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Batheja A, Bayer-Vile J, Silverstein E, Couser N. Congenital Myasthenic Syndrome associated with acetylcholine receptor deficiency: case report and review of the literature. Ophthalmic Genet 2024; 45:481-487. [PMID: 38832364 DOI: 10.1080/13816810.2024.2352391] [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: 12/21/2023] [Revised: 04/05/2024] [Accepted: 05/02/2024] [Indexed: 06/05/2024]
Abstract
INTRODUCTION Congenital Myasthenic Syndromes are a diverse group of conditions with a broad array of genetic underpinnings and phenotypic presentations. Acetylcholine receptor deficiency is one form that usually involves pathogenic variants in the Cholinergic Receptor Nicotinic Epsilon Subunit (CHRNE) gene encoding the ɛ-subunit of the acetylcholine receptor. METHODS We report a case of a 4-year-old male with suspected Congenital Myasthenic Syndrome with Acetylcholine Receptor Deficiency who presented with ocular symptoms and generalized muscle weakness. We additionally summarize published findings regarding the genetic, phenotypic, and clinical considerations of Congenital Myasthenic Syndrome with Acetylcholine Receptor Deficiency. RESULTS Exome sequencing revealed biallelic variants in CHRNE gene with a pathogenic frameshift variant and a variant of uncertain significance. After suboptimal response to pyridostigmine and albuterol, the patient experienced benefit with 3,4-DAP. The most commonly reported clinical characteristics in the literature are ptosis, muscle fatigability or weakness, and ophthalmoplegia. CONCLUSION We present the case of a patient with biallelic variants in CHRNE gene including a variant of uncertain significance. Evaluation of variants of this gene, including the variant of uncertain significance identified in this case report, through further cases and studies may improve our understanding of Congenital Myasthenic Syndrome with Acetylcholine Receptor deficiency.
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Affiliation(s)
- Aashish Batheja
- School of Medicine, Virginia Commonwealth University School of Medicine, Richmond, Virginia, USA
| | - Julie Bayer-Vile
- Department of Pediatrics, Virginia Commonwealth University School of Medicine, Richmond, Virginia, USA
| | - Evan Silverstein
- Department of Ophthalmology, Virginia Commonwealth University School of Medicine, Richmond, Virginia, USA
| | - Natario Couser
- Department of Pediatrics, Virginia Commonwealth University School of Medicine, Richmond, Virginia, USA
- Department of Ophthalmology, Virginia Commonwealth University School of Medicine, Richmond, Virginia, USA
- Department of Human and Molecular Genetics, Virginia Commonwealth University School of Medicine, Richmond, Virginia, USA
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De Rose DU, Ronci S, Caoci S, Maddaloni C, Diodato D, Catteruccia M, Fattori F, Bosco L, Pro S, Savarese I, Bersani I, Randi F, Trozzi M, Meucci D, Calzolari F, Salvatori G, Solinas A, Dotta A, Campi F. Vocal Cord Paralysis and Feeding Difficulties as Early Diagnostic Clues of Congenital Myasthenic Syndrome with Neonatal Onset: A Case Report and Review of Literature. J Pers Med 2023; 13:jpm13050798. [PMID: 37240968 DOI: 10.3390/jpm13050798] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Revised: 04/21/2023] [Accepted: 05/04/2023] [Indexed: 05/28/2023] Open
Abstract
Herein, we present a newborn female with congenital vocal cord paralysis who required a tracheostomy in the neonatal period. She also presented with feeding difficulties. She was later diagnosed with a clinical picture of congenital myasthenia, associated with three variants of the MUSK gene: the 27-month follow-up was described. In particular, the c.565C>T variant is novel and has never been described in the literature; it causes the insertion of a premature stop codon (p.Arg189Ter) likely leading to a consequent formation of a truncated nonfunctioning protein. We also systematically collected and summarized information on patients' characteristics of previous cases of congenital myasthenia with neonatal onset reported in the literature to date, and we compared them to our case. The literature reported 155 neonatal cases before our case, from 1980 to March 2022. Of 156 neonates with CMS, nine (5.8%) had vocal cord paralysis, whereas 111 (71.2%) had feeding difficulties. Ocular features were evident in 99 infants (63.5%), whereas facial-bulbar symptoms were found in 115 infants (73.7%). In one hundred sixteen infants (74.4%), limbs were involved. Respiratory problems were displayed by 97 infants (62.2%). The combination of congenital stridor, particularly in the presence of an apparently idiopathic bilateral vocal cord paralysis, and poor coordination between sucking and swallowing may indicate an underlying congenital myasthenic syndrome (CMS). Therefore, we suggest testing infants with vocal cord paralysis and feeding difficulties for MUSK and related genes to avoid a late diagnosis of CMS and improve outcomes.
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Affiliation(s)
| | - Sara Ronci
- Neonatal Intensive Care Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Stefano Caoci
- Neonatal Intensive Care Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Chiara Maddaloni
- Neonatal Intensive Care Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Daria Diodato
- Neuromuscular and Neurodegenerative Disorders Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Michela Catteruccia
- Neuromuscular and Neurodegenerative Disorders Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Fabiana Fattori
- Laboratory of Medical Genetics, Translational Cytogenomics Research Unit, Bambino Gesù Children Hospital, IRCCS, 00165 Rome, Italy
| | - Luca Bosco
- Neuromuscular and Neurodegenerative Disorders Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
- Department of Science, University Roma Tre, 00146 Rome, Italy
| | - Stefano Pro
- Developmental Neurology Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Immacolata Savarese
- Neonatal Intensive Care Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Iliana Bersani
- Neonatal Intensive Care Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Franco Randi
- Neurosurgery Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Marilena Trozzi
- Airway Surgery Unit, Pediatric Surgery Department, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Duino Meucci
- Airway Surgery Unit, Pediatric Surgery Department, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Flaminia Calzolari
- Neonatal Intensive Care Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Guglielmo Salvatori
- Neonatal Intensive Care Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Agostina Solinas
- Neonatal Intensive Care Unit, Sant'Anna Hospital of Ferrara, 44124 Ferrara, Italy
| | - Andrea Dotta
- Neonatal Intensive Care Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
| | - Francesca Campi
- Neonatal Intensive Care Unit, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
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3
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Younger DS. Neurogenetic motor disorders. HANDBOOK OF CLINICAL NEUROLOGY 2023; 195:183-250. [PMID: 37562870 DOI: 10.1016/b978-0-323-98818-6.00003-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/12/2023]
Abstract
Advances in the field of neurogenetics have practical applications in rapid diagnosis on blood and body fluids to extract DNA, obviating the need for invasive investigations. The ability to obtain a presymptomatic diagnosis through genetic screening and biomarkers can be a guide to life-saving disease-modifying therapy or enzyme replacement therapy to compensate for the deficient disease-causing enzyme. The benefits of a comprehensive neurogenetic evaluation extend to family members in whom identification of the causal gene defect ensures carrier detection and at-risk counseling for future generations. This chapter explores the many facets of the neurogenetic evaluation in adult and pediatric motor disorders as a primer for later chapters in this volume and a roadmap for the future applications of genetics in neurology.
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Affiliation(s)
- David S Younger
- Department of Clinical Medicine and Neuroscience, CUNY School of Medicine, New York, NY, United States; Department of Medicine, Section of Internal Medicine and Neurology, White Plains Hospital, White Plains, NY, United States.
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An Inside Job: Molecular Determinants for Postsynaptic Localization of Nicotinic Acetylcholine Receptors. Molecules 2021; 26:molecules26113065. [PMID: 34063759 PMCID: PMC8196675 DOI: 10.3390/molecules26113065] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 05/13/2021] [Accepted: 05/15/2021] [Indexed: 11/29/2022] Open
Abstract
Nicotinic acetylcholine receptors (nAChRs) mediate fast synaptic transmission at neuromuscular and autonomic ganglionic synapses in the peripheral nervous system. The postsynaptic localization of muscle ((α1)2β1γδ) and neuronal ((α3β4)2β4) nicotinic receptors at these synapses is mediated by interactions between the nAChR intracellular domains and cytoplasmic scaffolding proteins. Recent high resolution structures and functional studies provide new insights into the molecular determinants that mediate these interactions. Surprisingly, they reveal that the muscle nAChR binds 1–3 rapsyn scaffolding molecules, which dimerize and thereby form an interconnected lattice between receptors. Moreover, rapsyn binds two distinct sites on the nAChR subunit cytoplasmic loops; the MA-helix on one or more subunits and a motif specific to the β subunit. Binding at the latter site is regulated by agrin-induced phosphorylation of βY390, and increases the stoichiometry of rapsyn/AChR complexes. Similarly, the neuronal nAChR may be localized at ganglionic synapses by phosphorylation-dependent interactions with 14-3-3 adaptor proteins which bind specific motifs in each of the α3 subunit cytoplasmic loops. Thus, postsynaptic localization of nAChRs is mediated by regulated interactions with multiple scaffolding molecules, and the stoichiometry of these complexes likely helps regulate the number, density, and stability of receptors at the synapse.
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5
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Freed AS, Schwarz AC, Brei BK, Clowes Candadai SV, Thies J, Mah JK, Chabra S, Wang L, Innes AM, Bennett JT. CHRNB1-associated congenital myasthenia syndrome: Expanding the clinical spectrum. Am J Med Genet A 2020; 185:827-835. [PMID: 33296147 DOI: 10.1002/ajmg.a.62011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 10/28/2020] [Accepted: 10/30/2020] [Indexed: 11/09/2022]
Abstract
CHRNB1 encodes the β subunit of the acetylcholine receptor (AChR) at the neuromuscular junction. Inherited defects in the neuromuscular junction can lead to congenital myasthenia syndrome (CMS), a clinically and genetically heterogeneous group of disorders which includes fetal akinesia deformation sequence (FADS) on the severe end of the spectrum. Here, we report two unrelated families with biallelic CHRNB1 variants, and in each family, one child presented with lethal FADS. We contrast the diagnostic odysseys in the two families, one of which lasted 16 years while the other, utilizing rapid exome sequencing, led to specific treatment in the first 2 weeks of life. Furthermore, we note that CHRNB1 variants may be under-recognized because in both families, one of the variants is a single exon deletion that has been previously described but may not easily be detected in clinically available genetic testing.
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Affiliation(s)
- Amanda S Freed
- Division of Genetic Medicine, Department of Pediatrics, University of Washington, Seattle, Washington, USA.,Department of Genetics, SCPMG, Panorama City, California, USA
| | - Anisha C Schwarz
- Division of Pediatric Neurology, Department of Neurology, University of Washington, Seattle, Washington, USA.,General & Neuromuscular Pediatric Neurology, Mary Bridge Children's Hospital, Tacoma, Washington, USA
| | - Brianna K Brei
- Division of Neonatology, Department of Pediatrics, University of Washington, Seattle, Washington, USA.,Department of Neonatology, Children's Hospital & Medical Center, Omaha, Nebraska, USA
| | - Sarah V Clowes Candadai
- Department of Laboratories, Seattle Children's Hospital, Seattle, Washington, USA.,Patient-Centered Laboratory Utilization Guidance Services (PLUGS), Seattle Children's Hospital, Seattle, Washington, USA
| | - Jenny Thies
- Division of Genetic Medicine, Seattle Children's Hospital, Seattle, Washington, USA
| | - Jean K Mah
- Department of Pediatrics, Section of Neurology, Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Shilpi Chabra
- Division of Pediatric Neurology, Department of Neurology, University of Washington, Seattle, Washington, USA
| | - Leo Wang
- Division of Neuromuscular Neurology, Department of Neurology, University of Washington, Seattle, Washington, USA
| | - A Micheil Innes
- Department of Medical Genetics, Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Department of Pediatrics, Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - James T Bennett
- Division of Genetic Medicine, Department of Pediatrics, University of Washington, Seattle, Washington, USA.,Department of Neonatology, Children's Hospital & Medical Center, Omaha, Nebraska, USA.,Center for Developmental Biology and Regenerative Medicine, Seattle Children's Research Institute, Seattle, Washington, USA.,Brotman Baty Institute for Precision Medicine, Seattle, Washington, USA
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Ravenscroft G, Clayton JS, Faiz F, Sivadorai P, Milnes D, Cincotta R, Moon P, Kamien B, Edwards M, Delatycki M, Lamont PJ, Chan SH, Colley A, Ma A, Collins F, Hennington L, Zhao T, McGillivray G, Ghedia S, Chao K, O'Donnell-Luria A, Laing NG, Davis MR. Neurogenetic fetal akinesia and arthrogryposis: genetics, expanding genotype-phenotypes and functional genomics. J Med Genet 2020; 58:609-618. [PMID: 33060286 DOI: 10.1136/jmedgenet-2020-106901] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Revised: 05/16/2020] [Accepted: 07/05/2020] [Indexed: 12/19/2022]
Abstract
BACKGROUND Fetal akinesia and arthrogryposis are clinically and genetically heterogeneous and have traditionally been refractive to genetic diagnosis. The widespread availability of affordable genome-wide sequencing has facilitated accurate genetic diagnosis and gene discovery in these conditions. METHODS We performed next generation sequencing (NGS) in 190 probands with a diagnosis of arthrogryposis multiplex congenita, distal arthrogryposis, fetal akinesia deformation sequence or multiple pterygium syndrome. This sequencing was a combination of bespoke neurogenetic disease gene panels and whole exome sequencing. Only class 4 and 5 variants were reported, except for two cases where the identified variants of unknown significance (VUS) are most likely to be causative for the observed phenotype. Co-segregation studies and confirmation of variants identified by NGS were performed where possible. Functional genomics was performed as required. RESULTS Of the 190 probands, 81 received an accurate genetic diagnosis. All except two of these cases harboured class 4 and/or 5 variants based on the American College of Medical Genetics and Genomics guidelines. We identified phenotypic expansions associated with CACNA1S, CHRNB1, GMPPB and STAC3. We describe a total of 50 novel variants, including a novel missense variant in the recently identified gene for arthrogryposis with brain malformations-SMPD4. CONCLUSIONS Comprehensive gene panels give a diagnosis for a substantial proportion (42%) of fetal akinesia and arthrogryposis cases, even in an unselected cohort. Recently identified genes account for a relatively large proportion, 32%, of the diagnoses. Diagnostic-research collaboration was critical to the diagnosis and variant interpretation in many cases, facilitated genotype-phenotype expansions and reclassified VUS through functional genomics.
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Affiliation(s)
- Gina Ravenscroft
- Harry Perkins Institute of Medical Research, Perth, Western Australia, Australia .,Faculty of Health and Medical Sciences, University of Western Australia, Nedlands, Western Australia, Australia
| | - Joshua S Clayton
- Harry Perkins Institute of Medical Research, Perth, Western Australia, Australia.,Faculty of Health and Medical Sciences, University of Western Australia, Nedlands, Western Australia, Australia
| | - Fathimath Faiz
- PathWest Diagnostic Genomics, Nedlands, Western Australia, Australia
| | - Padma Sivadorai
- PathWest Diagnostic Genomics, Nedlands, Western Australia, Australia
| | - Di Milnes
- Genetic Health Queensland, Royal Brisbane and Women's Hospital, Herston, Queensland, Australia
| | - Rob Cincotta
- Maternal and Fetal Medicine, Mater Mothers' Hospital, Brisbane, Queensland, Australia
| | - Phillip Moon
- Department of Obstetrics, Redland Hospital, Cleveland, Queensland, Australia
| | - Ben Kamien
- Genetic Services WA, Women and Newborn Heath Service, Subiaco, Western Australia, Australia.,Hunter Genetics, Hunter New England Health, New Lambton, New South Wales, Australia
| | - Matthew Edwards
- Hunter Genetics, Hunter New England Health, New Lambton, New South Wales, Australia
| | - Martin Delatycki
- Victorian Clinical Genetics Service, Murdoch Children's Research Institute, Melbourne, Victoria, Australia
| | - Phillipa J Lamont
- Neurology, Royal Perth Hospital, Perth, Western Australia, Australia
| | - Sophelia Hs Chan
- Paediatric Neurology Division, Department of Paediatrics and Adolescent Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong, Hong Kong
| | - Alison Colley
- Clinical Genetics Services SWSLHD, Liverpool Hospital, Liverpool, New South Wales, Australia
| | - Alan Ma
- Department of Clinical Genetics, Children's Hospital Westmead, Sydney, New South Wales, Australia
| | - Felicity Collins
- Clinical Genetics Department, Western Sydney Genetics Program, Children's Hospitalat Westmead, Westmead, New South Wales, Australia
| | - Lucinda Hennington
- Mercy Health, Mercy Hospital for Women, Heidelberg, Victoria, Australia.,Austin Health, Melbourne, Victoria, Australia.,Alfred Health, Melbourne, Victoria, Australia
| | - Teresa Zhao
- Victorian Clinical Genetics Service, Murdoch Children's Research Institute, Melbourne, Victoria, Australia
| | - George McGillivray
- Victorian Clinical Genetics Service, Murdoch Children's Research Institute, Melbourne, Victoria, Australia
| | - Sondhya Ghedia
- Department of Clinical Genetics, Royal North Shore Hospital, Sydney, New South Wales, Australia
| | - Katherine Chao
- Center for Mendelian Genomics, Broad Institute of Massachusetts Institute of Technology and Harvard, Cambridge, Massachusetts, USA
| | - Anne O'Donnell-Luria
- Center for Mendelian Genomics, Broad Institute of Massachusetts Institute of Technology and Harvard, Cambridge, Massachusetts, USA
| | - Nigel G Laing
- Harry Perkins Institute of Medical Research, Perth, Western Australia, Australia.,Faculty of Health and Medical Sciences, University of Western Australia, Nedlands, Western Australia, Australia.,PathWest Diagnostic Genomics, Nedlands, Western Australia, Australia
| | - Mark R Davis
- PathWest Diagnostic Genomics, Nedlands, Western Australia, Australia
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Nicole S, Azuma Y, Bauché S, Eymard B, Lochmüller H, Slater C. Congenital Myasthenic Syndromes or Inherited Disorders of Neuromuscular Transmission: Recent Discoveries and Open Questions. J Neuromuscul Dis 2019; 4:269-284. [PMID: 29125502 PMCID: PMC5701762 DOI: 10.3233/jnd-170257] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Congenital myasthenic syndromes (CMS) form a heterogeneous group of rare diseases characterized by fatigable muscle weakness. They are genetically-inherited and caused by defective synaptic transmission at the cholinergic neuromuscular junction (NMJ). The number of genes known to cause CMS when mutated is currently 30, and the relationship between fatigable muscle weakness and defective functions is quite well-understood for many of them. However, some of the most recent discoveries in individuals with CMS challenge our knowledge of the NMJ, where the basis of the pathology has mostly been investigated in animal models. Frontier forms between CMS and congenital myopathy, which have been genetically and clinically identified, underline the poorly understood interplay between the synaptic and extrasynaptic molecules in the neuromuscular system. In addition, precise electrophysiological and histopathological investigations of individuals with CMS suggest an important role of NMJ plasticity in the response to CMS pathogenesis. While efficient drug-based treatments are already available to improve neuromuscular transmission for most forms of CMS, others, as well as neurological and muscular comorbidities, remain resistant. Taken together, the available pathological data point to physiological issues which remain to be understood in order to achieve precision medicine with efficient therapeutics for all individuals suffering from CMS.
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Affiliation(s)
- Sophie Nicole
- Inserm U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Université Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, 75013 Paris, France
| | - Yoshiteru Azuma
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Central Parkway, Newcastle upon Tyne, NE1 3BZ, UK
| | - Stéphanie Bauché
- Inserm U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Université Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, 75013 Paris, France
| | - Bruno Eymard
- Inserm U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Université Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, 75013 Paris, France.,AP-HP, Hôpital Pitié-Salpétrière, 75013 Paris, France
| | - Hanns Lochmüller
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Central Parkway, Newcastle upon Tyne, NE1 3BZ, UK
| | - Clarke Slater
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
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Effect of Inhibiting p38 on HuR Involving in β-AChR Post-transcriptional Mechanisms in Denervated Skeletal Muscle. Cell Mol Neurobiol 2019; 39:1029-1037. [PMID: 31172341 DOI: 10.1007/s10571-019-00698-0] [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] [Received: 12/13/2018] [Accepted: 06/03/2019] [Indexed: 10/26/2022]
Abstract
Previous studies reported that RNA-binding protein human antigen R (HuR) mediates changes in the stability of AChR β-subunit mRNA after skeletal muscle denervation; also, p38 pathway regulated the stability of AChR β-subunit mRNA in C2C12 myotubes. However, the relationship between HuR and p38 in regulating the stability of AChR β-subunit mRNA have not been clarified. In this study, we wanted to examine the effect of inhibiting p38 on HuR in denervated skeletal muscle. Denervation model was built and 10% DMSO or SB203580 were administered respectively follow denervation. Tibialis muscles were collected in 10% DMSO-administered contralateral (undenervated) leg, 10% DMSO-administered denervated leg, SB203580-administered contralateral (undenervated) leg, and SB203580-administered denervated leg, respectively. P38 protein, β-AChR mRNA and protein, HuR protein, β-AChR mRNA stability, and HuR binding with AChR β-subunit mRNAs were measured. Results demonstrated that the administration of SB203580 can inhibit the increase of β-AChR protein expression and mRNA expression and stability, and RNA-binding protein human antigen R (HuR) expression, in cytoplasmic and nuclear fractions in skeletal muscle cells following denervation. Importantly, we observed that SB203580 also inhibited the increased level of binding activity between HuR and AChR β-subunit mRNAs following denervation. Collectively, these results suggested that inhibition of p38 can post-transcriptionally inhibit β-AChR upregulation via HuR in denervated skeletal muscle.
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Vivekanandarajah A, Waters KA, Machaalani R. Cigarette smoke exposure effects on the brainstem expression of nicotinic acetylcholine receptors (nAChRs), and on cardiac, respiratory and sleep physiologies. Respir Physiol Neurobiol 2018; 259:1-15. [PMID: 30031221 DOI: 10.1016/j.resp.2018.07.007] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Revised: 07/16/2018] [Accepted: 07/17/2018] [Indexed: 12/15/2022]
Abstract
Cigarette smoking during pregnancy is the largest modifiable risk factor for adverse outcomes in the infant. Investigations have focused on the psychoactive component of cigarettes, nicotine. One proposed mechanism leading to adverse effects is the interaction between nicotine and its nicotinic acetylcholine receptors (nAChRs). Much data has been generated over the past three decades on the effects of cigarette smoke exposure (CSE) on the expression of the nAChRs in the brainstem and physiological parameters related to cardiac, respiration and sleep, in the offspring of smoking mothers and animal models of nicotine exposure. This review summarises this data and discusses the main findings, highlighting that findings in animal models closely correlate with those from human studies, and that the major brainstem sites where the expression level for the nAChRs are consistently affected include those that play vital roles in cardiorespiration (hypoglossal nucleus, dorsal motor nucleus of the vagus, nucleus of the solitary tract), chemosensation (nucleus of the solitary tract, arcuate nucleus) and arousal (rostral mesopontine sites such as the locus coeruleus and nucleus pontis oralis). These findings provide evidence for the adverse effects of CSE during and after pregnancy to the infant and the need to continue with the health campaign advising against CSE.
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Affiliation(s)
- Arunnjah Vivekanandarajah
- SIDS and Sleep Apnea Laboratory, Sydney Medical School, Medical Foundation Building K25, University of Sydney, NSW 2006, Australia.
| | - Karen A Waters
- SIDS and Sleep Apnea Laboratory, Sydney Medical School, Medical Foundation Building K25, University of Sydney, NSW 2006, Australia; Discipline of Paediatrics and Child Health, Children's Hospital Westmead, NSW, Australia
| | - Rita Machaalani
- SIDS and Sleep Apnea Laboratory, Sydney Medical School, Medical Foundation Building K25, University of Sydney, NSW 2006, Australia; Discipline of Paediatrics and Child Health, Children's Hospital Westmead, NSW, Australia
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10
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Salter CG, Beijer D, Hardy H, Barwick KES, Bower M, Mademan I, De Jonghe P, Deconinck T, Russell MA, McEntagart MM, Chioza BA, Blakely RD, Chilton JK, De Bleecker J, Baets J, Baple EL, Walk D, Crosby AH. Truncating SLC5A7 mutations underlie a spectrum of dominant hereditary motor neuropathies. NEUROLOGY-GENETICS 2018; 4:e222. [PMID: 29582019 PMCID: PMC5866402 DOI: 10.1212/nxg.0000000000000222] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Accepted: 11/15/2017] [Indexed: 11/29/2022]
Abstract
Objective To identify the genetic cause of disease in 2 previously unreported families with forms of distal hereditary motor neuropathies (dHMNs). Methods The first family comprises individuals affected by dHMN type V, which lacks the cardinal clinical feature of vocal cord paralysis characteristic of dHMN-VII observed in the second family. Next-generation sequencing was performed on the proband of each family. Variants were annotated and filtered, initially focusing on genes associated with neuropathy. Candidate variants were further investigated and confirmed by dideoxy sequence analysis and cosegregation studies. Thorough patient phenotyping was completed, comprising clinical history, examination, and neurologic investigation. Results dHMNs are a heterogeneous group of peripheral motor neuron disorders characterized by length-dependent neuropathy and progressive distal limb muscle weakness and wasting. We previously reported a dominant-negative frameshift mutation located in the concluding exon of the SLC5A7 gene encoding the choline transporter (CHT), leading to protein truncation, as the likely cause of dominantly-inherited dHMN-VII in an extended UK family. In this study, our genetic studies identified distinct heterozygous frameshift mutations located in the last coding exon of SLC5A7, predicted to result in the truncation of the CHT C-terminus, as the likely cause of the condition in each family. Conclusions This study corroborates C-terminal CHT truncation as a cause of autosomal dominant dHMN, confirming upper limb predominating over lower limb involvement, and broadening the clinical spectrum arising from CHT malfunction.
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Affiliation(s)
- Claire G Salter
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Danique Beijer
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Holly Hardy
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Katy E S Barwick
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Matthew Bower
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Ines Mademan
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Peter De Jonghe
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Tine Deconinck
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Mark A Russell
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Meriel M McEntagart
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Barry A Chioza
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Randy D Blakely
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - John K Chilton
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Jan De Bleecker
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Jonathan Baets
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Emma L Baple
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - David Walk
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
| | - Andrew H Crosby
- RILD Wellcome Wolfson Centre (C.G.S., H.H., K.E.S.B., M.A.R., B.A.C., J.K.C., E.L.B., A.H.C.), Royal Devon & Exeter NHS Foundation Trust, Exeter; Wessex Clinical Genetics Service (C.G.S.), Princess Anne Hospital, Southampton, United Kingdom; Neurogenetics Group (D.B., I.M., P.D.J., T.D., J.B.), Center for Molecular Neurology, VIB; Laboratory of Neuromuscular Pathology (D.B., I.M., P.D.J., T.D., J.B.), Institute Born-Bunge, University of Antwerp; Department of Neurology (M.B., D.W.), University of Minnesota, Minneapolis, MN; Department of Neurology (P.D.J., J.B.), Neuromuscular Reference Centre, Antwerp University Hospital, Antwerpen, Belgium; Clinical Genetics (M.M.M.), St. George's University of London, London, United Kingdom; Biomedical Science (R.D.B.), Florida Atlantic University, Jupiter Campus, FL; and Department of Neurology (J.D.B.), University Hospital Ghent, Ghent, Belgium; Peninsula Clinical Genetics Service (E.L.B.), Royal Devon and Exeter Hospital, Exeter, United Kingdom
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11
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Engel AG. Genetic basis and phenotypic features of congenital myasthenic syndromes. HANDBOOK OF CLINICAL NEUROLOGY 2018; 148:565-589. [PMID: 29478601 DOI: 10.1016/b978-0-444-64076-5.00037-5] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/06/2022]
Abstract
The congenital myasthenic syndromes (CMS) are heterogeneous disorders in which the safety margin of neuromuscular transmission is compromised by one or more specific mechanisms. The disease proteins reside in the nerve terminal, the synaptic basal lamina, or in the postsynaptic region, or at multiple sites at the neuromuscular junction as well as in other tissues. Targeted mutation analysis by Sanger or exome sequencing has been facilitated by characteristic phenotypic features of some CMS. No fewer than 20 disease genes have been recognized to date. In one-half of the currently identified probands, the disease stems from mutations in genes encoding subunits of the muscle form of the acetylcholine receptor (CHRNA1, CHRNB, CHRNAD1, and CHRNE). In 10-14% of the probands the disease is caused by mutations in RAPSN, DOK 7, or COLQ, and in 5% by mutations in CHAT. Other less frequently identified disease genes include LAMB2, AGRN, LRP4, MUSK, GFPT1, DPAGT1, ALG2, and ALG 14 as well as SCN4A, PREPL, PLEC1, DNM2, and MTM1. Identification of the genetic basis of each CMS is important not only for genetic counseling and disease prevention but also for therapy, because therapeutic agents that benefit one type of CMS can be harmful in another.
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Affiliation(s)
- Andrew G Engel
- Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN, 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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HuR Mediates Changes in the Stability of AChR β-Subunit mRNAs after Skeletal Muscle Denervation. J Neurosci 2015; 35:10949-62. [PMID: 26245959 DOI: 10.1523/jneurosci.1043-15.2015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Acetylcholine receptors (AChRs) are heteromeric membrane proteins essential for neurotransmission at the neuromuscular junction. Previous work showed that muscle denervation increases expression of AChR mRNAs due to transcriptional activation of AChR subunit genes. However, it remains possible that post-transcriptional mechanisms are also involved in controlling the levels of AChR mRNAs following denervation. We examined whether post-transcriptional events indeed regulate AChR β-subunit mRNAs in response to denervation. First, in vitro stability assays revealed that the half-life of AChR β-subunit mRNAs was increased in the presence of denervated muscle protein extracts. A bioinformatics analysis revealed the existence of a conserved AU-rich element (ARE) in the 3'-untranslated region (UTR) of AChR β-subunit mRNA. Furthermore, denervation of mouse muscle injected with a luciferase reporter construct containing the AChR β-subunit 3'UTR, caused an increase in luciferase activity. By contrast, mutation of this ARE prevented this increase. We also observed that denervation increased expression of the RNA-binding protein human antigen R (HuR) and induced its translocation to the cytoplasm. Importantly, HuR binds to endogenous AChR β-subunit transcripts in cultured myotubes and in vivo, and this binding is increased in denervated versus innervated muscles. Finally, p38 MAPK, a pathway known to activate HuR, was induced following denervation as a result of MKK3/6 activation and a decrease in MKP-1 expression, thereby leading to an increase in the stability of AChR β-subunit transcripts. Together, these results demonstrate the important contribution of post-transcriptional events in regulating AChR β-subunit mRNAs and point toward a central role for HuR in mediating synaptic gene expression. SIGNIFICANCE STATEMENT Muscle denervation is a convenient model to examine expression of genes encoding proteins of the neuromuscular junction, especially acetylcholine receptors (AChRs). Despite the accepted model of AChR regulation, which implicates transcriptional mechanisms, it remains plausible that such events cannot fully account for changes in AChR expression following denervation. We show that denervation increases expression of the RNA-binding protein HuR, which in turn, causes an increase in the stability of AChR β-subunit mRNAs in denervated muscle. Our findings demonstrate for the first time the contribution of post-transcriptional events in controlling AChR expression in skeletal muscle, and points toward a central role for HuR in mediating synaptic development while also paving the way for developing RNA-based therapeutics for neuromuscular diseases.
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Azuma Y, Nakata T, Tanaka M, Shen XM, Ito M, Iwata S, Okuno T, Nomura Y, Ando N, Ishigaki K, Ohkawara B, Masuda A, Natsume J, Kojima S, Sokabe M, Ohno K. Congenital myasthenic syndrome in Japan: ethnically unique mutations in muscle nicotinic acetylcholine receptor subunits. Neuromuscul Disord 2015; 25:60-9. [PMID: 25264167 DOI: 10.1016/j.nmd.2014.09.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Revised: 08/09/2014] [Accepted: 09/03/2014] [Indexed: 11/22/2022]
Abstract
Congenital myasthenic syndromes (CMS) are caused by mutations in genes expressed at the neuromuscular junction. Most CMS patients have been reported in Western and Middle Eastern countries, and only four patients with COLQ mutations have been reported in Japan. We here report six mutations in acetylcholine receptor (AChR) subunit genes in five Japanese patients. Five mutations are novel, and one mutation is shared with a European American patient but with a different haplotype. Among the observed mutations, p.Thr284Pro (p.Thr264Pro according to the legacy annotation) in the epsilon subunit causes a slow-channel CMS. Five other mutations in the delta and epsilon subunits are splice site, frameshift, null, or missense mutations causing endplate AChR deficiency. We also found a heteroallelic p.Met465Thr in the beta subunit in another patient. p.Met465Thr, however, was likely to be polymorphism, because single channel recordings showed mild shortening of channel openings without affecting cell surface expression of AChR, and the minor allelic frequency of p.Met465Thr was 5.1% in the Japanese population. Lack of shared mutant alleles between the Japanese and the other patients suggests that most mutations described here are ethnically unique or de novo in each family.
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Affiliation(s)
- Yoshiteru Azuma
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan; Department of Pediatrics, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Tomohiko Nakata
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan; Department of Pediatrics, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Motoki Tanaka
- Department of Physiology, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Xin-Ming Shen
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
| | - Mikako Ito
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Satoshi Iwata
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Tatsuya Okuno
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | | | - Naoki Ando
- Department of Pediatrics, Nagoya City University Graduate School of Medicine, Nagoya, Japan
| | - Keiko Ishigaki
- Department of Pediatrics, Tokyo Women's Medical University, Tokyo, Japan
| | - Bisei Ohkawara
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Akio Masuda
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Jun Natsume
- Department of Pediatrics, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Seiji Kojima
- Department of Pediatrics, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Masahiro Sokabe
- Department of Physiology, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Kinji Ohno
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan.
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15
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Schaaf CP. Nicotinic acetylcholine receptors in human genetic disease. Genet Med 2014; 16:649-56. [DOI: 10.1038/gim.2014.9] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Accepted: 01/13/2014] [Indexed: 01/26/2023] Open
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16
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Barwick KES, Wright J, Al-Turki S, McEntagart MM, Nair A, Chioza B, Al-Memar A, Modarres H, Reilly MM, Dick KJ, Ruggiero AM, Blakely RD, Hurles ME, Crosby AH. Defective presynaptic choline transport underlies hereditary motor neuropathy. Am J Hum Genet 2012; 91:1103-7. [PMID: 23141292 DOI: 10.1016/j.ajhg.2012.09.019] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Revised: 07/16/2012] [Accepted: 09/20/2012] [Indexed: 11/18/2022] Open
Abstract
The neuromuscular junction (NMJ) is a specialized synapse with a complex molecular architecture that provides for reliable transmission between the nerve terminal and muscle fiber. Using linkage analysis and whole-exome sequencing of DNA samples from subjects with distal hereditary motor neuropathy type VII, we identified a mutation in SLC5A7, which encodes the presynaptic choline transporter (CHT), a critical determinant of synaptic acetylcholine synthesis and release at the NMJ. This dominantly segregating SLC5A7 mutation truncates the encoded product just beyond the final transmembrane domain, eliminating cytosolic-C-terminus sequences known to regulate surface transporter trafficking. Choline-transport assays in both transfected cells and monocytes from affected individuals revealed significant reductions in hemicholinium-3-sensitive choline uptake, a finding consistent with a dominant-negative mode of action. The discovery of CHT dysfunction underlying motor neuropathy identifies a biological basis for this group of conditions and widens the spectrum of disorders that derive from impaired NMJ transmission. Our findings compel consideration of mutations in SLC5A7 or its functional partners in relation to unexplained motor neuronopathies.
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Affiliation(s)
- Katy E S Barwick
- Centre for Human Genetics, St. George's University of London, Cranmer Terrace, London SW17 0RE, UK
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17
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Engel AG. Current status of the congenital myasthenic syndromes. Neuromuscul Disord 2012; 22:99-111. [PMID: 22104196 PMCID: PMC3269564 DOI: 10.1016/j.nmd.2011.10.009] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2011] [Revised: 10/11/2011] [Accepted: 10/13/2011] [Indexed: 01/04/2023]
Abstract
Congenital myasthenic syndromes (CMS) are heterogeneous disorders in which the safety margin of neuromuscular transmission is compromised by one or more specific mechanisms. Clinical, electrophysiologic, and morphologic studies have paved the way for detecting CMS-related mutations in proteins residing in the nerve terminal, the synaptic basal lamina, and in the postsynaptic region of the motor endplate. The disease proteins identified to date include choline acetyltransferase (ChAT), the endplate species of acetylcholinesterase (AChE), β2-laminin, the acetylcholine receptor (AChR), rapsyn, plectin, Na(v)1.4, the muscle specific protein kinase (MuSK), agrin, downstream of tyrosine kinase 7 (Dok-7), and glutamine-fructose-6-phosphate transaminase 1 (GFPT1). Myasthenic syndromes associated with centronuclear myopathies were recently recognized. Analysis of properties of expressed mutant proteins contributed to finding improved therapy for most CMS. Despite these advances, the molecular basis of some phenotypically characterized CMS remains elusive. Moreover, other types of CMS and disease genes likely exist and await discovery.
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Affiliation(s)
- Andrew G Engel
- Department of Neurology, Mayo Clinic, Rochester, MN 55905, United States.
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18
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Modla S, Mendonca J, Czymmek KJ, Akins RE. Identification of neuromuscular junctions by correlative confocal and transmission electron microscopy. J Neurosci Methods 2010; 191:158-65. [PMID: 20600319 DOI: 10.1016/j.jneumeth.2010.06.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2009] [Revised: 06/07/2010] [Accepted: 06/16/2010] [Indexed: 11/16/2022]
Abstract
The physiological processes regulating neuromuscular transmission are highly dependent on the structural features of the motor neuron and motor endplate, and detailing the structure of neuromuscular junctions (NMJs) in muscle biopsies is a powerful method for research and diagnostics. The observation of NMJ ultrastructure, however, is complicated by the difficulty in locating NMJs for analysis by electron microscopy. Consequently, a correlative confocal-transmission electron microscopy method was developed. Fixed muscle samples were cryo-protected in sucrose, sectioned on a cryostat, and stained with fluorescent alpha-bungarotoxin for confocal microscopy. Sections containing junctions were mapped and then processed for transmission electron microscopy (TEM). Cryostat sections allowed large expanses of muscle tissue to be rapidly screened and enabled specific junctions to be targeted for TEM. The morphology of the junctions was well preserved with all essential features of the pre- and postsynaptic elements readily identifiable without freeze damage. Unlike NMJ correlative methods using histochemical stains and DAB photo-oxidation, no electron dense precipitate was deposited over the NMJ, enabling an unobstructed view of the pre- and postsynaptic structures.
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Affiliation(s)
- Shannon Modla
- Delaware Biotechnology Institute Bio-Imaging Center, University of Delaware, 15 Innovation Way, Suite 117, Newark, DE 19711, USA
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19
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Lee Y, Rudell J, Ferns M. Rapsyn interacts with the muscle acetylcholine receptor via alpha-helical domains in the alpha, beta, and epsilon subunit intracellular loops. Neuroscience 2009; 163:222-32. [PMID: 19482062 PMCID: PMC2728176 DOI: 10.1016/j.neuroscience.2009.05.057] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2009] [Revised: 05/01/2009] [Accepted: 05/25/2009] [Indexed: 12/12/2022]
Abstract
At the developing vertebrate neuromuscular junction, the acetylcholine receptor becomes aggregated at high density in the postsynaptic muscle membrane. Receptor localization is regulated by the motoneuron-derived factor, agrin, and requires an intracellular, scaffolding protein called rapsyn. However, it remains unclear where rapsyn binds on the acetylcholine receptor and how their interaction is regulated. In this study, we identified rapsyn's binding site on the acetylcholine receptor using chimeric constructs where the intracellular domain of CD4 was substituted for the major intracellular loop of each mouse acetylcholine receptor subunit. When expressed in heterologous cells, we found that rapsyn clustered and cytoskeletally anchored CD4-alpha, beta and epsilon subunit loops but not CD4-delta loop. Rapsyn-mediated clustering and anchoring was highest for beta loop, followed by epsilon and alpha, suggesting that rapsyn interacts with the loops with different affinities. Moreover, by making deletions within the beta subunit intracellular loop, we show that rapsyn interacts with the alpha-helical region, a secondary structural motif present in the carboxyl terminal portion of the subunit loops. When expressed in muscle cells, rapsyn co-immunoprecipitated together with a CD4-alpha helical region chimera, independent of agrin signaling. Together, these findings demonstrate that rapsyn interacts with the acetylcholine receptor via an alpha-helical structural motif conserved between the alpha, beta and epsilon subunits. Binding at this site likely mediates the critical rapsyn interaction involved in localizing the acetylcholine receptor at the neuromuscular junction.
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Affiliation(s)
- Y Lee
- Department of Anesthesiology and Physiology and Membrane Biology, University of California Davis, One Shields Avenue, Davis, CA 95616, USA
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20
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Masuda A, Shen XM, Ito M, Matsuura T, Engel AG, Ohno K. hnRNP H enhances skipping of a nonfunctional exon P3A in CHRNA1 and a mutation disrupting its binding causes congenital myasthenic syndrome. Hum Mol Genet 2008; 17:4022-35. [PMID: 18806275 PMCID: PMC2638575 DOI: 10.1093/hmg/ddn305] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Revised: 09/01/2008] [Accepted: 09/17/2008] [Indexed: 12/28/2022] Open
Abstract
In humans and great apes, CHRNA1 encoding the muscle nicotinic acetylcholine receptor alpha subunit carries an inframe exon P3A, the inclusion of which yields a nonfunctional alpha subunit. In muscle, the P3A(-) and P3A(+) transcripts are generated in a 1:1 ratio but the functional significance and regulation of the alternative splicing remain elusive. An intronic mutation (IVS3-8G>A), identified in a patient with congenital myasthenic syndrome, disrupts an intronic splicing silencer (ISS) and results in exclusive inclusion of the downstream P3A exon. We found that the ISS-binding splicing trans-factor was heterogeneous nuclear ribonucleoprotein (hnRNP) H and the mutation attenuated the affinity of hnRNP for the ISS approximately 100-fold. We next showed that direct placement of hnRNP H to the 3' end of intron 3 silences, and siRNA-mediated downregulation of hnRNP H enhances recognition of exon P3A. Analysis of the human genome suggested that the hnRNPH-binding UGGG motif is overrepresented close to the 3' ends of introns. Pursuing this clue, we showed that alternative exons of GRIP1, FAS, VPS13C and NRCAM are downregulated by hnRNP H. Our findings imply that the presence of the hnRNP H-binding motif close to the 3' end of an intron is an essential but underestimated splicing regulator of the downstream exon.
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Affiliation(s)
- Akio Masuda
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Xin-Ming Shen
- Department of Neurology, Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN, USA
| | - Mikako Ito
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Tohru Matsuura
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Andrew G. Engel
- Department of Neurology, Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN, USA
| | - Kinji Ohno
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya, Japan
- Department of Neurology, Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN, USA
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21
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Lo WY, Botzolakis EJ, Tang X, Macdonald RL. A conserved Cys-loop receptor aspartate residue in the M3-M4 cytoplasmic loop is required for GABAA receptor assembly. J Biol Chem 2008; 283:29740-52. [PMID: 18723504 DOI: 10.1074/jbc.m802856200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Members of the Cys-loop superfamily of ligand-gated ion channels, which mediate fast synaptic transmission in the nervous system, are assembled as heteropentamers from a large repertoire of neuronal subunits. Although several motifs in subunit N-terminal domains are known to be important for subunit assembly, increasing evidence points toward a role for C-terminal domains. Using a combination of flow cytometry, patch clamp recording, endoglycosidase H digestion, brefeldin A treatment, and analytic centrifugation, we identified a highly conserved aspartate residue at the boundary of the M3-M4 loop and the M4 domain that was required for binary and ternary gamma-aminobutyric acid type A receptor surface expression. Mutation of this residue caused mutant and partnering subunits to be retained in the endoplasmic reticulum, reflecting impaired forward trafficking. Interestingly although mutant and partnering wild type subunits could be coimmunoprecipitated, analytic centrifugation studies demonstrated decreased formation of pentameric receptors, suggesting that this residue played an important role in later steps of subunit oligomerization. We thus conclude that C-terminal motifs are also important determinants of Cys-loop receptor assembly.
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Affiliation(s)
- Wen-yi Lo
- Program in Neuroscience, Vanderbilt University, Nashville, Tennessee 37232, USA
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22
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Nieves-Cintrón M, Caballero-Rivera D, Silva WI, Navedo MF, Lasalde-Dominicci JA. Functional contribution of alpha3L8' to the neuronal nicotinic alpha3 receptor. J Neurosci Res 2008; 86:2884-94. [PMID: 18615639 DOI: 10.1002/jnr.21749] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The role of position L8', located in transmembrane domain 1 of the neuronal nicotinic alpha3 subunit, was characterized by using two-electrode voltage clamp in Xenopus oocytes. Four amino acids (Ala, Ser, Phe, and Tyr) were inserted at this conserved position, and the mutant subunit was coexpressed with either wild-type beta2 or beta4 subunits. These substitutions led to significant alterations in the pharmacodynamic parameters of cholinergic agents, resulting in loss of function. Ala and Ser substitutions resulted in losses in agonist (ACh, nicotine, and DMPP) potency and intrinsic activity at both alpha3beta2 and alpha3beta4 receptors. Similarly, significant changes in antagonist potency were produced by the Ala and Ser substitutions. Phe and Tyr mutations did not alter the receptor's EC(50) for ACh or nicotine but reduced the EC(50) for DMPP at both receptors. The Phe mutation also reduced the intrinsic activity of all agonists tested at both receptors. The Tyr mutation, though, led to a decrease in intrinsic activity for all agonists at the alpha3beta2 receptor, yet resulted in no changes for DMPP, a decrease for nicotine, and an increase for ACh at the alpha3beta4 receptor. The most dramatic changes in the receptor's functional properties were produced by substitutions that introduced the largest changes in amino acid volume. Additional replacements (Gly, Thr, and Val) suggested an inverse correlation between amino acid volume at position alpha3L8' and EC(50) for alpha3beta4 nAChRs; however, alpha3beta2 nAChRs displayed a nonlinear correlation. These data demonstrate that structural alterations at position alpha3L8' could propagate to the agonist-binding site.
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23
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Hartmann J, Garland T, Hannon RM, Kelly SA, Muñoz G, Pomp D. Fine mapping of "mini-muscle," a recessive mutation causing reduced hindlimb muscle mass in mice. J Hered 2008; 99:679-87. [PMID: 18544554 DOI: 10.1093/jhered/esn040] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Prolonged selective breeding of Hsd:ICR mice for high levels of voluntary wheel running has favored an unusual phenotype (mini-muscle [MM]), apparently caused by a single Mendelian recessive allele, in which hindlimb muscle mass is reduced by almost 50%. We recently described the creation and phenotypic characterization of a population suitable for mapping the genomic location of the MM gene. Specifically, we crossed females from a high-runner line fixed for the MM allele with male C57BL/6J. F1 males were then backcrossed to the MM parent females. Backcross (BC) mice exhibited a 50:50 ratio of normal to MM phenotypes. Here, we report on linkage mapping of MM in this BC population to a 2.6335-Mb interval on MMU11. This region harbors approximately 100 expressed or predicted genes, many of which have known roles in muscle development and/or function. Identification of the genetic variation that underlies MM could potentially be very important in understanding both normal muscle function and disregulation of muscle physiology leading to disease.
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Affiliation(s)
- John Hartmann
- Department of Nutrition, University of North Carolina, Chapel Hill, NC 27599, USA
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24
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25
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Baier CJ, Barrantes FJ. Sphingolipids are necessary for nicotinic acetylcholine receptor export in the early secretory pathway. J Neurochem 2007; 101:1072-84. [PMID: 17437537 DOI: 10.1111/j.1471-4159.2007.04561.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The nicotinic acetylcholine receptor (AChR) is the prototype ligand-gated ion channel, and its function is dependent on its lipid environment. In order to study the involvement of sphingolipids (SL) in AChR trafficking, we used pharmacological approaches to dissect the SL biosynthetic pathway in CHO-K1/A5 cells heterologously expressing the muscle-type AChR. When SL biosynthesis was impaired, the cell surface targeting of AChR diminished with a concomitant increase in the intracellular receptor pool. The SL-inhibiting drugs increased unassembled AChR forms, which were retained at the endoplasmic reticulum (ER). These effects on AChR biogenesis and trafficking could be reversed by the addition of exogenous SL, such as sphingomyelin. On the basis of these effects we propose a 'chaperone-like' SL intervention at early stages of the AChR biosynthetic pathway, affecting both the efficiency of the assembly process and subsequent receptor trafficking to the cell surface.
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Affiliation(s)
- C J Baier
- UNESCO Chair of Biophysics and Molecular Neurobiology and Instituto de Investigaciones Bioquímicas de Bahía Blanca, Bahía Blanca, Argentina
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26
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Peters JA, Carland JE, Cooper MA, Livesey MR, Deeb TZ, Hales TG, Lambert JJ. Novel structural determinants of single-channel conductance in nicotinic acetylcholine and 5-hydroxytryptamine type-3 receptors. Biochem Soc Trans 2007; 34:882-6. [PMID: 17052220 DOI: 10.1042/bst0340882] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Nicotinic ACh (acetylcholine) and 5-HT3 (5-hydroxytryptamine type-3) receptors are cation-selective ion channels of the Cys-loop transmitter-gated ion channel superfamily. Numerous lines of evidence indicate that the channel lining domain of such receptors is formed by the alpha-helical M2 domain (second transmembrane domain) contributed by each of five subunits present within the receptor complex. Specific amino acid residues within the M2 domain have accordingly been demonstrated to influence both single-channel conductance (gamma) and ion selectivity. However, it is now clear from work performed on the homomeric 5-HT3A receptor, heteromeric 5-HT3A/5-HT3B receptor and 5-HT3A/5-HT3B receptor subunit chimaeric constructs that an additional major determinant of gamma resides within a cytoplasmic domain of the receptor termed the MA-stretch (membrane-associated stretch). The MA-stretch, within the M3-M4 loop, is not traditionally thought to be implicated in ion permeation and selection. Here, we describe how such observations extend to a representative neuronal nicotinic ACh receptor composed of alpha4 and beta2 subunits and, by inference, probably other members of the Cys-loop family. In addition, we will attempt to interpret our results within the context of a recently developed atomic scale model of the nicotinic ACh receptor of Torpedo marmorata (marbled electric ray).
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Affiliation(s)
- J A Peters
- Neurosciences Institute, Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, The University of Dundee, Dundee DD1 9SY, UK.
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27
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Peters JA, Hales TG, Lambert JJ. Molecular determinants of single-channel conductance and ion selectivity in the Cys-loop family: insights from the 5-HT3 receptor. Trends Pharmacol Sci 2005; 26:587-94. [PMID: 16194573 DOI: 10.1016/j.tips.2005.09.011] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2005] [Revised: 08/19/2005] [Accepted: 09/13/2005] [Indexed: 10/25/2022]
Abstract
The molecular determinants of the ionic selectivity and single-channel conductance of the Cys-loop family of transmitter-gated ion channels are beginning to be understood with increasing precision, in part, as a result of the recent availability of refined ultrastructural information for the archetype of the family, the nicotinic acetylcholine receptor (nAChR). Studies of another member of this family, the 5-HT(3) receptor, have now provided insight into the structure of its channel pore, the location of its gate and mechanisms of ion selectivity and translocation. The anomaly of the extremely low single-channel conductance of the homo-oligomeric 5-HT(3A) receptor has recently been solved, revealing that an intracellular domain of the protein is an important determinant of single-channel conductance. Such data are interpreted, in this article, in light of the most recent developments in structural characterization of the nAChR.
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MESH Headings
- Amino Acid Sequence
- Animals
- Cysteine/chemistry
- Humans
- Ion Channel Gating
- Ion Channels/chemistry
- Ion Channels/genetics
- Ion Channels/metabolism
- Ions
- Models, Molecular
- Molecular Sequence Data
- Mutation
- Protein Structure, Quaternary
- Protein Structure, Tertiary
- Receptors, Nicotinic/chemistry
- Receptors, Nicotinic/genetics
- Receptors, Nicotinic/metabolism
- Receptors, Serotonin, 5-HT3/chemistry
- Receptors, Serotonin, 5-HT3/genetics
- Receptors, Serotonin, 5-HT3/metabolism
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Affiliation(s)
- John A Peters
- Neurosciences Institute, Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, The University of Dundee, Dundee DD1 9SY, UK.
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28
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Andreux F, Hantaï D, Eymard B. [Congenital myasthenic syndromes: phenotypic expression and pathophysiological characterisation]. Rev Neurol (Paris) 2004; 160:163-76. [PMID: 15034473 DOI: 10.1016/s0035-3787(04)70887-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Congenital Myasthenic Syndromes (CMS) are a heterogeneous group of diseases caused by genetic defects affecting neuromuscular transmission. The twenty five past Years saw major advances in identifying different types of CMS due to abnormal presynaptic, synaptic, and postsynaptic proteins. CMS diagnosis requires two steps: 1) positive diagnosis supported by myasthenic signs beginning in neonatal period, efficacy of anticholinesterase medications, positive family history, negative tests for anti-acetylcholine receptor (AChR) antibodies, electromyographic studies (decremental response at low frequency, repetitive CMAP after one single stimulation); 2) pathophysiological characterisation of CMS implying specific studies: light and electron microscopic analysis of endplate (EP) morphology, estimation of the number of AChR per EP, acetylcholinesterase (AChE) expression, molecular genetic analysis. Most CMS are postsynaptic due to mutations in the AChR subunits genes that alter the kinetic properties or decrease the expression of AChR. The kinetic mutations increase or decrease the synaptic response to ACh resulting respectively in Slow Channel Syndrome (characterized by a autosomal dominant transmission, repetitive CMAP, refractoriness to anticholinesterase medication) and fast channel, recessively transmitted. AChR deficiency without kinetic abnormalities is caused by recessive mutations in AChR genes (mostly epsilon subunit) or by primary rapsyn deficiency, a post synaptic protein involved in AChR concentration. Recently, mutations in SCN4A sodium channel have been reported in one patient. AChE deficiency is identified on the following data: recessive transmission, presence of repetitive CMAP, refractoriness to cholinesterase inhibitors, slow pupillary response to light and absent expression of the enzyme at EP. This synaptic CMS is caused by mutations in the collagenic tail subunit (ColQ) that anchors the catalytic subunits in the synaptic basal lamina. The most frequent presynaptic CMS is caused by mutations of choline acetyltransferase. Several CMS are still not characterized. Many EP molecules are potential etiological candidates. In these unidentified cases, other methods of investigations are required: linkage analysis, when sufficient number of informative relatives are available, microelectrophysiological studies performed in intercostal or anconeus muscles. Prognosis of CMS, depending on severity and evolution of symptoms, is difficult to assess, and it cannot not be simply derived from mutation identification. Most patients respond favourably to anticholinesterase medications or to 3,4 DAP which is effective not only in presynaptic but also in postsynaptic CMS. Specific therapies for slow channel CMS are quinidine and fluoxetine that normalize the prolonged opening episodes. Clinical benefits derived from the full characterisation of each case include genetic counselling and specific therapy.
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Affiliation(s)
- F Andreux
- INSERM 582 et Institut de Myologie, Hôpital de la Pitié-Salpêtrière
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29
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Giraud M, Eymard B, Tranchant C, Gajdos P, Garchon HJ. Association of the gene encoding the δ-subunit of the muscle acetylcholine receptor (CHRND) with acquired autoimmune myasthenia gravis. Genes Immun 2004; 5:80-3. [PMID: 14735155 DOI: 10.1038/sj.gene.6364041] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The muscle acetylcholine receptor (AChR) is the main target self-antigen in acquired autoimmune myasthenia gravis (MG). Here, we investigated an association of MG with the CHRND gene encoding the delta-subunit of the AChR. Using a microsatellite repeat located in the second intron of the gene, we observed a preferential transmission of the allele 268 in 114 one-generation families with one myasthenic child (Pc=0.0154). This allele was also over-represented in a group of 350 unrelated nonthymoma MG patients (OR=1.78, P=0.038), but not in 84 thymoma patients, compared to 168 healthy controls. Moreover, among nonthymoma patients, those lacking serum anti-titin antibodies appeared to be best associated (OR=2.07, P=0.017). In contrast, there was no distortion in the transmission of a single-nucleotide substitution polymorphisms (SNPs) in the 3' untranslated region of CHRND nor in that of two SNPs located in the closely linked CHRNG gene, 4.5 kb telomeric to CHRND. The data warrant a detailed investigation of CHRND polymorphism in MG patients.
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Affiliation(s)
- M Giraud
- INSERM U580, Hôpital Necker, Paris, France
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30
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Beeson D, Webster R, Ealing J, Croxen R, Brownlow S, Brydson M, Newsom-Davis J, Slater C, Hatton C, Shelley C, Colquhoun D, Vincent A. Structural abnormalities of the AChR caused by mutations underlying congenital myasthenic syndromes. Ann N Y Acad Sci 2003; 998:114-24. [PMID: 14592868 DOI: 10.1196/annals.1254.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The objective was to define the molecular mechanisms underlying congenital myasthenic syndromes (CMS) by studying mutations within genes encoding the acetylcholine receptor (AChR) and related proteins at the neuromuscular junction. It was found that mutations within muscle AChRs are the most common cause of CMS. The majority are located within the epsilon-subunit gene and result in AChR deficiency.
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MESH Headings
- Alleles
- Animals
- Cell Line
- DNA Mutational Analysis
- Exons
- Extracellular Space/genetics
- Extracellular Space/metabolism
- Female
- Humans
- In Situ Hybridization/methods
- Male
- Mutation
- Myasthenic Syndromes, Congenital/classification
- Myasthenic Syndromes, Congenital/diagnosis
- Myasthenic Syndromes, Congenital/genetics
- Myasthenic Syndromes, Congenital/physiopathology
- Neuromuscular Junction/abnormalities
- Neuromuscular Junction/genetics
- Neuromuscular Junction/metabolism
- Patch-Clamp Techniques
- Polymorphism, Single-Stranded Conformational
- Protein Structure, Secondary
- Protein Subunits/genetics
- Protein Subunits/metabolism
- Receptors, Cholinergic/chemistry
- Receptors, Cholinergic/deficiency
- Receptors, Cholinergic/genetics
- Receptors, Cholinergic/physiology
- Reverse Transcriptase Polymerase Chain Reaction
- Transfection
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Affiliation(s)
- David Beeson
- Neurosciences Group, Weatherall Institute of Molecular Medicine, The John Radcliffe, Headington, Oxford OX3 9DS, United Kingdom.
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31
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Wanamaker CP, Christianson JC, Green WN. Regulation of nicotinic acetylcholine receptor assembly. Ann N Y Acad Sci 2003; 998:66-80. [PMID: 14592864 DOI: 10.1196/annals.1254.009] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The four muscle-type nicotinic acetylcholine receptor (AChR) subunits, alpha, beta, gamma, and delta, assemble into functional alpha(2)betagammadelta pentamers in the endoplasmic reticulum (ER) through a series of interdependent folding and oligomerization events. The first stable assembly intermediate is a trimer composed of alpha, beta, and gamma subunits. The formation of alphabetagamma trimers initiates a series of subunit folding and processing events that allow addition of delta subunits to form alphabetagammadelta tetramers. Subunit folding and processing continue with formation of the ligand-binding sites on the alpha subunit of alphabetagammadelta tetramers and the second alpha subunit added to assemble alpha(2)betagammadelta pentamers. AChR assembly is inefficient. Only 20-30% of synthesized subunits assemble into mature receptors in the ER, while the remaining unassembled subunits are degraded. However, the efficiency of subunit assembly can be regulated under certain conditions leading to higher AChR expression. Increased intracellular cAMP levels cause a 2- to 3-fold increase in AChR assembly efficiency and a comparable increase in surface expression. Additionally, block of ubiquitin-proteasome degradation appears to enhance AChR assembly and expression. Thus, the regulation of AChR assembly through posttranslational mechanisms is a potential therapeutic target for increasing AChR expression in diseases in which expression is compromised.
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Affiliation(s)
- Christian P Wanamaker
- Department of Neurobiology, Pharmacology, and Physiology, University of Chicago, Chicago, Illinois 60637, USA
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32
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Maselli RA, Dunne V, Pascual-Pascual SI, Bowe C, Agius M, Frank R, Wollmann RL. Rapsyn mutations in myasthenic syndrome due to impaired receptor clustering. Muscle Nerve 2003; 28:293-301. [PMID: 12929188 DOI: 10.1002/mus.10433] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Rapsyn, a 43-kDa postsynaptic protein, is essential for anchoring and clustering acetylcholine receptors (AChRs) at the endplate (EP). Mutations in the rapsyn gene have been found to cause a postsynaptic congenital myasthenic syndrome (CMS). We detected six patients with CMS due to mutations in the rapsyn gene (RAPSN). In vitro studies performed in the anconeus muscle biopsies of four patients showed severe reduction of miniature EP potential amplitudes. Electron microscopy revealed various degrees of impaired development of postsynaptic membrane folds. All patients carried the N88K mutation. Three patients were homozygous for N88K and had less severe phenotypes and milder histopathologic abnormalities than the three patients who were heterozygous and carried a second mutation (either L14P, 46insC, or Y269X). Surprisingly, two N88K homozygous patients had one asymptomatic relative each who carried the same genotype, suggesting that additional genetic factors to RAPSN mutations are required for disease expression.
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MESH Headings
- Adolescent
- Child, Preschool
- Excitatory Postsynaptic Potentials/genetics
- Female
- Genetic Predisposition to Disease/genetics
- Genetic Testing
- Genotype
- Heterozygote
- Homozygote
- Humans
- Male
- Microscopy, Electron
- Muscle Proteins/deficiency
- Muscle Proteins/genetics
- Muscle, Skeletal/innervation
- Muscle, Skeletal/pathology
- Muscle, Skeletal/physiopathology
- Mutation/genetics
- Myasthenic Syndromes, Congenital/genetics
- Myasthenic Syndromes, Congenital/metabolism
- Myasthenic Syndromes, Congenital/physiopathology
- Neuromuscular Junction/genetics
- Neuromuscular Junction/pathology
- Neuromuscular Junction/ultrastructure
- Pedigree
- Phenotype
- Receptors, Cholinergic/genetics
- Receptors, Cholinergic/metabolism
- Receptors, Cholinergic/ultrastructure
- Synaptic Membranes/genetics
- Synaptic Membranes/pathology
- Synaptic Membranes/ultrastructure
- Synaptic Transmission/genetics
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Affiliation(s)
- Ricardo A Maselli
- Department of Neurology, University of California, 1515 Newton Court, Room 510, Davis, California 95616, USA.
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33
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Engel AG, Ohno K, Shen XM, Sine SM. Congenital Myasthenic Syndromes: Multiple Molecular Targets at the Neuromuscular Junction. Ann N Y Acad Sci 2003; 998:138-60. [PMID: 14592871 DOI: 10.1196/annals.1254.016] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Congenital myasthenic syndromes (CMS) stem from defects in presynaptic, synaptic, and postsynaptic proteins. The presynaptic CMS are associated with defects that curtail the evoked release of acetylcholine (ACh) quanta or ACh resynthesis. Defects in ACh resynthesis have now been traced to mutations in choline acetyltransferase. A synaptic CMS is caused by mutations in the collagenic tail subunit (ColQ) of the endplate species of acetylcholinesterase that prevent the tail subunit from associating with catalytic subunits or from becoming inserted into the synaptic basal lamina. Most postsynaptic CMS are caused by mutations in subunits of the acetylcholine receptor (AChR) that alter the kinetic properties or decrease the expression of AChR. The kinetic mutations increase or decrease the synaptic response to ACh and result in slow- and fast-channel syndromes, respectively. Most low-expressor mutations reside in the AChR epsilon subunit and are partially compensated by residual expression of the fetal-type gamma subunit. In a subset of CMS patients, endplate AChR deficiency is caused by mutations in rapsyn, a molecule that plays a critical role in concentrating AChR in the postsynaptic membrane.
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Affiliation(s)
- Andrew G Engel
- Neuromuscular Disease Research Laboratory, Department of Neurology, Mayo Clinic, Rochester, Minnesota 55905, USA.
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34
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Engel AG, Ohno K, Sine SM. Sleuthing molecular targets for neurological diseases at the neuromuscular junction. Nat Rev Neurosci 2003; 4:339-52. [PMID: 12728262 DOI: 10.1038/nrn1101] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Andrew G Engel
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, Minnesota 55905, USA.
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35
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Shen XM, Ohno K, Tsujino A, Brengman JM, Gingold M, Sine SM, Engel AG. Mutation causing severe myasthenia reveals functional asymmetry of AChR signature cystine loops in agonist binding and gating. J Clin Invest 2003; 111:497-505. [PMID: 12588888 PMCID: PMC151927 DOI: 10.1172/jci16997] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
We describe a highly disabling congenital myasthenic syndrome (CMS) associated with rapidly decaying, low-amplitude synaptic currents, and trace its cause to a valine to leucine mutation in the signature cystine loop (cys-loop) of the AChR alpha subunit. The recently solved crystal structure of an ACh-binding protein places the cys-loop at the junction between the extracellular ligand-binding and transmembrane domains where it may couple agonist binding to channel gating. We therefore analyzed the kinetics of ACh-induced single-channel currents to identify elementary steps in the receptor activation mechanism altered by the alphaV132L mutation. The analysis reveals that alphaV132L markedly impairs ACh binding to receptors in the resting closed state, decreasing binding affinity for the second binding step 30-fold, but attenuates gating efficiency only about twofold. By contrast, mutation of the equivalent valine residue in the delta subunit impairs channel gating approximately fourfold with little effect on ACh binding, while corresponding mutations in the beta and epsilon subunits are without effect. The unique functional contribution of the alpha subunit cys-loop likely owes to its direct connection via a beta strand to alphaW149 at the center of the ligand-binding domain. The overall findings reveal functional asymmetry between cys-loops of the different AChR subunits in contributing to ACh binding and channel gating.
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Affiliation(s)
- Xin-Ming Shen
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, Minnesota 55905, USA
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36
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Huebsch KA, Maimone MM. Rapsyn-mediated clustering of acetylcholine receptor subunits requires the major cytoplasmic loop of the receptor subunits. JOURNAL OF NEUROBIOLOGY 2003; 54:486-501. [PMID: 12532399 DOI: 10.1002/neu.10177] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
During synaptogenesis at the neuromuscular junction, nicotinic acetylcholine receptors (AChRs) are organized into high-density postsynaptic clusters that are critical for efficient synaptic transmission. Rapsyn, an AChR associated cytoplasmic protein, is essential for the aggregation and immobilization of AChRs at the neuromuscular junction. Previous studies have shown that when expressed in nonmuscle cells, both assembled and unassembled AChR subunits are clustered by rapsyn, and the clustering of the alpha subunit is dependent on its major cytoplasmic loop. In the present study, we investigated the mechanism of rapsyn-induced clustering of the AChR beta, gamma, and delta subunits by testing mutant subunits for the ability to cocluster with rapsyn in transfected QT6 cells. For each subunit, deletion of the major cytoplasmic loop, between the third and fourth transmembrane domains, dramatically reduced coclustering with rapsyn. Furthermore, each major cytoplasmic loop was sufficient to mediate clustering of an unrelated transmembrane protein. The AChR subunit mutants lacking the major cytoplasmic loops could assemble into alphadelta dimers, but these were poorly clustered by rapsyn unless at least one mutant was replaced with its wild-type counterpart. These results demonstrate that the major cytoplasmic loop of each AChR subunit is both necessary and sufficient for mediating efficient clustering by rapsyn, and that only one such domain is required for rapsyn-mediated clustering of an assembly intermediate, the alphadelta dimer.
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Affiliation(s)
- Kimberly A Huebsch
- Department of Cell and Developmental Biology, SUNY Upstate Medical University, 750 East Adams Street, Syracuse, New York 13210, USA
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37
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Abstract
Congenital myasthenic syndromes (CMS) stem from defects in presynaptic, synaptic basal lamina, and postsynaptic proteins. The presynaptic CMS are associated with defects that curtail the evoked release of acetylcholine (ACh) quanta or ACh resynthesis. Defects in ACh resynthesis have now been traced to mutations in choline acetyltransferase. A basal lamina CMS is caused by mutations in the collagenic tail subunit (ColQ) of the endplate species of acetylcholinesterase that prevent the tail subunit from associating with catalytic subunits or from becoming inserted into the synaptic basal lamina. Most postsynaptic CMS are caused by mutations in subunits of the acetylcholine receptor (AChR) that alter the kinetic properties or decrease the expression of AChR. The kinetic mutations increase or decrease the synaptic response to ACh and result in slow- and fast-channel syndromes, respectively. Most low-expressor mutations reside in the AChR epsilon subunit and are partially compensated by residual expression of the fetal type gamma subunit. In a subset of CMS patients, endplate AChR deficiency is caused by mutations in rapsyn, a molecule that plays a critical role in concentrating AChR in the postsynaptic membrane.
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Affiliation(s)
- Andrew G Engel
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, Minnesota 55905, USA.
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38
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Affiliation(s)
- Kinji Ohno
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA
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39
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Shen XM, Ohno K, Fukudome T, Tsujino A, Brengman JM, De Vivo DC, Packer RJ, Engel AG. Congenital myasthenic syndrome caused by low-expressor fast-channel AChR delta subunit mutation. Neurology 2002; 59:1881-8. [PMID: 12499478 DOI: 10.1212/01.wnl.0000042422.87384.2f] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE To determine the molecular basis of a disabling congenital myasthenic syndrome (CMS) observed in two related and one unrelated Arab kinship. BACKGROUND CMS can arise from defects in presynaptic, synaptic basal lamina-associated, or postsynaptic proteins. Most CMS are postsynaptic, and most reside in the AChR epsilon subunit; only two mutations have been reported in the AChR delta subunit to date. METHODS Cytochemistry, electron microscopy, alpha-bungarotoxin binding studies, microelectrode and patch-clamp recordings, mutation analysis, mutagenesis, and expression studies in human embryonic kidney cells were employed. RESULTS Endplate studies showed AChR deficiency, fast decaying, low-amplitude endplate currents, and abnormally brief channel opening events. Mutation analysis revealed a novel homozygous missense mutation (deltaP250Q) of the penultimate proline in the first transmembrane domain (TMD1) of the AChR delta subunit. Expression studies indicate that deltaP250Q (1) hinders delta/alpha subunit association during early AChR assembly; (2) hinders opening of the doubly occupied closed receptor (A(2)R); and (3) speeds the dissociation of acetylcholine from A(2)R. Mutagenesis studies indicate that deltaP250L also has fast-channel effects, whereas epsilon P245L and epsilon P245Q, identical mutations of the corresponding proline in the epsilon subunit, have mild slow-channel effects. CONCLUSIONS deltaP250Q represents the third mutation observed in the AChR delta subunit. The severe phenotype caused by deltaP250Q is attributed to endplate AChR deficiency, fast decay of the synaptic response, and lack of compensatory factors. That the penultimate prolines in TMD1 of the delta and epsilon subunits exert a reciprocal regulatory effect on the length of the channel opening bursts reveals an unexpected functional asymmetry between the two subunits.
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Affiliation(s)
- X-M Shen
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN 55905, USA
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40
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Abstract
The past decade saw remarkable advances in defining the molecular and genetic basis of the congenital myasthenic syndromes. These advances would not have been possible without antecedent clinical observations, electrophysiologic analysis, and careful morphologic studies that pointed to candidate genes or proteins. For example, a kinetic abnormality of the acetylcholine receptor (AChR) detected at the single channel level pointed to a kinetic mutation in an AChR subunit; endplate AChR deficiency suggested mutations residing in an AChR subunit or in rapsyn; absence of acetylcholinesterase (AChE) from the endplate predicted mutations in the catalytic or collagen-tailed subunit of this enzyme; and a history of abrupt episodes of apnea associated with a stimulation dependent decrease of endplate potentials and currents implicated proteins concerned with ACh resynthesis or vesicular filling. Discovery of mutations in endplate-specific proteins also prompted expression studies that afforded proof of pathogenicity, provided clues for rational therapy, lead to precise structure function correlations, and highlighted functionally significant residues or molecular domains that previous systematic mutagenesis studies had failed to detect. An overview of the spectrum of the congenital myasthenic syndromes suggests that most are caused by mutations in AChR subunits, and particularly in the epsilon subunit. Future studies will likely uncover new types of CMS that reside in molecules governing quantal release, organization of the synaptic basal lamina, and expression and aggregation of AChR on the postsynaptic junctional folds.
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Affiliation(s)
- Andrew G Engel
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN 55905, USA.
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41
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Sine SM, Wang HL, Bren N. Lysine scanning mutagenesis delineates structural model of the nicotinic receptor ligand binding domain. J Biol Chem 2002; 277:29210-23. [PMID: 12011092 DOI: 10.1074/jbc.m203396200] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nicotinic acetylcholine receptors (AChR) and their relatives mediate rapid chemical transmission throughout the nervous system, yet their atomic structures remain elusive. Here we use lysine scanning mutagenesis to determine the orientation of residue side chains toward core hydrophobic or surface hydrophilic environments and use this information to build a structural model of the ligand binding region of the AChR from adult human muscle. The resulting side-chain orientations allow assignment of residue equivalence between AChR subunits and an acetylcholine binding protein solved by x-ray crystallography, providing the foundation for homology modeling. The resulting structural model of the AChR provides a picture of the ACh binding site and predicts novel pairs of residues that stabilize subunit interfaces. The overall results suggest that lysine scanning can provide the basis for structural modeling of other members of the AChR superfamily as well as of other proteins with repeating structures delimiting a hydrophobic core.
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MESH Headings
- Amino Acid Sequence
- Binding, Competitive
- Cell Line
- Crystallography, X-Ray
- DNA, Complementary/metabolism
- Humans
- Kinetics
- Ligands
- Lysine/chemistry
- Lysine/metabolism
- Models, Biological
- Models, Chemical
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Mutation
- Plasmids/metabolism
- Protein Binding
- Protein Conformation
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Receptors, Nicotinic/metabolism
- Sequence Homology, Amino Acid
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Affiliation(s)
- Steven M Sine
- Receptor Biology Laboratory, Department of Physiology and Biophysics, Mayo Foundation, Rochester, Minnesota 55905, USA.
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42
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Abstract
Congenital myasthenic syndromes (CMS) constitute a heterogenous group of inherited disorders in which neuromuscular transmission is compromised by one or more specific mechanisms. Clinical evidence for the diagnosis of a CMS includes a history of increased fatigable weakness since infancy or early childhood, a decremental EMG response, and the absence of acetylcholine receptor (AChR) antibodies. There has been rapid progress in understanding of the molecular basis of CMS. Mutation analysis of the AChR subunits has revealed numerous disease-associated mutations. These mutations alter the response to acetylcholine. It is decreased in the fast-channel syndromes and in primary AChR deficiency; and it is increased in the slow-channel syndrome due to prolonged open-time of the AChR. Acetylcholinesterase deficiency is associated with mutations in the gene encoding the collagenic tail subunit of the enzyme. Mutations in the gene encoding for choline acetyltransferase causes the CMS associated with episodic apnea.
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Affiliation(s)
- Joern P Sieb
- Department of Neurology, Max Planck Institute of Psychiatry, Munich, Germany
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43
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Ohno K, Engel AG, Shen XM, Selcen D, Brengman J, Harper CM, Tsujino A, Milone M. Rapsyn mutations in humans cause endplate acetylcholine-receptor deficiency and myasthenic syndrome. Am J Hum Genet 2002; 70:875-85. [PMID: 11791205 PMCID: PMC379116 DOI: 10.1086/339465] [Citation(s) in RCA: 171] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2001] [Accepted: 01/04/2002] [Indexed: 01/22/2023] Open
Abstract
Congenital myasthenic syndromes (CMSs) stem from genetic defects in endplate (EP)-specific presynaptic, synaptic, and postsynaptic proteins. The postsynaptic CMSs identified to date stem from a deficiency or kinetic abnormality of the acetylcholine receptor (AChR). All CMSs with a kinetic abnormality of AChR, as well as many CMSs with a deficiency of AChR, have been traced to mutations in AChR-subunit genes. However, in a subset of patients with EP AChR deficiency, the genetic defect has remained elusive. Rapsyn, a 43-kDa postsynaptic protein, plays an essential role in the clustering of AChR at the EP. Seven tetratricopeptide repeats (TPRs) of rapsyn subserve self-association, a coiled-coil domain binds to AChR, and a RING-H2 domain associates with beta-dystroglycan and links rapsyn to the subsynaptic cytoskeleton. Rapsyn self-association precedes recruitment of AChR to rapsyn clusters. In four patients with EP AChR deficiency but with no mutations in AChR subunits, we identify three recessive rapsyn mutations: one patient carries L14P in TPR1 and N88K in TPR3; two are homozygous for N88K; and one carries N88K and 553ins5, which frameshifts in TPR5. EP studies in each case show decreased staining for rapsyn and AChR, as well as impaired postsynaptic morphological development. Expression studies in HEK cells indicate that none of the mutations hinders rapsyn self-association but that all three diminish coclustering of AChR with rapsyn.
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Affiliation(s)
- Kinji Ohno
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN 55905, USA
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44
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Ohno K, Engel AG. Congenital myasthenic syndromes: genetic defects of the neuromuscular junction. Curr Neurol Neurosci Rep 2002; 2:78-88. [PMID: 11898587 DOI: 10.1007/s11910-002-0057-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Congenital myasthenic syndromes (CMS) stem from defects in presynaptic, synaptic, and postsynaptic proteins. The presynaptic CMS are associated with defects that curtail the evoked release of acetylcholine (ACh) quanta or the resynthesis of ACh. Insufficient resynthesis of ACh is now known to be caused by mutations that reduce the expression, catalytic efficiency, or both of choline acetyltransferase. The synaptic CMS are caused by mutations in the collagenic tail subunit (ColQ) of the endplate species of acetylcholinesterase that prevent ColQ from associating with catalytic subunits or from insertion into the synaptic basal lamina. With one exception, postsynaptic CMS identified to date are associated with a kinetic abnormality or decreased expression of the acetylcholine receptor (AChR). Numerous mutations have now been identified in subunits of AChR that alter the kinetics or surface expression of the receptor. The kinetic mutations increase or decrease the synaptic response to ACh and result in slow- and fast-channel syndromes, respectively. Most mutations that reduce surface expression of AChR reside in the receptor's epsilon subunit and are partially compensated by residual expression of the fetal-type gamma subunit. Null mutations in both alleles of other AChR subunits are likely lethal, owing to absence of a substituting subunit.
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Affiliation(s)
- Kinji Ohno
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
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45
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Brownlow S, Webster R, Croxen R, Brydson M, Neville B, Lin JP, Vincent A, Newsom-Davis J, Beeson D. Acetylcholine receptor δ subunit mutations underlie a fast-channel myasthenic syndrome and arthrogryposis multiplex congenita. J Clin Invest 2001. [DOI: 10.1172/jci200112935] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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46
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Brownlow S, Webster R, Croxen R, Brydson M, Neville B, Lin JP, Vincent A, Newsom-Davis J, Beeson D. Acetylcholine receptor delta subunit mutations underlie a fast-channel myasthenic syndrome and arthrogryposis multiplex congenita. J Clin Invest 2001; 108:125-30. [PMID: 11435464 PMCID: PMC209343 DOI: 10.1172/jci12935] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Limitation of movement during fetal development may lead to multiple joint contractures in the neonate, termed arthrogryposis multiplex congenita. Neuromuscular disorders are among the many different causes of reduced fetal movement. Many congenital myasthenic syndromes (CMSs) are due to mutations of the adult-specific epsilon subunit of the acetylcholine receptor (AChR), and, thus, functional deficits do not arise until late in gestation. However, an earlier effect on the fetus might be predicted with some defects of other AChR subunits. We studied a child who presented at birth with joint contractures and was subsequently found to have a CMS. Mutational screening revealed heteroallelic mutation within the AChR delta subunit gene, delta 756ins2 and delta E59K. Expression studies demonstrate that delta 756ins2 is a null mutation. By contrast, both fetal and adult AChR containing delta E59K have shorter than normal channel activations that predict fast decay of endplate currents. Thus, delta E59K causes dysfunction of fetal as well as the adult AChR and would explain the presence of joint contractures on the basis of reduced fetal movement. This is the first report of the association of AChR gene mutations with arthrogryposis multiplex congenita. It is probable that mutations that severely disrupt function of fetal AChR will underlie additional cases.
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Affiliation(s)
- S Brownlow
- Neurosciences Group, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, United Kingdom
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47
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Changeux J, Edelstein SJ. Allosteric mechanisms in normal and pathological nicotinic acetylcholine receptors. Curr Opin Neurobiol 2001; 11:369-77. [PMID: 11399437 DOI: 10.1016/s0959-4388(00)00221-x] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Recent chemical and advanced structural studies on site-directed and naturally occurring pathological mutants of individual members of the multigene family of nicotinic acetylcholine receptors have yielded structure-function relationships supporting indirect 'allosteric' interactions between the acetylcholine-binding sites and the ion channel in signal transduction.
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Affiliation(s)
- J Changeux
- Laboratoire de Neurobiologie Moléculaire, Institut Pasteur, 25 rue du Dr Roux, 75724 Cedex 15, Paris, France.
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48
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Engel AE. 73(rd) ENMC International Workshop: congenital myasthenic syndromes. 22-23 October, 1999, Naarden, The Netherlands. Neuromuscul Disord 2001; 11:315-21. [PMID: 11297949 DOI: 10.1016/s0960-8966(00)00189-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- A E Engel
- Department of Neurology, Mayo Clinic, Rochester, MN 55905, USA
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49
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Abstract
OBJECTIVE To review the structure and function of membrane ion channels with special emphasis on inherited nervous system channel disorders or channelopathies. RESULTS Channels are pores in the cell membrane. Through these pores ions flow across the membrane and depolarize or hyperpolarize the cell. Channels can be classified into 3 types: non-gated, directly gated and second messenger gated channels. Among the important directly gated channels are voltage gated (Na(+), K(+), Ca(2+), Cl(-)) and ligand gated (ACh, Glutamate, GABA, Glycine) channels. Channels are macromolecular protein complexes within the lipid membrane. They are divided into distinct protein units called subunits. Each subunit has a specific function and is encoded by a different gene. The following inherited channelopathies are described. (1) Sodium channelopathies: familial generalized epilepsy with febrile seizures plus, hyperkalemic periodic paralysis, paramyotonias, hypokalemic periodic paralysis; (2) potassium channelopathies: benign infantile epilepsy, episodic ataxia type 1; (3) calcium channelopathies: episodic ataxia type 2, spinocerebellar ataxia type 6, familial hemiplegic migraine, hypokalemic periodic paralysis, central core disease, malignant hyperthermia syndrome, congenital stationary night blindness; (4) chloride channelopathies: myotonia congenitas; (5) ACh receptor channelopathies: autosomal dominant frontal lobe nocturnal epilepsy, congenital myasthenic syndromes; (6) glycine receptor channelopathies: hyperekplexia. CONCLUSIONS Studies of human inherited channelopathies have clarified the functions of many ion channels. More than one gene may regulate a function in a channel, thus different genetic mutations may manifest with the same disorder. The complex picture of the genetic and molecular structures of channels will require frequent updates.
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Affiliation(s)
- G G Celesia
- Department of Neurology, Loyola University Chicago, Stritch School of Medicine, 2160 S. First Avenue, IL, Maywood, USA.
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