaciones en Salud (INISA); Universidad de Costa Rica; San José Costa Rica
- Centro de Investigación en Neurociencias (CIN); Universidad de Costa Rica; San José Costa Rica
- Escuela de Medicina; Universidad de Costa Rica; Curridabat San José Costa Rica
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20
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Impaired surface membrane insertion of homo- and heterodimeric human muscle chloride channels carrying amino-terminal myotonia-causing mutations. Sci Rep 2015; 5:15382. [PMID: 26502825 PMCID: PMC4621517 DOI: 10.1038/srep15382] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Accepted: 09/23/2015] [Indexed: 12/03/2022] Open
Abstract
Mutations in the muscle chloride channel gene (CLCN1) cause myotonia congenita, an inherited condition characterized by muscle stiffness upon sudden forceful movement. We here studied the functional consequences of four disease-causing mutations that predict amino acid substitutions Q43R, S70L, Y137D and Q160H. Wild-type (WT) and mutant hClC-1 channels were heterologously expressed as YFP or CFP fusion protein in HEK293T cells and analyzed by whole-cell patch clamp and fluorescence recordings on individual cells. Q43R, Y137D and Q160H, but not S70L reduced macroscopic current amplitudes, but left channel gating and unitary current amplitudes unaffected. We developed a novel assay combining electrophysiological and fluorescence measurements at the single-cell level in order to measure the probability of ion channel surface membrane insertion. With the exception of S70L, all tested mutations significantly reduced the relative number of homodimeric hClC-1 channels in the surface membrane. The strongest effect was seen for Q43R that reduced the surface insertion probability by more than 99% in Q43R homodimeric channels and by 92 ± 3% in heterodimeric WT/Q43R channels compared to homodimeric WT channels. The new method offers a sensitive approach to investigate mutations that were reported to cause channelopathies, but display only minor changes in ion channel function.
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21
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Liu XL, Huang XJ, Shen JY, Zhou HY, Luan XH, Wang T, Chen SD, Wang Y, Tang HD, Cao L. Myotonia congenita: novel mutations in CLCN1 gene. Channels (Austin) 2015; 9:292-8. [PMID: 26260254 DOI: 10.1080/19336950.2015.1075676] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Myotonia congenita belongs to the group of non-dystrophic myotonia caused by mutations of CLCN1gene, which encodes human skeletal muscle chloride channel 1. It can be inherited either in autosomal dominant (Thomsen disease) or recessive (Becker disease) forms. Here we have sequenced all 23 exons and exon-intron boundaries of the CLCN1 gene, in a panel of 5 unrelated Chinese patients with myotonia congenita (2 with dominant and 3 with recessive form). In addition, detailed clinical analysis was performed in these patients to summarize their clinical characteristics in relation to their genotypes. Mutational analyses revealed 7 different point mutations. Of these, we have found 3 novel mutations including 2 missense (R47W, V229M), one splicing (IVS19+2T>C), and 4 known mutations (Y261C,G523D, M560T, G859D). Our data expand the spectrum of CLCN1 mutations and provide insights for genotype-phenotype correlations of myotonia congenita in the Chinese population.
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Affiliation(s)
- Xiao-Li Liu
- a Department of Neurology ; Rui Jin Hospital and Rui Jin Hospital North, Shanghai Jiao Tong University School of Medicine ; Shanghai , China
| | - Xiao-Jun Huang
- a Department of Neurology ; Rui Jin Hospital and Rui Jin Hospital North, Shanghai Jiao Tong University School of Medicine ; Shanghai , China
| | - Jun-Yi Shen
- a Department of Neurology ; Rui Jin Hospital and Rui Jin Hospital North, Shanghai Jiao Tong University School of Medicine ; Shanghai , China
| | - Hai-Yan Zhou
- a Department of Neurology ; Rui Jin Hospital and Rui Jin Hospital North, Shanghai Jiao Tong University School of Medicine ; Shanghai , China
| | - Xing-Hua Luan
- a Department of Neurology ; Rui Jin Hospital and Rui Jin Hospital North, Shanghai Jiao Tong University School of Medicine ; Shanghai , China
| | - Tian Wang
- a Department of Neurology ; Rui Jin Hospital and Rui Jin Hospital North, Shanghai Jiao Tong University School of Medicine ; Shanghai , China
| | - Sheng-Di Chen
- a Department of Neurology ; Rui Jin Hospital and Rui Jin Hospital North, Shanghai Jiao Tong University School of Medicine ; Shanghai , China
| | - Ying Wang
- a Department of Neurology ; Rui Jin Hospital and Rui Jin Hospital North, Shanghai Jiao Tong University School of Medicine ; Shanghai , China
| | - Hui-Dong Tang
- a Department of Neurology ; Rui Jin Hospital and Rui Jin Hospital North, Shanghai Jiao Tong University School of Medicine ; Shanghai , China
| | - Li Cao
- a Department of Neurology ; Rui Jin Hospital and Rui Jin Hospital North, Shanghai Jiao Tong University School of Medicine ; Shanghai , China
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22
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Gandolfi B, Daniel RJ, O'Brien DP, Guo LT, Youngs MD, Leach SB, Jones BR, Shelton GD, Lyons LA. A novel mutation in CLCN1 associated with feline myotonia congenita. PLoS One 2014; 9:e109926. [PMID: 25356766 PMCID: PMC4214686 DOI: 10.1371/journal.pone.0109926] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Accepted: 09/05/2014] [Indexed: 12/30/2022] Open
Abstract
Myotonia congenita (MC) is a skeletal muscle channelopathy characterized by inability of the muscle to relax following voluntary contraction. Worldwide population prevalence in humans is 1∶100,000. Studies in mice, dogs, humans and goats confirmed myotonia associated with functional defects in chloride channels and mutations in a skeletal muscle chloride channel (CLCN1). CLCN1 encodes for the most abundant chloride channel in the skeletal muscle cell membrane. Five random bred cats from Winnipeg, Canada with MC were examined. All cats had a protruding tongue, limited range of jaw motion and drooling with prominent neck and proximal limb musculature. All cats had blepharospasm upon palpebral reflex testing and a short-strided gait. Electromyograms demonstrated myotonic discharges at a mean frequency of 300 Hz resembling the sound of a ‘swarm of bees’. Muscle histopathology showed hypertrophy of all fiber types. Direct sequencing of CLCN1 revealed a mutation disrupting a donor splice site downstream of exon 16 in only the affected cats. In vitro translation of the mutated protein predicted a premature truncation and partial lack of the highly conserved CBS1 (cystathionine β-synthase) domain critical for ion transport activity and one dimerization domain pivotal in channel formation. Genetic screening of the Winnipeg random bred population of the cats' origin identified carriers of the mutation. A genetic test for population screening is now available and carrier cats from the feral population can be identified.
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Affiliation(s)
- Barbara Gandolfi
- Department of Veterinary Medicine and Surgery, School of Veterinary Medicine, University of Missouri – Columbia, Columbia, Missouri, United States of America
- * E-mail:
| | - Rob J. Daniel
- Department of Veterinary Medicine and Surgery, School of Veterinary Medicine, University of Missouri – Columbia, Columbia, Missouri, United States of America
| | - Dennis P. O'Brien
- Department of Veterinary Medicine and Surgery, School of Veterinary Medicine, University of Missouri – Columbia, Columbia, Missouri, United States of America
| | - Ling T. Guo
- Department of Pathology, University of California San Diego, La Jolla, California, United States of America
| | | | - Stacey B. Leach
- Department of Veterinary Medicine and Surgery, School of Veterinary Medicine, University of Missouri – Columbia, Columbia, Missouri, United States of America
| | - Boyd R. Jones
- Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand
| | - G. Diane Shelton
- Department of Pathology, University of California San Diego, La Jolla, California, United States of America
| | - Leslie A. Lyons
- Department of Veterinary Medicine and Surgery, School of Veterinary Medicine, University of Missouri – Columbia, Columbia, Missouri, United States of America
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Mutational Consequences of Aberrant Ion Channels in Neurological Disorders. J Membr Biol 2014; 247:1083-127. [DOI: 10.1007/s00232-014-9716-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2014] [Accepted: 07/25/2014] [Indexed: 12/25/2022]
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Ardissone A, Brugnoni R, Gandioli C, Milani M, Ciano C, Uziel G, Moroni I. Double-trouble in pediatric neurology: myotonia congenita combined with charcot-marie-tooth disease type 1a. Muscle Nerve 2014; 50:145-7. [PMID: 24515601 DOI: 10.1002/mus.24205] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Revised: 02/06/2014] [Accepted: 02/07/2014] [Indexed: 11/06/2022]
Affiliation(s)
- Anna Ardissone
- Child Neurology Unit, Foundation IRCCS "Carlo Besta" Neurological Institute, Milan, Italy
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25
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Asymptomatic myotonia congenita unmasked by severe hypothyroidism. Neuromuscul Disord 2014; 24:365-7. [PMID: 24530047 DOI: 10.1016/j.nmd.2014.01.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Revised: 12/19/2013] [Accepted: 01/14/2014] [Indexed: 11/20/2022]
Abstract
Myotonia congenita is an inherited muscle disorder sustained by mutations in the skeletal muscle chloride channel gene CLCN1. Symptoms vary from mild to severe and generalized myotonia and worsen with cold, stressful events and hormonal fluctuations. Here we report the case of a young woman who sought medical attention because of subacute onset of diffuse and severe limb myotonia. CLCN1 gene sequencing showed a heterozygous transversion (T550M), two polymorphisms and one silent mutation. Thyroid function screening revealed severe hypothyroidism. She was placed on l-thyroxine replacement therapy which dramatically improved myotonia. We conclude that hypothyroidism unmasked a genetically determined, clinically asymptomatic chloride channelopathy. Diagnostic work-up in patients with clinically isolated myotonia should not be limited to genetic screening of non-dystrophic or dystrophic myotonias. Considering the high prevalence of hypothyroidism in females, systematic thyroid function screening by looking for additional hypothyroid symptoms and serum TSH levels measurement is mandatory in these patients.
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Skálová D, Zídková J, Voháňka S, Mazanec R, Mušová Z, Vondráček P, Mrázová L, Kraus J, Réblová K, Fajkusová L. CLCN1 mutations in Czech patients with myotonia congenita, in silico analysis of novel and known mutations in the human dimeric skeletal muscle chloride channel. PLoS One 2013; 8:e82549. [PMID: 24349310 PMCID: PMC3859631 DOI: 10.1371/journal.pone.0082549] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2013] [Accepted: 10/26/2013] [Indexed: 11/18/2022] Open
Abstract
Myotonia congenita (MC) is a genetic disease caused by mutations in the skeletal muscle chloride channel gene (CLCN1) encoding the skeletal muscle chloride channel (ClC-1). Mutations of CLCN1 result in either autosomal dominant MC (Thomsen disease) or autosomal recessive MC (Becker disease). The ClC-1 protein is a homodimer with a separate ion pore within each monomer. Mutations causing recessive myotonia most likely affect properties of only the mutant monomer in the heterodimer, leaving the wild type monomer unaffected, while mutations causing dominant myotonia affect properties of both subunits in the heterodimer. Our study addresses two points: 1) molecular genetic diagnostics of MC by analysis of the CLCN1 gene and 2) structural analysis of mutations in the homology model of the human dimeric ClC-1 protein. In the first part, 34 different types of CLCN1 mutations were identified in 51 MC probands (14 mutations were new). In the second part, on the basis of the homology model we identified the amino acids which forming the dimer interface and those which form the Cl(-) ion pathway. In the literature, we searched for mutations of these amino acids for which functional analyses were performed to assess the correlation between localisation of a mutation and occurrence of a dominant-negative effect (corresponding to dominant MC). This revealed that both types of mutations, with and without a dominant-negative effect, are localised at the dimer interface while solely mutations without a dominant-negative effect occur inside the chloride channel. This work is complemented by structural analysis of the homology model which provides elucidation of the effects of mutations, including a description of impacts of newly detected missense mutations.
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Affiliation(s)
- Daniela Skálová
- Centre of Molecular Biology and Gene Therapy, University Hospital, Brno, Brno, Czech Republic
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
| | - Jana Zídková
- Centre of Molecular Biology and Gene Therapy, University Hospital, Brno, Brno, Czech Republic
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
| | - Stanislav Voháňka
- Department of Neurology, University Hospital Brno, Brno, Czech Republic
| | - Radim Mazanec
- Department of Neurology, Charles University Second Faculty of Medicine and University Hospital Motol, Prague, Czech Republic
| | - Zuzana Mušová
- Department of Biology and Medical Genetics, Charles University Second Faculty of Medicine and University Hospital Motol, Prague, Czech Republic
| | - Petr Vondráček
- Department of Child Neurology, University Hospital Brno, Brno, Czech Republic
| | - Lenka Mrázová
- Department of Child Neurology, University Hospital Brno, Brno, Czech Republic
| | - Josef Kraus
- Department of Child Neurology, Second School of Medicine, Charles University and University Hospital Motol, Prague, Czech Republic
| | - Kamila Réblová
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- * E-mail: (KR); (LF)
| | - Lenka Fajkusová
- Centre of Molecular Biology and Gene Therapy, University Hospital, Brno, Brno, Czech Republic
- Central European Institute of Technology, Masaryk University, Brno, Czech Republic
- * E-mail: (KR); (LF)
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Richardson RC, Tarleton JC, Bird TD, Gospe SM. Truncating CLCN1 mutations in myotonia congenita: Variable patterns of inheritance. Muscle Nerve 2013; 49:593-600. [DOI: 10.1002/mus.23976] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/16/2013] [Indexed: 11/11/2022]
Affiliation(s)
- Randal C. Richardson
- Division of Pediatric Neurology; Departments of Neurology and Pediatrics; University of Washington, and Seattle Children's Hospital; 4800 Sand Point Way NE, Neurology, MB.7.420 Seattle Washington USA 98105
| | - Jack C. Tarleton
- Fullerton Genetics Laboratory; Mission Hospitals; Asheville North Carolina USA
| | - Thomas D. Bird
- Geriatric Research Education Clinical Center; VA Puget Sound Health Care System; and Department of Neurology; University of Washington; Seattle Washington USA
| | - Sidney M. Gospe
- Division of Pediatric Neurology; Departments of Neurology and Pediatrics; University of Washington, and Seattle Children's Hospital; 4800 Sand Point Way NE, Neurology, MB.7.420 Seattle Washington USA 98105
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Keck M, Andrini O, Lahuna O, Burgos J, Cid LP, Sepúlveda FV, L‘Hoste S, Blanchard A, Vargas-Poussou R, Lourdel S, Teulon J. NovelCLCNKBMutations Causing Bartter Syndrome Affect Channel Surface Expression. Hum Mutat 2013; 34:1269-78. [DOI: 10.1002/humu.22361] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Accepted: 05/15/2013] [Indexed: 11/07/2022]
Affiliation(s)
- Mathilde Keck
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
| | - Olga Andrini
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
| | - Olivier Lahuna
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
| | - Johanna Burgos
- Centro de Estudios Científicos; Avenida Arturo Prat 514; Valdivia Chile
| | - L. Pablo Cid
- Centro de Estudios Científicos; Avenida Arturo Prat 514; Valdivia Chile
| | | | - Sébastien L‘Hoste
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
| | - Anne Blanchard
- Assistance Publique-Hôpitaux de Paris; Hôpital Européen Georges Pompidou; Centre d'Investigation Clinique; Paris France
- Université Paris-Descartes; Faculté de Médecine; Paris France
| | - Rosa Vargas-Poussou
- Université Paris-Descartes; Faculté de Médecine; Paris France
- Assistance Publique-Hôpitaux de Paris; Hôpital Européen Georges Pompidou; département de génétique; Paris France
| | - Stéphane Lourdel
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
| | - Jacques Teulon
- UPMC Université Paris 06, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
- INSERM, UMR_S 872; Laboratoire de génomique, physiologie et physiopathologie rénales; Paris France
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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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30
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Borges AS, Barbosa JD, Resende LAL, Mota LSLS, Amorim RM, Carvalho TL, Garcia JF, Oliveira-Filho JP, Oliveira CMC, Souza JES, Winand NJ. Clinical and molecular study of a new form of hereditary myotonia in Murrah water buffalo. Neuromuscul Disord 2013; 23:206-13. [PMID: 23339992 DOI: 10.1016/j.nmd.2012.11.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2012] [Revised: 11/04/2012] [Accepted: 11/12/2012] [Indexed: 10/27/2022]
Abstract
Hereditary myotonia caused by mutations in CLCN1 has been previously described in humans, goats, dogs, mice and horses. The goal of this study was to characterize the clinical, morphological and genetic features of hereditary myotonia in Murrah buffalo. Clinical and laboratory evaluations were performed on affected and normal animals. CLCN1 cDNA and the relevant genomic region from normal and affected animals were sequenced. The affected animals exhibited muscle hypertrophy and stiffness. Myotonic discharges were observed during EMG, and dystrophic changes were not present in skeletal muscle biopsies; the last 43 nucleotides of exon-3 of the CLCN1 mRNA were deleted. Cloning of the genomic fragment revealed that the exclusion of this exonic sequence was caused by aberrant splicing, which was associated with the presence of a synonymous SNP in exon-3 (c.396C>T). The mutant allele triggered the efficient use of an ectopic 5' splice donor site located at nucleotides 90-91 of exon-3. The predicted impact of this aberrant splicing event is the alteration of the CLCN1 translational reading frame, which results in the incorporation of 24 unrelated amino acids followed by a premature stop codon.
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Affiliation(s)
- Alexandre S Borges
- Department of Veterinary Clinical Science, College of Veterinary Medicine and Animal Science, Univ Estadual Paulista (UNESP), Botucatu, Brazil.
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31
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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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Gurgel-Giannetti J, Senkevics AS, Zilbersztajn-Gotlieb D, Yamamoto LU, Muniz VP, Pavanello RCM, Oliveira AB, Zatz M, Vainzof M. Thomsen or Becker myotonia? A novel autosomal recessive nonsense mutation in the CLCN1 gene associated with a mild phenotype. Muscle Nerve 2012; 45:279-83. [PMID: 22246887 DOI: 10.1002/mus.22252] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
We describe a large Brazilian consanguineous kindred with 3 clinically affected patients with a Thomsen myotonia phenotype. They carry a novel homozygous nonsense mutation in the CLCN1 gene (K248X). None of the 6 heterozygote carriers show any sign of myotonia on clinical evaluation or electromyography. These findings confirm the autosomal recessive inheritance of the novel mutation in this family, as well as the occurrence of phenotypic variability in the autosomal recessive forms of myotonia.
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Affiliation(s)
- Juliana Gurgel-Giannetti
- Centro de Estudos do Genoma Humano-IB-USP, Biosciences Institute, University of São Paulo, R. do Matão, 277, Sala 220, CEP 05508-900 São Paulo, Brazil
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33
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ClC transporters: discoveries and challenges in defining the mechanisms underlying function and regulation of ClC-5. Pflugers Arch 2010; 460:543-57. [PMID: 20049483 DOI: 10.1007/s00424-009-0769-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2009] [Revised: 11/27/2009] [Accepted: 11/30/2009] [Indexed: 02/03/2023]
Abstract
The involvement of several members of the chloride channel (ClC) family of membrane proteins in human disease highlights the need to define the mechanisms underlying their function and the consequences of disease-causing mutations. Despite the utility of high-resolution structural models, our understanding of the molecular basis for function of the chloride channels and transporters in the family remains incomplete. In this review, we focus on recent discoveries regarding molecular mechanisms underlying the regulated chloride:proton antiporter activity of ClC-5, the protein mutated in the Dent's disease-a kidney disease presenting with proteinuria and renal failure in severe cases. We discuss the putative role of ClC-5 in receptor-mediated endocytosis and protein uptake by the proximal renal tubule and the possible molecular and cellular consequences of disease-causing mutations. However, validation of these models will require future study of the intrinsic function of this transporter, in situ, in the membranes of recycling endosomes in proximal tubule epithelial cells.
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34
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Moon IS, Kim HS, Shin JH, Park YE, Park KH, Shin YB, Bae JS, Choi YC, Kim DS. Novel CLCN1 mutations and clinical features of Korean patients with myotonia congenita. J Korean Med Sci 2009; 24:1038-44. [PMID: 19949657 PMCID: PMC2775849 DOI: 10.3346/jkms.2009.24.6.1038] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2009] [Accepted: 07/22/2009] [Indexed: 11/20/2022] Open
Abstract
Myotonia congenita (MC) is a form of nondystrophic myotonia caused by a mutation of CLCN1, which encodes human skeletal muscle chloride channel (CLC-1). We performed sequence analysis of all coding regions of CLCN1 in patients clinically diagnosed with MC, and identified 10 unrelated Korean patients harboring mutations. Detailed clinical analysis was performed in these patients to identify their clinical characteristics in relation to their genotypes. The CLCN1 mutational analyses revealed nine different point mutations. Of these, six (p.M128I, p.S189C, p.M373L, p.P480S, p.G523D, and p.M609K) were novel and could be unique among Koreans. While some features including predominant lower extremity involvement and normal to slightly elevated creatine kinase levels were consistently observed, general clinical features were highly variable in terms of age of onset, clinical severity, aggravating factors, and response to treatment. Our study is the first systematic study of MC in Korea, and shows its expanding clinical and genetic spectrums.
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Affiliation(s)
- In-Soo Moon
- Department of Neurology, Dae-Dong Hospital, Busan, Korea
- Department of Neurology, Pusan National University School of Medicine, Yangsan, Korea
| | - Hyang-Sook Kim
- Medical Research Institute, Pusan National University School of Medicine, Yangsan, Korea
| | - Jin-Hong Shin
- Department of Neurology, Pusan National University School of Medicine, Yangsan, Korea
| | - Yeong-Eun Park
- Department of Neurology, Pusan National University School of Medicine, Yangsan, Korea
| | - Kyu-Hyun Park
- Department of Neurology, Pusan National University School of Medicine, Yangsan, Korea
- Medical Research Institute, Pusan National University School of Medicine, Yangsan, Korea
| | - Yong-Bum Shin
- Department of Rehabilitation Medicine, Pusan National University School of Medicine, Yangsan, Korea
- Medical Research Institute, Pusan National University School of Medicine, Yangsan, Korea
| | - Jong Seok Bae
- Department of Neurology, College of Medicine, Inje University, Busan, Korea
| | - Young-Chul Choi
- Department of Neurology, College of Medicine, Yonsei University, Seoul, Korea
| | - Dae-Seong Kim
- Department of Neurology, Pusan National University School of Medicine, Yangsan, Korea
- Medical Research Institute, Pusan National University School of Medicine, Yangsan, Korea
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35
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Burgunder JM, Huifang S, Beguin P, Baur R, Eng CS, Seet RC, Lim EC, Ong BK, Hunziker W, Sigel E. Novel chloride channel mutations leading to mild myotonia among Chinese. Neuromuscul Disord 2008; 18:633-40. [DOI: 10.1016/j.nmd.2008.05.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2007] [Revised: 05/10/2008] [Accepted: 05/15/2008] [Indexed: 10/21/2022]
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36
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Trip J, Drost G, Verbove DJ, van der Kooi AJ, Kuks JBM, Notermans NC, Verschuuren JJ, de Visser M, van Engelen BGM, Faber CG, Ginjaar IB. In tandem analysis of CLCN1 and SCN4A greatly enhances mutation detection in families with non-dystrophic myotonia. Eur J Hum Genet 2008; 16:921-9. [DOI: 10.1038/ejhg.2008.39] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
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Bernard G, Poulin C, Puymirat J, Sternberg D, Shevell M. Dosage effect of a dominant CLCN1 mutation: a novel syndrome. J Child Neurol 2008; 23:163-6. [PMID: 18263754 DOI: 10.1177/0883073807307974] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Multiple mutations in the CLCN1 gene coding for the voltage-gated chloride channel have been documented to cause myotonia congenita. We report a kindred featuring an index patient who possesses 2 copies of a dominantly inherited mutated CLCN1 allele with a resulting novel phenotypic presentation. The index patient is a boy who presented initially for evaluation at the age of 5 years with a 2-year history of gait problems. Both parents and 3 male siblings were entirely well. Examination revealed a striking diffuse muscular hypertrophy, diffuse mild to moderate weakness, Gower sign, percussion, and grip myotonia. Electromyography confirmed myotonia, and molecular analysis revealed 2 copies of the T310M mutation on the CLCN1 gene. Testing of family members revealed a normal neurological examination without clinical myotonia in all and electromyographic evidence of myotonia and a single copy of the T310M mutation in both parents and 2 siblings. Our kindred is the initial demonstration of the dosage effect of a dominant mutated allele in the CLCN1 gene.
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Affiliation(s)
- Geneviève Bernard
- Department of Neurology/Neurosurgery, McGill University Health Center, Montreal, Canada
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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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40
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41
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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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42
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Chen L, Schaerer M, Lu ZH, Lang D, Joncourt F, Weis J, Fritschi J, Kappeler L, Gallati S, Sigel E, Burgunder JM. Exon 17 skipping in CLCN1 leads to recessive myotonia congenita. Muscle Nerve 2004; 29:670-6. [PMID: 15116370 DOI: 10.1002/mus.20005] [Citation(s) in RCA: 12] [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
Mutations in CLCN1, the gene encoding the ClC-1 chloride channel in skeletal muscle, lead to myotonia congenita. The effects on the intramembranous channel forming domains have been investigated more than that at the intracellular C-terminus. We have performed a mutation screen involving the whole CLCN1 gene of patients with myotonia congenita by polymerase chain reaction (PCR), single-strand conformation polymorphism studies, and sequencing. Two unrelated patients harbored the same homozygous G-to-T mutation on the donor splice site of intron 17. This led to the skipping of exon 17, as evidenced by the reverse transcriptase PCR. When the exon 17-deleted CLCN1 was expressed in Xenopus oocytes, no chloride current was measurable. This function could be restored by coexpression with the wild-type channel. Our data suggest an important role of this C-terminal region and that exon 17 skipping resulting from a homozygous point mutation in CLCN1 can lead to recessive myotonia congenita.
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Affiliation(s)
- Lie Chen
- Departments of Neurology and Clinical Research, Laboratory of Neuromorphology, University of Berne, Berne, Switzerland
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Ebralidze A, Wang Y, Petkova V, Ebralidse K, Junghans RP. RNA leaching of transcription factors disrupts transcription in myotonic dystrophy. Science 2004; 303:383-7. [PMID: 14657503 DOI: 10.1126/science.1088679] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Myotonic dystrophy type 1 (DM1) is caused by a CUGn expansion (n approximately 50 to 5000) in the 3' untranslated region of the mRNA of the DM protein kinase gene. We show that mutant RNA binds and sequesters transcription factors (TFs), with up to 90% depletion of selected TFs from active chromatin. Diverse genes are consequently reduced in expression, including the ion transporter CIC-1, which has been implicated in myotonia. When TF specificity protein 1 (Sp1) was overexpressed in DM1-affected cells, low levels of messenger RNA for CIC-1 were restored to normal. Transcription factor leaching from chromatin by mutant RNA provides a potentially unifying pathomechanistic explanation for this disease.
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Affiliation(s)
- A Ebralidze
- Biotherapeutics Development Lab, Harvard Institute of Human Genetics, Harvard Medical School and Division of Hematology-Oncology, Beth Israel Deaconess Medical Center, 4 Blackfan Circle, Boston, MA 02215, USA
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Abstract
Although the genetic neurologic channelopathies are uncommon, they serve as models that further understanding of disease mechanisms in paroxysmal disorders. Many other neurologic channelopathies likely will be identified in the future.
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Affiliation(s)
- Hemant K Pandey
- West Virginia University School of Medicine, Morgantown, West Virginia, USA
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Mohammad-Panah R, Harrison R, Dhani S, Ackerley C, Huan LJ, Wang Y, Bear CE. The chloride channel ClC-4 contributes to endosomal acidification and trafficking. J Biol Chem 2003; 278:29267-77. [PMID: 12746443 DOI: 10.1074/jbc.m304357200] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mutations in the gene coding for the chloride channel ClC-5 cause Dent's disease, a disease associated with proteinuria and renal stones. Studies in ClC-5 knockout mice suggest that this phenotype is related to defective endocytosis of low molecular weight proteins and membrane proteins by the renal proximal tubule. In this study, confocal micrographs of proximal tubules and cultured epithelial cells revealed that the related protein ClC-4 is expressed in endosomal membranes suggesting that this channel may also contribute to the function of this organelle. In support of this hypothesis, specific disruption of endogenous ClC-4 expression by transfection of ClC-4 antisense cDNA acidified endosomal pH and altered transferrin trafficking in cultured epithelial cells to the same extent as the specific disruption of ClC-5. Both channels can be co-immunoprecipitated, arguing that they may partially contribute to endosomal function as a channel complex. These studies prompt future investigation of the role of ClC-4 in renal function in health and in Dent's disease. Future studies will assess whether the severity of Dent's disease relates not only to the impact of particular mutations on ClC-5 but also on the consequences of those mutations on the functional expression of ClC-4.
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Affiliation(s)
- Raha Mohammad-Panah
- Programme in Structural Biology and Biochemistry, Research Institute, Hospital for Sick Children, Toronto, Ontario M5X 1G8, Canada
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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: 934] [Impact Index Per Article: 42.5] [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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Sun C, Tranebjaerg L, Torbergsen T, Holmgren G, Van Ghelue M. Spectrum of CLCN1 mutations in patients with myotonia congenita in Northern Scandinavia. Eur J Hum Genet 2001; 9:903-9. [PMID: 11840191 DOI: 10.1038/sj.ejhg.5200736] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2001] [Revised: 09/26/2001] [Accepted: 10/06/2001] [Indexed: 11/09/2022] Open
Abstract
Myotonia congenita is a non-dystrophic muscle disorder affecting the excitability of the skeletal muscle membrane. It can be inherited either as an autosomal dominant (Thomsen's myotonia) or an autosomal recessive (Becker's myotonia) trait. Both types are characterised by myotonia (muscle stiffness) and muscular hypertrophy, and are caused by mutations in the muscle chloride channel gene, CLCN1. At least 50 different CLCN1 mutations have been described worldwide, but in many studies only about half of the patients showed mutations in CLCN1. Limitations in the mutation detection methods and genetic heterogeneity might be explanations. In the current study, we sequenced the entire CLCN1 gene in 15 Northern Norwegian and three Northern Swedish MC families. Our data show a high prevalence of myotonia congenita in Northern Norway similar to Northern Finland, but with a much higher degree of mutation heterogeneity. In total, eight different mutations and three polymorphisms (T87T, D718D, and P727L) were detected. Three mutations (F287S, A331T, and 2284+5C>T) were novel while the others (IVS1+3A>T, 979G>A, F413C, A531V, and R894X) have been reported previously. The mutations F413C, A531V, and R894X predominated in our patient material. Compound heterozygosity for A531V/R894X was the predominant genotype. In two probands, three mutations cosegregated with myotonia. No CLCN1 mutations were identified in two families. Our data support the presence of genetic heterogeneity and additional modifying factors in myotonia congenita.
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Affiliation(s)
- C Sun
- Department of Medical Genetics, University Hospital of Tromsø, Tromsø, Norway.
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Abstract
Diseases as different as cardiac arrhythmias, epilepsy, myotonia, malignant hyperthermia, familial hyperinsulinism, and Bartter syndrome have all been linked to mutations in genes encoding ion channels. This has been made possible by an exciting and fruitful collaboration between clinicians, geneticists, and physiologists. It has led to a more detailed understanding not only of pathology but also of physiology, as the deficiency of a certain gene helps unravel its physiologic role. Some exciting and surprising findings have recently been made in the field of "channelopathies." Understanding these diseases on the molecular level will provide the basis for a rational therapeutic approach to affected patients.
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Affiliation(s)
- D Bockenhauer
- Yale University School of Medicine, Department of Pediatric Nephrology, New Haven, Connecticut 06510, USA.
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