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Ohno K. Glycosylation defects as an emerging novel cause leading to a limb-girdle type of congenital myasthenic syndromes. J Neurol Neurosurg Psychiatry 2013; 84:1064. [PMID: 23457230 DOI: 10.1136/jnnp-2013-304931] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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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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Selcen D, Shen XM, Milone M, Brengman J, Ohno K, Deymeer F, Finkel R, Rowin J, Engel AG. GFPT1-myasthenia: clinical, structural, and electrophysiologic heterogeneity. Neurology 2013; 81:370-8. [PMID: 23794683 DOI: 10.1212/wnl.0b013e31829c5e9c] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE To identify patients with GFPT1-related limb-girdle myasthenia and analyze phenotypic consequences of the mutations. METHODS We performed genetic analysis, histochemical, immunoblot, and ultrastructural studies and in vitro electrophysiologic analysis of neuromuscular transmission. RESULTS We identified 16 recessive mutations in GFPT1 in 11 patients, of which 12 are novel. Ten patients had slowly progressive limb-girdle weakness responsive to cholinergic agonists with onset between infancy and age 19 years. One patient (no. 6) harbored a nonsense mutation and a second mutation that disrupts the muscle-specific GFPT1 exon. This patient never moved in utero, was apneic and arthrogrypotic at birth, and was bedfast, tube-fed, and barely responded to therapy at age 6 years. Histochemical studies in 9 of 11 patients showed tubular aggregates in 6 and rimmed vacuoles in 3. Microelectrode studies of intercostal muscle endplates in 5 patients indicated reduced synaptic response to acetylcholine in 3 and severely reduced quantal release in patient 6. Endplate acetylcholine receptor content was moderately reduced in only one patient. The synaptic contacts were small and single or grape-like, and quantitative electron microscopy revealed hypoplastic endplate regions. Numerous muscle fibers of patient 6 contained myriad dilated and degenerate vesicular profiles, autophagic vacuoles, and bizarre apoptotic nuclei. Glycoprotein expression in muscle was absent in patient 6 and reduced in 5 others. CONCLUSIONS GFPT1-myasthenia is more heterogeneous than previously reported. Different parameters of neuromuscular transmission are variably affected. When disruption of muscle-specific isoform determines the phenotype, this has devastating clinical, pathologic, and biochemical consequences.
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Affiliation(s)
- Duygu Selcen
- Department of Neurology, Mayo Clinic, Rochester, MN, USA.
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Clinical features in a large Iranian family with a limb-girdle congenital myasthenic syndrome due to a mutation in DPAGT1. Neuromuscul Disord 2013; 23:469-72. [PMID: 23591138 PMCID: PMC3746154 DOI: 10.1016/j.nmd.2013.03.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2012] [Revised: 02/28/2013] [Accepted: 03/06/2013] [Indexed: 12/26/2022]
Abstract
Mutations in DPAGT1 are a newly recognised cause of congenital myasthenic syndrome. DPAGT1 encodes an early component of the N-linked glycosylation pathway. Initially mutations in DPAGT1 have been associated with the onset of the severe multisystem disorder – congenital disorder of glycosylation type 1J. However, recently it was established that certain mutations in this gene can cause symptoms restricted to muscle weakness resulting from defective neuromuscular transmission. We report four cases from a large Iranian pedigree with prominent limb-girdle weakness and minimal craniobulbar symptoms who harbour a novel mutation in DPAGT1, c.652C>T, p.Arg218Trp. This myasthenic syndrome may mimic myopathic disorders and is likely under-diagnosed.
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Zoltowska K, Webster R, Finlayson S, Maxwell S, Cossins J, Müller J, Lochmüller H, Beeson D. Mutations in GFPT1 that underlie limb-girdle congenital myasthenic syndrome result in reduced cell-surface expression of muscle AChR. Hum Mol Genet 2013; 22:2905-13. [DOI: 10.1093/hmg/ddt145] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Maselli RA, Arredondo J, Nguyen J, Lara M, Ng F, Ngo M, Pham JM, Yi Q, Stajich JM, McDonald K, Hauser MA, Wollmann RL. Exome sequencing detection of two untranslated GFPT1 mutations in a family with limb-girdle myasthenia. Clin Genet 2013; 85:166-71. [PMID: 23488891 DOI: 10.1111/cge.12118] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Revised: 02/01/2013] [Accepted: 02/01/2013] [Indexed: 11/26/2022]
Abstract
The term 'limb-girdle myasthenia' (LGM) was first used to describe three siblings with proximal limb weakness without oculobulbar involvement, but with EMG decrement and responsiveness to anticholinesterase medication. We report here that exome sequencing in the proband of this family revealed several sequence variations in genes linked to proximal limb weakness. However, the only mutations that cosegregated with disease were an intronic IVS7-8A>G mutation and the previously reported 3'-UTR c.*22C>A mutation in GFPT1, a gene linked to LGM. A minigene assay showed that IVS7-8A>G activates an alternative splice acceptor that results in retention of the last seven nucleotides of intron 7 and a frameshift leading to a termination codon 13 nucleotides downstream from the new splice site. An anconeus muscle biopsy revealed mild reduction of the axon terminal size and postsynaptic fold simplification. The amplitudes of miniature endplate potentials and quantal release were also diminished. The DNA of the mildly affected father of the proband showed only the intronic mutation along with sequence variations in other genes potentially relevant to LGM. Thus, this study performed in the family originally described with LGM showed two GFPT1 untranslated mutations, which may cause disease by reducing GFPT1 expression and ultimately impairing protein glycosylation.
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Affiliation(s)
- R A Maselli
- Department of Neurology, University of California Davis, Davis, CA, USA
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Belaya K, Finlayson S, Cossins J, Liu WW, Maxwell S, Palace J, Beeson D. Identification of DPAGT1 as a new gene in which mutations cause a congenital myasthenic syndrome. Ann N Y Acad Sci 2012; 1275:29-35. [PMID: 23278575 PMCID: PMC6044425 DOI: 10.1111/j.1749-6632.2012.06790.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Congenital myasthenic syndromes (CMS) are a group of inherited disorders that arise from impaired signal transmission at the neuromuscular synapse. They are characterized by fatigable muscle weakness. This is a heterogenous group of disorders with 15 different genes implicated in the development of the disease. Using whole-exome sequencing we identified DPAGT1 as a new gene associated with CMS. DPAGT1 catalyses the first step of N-linked protein glycosylation. DPAGT1 patients are characterized by weakness of limb muscles, response to treatment with cholinesterase inhibitors, and the presence of tubular aggregates on muscle biopsy. We showed that DPAGT1 is required for glycosylation of acetylcholine receptor (AChR) subunits and efficient export of AChR to the cell surface. We suggest that the primary pathogenic mechanism of DPAGT1-associated CMS is reduced levels of AChRs at the endplate region. This finding demonstrates that impairment of the N-linked glycosylation pathway can lead to the development of CMS.
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Affiliation(s)
- Katsiaryna Belaya
- Neurosciences Group, Nuffield Department of Clinical Neurosciences, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom.
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Belaya K, Finlayson S, Slater C, Cossins J, Liu W, Maxwell S, McGowan S, Maslau S, Twigg S, Walls T, Pascual Pascual S, Palace J, Beeson D. Mutations in DPAGT1 cause a limb-girdle congenital myasthenic syndrome with tubular aggregates. Am J Hum Genet 2012; 91:193-201. [PMID: 22742743 PMCID: PMC3397259 DOI: 10.1016/j.ajhg.2012.05.022] [Citation(s) in RCA: 111] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2012] [Revised: 04/18/2012] [Accepted: 05/29/2012] [Indexed: 11/28/2022] Open
Abstract
Congenital myasthenic syndromes are a heterogeneous group of inherited disorders that arise from impaired signal transmission at the neuromuscular synapse. They are characterized by fatigable muscle weakness. We performed whole-exome sequencing to determine the underlying defect in a group of individuals with an inherited limb-girdle pattern of myasthenic weakness. We identify DPAGT1 as a gene in which mutations cause a congenital myasthenic syndrome. We describe seven different mutations found in five individuals with DPAGT1 mutations. The affected individuals share a number of common clinical features, including involvement of proximal limb muscles, response to treatment with cholinesterase inhibitors and 3,4-diaminopyridine, and the presence of tubular aggregates in muscle biopsies. Analyses of motor endplates from two of the individuals demonstrate a severe reduction of endplate acetylcholine receptors. DPAGT1 is an essential enzyme catalyzing the first committed step of N-linked protein glycosylation. Our findings underscore the importance of N-linked protein glycosylation for proper functioning of the neuromuscular junction. Using the DPAGT1-specific inhibitor tunicamycin, we show that DPAGT1 is required for efficient glycosylation of acetylcholine-receptor subunits and for efficient export of acetylcholine receptors to the cell surface. We suggest that the primary pathogenic mechanism of DPAGT1 mutations is reduced levels of acetylcholine receptors at the endplate region. These individuals share clinical features similar to those of congenital myasthenic syndrome due to GFPT1 mutations, and their disorder might be part of a larger subgroup comprising the congenital myasthenic syndromes that result from defects in the N-linked glycosylation pathway and that manifest through impaired neuromuscular transmission.
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Affiliation(s)
- Katsiaryna Belaya
- Neurosciences Group, Nuffield Department of Clinical Neurosciences, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3QX, UK
| | - Sarah Finlayson
- Neurosciences Group, Nuffield Department of Clinical Neurosciences, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK
- Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, Oxford OX3 9DU, UK
| | - Clarke R. Slater
- Institute of Neuroscience, Newcastle Biomedicine, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
| | - Judith Cossins
- Neurosciences Group, Nuffield Department of Clinical Neurosciences, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK
| | - Wei Wei Liu
- Neurosciences Group, Nuffield Department of Clinical Neurosciences, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK
| | - Susan Maxwell
- Neurosciences Group, Nuffield Department of Clinical Neurosciences, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK
| | - Simon J. McGowan
- Computational Biology Research Group, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK
| | - Siarhei Maslau
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3QX, UK
| | - Stephen R.F. Twigg
- Clinical Genetics, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK
| | - Timothy J. Walls
- Department of Neurology, Regional Neurosciences Centre, Newcastle General Hospital, Newcastle upon Tyne NE1 4LP, UK
| | - Samuel I. Pascual Pascual
- Servicio de Neurologia Pediátrica. Hospital Universitario La Paz, Departamento de Pediatria, Universidad Autónoma de Madrid, Madrid 28046, Spain
| | - Jacqueline Palace
- Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, Oxford OX3 9DU, UK
| | - David Beeson
- Neurosciences Group, Nuffield Department of Clinical Neurosciences, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK
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Abicht A, Dusl M, Gallenmüller C, Guergueltcheva V, Schara U, Della Marina A, Wibbeler E, Almaras S, Mihaylova V, von der Hagen M, Huebner A, Chaouch A, Müller JS, Lochmüller H. Congenital myasthenic syndromes: Achievements and limitations of phenotype-guided gene-after-gene sequencing in diagnostic practice: A study of 680 patients. Hum Mutat 2012; 33:1474-84. [DOI: 10.1002/humu.22130] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Accepted: 04/30/2012] [Indexed: 11/09/2022]
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Lorenzoni PJ, Scola RH, Kay CSK, Werneck LC. Congenital myasthenic syndrome: a brief review. Pediatr Neurol 2012; 46:141-8. [PMID: 22353287 DOI: 10.1016/j.pediatrneurol.2011.12.001] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/04/2011] [Accepted: 12/22/2011] [Indexed: 01/04/2023]
Abstract
Congenital myasthenic syndromes comprise heterogeneous genetic diseases characterized by compromised neuromuscular transmission. Congenital myasthenic syndromes are classified as presynaptic, synaptic, or postsynaptic, depending on the primary defect's location within the neuromuscular junction. Presynaptic forms are the rarest, affecting an estimated 7-8% of patients; synaptic forms account for approximately 14-15% of patients; and the remaining 75-80% are attributable to postsynaptic defects. Clinical manifestations vary by congenital myasthenic syndrome subtype. Electrophysiologic, morphologic, and molecular descriptions of various forms of congenital myasthenic syndromes have led to an enhanced understanding of clinical manifestations and disease pathophysiology. Although congenital myasthenic syndromes are indicated by clinical manifestations, family history, electrophysiologic studies, and responses to acetylcholinesterase inhibitors, overlap in some presentations occurs. Therefore, genetic testing may be necessary to identify specific mutations in CHAT, COLQ, LAMB2, CHRNA, CHRNB, CHRND, CHRNE, CHRNG, RAPSN, DOK7, MUSK, AGRN, SCN4A, GFPT1, or PLEC1 genes. The identification of congenital myasthenic syndromes subtypes will prove important in the treatment of these patients. Different drugs may be beneficial, or should be avoided because they are ineffective or worsen some forms of congenital myasthenic syndromes. We explore the classification, clinical manifestations, electrophysiologic features, genetics, and treatment responses of each congenital myasthenic syndrome subtype.
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Affiliation(s)
- Paulo José Lorenzoni
- Neuromuscular Disorders Unit, Division of Neurology, Department of Internal Medicine, Hospital de Clínicas da Universidade Federal do Paraná, Curitiba, PR, Brazil
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