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Zhang Z, Zhang X, Xue H, Chu L, Hu L, Bi X, Zhu P, Zhang D, Chen J, Cui X, Kong L, Liang B, Wu X. Preimplantation genetic testing as a means of preventing hereditary congenital myasthenic syndrome caused by RAPSN. Mol Genet Genomic Med 2024; 12:e2409. [PMID: 38511267 PMCID: PMC10955331 DOI: 10.1002/mgg3.2409] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Revised: 01/30/2024] [Accepted: 02/13/2024] [Indexed: 03/22/2024] Open
Abstract
BACKGROUND Congenital myasthenic syndrome is a heterogeneous group of inherited neuromuscular transmission disorders. Variants in RAPSN are a common cause of CMS, accounting for approximately 14%-27% of all CMS cases. Whether preimplantation genetic testing for monogenic disease (PGT-M) could be used to prevent the potential birth of CMS-affected children is unclear. METHODS Application of WES (whole-exome sequencing) for carrier testing and guidance for the PGT-M in the absence of a genetically characterized index patient as well as assisted reproductive technology were employed to prevent the occurrence of birth defects in subsequent pregnancy. The clinical phenotypes of stillborn fetuses were also assessed. RESULTS The family carried two likely pathogenic variants in RAPSN(NM_005055.5): c.133G>A (p.V45M) and c.280G>A (p.E94K). And the potential birth of CMS-affected child was successfully prevented, allowing the family to have offspring devoid of disease-associated variants and exhibiting a normal phenotype. CONCLUSION This report constitutes the first documented case of achieving a CMS-free offspring through PGT-M in a CMS-affected family. By broadening the known variant spectrum of RAPSN in the Chinese population, our findings underscore the feasibility and effectiveness of PGT-M for preventing CMS, offering valuable insights for similarly affected families.
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Affiliation(s)
- Zhiping Zhang
- Center of Reproductive MedicineAffiliated Children's Hospital of Shanxi & Women Health Center of Shanxi Medicine UniversityTaiyuanShanxiChina
| | - Xueluo Zhang
- Center of Reproductive MedicineAffiliated Children's Hospital of Shanxi & Women Health Center of Shanxi Medicine UniversityTaiyuanShanxiChina
| | - Huiqin Xue
- Center of Reproductive MedicineAffiliated Children's Hospital of Shanxi & Women Health Center of Shanxi Medicine UniversityTaiyuanShanxiChina
| | - Liming Chu
- Basecare Medical Device Co., LtdSuzhouChina
| | - Lina Hu
- Basecare Medical Device Co., LtdSuzhouChina
| | - Xingyu Bi
- Center of Reproductive MedicineAffiliated Children's Hospital of Shanxi & Women Health Center of Shanxi Medicine UniversityTaiyuanShanxiChina
| | - Pengfei Zhu
- Center of Reproductive MedicineAffiliated Children's Hospital of Shanxi & Women Health Center of Shanxi Medicine UniversityTaiyuanShanxiChina
| | - Dongdong Zhang
- Center of Reproductive MedicineAffiliated Children's Hospital of Shanxi & Women Health Center of Shanxi Medicine UniversityTaiyuanShanxiChina
| | - Jiayao Chen
- Center of Reproductive MedicineAffiliated Children's Hospital of Shanxi & Women Health Center of Shanxi Medicine UniversityTaiyuanShanxiChina
| | - Xiangrong Cui
- Center of Reproductive MedicineAffiliated Children's Hospital of Shanxi & Women Health Center of Shanxi Medicine UniversityTaiyuanShanxiChina
| | | | - Bo Liang
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
| | - Xueqing Wu
- Center of Reproductive MedicineAffiliated Children's Hospital of Shanxi & Women Health Center of Shanxi Medicine UniversityTaiyuanShanxiChina
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Polavarapu K, Sunitha B, Töpf A, Preethish-Kumar V, Thompson R, Vengalil S, Nashi S, Bardhan M, Sanka SB, Huddar A, Unnikrishnan G, Arunachal G, Girija MS, Porter A, Azuma Y, Lorenzoni PJ, Baskar D, Anjanappa RM, Keertipriya M, Padmanabh H, Harikrishna GV, Laurie S, Matalonga L, Horvath R, Nalini A, Lochmüller H. Clinical and genetic characterisation of a large Indian congenital myasthenic syndrome cohort. Brain 2024; 147:281-296. [PMID: 37721175 PMCID: PMC10766255 DOI: 10.1093/brain/awad315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Revised: 06/20/2023] [Accepted: 08/10/2023] [Indexed: 09/19/2023] Open
Abstract
Congenital myasthenic syndromes (CMS) are a rare group of inherited disorders caused by gene defects associated with the neuromuscular junction and potentially treatable with commonly available medications such as acetylcholinesterase inhibitors and β2 adrenergic receptor agonists. In this study, we identified and genetically characterized the largest cohort of CMS patients from India to date. Genetic testing of clinically suspected patients evaluated in a South Indian hospital during the period 2014-19 was carried out by standard diagnostic gene panel testing or using a two-step method that included hotspot screening followed by whole-exome sequencing. In total, 156 genetically diagnosed patients (141 families) were characterized and the mutational spectrum and genotype-phenotype correlation described. Overall, 87 males and 69 females were evaluated, with the age of onset ranging from congenital to fourth decade (mean 6.6 ± 9.8 years). The mean age at diagnosis was 19 ± 12.8 (1-56 years), with a mean diagnostic delay of 12.5 ± 9.9 (0-49 years). Disease-causing variants in 17 CMS-associated genes were identified in 132 families (93.6%), while in nine families (6.4%), variants in genes not associated with CMS were found. Overall, postsynaptic defects were most common (62.4%), followed by glycosylation defects (21.3%), synaptic basal lamina genes (4.3%) and presynaptic defects (2.8%). Other genes found to cause neuromuscular junction defects (DES, TEFM) in our cohort accounted for 2.8%. Among the individual CMS genes, the most commonly affected gene was CHRNE (39.4%), followed by DOK7 (14.4%), DPAGT1 (9.8%), GFPT1 (7.6%), MUSK (6.1%), GMPPB (5.3%) and COLQ (4.5%). We identified 22 recurrent variants in this study, out of which eight were found to be geographically specific to the Indian subcontinent. Apart from the known common CHRNE variants p.E443Kfs*64 (11.4%) and DOK7 p.A378Sfs*30 (9.3%), we identified seven novel recurrent variants specific to this cohort, including DPAGT1 p.T380I and DES c.1023+5G>A, for which founder haplotypes are suspected. This study highlights the geographic differences in the frequencies of various causative CMS genes and underlines the increasing significance of glycosylation genes (DPAGT1, GFPT1 and GMPPB) as a cause of neuromuscular junction defects. Myopathy and muscular dystrophy genes such as GMPPB and DES, presenting as gradually progressive limb girdle CMS, expand the phenotypic spectrum. The novel genes MACF1 and TEFM identified in this cohort add to the expanding list of genes with new mechanisms causing neuromuscular junction defects.
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Affiliation(s)
- Kiran Polavarapu
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
- Children’s Hospital of Eastern Ontario Research Institute, Ottawa, ON K1H 8L1, Canada
| | - Balaraju Sunitha
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne NE1 3BZ, UK
- Department of Clinical Neurosciences, University of Cambridge School of Clinical Medicine, Cambridge CB2 0SP, UK
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 9DU, UK
| | - Ana Töpf
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne NE1 3BZ, UK
| | - Veeramani Preethish-Kumar
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
- Department of Neurology, Neurofoundation, Salem, Tamil Nadu 636009, India
| | - Rachel Thompson
- Children’s Hospital of Eastern Ontario Research Institute, Ottawa, ON K1H 8L1, Canada
| | - Seena Vengalil
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
| | - Saraswati Nashi
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
| | - Mainak Bardhan
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
| | - Sai Bhargava Sanka
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
| | - Akshata Huddar
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
- Department of Neurology, St Johns Medical College Hospital, Bangalore 560034, India
| | - Gopikrishnan Unnikrishnan
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
- Department of Neurology, Amruta Institute of Medical Sciences, Kochi 682041, India
| | - Gautham Arunachal
- Department of Human Genetics, National Institute of Mental Health and Neurosciences, Bengaluru 560029, India
| | - Manu Santhappan Girija
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
| | - Anna Porter
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne NE1 3BZ, UK
| | - Yoshiteru Azuma
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne NE1 3BZ, UK
| | - Paulo José Lorenzoni
- Neuromuscular Disorders Division, Service of Neurology, Department of Internal Medicine, Hospital de Clínicas, Universidade Federal do Paraná, Rua General Carneiro, Curitiba - PR 80060-900, Brazil
| | - Dipti Baskar
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
| | - Ram Murthy Anjanappa
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
| | - Madassu Keertipriya
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
| | - Hansashree Padmanabh
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
| | | | - Steve Laurie
- Centro Nacional de Análisis Genómico (CNAG-CRG), Center for Genomic Regulation, Barcelona Institute of Science and Technology (BIST), Barcelona, Catalonia 08028, Spain
| | - Leslie Matalonga
- Centro Nacional de Análisis Genómico (CNAG-CRG), Center for Genomic Regulation, Barcelona Institute of Science and Technology (BIST), Barcelona, Catalonia 08028, Spain
| | - Rita Horvath
- Department of Clinical Neurosciences, University of Cambridge School of Clinical Medicine, Cambridge CB2 0SP, UK
| | - Atchayaram Nalini
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore 560029, India
| | - Hanns Lochmüller
- Children’s Hospital of Eastern Ontario Research Institute, Ottawa, ON K1H 8L1, Canada
- Centro Nacional de Análisis Genómico (CNAG-CRG), Center for Genomic Regulation, Barcelona Institute of Science and Technology (BIST), Barcelona, Catalonia 08028, Spain
- Brain and Mind Research Institute, University of Ottawa, Ottawa, ON K1H 8M5, Canada
- Division of Neurology, Department of Medicine, The Ottawa Hospital, Ottawa, ON K1H 8M5, Canada
- Department of Neuropediatrics and Muscle Disorders, Medical Center–University of Freiburg, Faculty of Medicine, Freiburg 79110, Germany
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Muñoz-García MI, Guerrero-Molina MP, de Fuenmayor-Fernández de la Hoz CP, Bermejo-Guerrero L, Arteche-López A, Hernández-Laín A, Martín MA, Domínguez-González C. Delayed Diagnosis of Congenital Myasthenic Syndromes Erroneously Interpreted as Mitochondrial Myopathies. J Clin Med 2023; 12:jcm12093308. [PMID: 37176748 PMCID: PMC10179722 DOI: 10.3390/jcm12093308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2023] [Revised: 04/02/2023] [Accepted: 05/04/2023] [Indexed: 05/15/2023] Open
Abstract
BACKGROUND Congenital myasthenic syndromes (CMSs) and primary mitochondrial myopathies (PMMs) can present with ptosis, external ophthalmoplegia, and limb weakness. METHODS Our method involved the description of three cases of CMS that were initially characterized as probable PMM. RESULTS All patients were male and presented with ptosis and/or external ophthalmoplegia at birth, with proximal muscle weakness and fatigue on physical exertion. After normal repetitive nerve stimulation (RNS) studies performed on facial muscles, a muscle biopsy (at a median age of 9) was performed to rule out congenital myopathies. In all three cases, the biopsy findings (COX-negative fibers or respiratory chain defects) pointed to PMM. They were referred to our neuromuscular unit in adulthood to establish a genetic diagnosis. However, at this time, fatigability was evident in the physical exams and RNS in the spinal accessory nerve showed a decremental response in all cases. Targeted genetic studies revealed pathogenic variants in the MUSK, DOK7, and RAPSN genes. The median diagnostic delay was 29 years. Treatment resulted in functional improvement in all cases. CONCLUSIONS Early identification of CMS is essential as medical treatment can provide clear benefits. Its diagnosis can be challenging due to phenotypic overlap with other debilitating disorders. Thus, a high index of suspicion is necessary to guide the diagnostic strategy.
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Affiliation(s)
- Mariana I Muñoz-García
- Neuromuscular Unit, Neurology Department, Hospital Universitario 12 de Octubre, 28041 Madrid, Spain
| | | | | | - Laura Bermejo-Guerrero
- Neuromuscular Unit, Neurology Department, Hospital Universitario 12 de Octubre, 28041 Madrid, Spain
| | - Ana Arteche-López
- Genetics Department, Hospital Universitario 12 de Octubre, 28041 Madrid, Spain
| | | | - Miguel A Martín
- Genetics Department, Hospital Universitario 12 de Octubre, 28041 Madrid, Spain
- Spanish Network for Biomedical Research in Rare Diseases (CIBERER), 28041 Madrid, Spain
- Mitochondrial and Neuromuscular Diseases Research Group, 12 de Octubre, Hospital Research Institute (imas12), 28041 Madrid, Spain
| | - Cristina Domínguez-González
- Neuromuscular Unit, Neurology Department, Hospital Universitario 12 de Octubre, 28041 Madrid, Spain
- Spanish Network for Biomedical Research in Rare Diseases (CIBERER), 28041 Madrid, Spain
- Mitochondrial and Neuromuscular Diseases Research Group, 12 de Octubre, Hospital Research Institute (imas12), 28041 Madrid, Spain
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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: 36] [Impact Index Per Article: 36.0] [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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Younger DS. Neonatal and infantile hypotonia. HANDBOOK OF CLINICAL NEUROLOGY 2023; 195:401-423. [PMID: 37562880 DOI: 10.1016/b978-0-323-98818-6.00011-x] [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
The underlying etiology of neonatal and infantile hypotonia can be divided into primary peripheral and central nervous system and acquired or genetic disorders. The approach to identifying the likeliest cause of hypotonia begins with a bedside assessment followed by a careful review of the birth history and early development and family pedigree and obtaining available genetic studies and age- and disease-appropriate laboratory investigations. Until about a decade ago, the main goal was to identify the clinical signs and a battery of basic investigations including electrophysiology to confirm or exclude a given neuromuscular disorder, however the availability of whole-exome sequencing and next generation sequencing and transcriptome sequencing has simplified the identification of specific underlying genetic defect and improved the accuracy of diagnosis in many related Mendelian disorders.
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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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Keene KR, Kan HE, van der Meeren S, Verbist BM, Tannemaat MR, Beenakker JM, Verschuuren JJ. Clinical and imaging clues to the diagnosis and follow-up of ptosis and ophthalmoparesis. J Cachexia Sarcopenia Muscle 2022; 13:2820-2834. [PMID: 36172973 PMCID: PMC9745561 DOI: 10.1002/jcsm.13089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Revised: 08/15/2022] [Accepted: 08/19/2022] [Indexed: 12/15/2022] Open
Abstract
Ophthalmoparesis and ptosis can be caused by a wide range of rare or more prevalent diseases, several of which can be successfully treated. In this review, we provide clues to aid in the diagnosis of these diseases, based on the clinical symptoms, the involvement pattern and imaging features of extra-ocular muscles (EOM). Dysfunction of EOM including the levator palpebrae can be due to muscle weakness, anatomical restrictions or pathology affecting the innervation. A comprehensive literature review was performed to find clinical and imaging clues for the diagnosis and follow-up of ptosis and ophthalmoparesis. We used five patterns as a framework for differential diagnostic reasoning and for pattern recognition in symptomatology, EOM involvement and imaging results of individual patients. The five patterns were characterized by the presence of combination of ptosis, ophthalmoparesis, diplopia, pain, proptosis, nystagmus, extra-orbital symptoms, symmetry or fluctuations in symptoms. Each pattern was linked to anatomical locations and either hereditary or acquired diseases. Hereditary muscle diseases often lead to ophthalmoparesis without diplopia as a predominant feature, while in acquired eye muscle diseases ophthalmoparesis is often asymmetrical and can be accompanied by proptosis and pain. Fluctuation is a hallmark of an acquired synaptic disease like myasthenia gravis. Nystagmus is indicative of a central nervous system lesion. Second, specific EOM involvement patterns can also provide valuable diagnostic clues. In hereditary muscle diseases like chronic progressive external ophthalmoplegia (CPEO) and oculo-pharyngeal muscular dystrophy (OPMD) the superior rectus is often involved. In neuropathic disease, the pattern of involvement of the EOM can be linked to specific cranial nerves. In myasthenia gravis this pattern is variable within patients over time. Lastly, orbital imaging can aid in the diagnosis. Fat replacement of the EOM is commonly observed in hereditary myopathic diseases, such as CPEO. In contrast, inflammation and volume increases are often observed in acquired muscle diseases such as Graves' orbitopathy. In diseases with ophthalmoparesis and ptosis specific patterns of clinical symptoms, the EOM involvement pattern and orbital imaging provide valuable information for diagnosis and could prove valuable in the follow-up of disease progression and the understanding of disease pathophysiology.
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Affiliation(s)
- Kevin R. Keene
- CJ Gorter MRI Center, Department of RadiologyLeiden University Medical CenterLeidenThe Netherlands
- Department of NeurologyLeiden University Medical CenterLeidenThe Netherlands
| | - Hermien E. Kan
- CJ Gorter MRI Center, Department of RadiologyLeiden University Medical CenterLeidenThe Netherlands
- Duchenne CenterThe Netherlands
| | - Stijn van der Meeren
- Department of OphthalmologyLeiden University Medical CenterLeidenThe Netherlands
- Orbital Center, Department of OphthalmologyAmsterdam University Medical CentersAmsterdamThe Netherlands
| | - Berit M. Verbist
- Department of RadiologyLeiden University Medical CenterLeidenThe Netherlands
| | | | - Jan‐Willem M. Beenakker
- CJ Gorter MRI Center, Department of RadiologyLeiden University Medical CenterLeidenThe Netherlands
- Department of OphthalmologyLeiden University Medical CenterLeidenThe Netherlands
- Department of Radiation OncologyLeiden University Medical CenterLeidenThe Netherlands
| | - Jan J.G.M. Verschuuren
- Department of NeurologyLeiden University Medical CenterLeidenThe Netherlands
- Duchenne CenterThe Netherlands
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Bodkin C, Comer A, Felker M, Gutmann L, Jones KA, Kincaid J, Payne KK, Skinner B. Challenging Neuromuscular Disease Cases. Semin Neurol 2022; 42:716-722. [PMID: 36417990 DOI: 10.1055/a-1985-0230] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The diagnosis of neuromuscular disorders requires a thorough history including family history and examination, with the next steps broadened now beyond electromyography and neuropathology to include genetic testing. The challenge in diagnosis can often be putting all the information together. With advances in genetic testing, some diagnoses that adult patients may have received as children deserve a second look and may result in diagnoses better defined or alternative diagnoses made. Clearly defining or redefining a diagnosis can result in understanding of potential other systems involved, prognosis, or potential treatments. This article presents several cases and approach to diagnosis as well as potential treatment and prognostic concerns, including seipinopathy, congenital myasthenic syndrome, central core myopathy, and myotonic dystrophy type 2.
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Affiliation(s)
- Cynthia Bodkin
- Department of Neurology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Adam Comer
- Department of Neurology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Marcia Felker
- Division of Pediatric Neurology, Department of Neurology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Laurie Gutmann
- Department of Neurology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Karra A Jones
- Department of Pathology, Duke University Medical Center, Durham, North Carolina
| | - John Kincaid
- Department of Neurology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Katelyn K Payne
- Department of Neurology, Indiana University School of Medicine, Indianapolis, Indiana.,Department of Medical Genetics and Genomics, Indiana University School of Medicine, Indianapolis, Indiana
| | - Blair Skinner
- Department of Neurology, Indiana University School of Medicine, Indianapolis, Indiana
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Lorenzoni PJ, Ducci RDP, Arndt RC, Hrysay NMC, Fustes OJH, Töpf A, Lochmüller H, Werneck LC, Kay CSK, Scola RH. Congenital myasthenic syndrome in a cohort of patients with 'double' seronegative myasthenia gravis. ARQUIVOS DE NEURO-PSIQUIATRIA 2021; 80:69-74. [PMID: 34932651 PMCID: PMC9651496 DOI: 10.1590/0004-282x-anp-2020-0575] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Accepted: 02/27/2021] [Indexed: 11/22/2022]
Abstract
BACKGROUND Congenital myasthenic syndromes (CMS) have some phenotypic overlap with seronegative myasthenia gravis (SNMG). OBJECTIVE The aim of this single center study was to assess the minimum occurrence of CMS misdiagnosed as double SNMG in a Brazilian cohort. METHODS The genetic analysis of the most common mutations in CHRNE, RAPSN, and DOK7 genes was used as the main screening tool. RESULTS We performed genetic analysis in 22 patients with a previous diagnosis of 'double' SNMG. In this study, one CMS patient was confirmed due to the presence of compound heterozygous variants in the CHRNE gene (c.130insG/p.Cys210Phe). CONCLUSIONS This study confirmed that CMS due to CHNRE mutations can be mistaken for SNMG. In addition, our study estimated the prevalence of misdiagnosed CMS to be 4.5% in 'double' SNMG patients of our center. Based on our findings, genetic screening could be helpful in the diagnostic workup of patients with 'double' SNMG in whom differential diagnosis is recommended.
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Affiliation(s)
- Paulo José Lorenzoni
- Universidade Federal do Paraná, Hospital de Clínicas, Departamento de Clínica Médica, Serviço de Doenças Neuromusculares, Curitiba PR, Brazil
| | - Renata Dal-Pra Ducci
- Universidade Federal do Paraná, Hospital de Clínicas, Departamento de Clínica Médica, Serviço de Doenças Neuromusculares, Curitiba PR, Brazil
| | - Raquel Cristina Arndt
- Universidade Federal do Paraná, Hospital de Clínicas, Departamento de Clínica Médica, Serviço de Doenças Neuromusculares, Curitiba PR, Brazil
| | - Nyvia Milicio Coblinski Hrysay
- Universidade Federal do Paraná, Hospital de Clínicas, Departamento de Clínica Médica, Serviço de Doenças Neuromusculares, Curitiba PR, Brazil
| | - Otto Jesus Hernandez Fustes
- Universidade Federal do Paraná, Hospital de Clínicas, Departamento de Clínica Médica, Serviço de Doenças Neuromusculares, Curitiba PR, Brazil
| | - Ana Töpf
- Newcastle University, Institute of Genetic Medicine, John Walton Muscular Dystrophy Research Centre, Newcastle upon Tyne, UK
| | - Hanns Lochmüller
- University of Ottawa, Children's Hospital of Eastern Ontario Research Institute, Department of Medicine, Division of Neurology, Ottawa, Canada.,University of Ottawa, The Ottawa Hospital, Brain and Mind Research Institute, Ottawa, Canada
| | - Lineu Cesar Werneck
- Universidade Federal do Paraná, Hospital de Clínicas, Departamento de Clínica Médica, Serviço de Doenças Neuromusculares, Curitiba PR, Brazil
| | - Cláudia Suemi Kamoi Kay
- Universidade Federal do Paraná, Hospital de Clínicas, Departamento de Clínica Médica, Serviço de Doenças Neuromusculares, Curitiba PR, Brazil
| | - Rosana Herminia Scola
- Universidade Federal do Paraná, Hospital de Clínicas, Departamento de Clínica Médica, Serviço de Doenças Neuromusculares, Curitiba PR, Brazil
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9
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Prior DE, Ghosh PS. Congenital Myasthenic Syndrome From a Single Center: Phenotypic and Genotypic features. J Child Neurol 2021; 36:610-617. [PMID: 33471587 DOI: 10.1177/0883073820987755] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND Congenital myasthenic syndrome is a group of rare genetic disorders affecting transmission across the neuromuscular junction. Patients present with variable ocular, bulbar, respiratory, and extremity weakness that may respond to symptomatic therapies. METHODS We identified 18 patients with congenital myasthenic syndrome from a pediatric neuromuscular center over a decade. Through a retrospective chart review, we characterize demographic profile, clinical features, genetic variants, treatment, and follow-up of these patients. RESULTS Patients had the following genetic subtypes: CHRNE (6), CHAT (2), MUSK (2), DOK7 (2), COLQ (1), RAPSN (1), PREPL (1), GFPT1 (1), CHRBB1 (1), and CHRNA1 (1). The phenotype varied based on the genetic variants, though most patients have generalized fatigable weakness affecting ocular, bulbar, and extremity muscles. There was a significant delay in the diagnosis of this condition from the onset of symptoms. Although most patients improved with pyridostigmine, some subtypes showed worsening with pyridostigmine and others benefited from albuterol, ephedrine, or 3,4-diaminopyridine treatment. CONCLUSION Increasing recognition of this rare syndrome will lead to early diagnosis and prompt treatment. Prompt utilization of genetic testing will identify novel variants and the expanding phenotype of this condition.
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Affiliation(s)
- Devin E Prior
- Department of Neurology, 2094Mount Auburn Hospital, Cambridge, MA, USA.,Department of Neurology, 1862Boston Children's Hospital, Boston MA, USA
| | - Partha S Ghosh
- Department of Neurology, 1862Boston Children's Hospital, Boston MA, USA
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Della Marina A, Wibbeler E, Abicht A, Kölbel H, Lochmüller H, Roos A, Schara U. Long Term Follow-Up on Pediatric Cases With Congenital Myasthenic Syndromes-A Retrospective Single Centre Cohort Study. Front Hum Neurosci 2020; 14:560860. [PMID: 33364925 PMCID: PMC7750519 DOI: 10.3389/fnhum.2020.560860] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2020] [Accepted: 11/16/2020] [Indexed: 02/01/2023] Open
Abstract
Introduction: Congenital myasthenic syndromes (CMS) refer to a heterogenic group of neuromuscular transmission disorders. CMS-subtypes are diverse regarding exercise intolerance and muscular weakness, varying from mild symptoms to life-limiting forms with neonatal onset. Long-term follow-up studies on disease progression and treatment-response in pediatric patients are rare. Patients and Methods: We analyzed retrospective clinical and medication data in a cohort of 32 CMS-patients including the application of a standardized, not yet validated test (CMS-ST) to examine muscular strength and endurance in 21 patients at the last follow-up. Findings obtained in our cohort were compared with long-term follow-up studies of (adult) CMS-cohorts from the literature by considering the underlying molecular mechanisms. Outcomes of CMS-ST were compared to results of normal clinical assessment. Results: Thirty-two pediatric patients with defects in eight different CMS-genes were followed by a median time of 12.8 years. Fifty-nine percentage of patients manifested with first symptoms as neonates, 35% as infants. While 53% of patients presented a reduced walking distance, 34% were wheelchair-bound. Even under adequate therapy with pyridostigmine (PS) and 3,4-diaminopyridine, CHAT-mutations led to the progression of muscular weakness partly in combination with persistent respiratory and bulbar symptoms. RAPSN, CHRND, and CHRNB1 patients with neonatal manifestation, early respiratory problems, and bulbar symptoms showed a good and maintained treatment response. CHAT and CHRNE patients required higher PS dosages, whereas RAPSN patients needed a lower mean dosage at the last follow-up. The benefits of short-term medication and long-term progression of symptoms were highly dependent on the specific genetic defect. CMS-ST was carried out in 17/21 patients, determined affected muscle groups including bulbar and ocular symptoms, some of which were not reported by the patients. Conclusions: Our findings and comparison with the literature- suggest a better treatment-response and less severe progression of symptoms present in patients suffering from mutations in CMS-genes directly associated with receptor deficiency, while patients with defects leading to synaptopathy and presynaptic defects tend to have worse outcomes. Assessment of affected muscular groups and clinical symptoms by CMS-ST may be a useful tool for optimal therapeutic management of the patients, especially for future clinical studies.
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Affiliation(s)
- Adela Della Marina
- Department of Neuropediatrics, Developmental Neurology and Social Pediatrics, University Children's Hospital Essen, University Duisburg-Essen, Essen, Germany
| | - Eva Wibbeler
- Children's Hospital, University Medical Center Hamburg Eppendorf, Hamburg, Germany
| | - Angela Abicht
- Medical Genetic Center Munich, Munich, Germany.,Friedrich-Baur Institute, Ludwig Maximilian University, Munich, Germany
| | - Heike Kölbel
- Department of Neuropediatrics, Developmental Neurology and Social Pediatrics, University Children's Hospital Essen, University Duisburg-Essen, Essen, Germany
| | - Hanns Lochmüller
- Children's Hospital of Eastern Ontario Research Institute, Division of Neurology, Department of Medicine, The Ottawa Hospital, Brain and Mind Research Institute, University of Ottawa, Ottawa, ON, Canada.,Department of Neuropediatrics and Muscle Disorders, Faculty of Medicine, Medical Center-University of Freiburg, Freiburg, Germany.,Centro Nacional de Análisis Genómico (CNAG-CRG), Center for Genomic Regulation, Barcelona Institute of Science and Technology (BIST), Barcelona, Spain
| | - Andreas Roos
- Department of Neuropediatrics, Developmental Neurology and Social Pediatrics, University Children's Hospital Essen, University Duisburg-Essen, Essen, Germany
| | - Ulrike Schara
- Department of Neuropediatrics, Developmental Neurology and Social Pediatrics, University Children's Hospital Essen, University Duisburg-Essen, Essen, Germany
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11
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Congenital myasthenic syndromes in the Thai population: Clinical findings and novel mutations. Neuromuscul Disord 2020; 30:851-858. [PMID: 32978031 DOI: 10.1016/j.nmd.2020.08.362] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2019] [Revised: 08/26/2020] [Accepted: 08/27/2020] [Indexed: 11/23/2022]
Abstract
Congenital myasthenic syndromes (CMS) comprise a heterogeneous group of genetic disorders of the neuromuscular junction. Next generation sequencing has been increasingly used for molecular diagnosis in CMS patients. This study aimed to identify the disease-causing variants in Thai patients. We recruited patients with a diagnosis of CMS based on clinical and electrophysiologic findings, and whole exome sequencing was performed. Thirteen patients aged from 2 to 54 years (median: 8 years) from 12 families were enrolled. Variants were identified in 9 of 13 patients (69%). Five novel variants and two previously reported variant were found in the COLQ, RAPSN and CHRND gene. The previously reported c.393+1G>A splice site variant in the COLQ gene was found in a majority of patients. Five patients harbor the homozygous splice site c.393+1G>A variant, and two patients carry compound heterozygous c.393+1G>A, c.718-1G>T, and c.393+1G>A, c.865G>T (p.Gly289Ter) variants. The novel variants were also found in RAPSN (p.Cys251del, p.Arg282Cys) and CHRND (p.Met481del). Molecular diagnosis in CMS patients can guide treatment decisions and may be life changing, especially in patients with COLQ mutations.
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12
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Barnett C, Tabasinejad R, Bril V. Current pharmacotherapeutic options for myasthenia gravis. Expert Opin Pharmacother 2019; 20:2295-2303. [PMID: 31670984 DOI: 10.1080/14656566.2019.1682548] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Introduction: Novel options for immune-based therapy in myasthenia gravis are improving the therapeutic outlook for patients. Multiple clinical trials on immunomodulation, complement inhibitors, and FcR inhibitors are providing evidence for novel immune-based therapies that promise to improve outcomes in myasthenia patients. These more focused immune treatments are reviewed in this paper.Areas covered: This paper outlines classical treatment for myasthenia gravis and then reviews recent clinical trial evidence for novel immune therapies, particularly complement inhibitors and FcR inhibitors. Further, as immune therapies expand in other areas of medicine, such as oncology, iatrogenic myasthenia is being observed as a complication of some novel treatments.Expert opinion: Exciting new options to help patients with myasthenia gravis are now available or in phase 3 trials based on promising phase 2 results. Manipulation of the immune system can also lead to iatrogenic MG. Although novel treatments can improve care for myasthenia gravis patients, future developments that prevent the production of specific abnormal auto-antibodies are desirable.
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Affiliation(s)
- Carolina Barnett
- Department of Medicine (Neurology), University Health Network, University of Toronto - Neurology, Toronto, Ontario, Canada
| | - Raha Tabasinejad
- Department of Medicine (Neurology), University Health Network, University of Toronto - Neurology, Toronto, Ontario, Canada
| | - Vera Bril
- Department of Medicine (Neurology), University Health Network, University of Toronto - Neurology, Toronto, Ontario, Canada
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13
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Xing G, Jing H, Zhang L, Cao Y, Li L, Zhao K, Dong Z, Chen W, Wang H, Cao R, Xiong WC, Mei L. A mechanism in agrin signaling revealed by a prevalent Rapsyn mutation in congenital myasthenic syndrome. eLife 2019; 8:e49180. [PMID: 31549961 PMCID: PMC6779466 DOI: 10.7554/elife.49180] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2019] [Accepted: 09/23/2019] [Indexed: 12/15/2022] Open
Abstract
Neuromuscular junction is a synapse between motoneurons and skeletal muscles, where acetylcholine receptors (AChRs) are concentrated to control muscle contraction. Studies of this synapse have contributed to our understanding of synapse assembly and pathological mechanisms of neuromuscular disorders. Nevertheless, underlying mechanisms of NMJ formation was not well understood. To this end, we took a novel approach - studying mutant genes implicated in congenital myasthenic syndrome (CMS). We showed that knock-in mice carrying N88K, a prevalent CMS mutation of Rapsyn (Rapsn), died soon after birth with profound NMJ deficits. Rapsn is an adapter protein that bridges AChRs to the cytoskeleton and possesses E3 ligase activity. In investigating how N88K impairs the NMJ, we uncovered a novel signaling pathway by which Agrin-LRP4-MuSK induces tyrosine phosphorylation of Rapsn, which is required for its self-association and E3 ligase activity. Our results also provide insight into pathological mechanisms of CMS.
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Affiliation(s)
- Guanglin Xing
- Department of Neurosciences, School of MedicineCase Western Reserve UniversityClevelandUnited States
| | - Hongyang Jing
- Department of Neurosciences, School of MedicineCase Western Reserve UniversityClevelandUnited States
| | - Lei Zhang
- Department of Neurosciences, School of MedicineCase Western Reserve UniversityClevelandUnited States
| | - Yu Cao
- Department of Neuroscience and Regenerative MedicineAugusta UniversityAugustaUnited States
| | - Lei Li
- Department of Neurosciences, School of MedicineCase Western Reserve UniversityClevelandUnited States
| | - Kai Zhao
- Department of Neurosciences, School of MedicineCase Western Reserve UniversityClevelandUnited States
- Department of Neuroscience and Regenerative MedicineAugusta UniversityAugustaUnited States
| | - Zhaoqi Dong
- Department of Neurosciences, School of MedicineCase Western Reserve UniversityClevelandUnited States
| | - Wenbing Chen
- Department of Neurosciences, School of MedicineCase Western Reserve UniversityClevelandUnited States
| | - Hongsheng Wang
- Department of Neurosciences, School of MedicineCase Western Reserve UniversityClevelandUnited States
| | - Rangjuan Cao
- Department of Neurosciences, School of MedicineCase Western Reserve UniversityClevelandUnited States
| | - Wen-Cheng Xiong
- Department of Neurosciences, School of MedicineCase Western Reserve UniversityClevelandUnited States
- Louis Stokes Cleveland Veterans Affairs Medical CenterClevelandUnited States
| | - Lin Mei
- Department of Neurosciences, School of MedicineCase Western Reserve UniversityClevelandUnited States
- Louis Stokes Cleveland Veterans Affairs Medical CenterClevelandUnited States
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14
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Rivner MH, Pasnoor M, Dimachkie MM, Barohn RJ, Mei L. Muscle-Specific Tyrosine Kinase and Myasthenia Gravis Owing to Other Antibodies. Neurol Clin 2019; 36:293-310. [PMID: 29655451 DOI: 10.1016/j.ncl.2018.01.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Around 20% of patients with myasthenia gravis are acetylcholine receptor antibody negative; muscle-specific tyrosine kinase antibodies (MuSK) were identified as the cause of myasthenia gravis in 30% to 40% of these cases. Anti MuSK myasthenia gravis is associated with specific clinical phenotypes. One is a bulbar form with fewer ocular symptoms. Others show an isolated head drop or symptoms indistinguishable from acetylcholine receptor-positive myasthenia gravis. These patients usually respond well to immunosuppressive therapy, but not as well to cholinesterase inhibitors. Other antibodies associated with myasthenia gravis, including low-density lipoprotein receptor-related protein 4, are discussed.
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Affiliation(s)
- Michael H Rivner
- EMG Lab, Augusta University, 1120 15th Street, BP-4390, Augusta, GA 30912, USA.
| | - Mamatha Pasnoor
- Department of Neurology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA
| | - Mazen M Dimachkie
- Department of Neurology, University of Kansas Medical Center, 3599 Rainbow Boulevard, Mail Stop 2012, Kansas City, KS 66103, USA
| | - Richard J Barohn
- Department of Neurology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Mail Stop 4017, Kansas City, KS 66160, USA
| | - Lin Mei
- Department of Neuroscience and Regenerative Medicine, Augusta University, 1120 15th Street, CA-2014, Augusta, GA 30912, USA
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15
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Estephan EDP, Zambon AA, Marchiori PE, da Silva AMS, Caldas VM, Moreno CAM, Reed UC, Horvath R, Töpf A, Lochmüller H, Zanoteli E. Clinical variability of early-onset congenital myasthenic syndrome due to biallelic RAPSN mutations in Brazil. Neuromuscul Disord 2018; 28:961-964. [DOI: 10.1016/j.nmd.2018.08.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 08/22/2018] [Indexed: 10/28/2022]
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16
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Kumar A, Asghar S, Kavanagh R, Wicklund MP. Unique presentation of rapidly fluctuating symptoms in a child with congenital myasthenic syndrome due to RAPSN mutation. Muscle Nerve 2018; 58:E23-E24. [PMID: 30028532 DOI: 10.1002/mus.26200] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Revised: 06/09/2018] [Accepted: 06/12/2018] [Indexed: 10/28/2022]
Affiliation(s)
- Ashutosh Kumar
- Division of Pediatric Neurology, Penn State Milton S. Hershey Medical Center, 500 University Drive, Hershey, Pennsylvania, 17033, USA
| | - Sheila Asghar
- Division of Pediatric Neurology, Penn State Milton S. Hershey Medical Center, 500 University Drive, Hershey, Pennsylvania, 17033, USA
| | - Robert Kavanagh
- Division of Pediatric Critical Care, Penn State Milton S. Hershey Medical Center, Hershey, Pennsylvania, USA
| | - Matthew P Wicklund
- Department of Neurology, University of Colorado School of Medicine, Aurora, Colorado, USA
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17
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Farmakidis C, Pasnoor M, Barohn RJ, Dimachkie MM. Congenital Myasthenic Syndromes: a Clinical and Treatment Approach. Curr Treat Options Neurol 2018; 20:36. [DOI: 10.1007/s11940-018-0520-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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18
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Rodríguez Cruz PM, Palace J, Beeson D. The Neuromuscular Junction and Wide Heterogeneity of Congenital Myasthenic Syndromes. Int J Mol Sci 2018; 19:ijms19061677. [PMID: 29874875 PMCID: PMC6032286 DOI: 10.3390/ijms19061677] [Citation(s) in RCA: 74] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 05/17/2018] [Accepted: 05/21/2018] [Indexed: 01/16/2023] Open
Abstract
Congenital myasthenic syndromes (CMS) are genetic disorders characterised by impaired neuromuscular transmission. This review provides an overview on CMS and highlights recent advances in the field, including novel CMS causative genes and improved therapeutic strategies. CMS due to mutations in SLC5A7 and SLC18A3, impairing the synthesis and recycling of acetylcholine, have recently been described. In addition, a novel group of CMS due to mutations in SNAP25B, SYT2, VAMP1, and UNC13A1 encoding molecules implicated in synaptic vesicles exocytosis has been characterised. The increasing number of presynaptic CMS exhibiting CNS manifestations along with neuromuscular weakness demonstrate that the myasthenia can be only a small part of a much more extensive disease phenotype. Moreover, the spectrum of glycosylation abnormalities has been increased with the report that GMPPB mutations can cause CMS, thus bridging myasthenic disorders with dystroglycanopathies. Finally, the discovery of COL13A1 mutations and laminin α5 deficiency has helped to draw attention to the role of extracellular matrix proteins for the formation and maintenance of muscle endplates. The benefit of β2-adrenergic agonists alone or combined with pyridostigmine or 3,4-Dyaminopiridine is increasingly being reported for different subtypes of CMS including AChR-deficiency and glycosylation abnormalities, thus expanding the therapeutic repertoire available.
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Affiliation(s)
- Pedro M Rodríguez Cruz
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, UK.
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford OX3 9DS, UK.
| | - Jacqueline Palace
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, UK.
| | - David Beeson
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, UK.
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford OX3 9DS, UK.
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20
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Lee M, Beeson D, Palace J. Therapeutic strategies for congenital myasthenic syndromes. Ann N Y Acad Sci 2018; 1412:129-136. [DOI: 10.1111/nyas.13538] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 09/28/2017] [Accepted: 10/02/2017] [Indexed: 12/20/2022]
Affiliation(s)
- Manon Lee
- Nuffield Department of Clinical Neurosciences; John Radcliffe Hospital; Oxford United Kingdom
| | - David Beeson
- The Weatherall Institute of Molecular Medicine, John Radcliffe Hospital; University of Oxford; Oxford United Kingdom
| | - Jacqueline Palace
- Nuffield Department of Clinical Neurosciences; John Radcliffe Hospital; Oxford United Kingdom
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21
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McMacken G, Whittaker RG, Evangelista T, Abicht A, Dusl M, Lochmüller H. Congenital myasthenic syndrome with episodic apnoea: clinical, neurophysiological and genetic features in the long-term follow-up of 19 patients. J Neurol 2018; 265:194-203. [PMID: 29189923 PMCID: PMC5760613 DOI: 10.1007/s00415-017-8689-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2017] [Revised: 11/19/2017] [Accepted: 11/20/2017] [Indexed: 12/14/2022]
Abstract
BACKGROUND Congenital myasthenic syndrome with episodic apnoea (CMS-EA) is a rare but potentially treatable cause of apparent life-threatening events in infancy. The underlying mechanisms for sudden and recurrent episodes of respiratory arrest in these patients are unclear. Whilst CMS-EA is most commonly caused by mutations in CHAT, the list of associated genotypes is expanding. METHODS We reviewed clinical information from 19 patients with CMS-EA, including patients with mutations in CHAT, SLC5A7 and RAPSN, and patients lacking a genetic diagnosis. RESULTS Lack of genetic diagnosis was more common in CMS-EA than in CMS without EA (56% n = 18, compared to 7% n = 97). Most patients manifested intermittent apnoea in the first 4 months of life (74%, n = 14). A degree of clinical improvement with medication was observed in most patients (74%, n = 14), but the majority of cases also showed a tendency towards complete remission of apnoeic events with age (mean age of resolution 2 years 5 months). Signs of impaired neuromuscular transmission were detected on neurophysiology studies in 79% (n = 15) of cases, but in six cases, this was only apparent following specific neurophysiological testing protocols (prolonged high-frequency stimulation). CONCLUSIONS A relatively large proportion of CMS-EA remains genetically undiagnosed, which suggests the existence of novel causative CMS genes which remain uncharacterised. In light of the potential for recurrent life-threatening apnoeas in early life and the positive response to therapy, early diagnostic consideration of CMS-EA is critical, but without specific neurophysiology tests, it may go overlooked.
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Affiliation(s)
- Grace McMacken
- John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK.
| | - Roger G Whittaker
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - Teresinha Evangelista
- John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Angela Abicht
- Friedrich-Baur-Institute, Ludwig Maximilians University, Munich, Germany
| | - Marina Dusl
- Friedrich-Baur-Institute, Ludwig Maximilians University, Munich, Germany
| | - Hanns Lochmüller
- John Walton Muscular Dystrophy Research Centre, MRC Centre for Neuromuscular Diseases, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
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Winters L, Van Hoof E, De Catte L, Van Den Bogaert K, de Ravel T, De Waele L, Corveleyn A, Breckpot J. Massive parallel sequencing identifies RAPSN and PDHA1 mutations causing fetal akinesia deformation sequence. Eur J Paediatr Neurol 2017; 21:745-753. [PMID: 28495245 DOI: 10.1016/j.ejpn.2017.04.641] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Revised: 04/12/2017] [Accepted: 04/19/2017] [Indexed: 02/07/2023]
Abstract
INTRODUCTION Fetal akinesia deformation sequence (FADS) or arthrogryposis multiplex congenita (AMC) is characterized by clinical ambiguity and genetic heterogeneity, hampering genetic diagnosis via traditional sequencing methods. Next generation sequencing (NGS) of all known disease-causing genes offers an elegant solution to identify the genetic etiology of AMC/FADS in a diagnostic setting. METHODS An in-house developed disease-associated gene panel was conducted in two unrelated fetuses with FADS. First, a de novo analysis was performed on the entire disease-associated gene panel. If no pathogenic mutation was identified, analysis of variants retained in a specific subpanel with arthrogryposis/fetal akinesia-causing genes was performed. RESULTS In the first family, FADS relates to a homozygous c.484G > A (p.Glu162Lys) mutation in the gene RAPSN. The second case concerns a sporadic patient with brain anomalies and arthrogryposis due to a de novo hemizygous c.498C > T splice-site mutation in the pyruvate dehydrogenase-alpha 1 (PDHA1) gene. DISCUSSION NGS facilitated genetic diagnosis, and hence genetic counseling, for both families with AMC/FADS. Biallelic RAPSN mutations typically result in congenital myasthenia syndrome, or occasionally in FADS. This is the first report attributing the RAPSN mutation c.484G > A, identified in a homozygous state in patient 1, to FADS. The second patient represents the first case of AMC due to a PDHA1 mutation, advocating that pyruvate dehydrogenase deficiency should be considered in the differential diagnosis of fetal akinesia. This study illustrates the relevance of a disease-associated-gene panel as a diagnostic tool in pregnancies complicated by this genetically heterogeneous condition.
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Affiliation(s)
- Lore Winters
- Department of Pediatrics, University Hospitals Leuven, Catholic University Leuven, Leuven, Belgium
| | - Evelien Van Hoof
- Center for Human Genetics, University Hospitals Leuven, Catholic University Leuven, Leuven, Belgium
| | - Luc De Catte
- Division of Woman and Child, Clinical Department of Obstetrics and Gynecology, Fetal Medicine Unit, University Hospitals Leuven, Leuven, Belgium
| | - Kris Van Den Bogaert
- Center for Human Genetics, University Hospitals Leuven, Catholic University Leuven, Leuven, Belgium
| | - Thomy de Ravel
- Center for Human Genetics, University Hospitals Leuven, Catholic University Leuven, Leuven, Belgium
| | - Liesbeth De Waele
- Department of Pediatric Neurology, University Hospitals Leuven, Leuven, Belgium
| | - Anniek Corveleyn
- Center for Human Genetics, University Hospitals Leuven, Catholic University Leuven, Leuven, Belgium
| | - Jeroen Breckpot
- Center for Human Genetics, University Hospitals Leuven, Catholic University Leuven, Leuven, Belgium.
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23
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Pitt MC. Use of stimulated electromyography in the analysis of the neuromuscular junction in children. Muscle Nerve 2017; 56:841-847. [DOI: 10.1002/mus.25685] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 04/18/2017] [Accepted: 05/01/2017] [Indexed: 11/09/2022]
Affiliation(s)
- Matthew C. Pitt
- Department of Clinical NeurophysiologyGreat Ormond Street Hospital for Children NHS Foundation TrustGreat Ormond Street, LondonWC1N 3JH United Kingdom
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Roy B, Chahin N. Clinical Reasoning: A 14-year-old boy with fatigue and episodic worsening of weakness. Neurology 2017; 88:e96-e100. [DOI: 10.1212/wnl.0000000000003718] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Visser AC, Laughlin RS, Litchy WJ, Benarroch EE, Milone M. Rapsyn congenital myasthenic syndrome worsened by fluoxetine. Muscle Nerve 2016; 55:131-135. [DOI: 10.1002/mus.25244] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/02/2016] [Indexed: 11/08/2022]
Affiliation(s)
- Amy C. Visser
- Department of NeurologyMayo Clinic200 First Street SWRochester Minnesota55905 USA
| | - Ruple S. Laughlin
- Department of NeurologyMayo Clinic200 First Street SWRochester Minnesota55905 USA
| | - William J. Litchy
- Department of NeurologyMayo Clinic200 First Street SWRochester Minnesota55905 USA
| | - Eduardo E. Benarroch
- Department of NeurologyMayo Clinic200 First Street SWRochester Minnesota55905 USA
| | - Margherita Milone
- Department of NeurologyMayo Clinic200 First Street SWRochester Minnesota55905 USA
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Garg N, Yiannikas C, Hardy TA, Belaya K, Cheung J, Beeson D, Reddel SW. Late presentations of congenital myasthenic syndromes: How many do we miss? Muscle Nerve 2016; 54:721-7. [DOI: 10.1002/mus.25085] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/16/2016] [Indexed: 11/11/2022]
Affiliation(s)
- Nidhi Garg
- Neuroimmunology Clinic; Concord Hospital and University of Sydney; NSW Australia
| | - Con Yiannikas
- Departments of Neurology and Molecular Medicine; University of Sydney, Concord Hospital; Sydney New South Wales 2139 Australia
| | - Todd A. Hardy
- Neuroimmunology Clinic; Concord Hospital and University of Sydney; NSW Australia
| | - Katsiaryna Belaya
- The Weatherall Institute of Molecular Medicine; University of Oxford, John Radcliffe Hospital; Oxford UK
| | - Jonathan Cheung
- The Weatherall Institute of Molecular Medicine; University of Oxford, John Radcliffe Hospital; Oxford UK
| | - David Beeson
- The Weatherall Institute of Molecular Medicine; University of Oxford, John Radcliffe Hospital; Oxford UK
| | - Stephen W. Reddel
- Neuroimmunology Clinic; Concord Hospital and University of Sydney; NSW Australia
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Natera-de Benito D, Bestué M, Vilchez JJ, Evangelista T, Töpf A, García-Ribes A, Trujillo-Tiebas MJ, García-Hoyos M, Ortez C, Camacho A, Jiménez E, Dusl M, Abicht A, Lochmüller H, Colomer J, Nascimento A. Long-term follow-up in patients with congenital myasthenic syndrome due to RAPSN mutations. Neuromuscul Disord 2015; 26:153-9. [PMID: 26782015 DOI: 10.1016/j.nmd.2015.10.013] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Revised: 10/27/2015] [Accepted: 10/29/2015] [Indexed: 11/19/2022]
Abstract
Rapsyn (RAPSN) mutations are a common cause of postsynaptic congenital myasthenic syndromes. We present a comprehensive description of the clinical and molecular findings of ten patients with CMS due to mutations in RAPSN, mostly with a long-term follow-up. Two patients were homozygous and eight were heterozygous for the common p.Asn88Lys mutation. In three of the heterozygous patients we have identified three novel mutations (c.869T > C; p.Leu290Pro, c.1185delG; p.Thr396Profs*12, and c.358delC; p.Gln120Serfs*8). In our cohort, the RAPSN mutations lead to a relatively homogeneous phenotype, characterized by fluctuating ptosis, occasional bulbar symptoms, neck muscle weakness, and mild proximal muscle weakness with exacerbations precipitated by minor infections. Interestingly, episodic exacerbations continue to occur during adulthood. These were characterized by proximal limb girdle weakness and ptosis, and not so much by respiratory insufficiency after age 6. All patients presented during neonatal period and responded to cholinergic agonists. In most of the affected patients, additional use of 3,4-diaminopyridine resulted in significant clinical benefit. The disease course is stable except for intermittent worsening.
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Affiliation(s)
- D Natera-de Benito
- Department of Pediatrics, Hospital Universitario de Fuenlabrada, Madrid, Spain.
| | - M Bestué
- Department of Neurology, Hospital General San Jorge, Huesca, Spain
| | - J J Vilchez
- Department of Neurology, Hospital Universitari La Fe, Valencia, Spain
| | - T Evangelista
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne NE1 3BZ, UK
| | - A Töpf
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne NE1 3BZ, UK
| | - A García-Ribes
- Department of Pediatrics, Hospital Universitario Cruces, Bilbao, Spain
| | - M J Trujillo-Tiebas
- Department of Genetics, Hospital Universitario Fundación Jiménez Díaz, Madrid, Spain
| | - M García-Hoyos
- Department of Genetics, Instituto de Medicina Genómica, Valencia, Spain
| | - C Ortez
- Department of Neuromuscular Diseases, Hospital Sant Joan de Déu, Barcelona, Spain
| | - A Camacho
- Department of Pediatric Neurology, Hospital Universitario 12 de Octubre, Madrid, Spain
| | - E Jiménez
- Department of Pediatrics, Hospital Universitario Rey Juan Carlos, Madrid, Spain
| | - M Dusl
- Friedrich-Baur-Institute, Ludwig-Maximilians-University Munich, Munich 80336,Germany
| | - A Abicht
- Friedrich-Baur-Institute, Ludwig-Maximilians-University Munich, Munich 80336,Germany; Medical Genetics Center, Munich, Germany
| | - H Lochmüller
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne NE1 3BZ, UK
| | - J Colomer
- Department of Neuromuscular Diseases, Hospital Sant Joan de Déu, Barcelona, Spain
| | - A Nascimento
- Department of Neuromuscular Diseases, Hospital Sant Joan de Déu, Barcelona, Spain
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28
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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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29
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McKie AB, Alsaedi A, Vogt J, Stuurman KE, Weiss MM, Shakeel H, Tee L, Morgan NV, Nikkels PGJ, van Haaften G, Park SM, van der Smagt JJ, Bugiani M, Maher ER. Germline mutations in RYR1 are associated with foetal akinesia deformation sequence/lethal multiple pterygium syndrome. Acta Neuropathol Commun 2014; 2:148. [PMID: 25476234 PMCID: PMC4271450 DOI: 10.1186/s40478-014-0148-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Accepted: 10/06/2014] [Indexed: 11/10/2022] Open
Abstract
INTRODUCTION Foetal akinesia deformation sequence syndrome (FADS) is a genetically heterogeneous disorder characterised by the combination of foetal akinesia and developmental defects which may include pterygia (joint webbing). Traditionally multiple pterygium syndrome (MPS) has been divided into two forms: prenatally lethal (LMPS) and non-lethal Escobar type (EVMPS) types. Interestingly, FADS, LMPS and EVMPS may be allelic e.g. each of these phenotypes may result from mutations in the foetal acetylcholine receptor gamma subunit gene (CHRNG). Many cases of FADS and MPS do not have a mutation in a known FADS/MPS gene and we undertook molecular genetic studies to identify novel causes of these phenotypes. RESULTS After mapping a novel locus for FADS/LMPS to chromosome 19, we identified a homozygous null mutation in the RYR1 gene in a consanguineous kindred with recurrent LMPS pregnancies. Resequencing of RYR1 in a cohort of 66 unrelated probands with FADS/LMPS/EVMPS (36 with FADS/LMPS and 30 with EVMPS) revealed two additional homozygous mutations (in frame deletions). The overall frequency of RYR1 mutations in probands with FADS/LMPS was 8.3%. CONCLUSIONS Our findings report, for the first time, a homozygous RYR1 null mutation and expand the range of RYR1-related phenotypes to include early lethal FADS/LMPS. We suggest that RYR1 mutation analysis should be performed in cases of severe FADS/LMPS even in the absence of specific histopathological indicators of RYR1-related disease.
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Affiliation(s)
- Arthur B McKie
- Department of Medical Genetics, University of Cambridge and NIHR Cambridge Biomedical Research Centre, Cambridge Biomedical Campus, Cambridge, CB2 0QQ, UK.
| | - Atif Alsaedi
- Centre for Rare Diseases and Personalised Medicine, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
| | - Julie Vogt
- West Midlands Regional Genetics Service, Birmingham Women's Hospital, Birmingham, B15 2TG, UK.
| | - Kyra E Stuurman
- Department of Clinical Genetics, VU University Medical Center, Amsterdam, The Netherlands.
| | - Marjan M Weiss
- Department of Clinical Genetics, VU University Medical Center, Amsterdam, The Netherlands.
| | - Hassan Shakeel
- Department of Medical Genetics, University of Cambridge and NIHR Cambridge Biomedical Research Centre, Cambridge Biomedical Campus, Cambridge, CB2 0QQ, UK.
| | - Louise Tee
- Centre for Rare Diseases and Personalised Medicine, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
| | - Neil V Morgan
- Centre for Rare Diseases and Personalised Medicine, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
| | - Peter G J Nikkels
- Department of Pathology, University Medical Center Utrecht, Utrecht, The Netherlands.
| | - Gijs van Haaften
- Department of Medical Genetics, University Medical Center Utrecht, University of Utrecht, Utrecht, The Netherlands.
| | - Soo-Mi Park
- Department of Clinical Genetics, Addenbrooke's Treatment Centre, Cambridge University Hospitals NHS Foundation Trust, Hills Road, Cambridge, CB2 0QQ, UK.
| | - Jasper J van der Smagt
- Department of Medical Genetics, University Medical Center Utrecht, University of Utrecht, Utrecht, The Netherlands.
| | - Marianna Bugiani
- Department of Pathology, VU University Medical Center, Amsterdam, the Netherlands.
| | - Eamonn R Maher
- Department of Medical Genetics, University of Cambridge and NIHR Cambridge Biomedical Research Centre, Cambridge Biomedical Campus, Cambridge, CB2 0QQ, UK.
- Centre for Rare Diseases and Personalised Medicine, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
- Department of Clinical Genetics, Addenbrooke's Treatment Centre, Cambridge University Hospitals NHS Foundation Trust, Hills Road, Cambridge, CB2 0QQ, UK.
- Department of Medical Genetics, School of Clinical Medicine, University of Cambridge, Addenbrooke's Treatment Centre, Cambridge Biomedical Campus, Box 238, Cambridge, CB2 0QQ, United Kingdom.
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30
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McElnea EM, Stephenson K, Lanigan B, Flitcroft I. An ocular motility conundrum. BMJ Case Rep 2014; 2014:bcr-2014-206862. [PMID: 25349186 DOI: 10.1136/bcr-2014-206862] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Two siblings, an 11-year-old boy and a 7-year-old girl presented with bilateral symmetrical ptosis and limited eye movements. Having already been reviewed on a number of occasions by a variety of specialists in multiple hospital settings a diagnosis of their ocular motility disorder had remained elusive. We describe their cases, outline the differential diagnosis and review the investigations performed which were influential in finally making a diagnosis.
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Affiliation(s)
| | - Kirk Stephenson
- Department of Ophthalmology, Temple Street Children's University Hospital, Dublin 1, Ireland
| | - Bernie Lanigan
- Department of Ophthalmology, Temple Street Children's University Hospital, Dublin 1, Ireland
| | - Ian Flitcroft
- Department of Ophthalmology, Temple Street Children's University Hospital, Dublin 1, Ireland
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31
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Eymard B, Stojkovic T, Sternberg D, Richard P, Nicole S, Fournier E, Béhin A, Laforêt P, Servais L, Romero N, Fardeau M, Hantaï D. [Congenital myasthenic syndromes: difficulties in the diagnosis, course and prognosis, and therapy--The French National Congenital Myasthenic Syndrome Network experience]. Rev Neurol (Paris) 2013; 169 Suppl 1:S45-55. [PMID: 23452772 DOI: 10.1016/s0035-3787(13)70060-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders caused by genetic defects affecting neuromuscular transmission and leading to muscle weakness accentuated by exertion. Three different aspects have been investigated by members of the national French CMS Network: the difficulties in making a proper diagnosis; the course and long-term prognosis; and the response to therapy, especially for CMS that do not respond to cholinesterase inhibitors. CMS diagnosis is late in most cases because of confusion with other entities such as: congenital myopathies, due to the frequent presentation in patients of myopathies such as permanent muscle weakness, atrophy and scoliosis, and the abnormalities of internal structure, diameter and distribution of fibers (type I predominance, type II atrophy) seen on biopsy; seronegative autoimmune myasthenia gravis, when CMS is of late onset; and metabolic myopathy, with the presence of lipidosis in muscle. The long-term prognosis of CMS was studied in a series of 79 patients recruited with the following gene mutations: CHRNA; CHRNE; DOK7; COLQ; RAPSN; AGRN; and MUSK. Disease-course patterns (progressive worsening, exacerbation, stability, improvement) could be variable throughout life in a given patient. DOK7 patients had the most severe disease course with progressive worsening: of the eight wheelchair-bound and ventilated patients, six had mutations of this gene. Pregnancy was a frequent cause of exacerbation. Anticholinesterase agents are the first-line therapy for CMS patients, except for cases of slow-channel CMS, COLQ and DOK7. In our experience, 3,4-DAP was a useful complement for several patients harboring CMS with AChR loss or RAPSN gene mutations. Ephedrine was given to 18 patients (eight DOK7, five COLQ, four AGRN and one RAPSN). Tolerability was good. Therapeutic responses were encouraging even in the most severely affected patients, particularly with DOK7 and COLQ. Salbutamol was a good alternative in one patient who was allergic to ephedrine.
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Affiliation(s)
- B Eymard
- Centre de référence des affections neuromusculaires Paris-Est, service de Neurologie 2, Institut de Myologie, Hôpital de la Pitié-Salpêtrière, 47 bd de l'Hôpital, 75013 Paris, France.
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32
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Abstract
Congenital myasthenic syndromes (CMS) represent a heterogeneous group of 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, or in the postsynaptic region of the motor endplate. The disease proteins identified to date include the acetylcholine receptor, acetylcholinesterase, choline acetyltransferase, rapsyn, and Na(v)1.4, muscle-specific kinase, agrin, β2-laminin, downstream of tyrosine kinase 7, and glutamine-fructose-6-phosphate transaminase 1. Analysis of electrophysiologic and biochemical properties of mutant proteins expressed in heterologous systems have contributed crucially to defining the molecular consequences of the observed mutations and have resulted in improved therapy of most CMS.
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Affiliation(s)
- Andrew G Engel
- Department of Neurology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
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33
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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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34
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Shen XM, Crawford TO, Brengman J, Acsadi G, Iannaconne S, Karaca E, Khoury C, Mah JK, Edvardson S, Bajzer Z, Rodgers D, Engel AG. Functional consequences and structural interpretation of mutations of human choline acetyltransferase. Hum Mutat 2011; 32:1259-67. [PMID: 21786365 PMCID: PMC3196808 DOI: 10.1002/humu.21560] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Accepted: 06/22/2011] [Indexed: 12/12/2022]
Abstract
Choline acetyltransferase (ChAT; EC 2.3.1.6) catalyzes synthesis of acetylcholine from acetyl-CoA (AcCoA) and choline in cholinergic neurons. Mutations in CHAT cause potentially lethal congenital myasthenic syndromes associated with episodic apnea (ChAT-CMS). Here, we analyze the functional consequences of 12 missense and one nonsense mutations of CHAT in 11 patients. Nine of the mutations are novel. We examine expression of the recombinant missense mutants in Bosc 23 cells, determine their kinetic properties and thermal stability, and interpret the functional effects of 11 mutations in the context of the atomic structural model of human ChAT. Five mutations (p.Trp421Ser, p.Ser498Pro, p.Thr553Asn, p.Ala557Thr, and p.Ser572Trp) reduce enzyme expression to less than 50% of wild-type. Mutations with severe kinetic effects are located in the active-site tunnel (p.Met202Arg, p.Thr553Asn, and p.Ala557Thr) or adjacent to the substrate binding site (p.Ser572Trp), or exert their effect allosterically (p.Trp421Ser and p.Ile689Ser). Two mutations with milder kinetic effects (p.Val136Met and p.Ala235Thr) are also predicted to act allosterically. One mutation (p.Thr608Asn) below the nucleotide binding site of CoA enhances dissociation of AcCoA from the enzyme-substrate complex. Two mutations introducing a proline residue into an α-helix (p.Ser498Pro and p.Ser704Pro) impair the thermal stability of ChAT.
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Affiliation(s)
- Xin-Ming Shen
- Department of Neurology and Muscle Research Laboratory, Mayo Clinic, Rochester, Minnesota 55905, USA
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35
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Abstract
Hypotonia in infants in the first year of life is a common diagnostic and management challenge for pediatricians and neonatologists. Several published clinical studies have shown that a substantial proportion of cases are accounted for by genetic disorders. Rapid advances in biotechnology, bioinformatics, and molecular genetic testing have made it possible to offer specific genetic diagnoses in a timely manner. The value of clinical examination in the localization of hypotonia within the nervous system as the first step towards a diagnosis cannot be overemphasized. Due importance should be given to specific features on examination and in the selection of appropriate laboratory tests to minimize laboratory costs. Inborn errors of metabolism, although infrequently encountered, are of importance. Based on clinical evidence from published studies, an algorithm is suggested that would incorporate the clinical features and testing modalities in providing a high diagnostic yield for the clinician.
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Affiliation(s)
- A N Prasad
- Department of Pediatrics, University of Western Ontario, London, Ontario, Canada.
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36
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Vrolix K, Niks EH, Le Panse R, van Ostaijen-ten Dam MM, Muris AH, Jol-van der Zijde CM, van Tol MJ, Losen M, Molenaar PC, van Zoelen EJ, Berrih-Aknin S, De Baets MH, Verschuuren JJ, Martínez-Martínez P. Reduced thymic expression of ErbB receptors without auto-antibodies against synaptic ErbB in myasthenia gravis. J Neuroimmunol 2011; 232:158-65. [DOI: 10.1016/j.jneuroim.2010.10.024] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 09/27/2010] [Accepted: 10/21/2010] [Indexed: 11/15/2022]
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37
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Alseth EH, Maniaol AH, Elsais A, Nakkestad HL, Tallaksen C, Gilhus NE, Skeie GO. Investigation for RAPSN and DOK-7 mutations in a cohort of seronegative myasthenia gravis patients. Muscle Nerve 2011; 43:574-7. [DOI: 10.1002/mus.21919] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/14/2011] [Indexed: 11/12/2022]
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38
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Gomez AM, Van Den Broeck J, Vrolix K, Janssen SP, Lemmens MAM, Van Der Esch E, Duimel H, Frederik P, Molenaar PC, Martínez-Martínez P, De Baets MH, Losen M. Antibody effector mechanisms in myasthenia gravis-pathogenesis at the neuromuscular junction. Autoimmunity 2010; 43:353-70. [PMID: 20380584 DOI: 10.3109/08916930903555943] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Myasthenia gravis (MG) is an autoimmune disorder caused by autoantibodies that are either directed to the muscle nicotinic acetylcholine receptor (AChR) or to the muscle-specific tyrosine kinase (MuSK). These autoantibodies define two distinct subforms of the disease-AChR-MG and MuSK-MG. Both AChR and MuSK are expressed on the postsynaptic membrane of the neuromuscular junction (NMJ), which is a highly specialized region of the muscle dedicated to receive and process signals from the motor nerve. Autoantibody binding to proteins of the postsynaptic membrane leads to impaired neuromuscular transmission and muscle weakness. Pro-inflammatory antibodies of the human IgG1 and IgG3 subclass modulate the AChR, cause complement activation, and attract lymphocytes; together acting to decrease levels of the AChR and AChR-associated proteins and to reduce postsynaptic folding. In patients with anti-MuSK antibodies, there is no evidence of loss of junctional folds and no apparent loss of AChR density. Anti-MuSK antibodies are predominantly of the IgG4 isotype, which functionally differs from other IgG subclasses in its anti-inflammatory activity. Moreover, IgG4 undergoes a posttranslational modification termed Fab arm exchange that prevents cross-linking of antigens. These findings suggest that MuSK-MG may be different in etiological and pathological mechanisms from AChR-MG. The effector functions of IgG subclasses on synapse structure and function are discussed in this review.
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Affiliation(s)
- Alejandro M Gomez
- Neuroimmunology Group, Department of Neuroscience, School of Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands
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39
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Argov Z. Current approach to seronegative myasthenia. J Neurol 2010; 258:14-8. [PMID: 20852878 DOI: 10.1007/s00415-010-5746-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2010] [Accepted: 09/03/2010] [Indexed: 10/19/2022]
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40
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Verschuuren JJGM, Palace J, Erik Gilhus N. Clinical aspects of myasthenia explained. Autoimmunity 2010; 43:344-52. [DOI: 10.3109/08916931003602130] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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41
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Milone M, Shen XM, Selcen D, Ohno K, Brengman J, Iannaccone ST, Harper CM, Engel AG. Myasthenic syndrome due to defects in rapsyn: Clinical and molecular findings in 39 patients. Neurology 2009; 73:228-35. [PMID: 19620612 PMCID: PMC2715575 DOI: 10.1212/wnl.0b013e3181ae7cbc] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND Pathogenic mutations in rapsyn result in endplate acetylcholine receptor (AChR) deficiency and are a common cause of postsynaptic congenital myasthenic syndromes. METHODS Clinical, electrophysiologic, pathologic, and molecular studies were done in 39 patients. RESULTS In all but one patient, the disease presented in the first 2 years of life. In 9 patients, the myasthenic symptoms included constant or episodic ophthalmoparesis, and 1 patient had a pure limb-girdle phenotype. More than one-half of the patients experienced intermittent exacerbations. Long-term follow-up was available in 25 patients after start of cholinergic therapy: 21 became stable or were improved and 2 of these became asymptomatic; 3 had a progressive course; and 1 died in infancy. In 7 patients who had endplate studies, the average counts of AChR per endplate and the synaptic response to ACh were less reduced than in patients harboring low AChR expressor mutations. Eight patients were homozygous and 23 heterozygous for the common p.N88K mutation. Six mutations, comprising 3 missense mutations, an in-frame deletion, a splice-site mutation, and a nonsense mutation, are novel. Homozygosity for p.N88K was associated with varying grades of severity. No genotype-phenotype correlations were observed except in 8 Near-Eastern patients homozygous for the promoter mutation (c.-38A>G), who had a mild course. CONCLUSIONS All but 1 patient presented early in life and most responded to cholinergic agonists. With early diagnosis and therapy, rapsyn deficiency has a benign course in most patients. There was no consistent phenotype-genotype correlation except for an E-box mutation associated with jaw deformities.
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Affiliation(s)
- M Milone
- Department of Neurology, Mayo Clinic, Rochester, MN 55905, USA.
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42
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Affiliation(s)
- Michael Bamshad
- Division of Genetic Medicine, Department of Pediatrics, University of Washington, Seattle Children's Hospital, 1959 Northeast Pacific Street, HSC RR349, M/S Box 356320, Seattle, WA 98195. E-mail address:
| | - Ann E. Van Heest
- Department of Orthopaedic Surgery, University of Minnesota, 2450 Riverside Avenue, Suite R200, Minneapolis, MN 55454
| | - David Pleasure
- Departments of Neurology and Pediatrics, UC Davis School of Medicine, c/o Shriners Hospital, 2425 Stockton Boulevard, Sacramento, CA 95817
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43
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Martínez-Martínez P, Phernambucq M, Steinbusch L, Schaeffer L, Berrih-Aknin S, Duimel H, Frederik P, Molenaar P, De Baets MH, Losen M. Silencing rapsyn in vivo decreases acetylcholine receptors and augments sodium channels and secondary postsynaptic membrane folding. Neurobiol Dis 2009; 35:14-23. [PMID: 19344765 DOI: 10.1016/j.nbd.2009.03.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2008] [Revised: 02/23/2009] [Accepted: 03/18/2009] [Indexed: 10/21/2022] Open
Abstract
The receptor-associated protein of the synapse (rapsyn) is required for anchoring and stabilizing the nicotinic acetylcholine receptor (AChR) in the postsynaptic membrane of the neuromuscular junction (NMJ) during development. Here we studied the role of rapsyn in the maintenance of the adult NMJ by reducing rapsyn expression levels with short hairpin RNA (shRNA). Silencing rapsyn led to the average reduction of the protein levels of rapsyn (31% loss) and AChR (36% loss) at the NMJ within 2 weeks, corresponding to previously reported half life of these proteins. On the other hand, the sodium channel protein expression was augmented (66%) in rapsyn-silenced muscles. Unexpectedly, at the ultrastructural level a significant increase in the amount of secondary folds of the postsynaptic membrane in silenced muscles was observed. The neuromuscular transmission in rapsyn-silenced muscles was mildly impaired. The results suggest that the adult NMJ can rapidly produce postsynaptic folds to compensate for AChR and rapsyn loss.
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Affiliation(s)
- Pilar Martínez-Martínez
- Department of Neuroscience, School of Mental Health and Neuroscience, Maastricht University, Maastricht, The Netherlands, Maastricht, The Netherlands.
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Nogajski JH, Kiernan MC, Ouvrier RA, Andrews PI. Congenital myasthenic syndromes. J Clin Neurosci 2008; 16:1-11. [PMID: 19017561 DOI: 10.1016/j.jocn.2008.05.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2006] [Revised: 04/10/2008] [Accepted: 05/04/2008] [Indexed: 10/21/2022]
Abstract
Congenital myasthenic syndromes (CMS) are a heterogeneous group of uncommon, inherited disorders affecting the neuromuscular junction. The defects interfere with presynaptic, synaptic, or postsynaptic function and compromise neuromuscular transmission. Most patients with CMS have similar clinical features regardless of the underlying defect, but attention to clinical and electrodiagnostic parameters can narrow the diagnostic spectrum. Recent advances in our understanding of the cellular mechanisms underlying specific syndromes allow DNA testing for some forms of CMS. Diagnosis of CMS enables a rationale for management to be developed. Two cases of genetically determined CMS as well as an undiagnosed infant are presented to highlight the clinical and electrophysiological difficulties associated with the diagnosis and management of such syndromes.
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Affiliation(s)
- Joseph H Nogajski
- Institute of Neurological Sciences, Prince of Wales Hospital, Randwick, New South Wales, Australia
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Selcen D, Milone M, Shen XM, Harper CM, Stans AA, Wieben ED, Engel AG. Dok-7 myasthenia: phenotypic and molecular genetic studies in 16 patients. Ann Neurol 2008; 64:71-87. [PMID: 18626973 DOI: 10.1002/ana.21408] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
OBJECTIVE Detailed analysis of phenotypic and molecular genetic aspects of Dok-7 myasthenia in 16 patients. METHODS We assessed our patients by clinical and electromyographic studies, by intercostal muscle biopsies for in vitro microelectrode analysis of neuromuscular transmission and quantitative electron microscopy EM of 409 end plates (EPs), and by mutation analysis, and expression studies of the mutants. RESULTS The clinical spectrum varied from mild static limb-girdle weakness to severe generalized progressive disease. The synaptic contacts were single or multiple, and some, but not all, were small. In vitro microelectrode studies indicated variable decreases of the number of released quanta and of the synaptic response to acetylcholine; acetylcholine receptor (AChR) channel kinetics were normal. EM analysis demonstrated widespread and previously unrecognized destruction and remodeling of the EPs. Each patient carries 2 or more heteroallelic mutations: 11 in genomic DNA, 7 of which are novel; and 6 identifiable only in complementary DNA or cloned complementary DNA, 3 of which are novel. The pathogenicity of the mutations was confirmed by expression studies. Although the functions of Dok-7 include AChR beta-subunit phosphorylation and maintaining AChR site density, patient EPs showed normal AChR beta-subunit phosphorylation, and the AChR density on the remaining junctional folds appeared normal. INTERPRETATION First, the clinical features of Dok-7 myasthenia are highly variable. Second, some mutations are complex and identifiable only in cloned complementary DNA. Third, Dok-7 is essential for maintaining not only the size but also the structural integrity of the EP. Fourth, the profound structural alterations at the EPs likely contribute importantly to the reduced safety margin of neuromuscular transmission.
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Affiliation(s)
- Duygu Selcen
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN 55905, USA
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The congenital myasthenic syndromes. J Neuroimmunol 2008; 201-202:2-5. [DOI: 10.1016/j.jneuroim.2008.05.030] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2008] [Revised: 05/29/2008] [Accepted: 05/30/2008] [Indexed: 11/19/2022]
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Kinali M, Beeson D, Pitt M, Jungbluth H, Simonds A, Aloysius A, Cockerill H, Davis T, Palace J, Manzur A, Jimenez-Mallebrera C, Sewry C, Muntoni F, Robb S. Congenital Myasthenic Syndromes in childhood: Diagnostic and management challenges. J Neuroimmunol 2008; 201-202:6-12. [DOI: 10.1016/j.jneuroim.2008.06.026] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2008] [Revised: 06/07/2008] [Accepted: 06/09/2008] [Indexed: 10/21/2022]
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Michalk A, Stricker S, Becker J, Rupps R, Pantzar T, Miertus J, Botta G, Naretto VG, Janetzki C, Yaqoob N, Ott CE, Seelow D, Wieczorek D, Fiebig B, Wirth B, Hoopmann M, Walther M, Körber F, Blankenburg M, Mundlos S, Heller R, Hoffmann K. Acetylcholine receptor pathway mutations explain various fetal akinesia deformation sequence disorders. Am J Hum Genet 2008; 82:464-76. [PMID: 18252226 DOI: 10.1016/j.ajhg.2007.11.006] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2007] [Revised: 11/21/2007] [Accepted: 11/21/2007] [Indexed: 01/21/2023] Open
Abstract
Impaired fetal movement causes malformations, summarized as fetal akinesia deformation sequence (FADS), and is triggered by environmental and genetic factors. Acetylcholine receptor (AChR) components are suspects because mutations in the fetally expressed gamma subunit (CHRNG) of AChR were found in two FADS disorders, lethal multiple pterygium syndrome (LMPS) and Escobar syndrome. Other AChR subunits alpha1, beta1, and delta (CHRNA1, CHRNB1, CHRND) as well as receptor-associated protein of the synapse (RAPSN) previously revealed missense or compound nonsense-missense mutations in viable congenital myasthenic syndrome; lethality of homozygous null mutations was predicted but never shown. We provide the first report to our knowledge of homozygous nonsense mutations in CHRNA1 and CHRND and show that they were lethal, whereas novel recessive missense mutations in RAPSN caused a severe but not necessarily lethal phenotype. To elucidate disease-associated malformations such as frequent abortions, fetal edema, cystic hygroma, or cardiac defects, we studied Chrna1, Chrnb1, Chrnd, Chrng, and Rapsn in mouse embryos and found expression in skeletal muscles but also in early somite development. This indicates that early developmental defects might be due to somite expression in addition to solely muscle-specific effects. We conclude that complete or severe functional disruption of fetal AChR causes lethal multiple pterygium syndrome whereas milder alterations result in fetal hypokinesia with inborn contractures or a myasthenic syndrome later in life.
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