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Islam Kediha M, Tazir M, Sternberg D, Eymard B, Ali Pacha L. [Congenital myasthenic syndromes with kinetic abnormalities of the acetylcholine receptor]. Med Sci (Paris) 2023; 39 Hors série n° 1:58-63. [PMID: 37975772 DOI: 10.1051/medsci/2023135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2023] Open
Abstract
Congenital myasthenic syndromes (CMS) are genetically and phenotypically very heterogeneous conditions resulting in a defect in the neuromuscular transmission. Post-synaptic forms are the most frequent CMSs, and acetyl choline receptor (low expressor) deficiency is the most commonly involved pathophysiological mechanism. CMS with kinetic abnormalities of the acetylcholine receptor (AChr) are much rarer and can give rise to potentially life-threatening phenotypes. Among them, two types have been described: the slow channel syndrome (SCS) and the fast channel syndrome (FCS). Diagnosis and therapeutic management of such entities are specific to each type. In this work, we will illustrate the phenotypic aspects of CMS with kinetic abnormalities of the AChR by a narrative review of three Algerian families.
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Affiliation(s)
- Mohamed Islam Kediha
- Service de Neurologie, CHU Mustapha Bacha, Place 1er mai, 16000 Alger, Algérie. Université Benyoucef Benkhedda, Alger 1
| | - Meriem Tazir
- Service de Neurologie, CHU Mustapha Bacha, Place 1er mai, 16000 Alger, Algérie. Université Benyoucef Benkhedda, Alger 1
| | - Damien Sternberg
- Myogenetics unit, Département de biochimie métabolique, Hôpital universitaire Pitié-Salpêtrière, 75651 Paris Cedex 13, France
| | | | - Lamia Ali Pacha
- Service de Neurologie, CHU Mustapha Bacha, Place 1er mai, 16000 Alger, Algérie. Université Benyoucef Benkhedda, Alger 1
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Ohno K, Ohkawara B, Shen XM, Selcen D, Engel AG. Clinical and Pathologic Features of Congenital Myasthenic Syndromes Caused by 35 Genes-A Comprehensive Review. Int J Mol Sci 2023; 24:ijms24043730. [PMID: 36835142 PMCID: PMC9961056 DOI: 10.3390/ijms24043730] [Citation(s) in RCA: 34] [Impact Index Per Article: 34.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2023] [Revised: 02/09/2023] [Accepted: 02/09/2023] [Indexed: 02/16/2023] Open
Abstract
Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders characterized by impaired neuromuscular signal transmission due to germline pathogenic variants in genes expressed at the neuromuscular junction (NMJ). A total of 35 genes have been reported in CMS (AGRN, ALG14, ALG2, CHAT, CHD8, CHRNA1, CHRNB1, CHRND, CHRNE, CHRNG, COL13A1, COLQ, DOK7, DPAGT1, GFPT1, GMPPB, LAMA5, LAMB2, LRP4, MUSK, MYO9A, PLEC, PREPL, PURA, RAPSN, RPH3A, SCN4A, SLC18A3, SLC25A1, SLC5A7, SNAP25, SYT2, TOR1AIP1, UNC13A, VAMP1). The 35 genes can be classified into 14 groups according to the pathomechanical, clinical, and therapeutic features of CMS patients. Measurement of compound muscle action potentials elicited by repetitive nerve stimulation is required to diagnose CMS. Clinical and electrophysiological features are not sufficient to identify a defective molecule, and genetic studies are always required for accurate diagnosis. From a pharmacological point of view, cholinesterase inhibitors are effective in most groups of CMS, but are contraindicated in some groups of CMS. Similarly, ephedrine, salbutamol (albuterol), amifampridine are effective in most but not all groups of CMS. This review extensively covers pathomechanical and clinical features of CMS by citing 442 relevant articles.
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Affiliation(s)
- Kinji Ohno
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan
- Correspondence: (K.O.); (A.G.E.)
| | - Bisei Ohkawara
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan
| | - Xin-Ming Shen
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN 55905, USA
| | - Duygu Selcen
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN 55905, USA
| | - Andrew G. Engel
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN 55905, USA
- Correspondence: (K.O.); (A.G.E.)
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Chan C, Emery L, Maltese C, Kumar A, Aliu E, Naik S, Paul D. A Novel Homozygous Variant in the CHRNE Gene in 2 Siblings with Congenital Myasthenic Syndrome. Child Neurol Open 2023; 10:2329048X231216432. [PMID: 38034490 PMCID: PMC10685742 DOI: 10.1177/2329048x231216432] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Revised: 09/20/2023] [Accepted: 10/16/2023] [Indexed: 12/02/2023] Open
Abstract
Cholinergic receptor nicotinic epsilon (CHRNE) subunit mutations cause postsynaptic type of congenital myasthenic syndrome either as a primary acetylcholine-receptor deficiency or abnormal channel kinetics in the receptor. We report a novel homozygous variant (c.322C > T, p.Pro108Ser) in the epsilon subunit causing primary acetylcholine-receptor deficiency in two siblings. Two siblings presented with fatigable weakness. Both siblings had whole exome sequencing showing a homozygous variant (c.322C > T, p.Pro108Ser) of unknown significance in the epsilon subunit. Electromyography/nerve conduction study with repetitive nerve stimulation on one sibling showed a defect in neuromuscular junction transmission. Pseudoephedrine and fluoxetine for suspected slow-channel congenital myasthenic syndrome yielded no improvement. A trial of pyridostigmine led to clinical improvement. Given the clinical presentation, consanguinity, homozygous genetic variant, and response to pyridostigmine, we rationalize the homozygous variant (c.322C > T, p.Pro108Ser) in cholinergic receptor nicotinic epsilon subunit causes the primary acetylcholine-receptor deficiency congenital myasthenic syndrome.
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Affiliation(s)
- Cassie Chan
- Department of Neurology, Penn State Health Milton S. Hershey Medical Center, Hershey, PA, USA
| | - Lucy Emery
- Penn State Health College of Medicine, Hershey, PA, USA
| | | | - Ashutosh Kumar
- Department of Neurology, Penn State Health Milton S. Hershey Medical Center, Hershey, PA, USA
- Department of Pediatrics, Penn State Health Milton S. Hershey Medical Center, Hershey, PA, USA
| | - Ermal Aliu
- Department of Genetics, Penn State Health Milton S. Hershey Medical Center, Hershey, PA, USA
| | - Sunil Naik
- Department of Neurology, Penn State Health Milton S. Hershey Medical Center, Hershey, PA, USA
- Department of Pediatrics, Penn State Health Milton S. Hershey Medical Center, Hershey, PA, USA
| | - Dustin Paul
- Department of Neurology, Penn State Health Milton S. Hershey Medical Center, Hershey, PA, USA
- Department of Pediatrics, Penn State Health Milton S. Hershey Medical Center, Hershey, PA, USA
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Fatema K, Rahman M. Fast channel congenital myesthenic syndrome: Reporting two cases with mutation of CHRNE gene and short review. J Pediatr Neurosci 2022. [DOI: 10.4103/jpn.jpn_124_21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
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Hernandez CC, Macdonald RL. A structural look at GABA A receptor mutations linked to epilepsy syndromes. Brain Res 2019; 1714:234-247. [PMID: 30851244 DOI: 10.1016/j.brainres.2019.03.004] [Citation(s) in RCA: 58] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 02/25/2019] [Accepted: 03/06/2019] [Indexed: 12/12/2022]
Abstract
Understanding the genetic variation in GABAA receptor subunit genes (GABRs), GABRA1-6, GABRB1-3, GABRG1-3 and GABRD, in individuals affected by epilepsy may improve the diagnosis and treatment of epilepsy syndromes through identification of disease-associated variants. However, the lack of functional analysis and validation of many novel and previously reported familial and de novo mutations have made it challenging to address meaningful gene associations with epilepsy syndromes. GABAA receptors belong to the Cys-loop receptor family. Even though GABAA receptor mutant residues are widespread among different GABRs, their frequent occurrence in important structural domains that share common functional features suggests associations between structure and function.
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Affiliation(s)
- Ciria C Hernandez
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA.
| | - Robert L Macdonald
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN, USA
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Abstract
OBJECTIVES Congenital myasthenic syndromes (CMSs) are a genotypically and phenotypically heterogeneous group of neuromuscular disorders, which have in common an impaired neuromuscular transmission. Since the field of CMSs is steadily expanding, the present review aimed at summarizing and discussing current knowledge and recent advances concerning the etiology, clinical presentation, diagnosis, and treatment of CMSs. METHODS Systematic literature review. RESULTS Currently, mutations in 32 genes are made responsible for autosomal dominant or autosomal recessive CMSs. These mutations concern 8 presynaptic, 4 synaptic, 15 post-synaptic, and 5 glycosilation proteins. These proteins function as ion-channels, enzymes, or structural, signalling, sensor, or transporter proteins. The most common causative genes are CHAT, COLQ, RAPSN, CHRNE, DOK7, and GFPT1. Phenotypically, these mutations manifest as abnormal fatigability or permanent or fluctuating weakness of extra-ocular, facial, bulbar, axial, respiratory, or limb muscles, hypotonia, or developmental delay. Cognitive disability, dysmorphism, neuropathy, or epilepsy are rare. Low- or high-frequency repetitive nerve stimulation may show an abnormal increment or decrement, and SF-EMG an increased jitter or blockings. Most CMSs respond favourably to acetylcholine-esterase inhibitors, 3,4-diamino-pyridine, salbutamol, albuterol, ephedrine, fluoxetine, or atracurium. CONCLUSIONS CMSs are an increasingly recognised group of genetically transmitted defects, which usually respond favorably to drugs enhancing the neuromuscular transmission. CMSs need to be differentiated from neuromuscular disorders due to muscle or nerve dysfunction.
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Affiliation(s)
- Josef Finsterer
- Krankenanstalt Rudolfstiftung, Messerli Institute, Veterinary University of Vienna, Postfach 20, 1180, Vienna, Austria.
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Feng H, Zhou H. New compound heterozygous variants of the cholinergic receptor nicotinic delta subunit gene in a Chinese male with congenital myasthenic syndrome: A case report. Medicine (Baltimore) 2017; 96:e8981. [PMID: 29390429 PMCID: PMC5758131 DOI: 10.1097/md.0000000000008981] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
INTRODUCTION Congenital myasthenic syndromes (CMS) are a group of genetic disorders that stem mostly from molecular defects in nicotinic acetylcholine receptors (AChRs). Defects in the cholinergic receptor nicotinic delta subunit (CHRND) gene can cause a series of myasthenic syndromes. Here, we report 2 new compound heterozygous variants of the CHRND gene in a Chinese male with CMS. CASE PRESENTATION A 43-year-old Chinese male presented with progressive muscle weakness, difficulty chewing, and an inability to lift his head from the time he was 8 years old. He was treated with pyridostigmine, which was partially effective. Two weeks prior, he was hospitalized for dyspnea. Upon examination, he was unable to drum his cheeks and exhibited fatigable muscle weakness and facial muscle atrophy. Sequencing of his exome revealed 2 previously unreported mutations in CHRND, c.59G>A (exon2) and c.423G>C (exon5). CONCLUSIONS We identified a new mutational site that contributes to the onset of CMS.
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Tan JZ, Man Y, Xiao F. A Missense Mutation in Epsilon-subunit of Acetylcholine Receptor Causing Autosomal Dominant Slow-channel Congenital Myasthenic Syndrome in a Chinese Family. Chin Med J (Engl) 2017; 129:2596-2602. [PMID: 27779167 PMCID: PMC5125339 DOI: 10.4103/0366-6999.192780] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND Congenital myasthenic syndromes are a group of rare disorders that are clinically and genetically heterogeneous and caused by mutations in the genes encoding proteins of the neuromuscular junction. Here, we described a Chinese family that presented with phenotypes of classic slow-channel congenital myasthenic syndrome (SCCMS). METHODS Clinical characteristics and electrophysiological features of three patients from a Chinese family were examined, and next-generation sequencing followed by direct sequencing was carried out. RESULTS The patients revealed variability in clinical and electrophysiological features. However, weakness, scoliosis, and repetitive-compound muscle action potential were found in all affected members in the family. A heterozygous C>T missense mutation at nucleotide 865 in acetylcholine receptor epsilon-subunit (CHRNE) gene that causes a leucine-to-phenylalanine substitution at position 289 (L289F) was found. CONCLUSIONS We reported a SCCMS family of Chinese origin. In the family, classical clinical phenotype with phenotypic variability among different members was found. Genetic testing could help diagnose this rare disease.
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Affiliation(s)
- Jia-Ze Tan
- Department of Neurology, The First Affiliated Hospital of Chongqing Medical University, Chongqing Key Laboratory of Neurology, Chongqing 400016, China
| | - Yuan Man
- Department of Neurology, The First Affiliated Hospital of Chongqing Medical University, Chongqing Key Laboratory of Neurology, Chongqing 400016, China
| | - Fei Xiao
- Department of Neurology, The First Affiliated Hospital of Chongqing Medical University, Chongqing Key Laboratory of Neurology, Chongqing 400016, China
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Hernandez CC, Klassen TL, Jackson LG, Gurba K, Hu N, Noebels JL, Macdonald RL. Deleterious Rare Variants Reveal Risk for Loss of GABAA Receptor Function in Patients with Genetic Epilepsy and in the General Population. PLoS One 2016; 11:e0162883. [PMID: 27622563 PMCID: PMC5021343 DOI: 10.1371/journal.pone.0162883] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 08/30/2016] [Indexed: 12/02/2022] Open
Abstract
Genetic epilepsies (GEs) account for approximately 50% of all seizure disorders, and familial forms include mutations in single GABAA receptor subunit genes (GABRs). In 144 sporadic GE cases (GECs), exome sequencing of 237 ion channel genes identified 520 GABR variants. Among these variants, 33 rare variants in 11 GABR genes were present in 24 GECs. To assess functional risk of variants in GECs, we selected 8 variants found in GABRA, 3 in GABRB, and 3 in GABRG and compared them to 18 variants found in the general population for GABRA1 (n = 9), GABRB3 (n = 7), and GABRG2 (n = 2). To identify deleterious variants and gain insight into structure-function relationships, we studied the gating properties, surface expression and structural perturbations of the 32 variants. Significant reduction of GABAA receptor function was strongly associated with variants scored as deleterious and mapped within the N-terminal and transmembrane domains. In addition, 12 out of 17 variants mapped along the β+/α- GABA binding interface, were associated with reduction in channel gating and were predicted to cause structural rearrangements of the receptor by in silico simulations. Missense or nonsense mutations of GABRA1, GABRB3 and GABRG2 primarily impair subunit biogenesis. In contrast, GABR variants affected receptor function by impairing gating, suggesting that different mechanisms are operating in GABR epilepsy susceptibility variants and disease-causing mutations. The functional impact of single GABR variants found in individuals with sporadic GEs warrants the use of molecular diagnosis and will ultimately improve the treatment of genetic epilepsies by using a personalized approach.
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Affiliation(s)
- Ciria C. Hernandez
- Department of Neurology, Vanderbilt University, Nashville, Tennessee, 37232, United States of America
- * E-mail: (RLM); (CCH)
| | - Tara L. Klassen
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, V6S 1Z3, Canada
| | - Laurel G. Jackson
- Program in Neuroscience, Vanderbilt University, Nashville, Tennessee, 37232, United States of America
| | - Katharine Gurba
- Program in Neuroscience, Vanderbilt University, Nashville, Tennessee, 37232, United States of America
| | - Ningning Hu
- Department of Neurology, Vanderbilt University, Nashville, Tennessee, 37232, United States of America
| | - Jeffrey L. Noebels
- Department of Neurology, Baylor College of Medicine, Houston, Texas, 77030, United States of America
| | - Robert L. Macdonald
- Department of Neurology, Vanderbilt University, Nashville, Tennessee, 37232, United States of America
- * E-mail: (RLM); (CCH)
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Engel AG, Shen XM, Selcen D, Sine SM. Congenital myasthenic syndromes: pathogenesis, diagnosis, and treatment. Lancet Neurol 2015; 14:420-34. [PMID: 25792100 PMCID: PMC4520251 DOI: 10.1016/s1474-4422(14)70201-7] [Citation(s) in RCA: 336] [Impact Index Per Article: 37.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The congenital myasthenic syndromes (CMS) are a diverse group of genetic disorders caused by abnormal signal transmission at the motor endplate, a special synaptic contact between motor axons and each skeletal muscle fibre. Most CMS stem from molecular defects in the muscle nicotinic acetylcholine receptor, but they can also be caused by mutations in presynaptic proteins, mutations in proteins associated with the synaptic basal lamina, defects in endplate development and maintenance, or defects in protein glycosylation. The specific diagnosis of some CMS can sometimes be reached by phenotypic clues pointing to the mutated gene. In the absence of such clues, exome sequencing is a useful technique for finding the disease gene. Greater understanding of the mechanisms of CMS have been obtained from structural and electrophysiological studies of the endplate, and from biochemical studies. Present therapies for the CMS include cholinergic agonists, long-lived open-channel blockers of the acetylcholine receptor ion channel, and adrenergic agonists. Although most CMS are treatable, caution should be exercised as some drugs that are beneficial in one syndrome can be detrimental in another.
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Affiliation(s)
- Andrew G Engel
- Department of Neurology, Mayo Clinic, Rochester, MN, USA.
| | - Xin-Ming Shen
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
| | - Duygu Selcen
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
| | - Steven M Sine
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, USA
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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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13
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Inherited disorders of the neuromuscular junction: an update. J Neurol 2014; 261:2234-43. [PMID: 25305004 DOI: 10.1007/s00415-014-7520-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Accepted: 09/23/2014] [Indexed: 10/24/2022]
Abstract
Congenital myasthenic syndromes (CMSs) are a group of heterogeneous inherited disorders caused by mutations in genes affecting the function and structure of the neuromuscular junction. This review updates the reader on established and novel subtypes of congenital myasthenia, and the treatment strategies for these increasingly heterogeneous disorders. The discovery of mutations associated with the N-glycosylation pathway and in the family of serine peptidases has shown that causative genes encoding ubiquitously expressed molecules can produce defects at the human neuromuscular junction. By contrast, mutations in lipoprotein-like receptor 4 (LRP4), a long-time candidate gene for congenital myasthenia, and a novel phenotype of myasthenia with distal weakness and atrophy due to mutations in AGRN have now been described. In addition, a pathogenic splicing mutation in a nonfunctional exon of CHRNA1 has been reported emphasizing the importance of analysing nonfunctional exons in genetic analysis. The benefit of salbutamol and ephedrine alone or combined with pyridostigmine or 3,4-DAP is increasingly being reported for particular subtypes of CMS.
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15
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Belfield WJ, Cole DJ, Martin IL, Payne MC, Chau PL. Constrained geometric simulation of the nicotinic acetylcholine receptor. J Mol Graph Model 2014; 52:1-10. [PMID: 24955489 DOI: 10.1016/j.jmgm.2014.05.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Revised: 05/01/2014] [Accepted: 05/02/2014] [Indexed: 10/25/2022]
Abstract
Constrained geometric simulations have been performed for the recently published closed-channel state of the nicotinic acetylcholine receptor. These simulations support the theory that correlated motion in the flexible β-sheet structure of the extracellular domain helps to communicate a "conformational wave", spreading from the acetylcholine binding pocket. Furthermore, we have identified key residues that act at the interface between subunits and between domains that could potentially facilitate rapid communication between the binding site and the transmembrane gate.
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Affiliation(s)
- William J Belfield
- Theory of Condensed Matter Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - Daniel J Cole
- Theory of Condensed Matter Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge CB3 0HE, United Kingdom; Department of Chemistry, Yale University, New Haven, CT 06520-8107, United States
| | - Ian L Martin
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
| | - Mike C Payne
- Theory of Condensed Matter Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - P-L Chau
- Bioinformatique Structurale, CNRS UMR 3528, Institut Pasteur, 75724 Paris, France.
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Abstract
PURPOSE OF REVIEW Congenital myasthenic syndromes (CMSs) form a heterogeneous group of genetic diseases characterized by a dysfunction of neuromuscular transmission because of mutations in numerous genes. This review will focus on the causative genes recently identified and on the therapy of CMSs. RECENT FINDINGS Advances in exome sequencing allowed the discovery of a new group of genes that did not code for the known molecular components of the neuromuscular junction, and the definition of a new group of glycosylation-defective CMS. Rather than the specific drugs used, some of them having been known for decades, it is the rigorous therapeutic strategy that is now offered to the patient in relation to the identified mutated gene that is novel and promising. SUMMARY In addition to the above main points, we also present new data on the genes that were already known with an emphasis on the clinic and on animal models that may be of use to understand the pathophysiology of the disease. We also stress not only the diagnosis difficulties between congenital myopathies and CMSs, but also the continuum that may exist between the two.
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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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Webster R, Liu WW, Chaouch A, Lochmüller H, Beeson D. Fast-channel congenital myasthenic syndrome with a novel acetylcholine receptor mutation at the α-ε subunit interface. Neuromuscul Disord 2013; 24:143-7. [PMID: 24295813 DOI: 10.1016/j.nmd.2013.10.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2013] [Revised: 10/22/2013] [Accepted: 10/25/2013] [Indexed: 01/24/2023]
Abstract
Congenital myasthenic syndromes (CMS) result from the failure to achieve muscle depolarisation due to disorders in the structure and/or function of the neuromuscular synapse. Mutations of the nicotinic acetylcholine receptor (nAChR) form a major subset of CMS. We describe a patient who presented with recurrent apnoeic crises in the neonatal period requiring ventilator support. Electromyography revealed compound muscle action potential decrement upon repetitive stimulation. Sequencing of nAChR subunit genes revealed two missense mutations. One previously reported null mutation p.εTyr15His, and a second novel missense mutation, p.εThr38Lys, that is well expressed in mammalian cell culture and thus likely to exert its effect via alteration of ion channel kinetics. Functional analysis revealed abbreviated ion channel bursts characteristic of a fast channel CMS. The mutation p.εThr38Lys occurs at the interface between the α and ε subunits of the nAChR pentamer and leads to instability of the open channel. The effects of this mutation on channel function were investigated in relation to other fast channel mutants at an analogous subunit interface within the nAChR pentamer. Fast channel syndromes are frequently characterised by severe myasthenic weakness with apnoeic crises; knowledge of the underlying mutation and its functional consequences can be vital for appropriate therapy and patient management.
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Affiliation(s)
- Richard Webster
- Neurosciences Group, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Headley Way, Oxford, UK
| | - Wei-Wei Liu
- Neurosciences Group, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Headley Way, Oxford, UK
| | - Amina Chaouch
- Institute of Genetic Medicine, International Centre for Life, Newcastle upon Tyne, UK
| | - Hanns Lochmüller
- Institute of Genetic Medicine, International Centre for Life, Newcastle upon Tyne, UK
| | - David Beeson
- Neurosciences Group, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Headley Way, Oxford, UK.
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Abstract
During the past five years an increasing number of patients have been diagnosed with congenital myasthenic syndromes (CMS) and a number of novel syndromes have been recognized and investigated. This presentation focuses on the CMS caused by defects in choline acetyltransferase, novel fast-channel syndromes that hinder isomerization of the acetylcholine receptor from the closed to the open state, the consequences of deleterious mutations in the intermediate filament linker plectin, altered neuromuscular transmission in a centronuclear myopathy, and two recently identified CMS caused by congenital defects in glycosylation.
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Affiliation(s)
- Andrew G Engel
- Neuromuscular Research Laboratory, Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA.
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