The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

David Beeson - One of the best experts on this subject based on the ideXlab platform.

  • covid 19 in a cohort of patients with Congenital Myasthenic Syndrome
    Journal of neuromuscular diseases, 2021
    Co-Authors: David Beeson, Sithara Ramdas, Setareh Alabaf, Karen Oconnell, J Palace
    Abstract:

    Congenital Myasthenic Syndrome (CMS) are a rare group of genetic disorders of neuromuscular transmission. Some subtypes of CMS can be associated with respiratory and bulbar weakness and these patients may therefore be at high risk of developing a severe disease from COVID-19. We screened 73 patients with genetically confirmed CMS who were attending the UK national referral centre for evidence of previous Severe Acute Respiratory Syndrome Corona Virus 2 infection and their clinical outcome. Of 73 patients, seven had history of confirmed COVID-19. None of the infected patients developed a severe disease, and there were no signals that CMS alone carries a high risk of severe disease from COVID-19.

  • novel sea and lg2 agrin mutations causing Congenital Myasthenic Syndrome
    Orphanet Journal of Rare Diseases, 2017
    Co-Authors: Chong Yan, David Beeson, Wei Wei Liu, Kai Qiao, Jie Lin, Xia Tian, Leejun Wong, Chongbo Zhao
    Abstract:

    Congenital Myasthenic Syndrome caused by mutations in AGRN, a gene encoding a protein with a crucial function at the neuromuscular junction, is a rare disorder. There are few studies in this area. We here present two cases with novel mutations of AGRN of which we further investigated possible pathogenesis. Patient 1 had general limb weakness with fluctuation and deterioration in the afternoon and in hot weather. Patient 2 had early-onset weakness of lower extremities with suspected fluctuation in the early stages, which then progressed to the upper limbs. Both distal and proximal muscles were involved. Repetitive stimulation on EMG in both patients showed decrement in proximal and distal limbs. Patient 2 showed a marked response to salbutamol while Patient 1 did not. By targeted exome sequencing, two novel homozygous missense variants, p.L1176P and p.R1698C, in the SEA and LG2 domain of agrin were identified respectively. Further functional analysis revealed instability of the protein and impaired clustering of the acetylcholine receptor (AChR) by both mutations. The mutations identified in AGRN in our study may cause Congenital Myasthenic Syndrome by damaging protein stability and interfering with AChR clustering. These results broaden the understandings on the phenotype, genotype and pathogenesis of this rare disorder.

  • novel mutations in the c terminal region of gmppb causing limb girdle muscular dystrophy overlapping with Congenital Myasthenic Syndrome
    Neuromuscular Disorders, 2017
    Co-Authors: Sushan Luo, Susan Maxwell, David Beeson, Kai Qiao, Shuang Cai, Dongyue Yue, Wenhua Zhu, Zhen Zhu, Lei Zhou, Chongbo Zhao
    Abstract:

    Mutations in the GMPPB gene may underlie both limb girdle muscular dystrophy (LGMD) and Congenital Myasthenic Syndrome (CMS). Forty-one cases have been reported to date and hotspot mutations are emerging in the Caucasian population. Clinical and pathological features of 5 patients with compound heterozygous GMPPB mutations were collected and retrospectively reviewed. In vitro functional analysis was performed to investigate the pathogeneity of GMPPB variants. The patients presented with proximal limb weakness in their first to second decades. Fluctuating muscle weakness, myalgia and calf hypertrophy were the major complaints. Myogenic changes on electromyography and marked attenuation on 3 Hz repetitive nerve stimulation were observed in all patients. Four reported a beneficial response to pyridostigmine. Muscle MRI showed selective involvement in the calf in case 1. Immunolabeling of α-dystroglycan was abnormal for case 1 and case 2. Four novel missense mutations in the C-terminal region of GMPPB were identified, with p.(Arg357His) being present in all the cases. In vitro functional assays demonstrated that these variants did not markedly reduce the amount of GMPPB, but gave rise to an increased propensity for protein aggregation. Increasingly, patients with GMPPB mutations are found to present with an overlapping LGMD/Myasthenic Syndrome. The mutation spectrum in Chinese patients may differ from that of European populations, with the mutation p.(Arg357His) most frequently found. These mutations may lead to abnormal folding of GMPPB leading to protein aggregates in the cytoplasm rather than an overall loss in protein expression.

  • mutations in gfpt1 that underlie limb girdle Congenital Myasthenic Syndrome result in reduced cell surface expression of muscle achr
    Human Molecular Genetics, 2013
    Co-Authors: Katarzyna Marta Zoltowska, Sarah Finlayson, Susan Maxwell, Judith Cossins, Juliane S Muller, Hanns Lochmüller, Richard Webster, David Beeson
    Abstract:

    : Mutations in GFPT1 underlie a Congenital Myasthenic Syndrome (CMS) characterized by a limb-girdle pattern of muscle weakness. Glutamine-fructose-6-phosphate transaminase 1 (GFPT1) is a key rate-limiting enzyme in the hexosamine biosynthetic pathway providing building blocks for the glycosylation of proteins and lipids. It is expressed ubiquitously and it is not readily apparent why mutations in this gene should cause a Syndrome with symptoms restricted to muscle and, in particular, to the neuromuscular junction. Data from a muscle biopsy obtained from a patient with GFPT1 mutations indicated that there were reduced endplate acetylcholine receptors. We, therefore, further investigated the relationship between identified mutations in GFPT1 and expression of the muscle acetylcholine receptor. Cultured myotubes derived from two patients with GFPT1 mutations showed a significant reduction in cell-surface AChR expression (Pt1 P < 0.0001; Pt2 P = 0.0097). Inhibition of GFPT1 enzymatic activity or siRNA silencing of GFPT1 expression both resulted in reduced AChR cell-surface expression. Western blot and gene-silencing experiments indicate this is due to reduced steady-state levels of AChR α, δ, e, but not β subunits rather than altered transcription of AChR-subunit RNA. Uridine diphospho-N-acetylglucosamine, a product of the hexosamine synthetic pathway, acts as a substrate at an early stage in the N-linked glycosylation pathway. Similarity between CMS due to GFPT1 mutations and CMS due to DPAGT1 mutations would suggest that reduced endplate AChR due to defective N-linked glycosylation is a primary disease mechanism in this disorder.

  • clinical features in a large iranian family with a limb girdle Congenital Myasthenic Syndrome due to a mutation in dpagt1
    Neuromuscular Disorders, 2013
    Co-Authors: Keivan Basiri, Susan Maxwell, Katsiaryna Belaya, Maryam Sedghi, Wei Wei Liu, David Beeson
    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.

Andrew G Engel - One of the best experts on this subject based on the ideXlab platform.

  • a homozygous mutation in gmppb leads to centronuclear myopathy with combined pre and postsynaptic defects of neuromuscular transmission
    Neuromuscular Disorders, 2019
    Co-Authors: Stefan Nicolau, Xin Ming Shen, Duygu Selcen, Andrew G Engel, Teerin Liewluck, Margherita Milone
    Abstract:

    Abstract Mutations in GMPPB cause a wide spectrum of neuromuscular Syndromes, including muscular dystrophies and Congenital Myasthenic Syndrome. The mechanisms by which GMPPB mutations impair neuromuscular transmission however remain incompletely understood. We expand here upon a previous report of one such patient presenting with a myopathy-Congenital Myasthenic Syndrome overlap phenotype. Fatigable proximal muscle weakness developed gradually between 13 and 25 years of age, with subsequent stabilization. Low-frequency repetitive nerve stimulation showed a decrement, while a muscle biopsy demonstrated the presence of a centronuclear myopathy. Genetic testing identified a homozygous c.458C > T (p.Thr153Ile) variant in GMPPB. In-vitro microelectrode recordings and ultrastructural studies showed impairment of both pre- and postsynaptic neuromuscular transmission, thus demonstrating the presence of not only postsynaptic, but also presynaptic pathology in GMPPB-related disorders.

  • Congenital Myasthenic Syndrome due to rapsyn deficiency a case report with a new mutation and compound heterozygosity
    Medwave, 2019
    Co-Authors: Ivan O Espinoza, Carolina Reynoso, Giulliana Chavez, Andrew G Engel
    Abstract:

    Introduction The Congenital Myasthenic Syndromes are a heterogeneous group of genetic disorders characterized by an abnormal synaptic transmission in the neuromuscular plate. Report We present a two-year-old patient, male, with hypotonia, palpebral ptosis, and proximal symmetric weakness with a neonatal onset that motivated several and prolonged hospitalizations for pneumonia and respiratory failure. From two years of age, the parents noticed that the facial and general weakness worsened in the afternoons and with repeated or prolonged physical activity. The physical examination showed palpebral ptosis, predominantly proximal weakness, and fatigability with sustained muscular effort. The electromyography showed a 27% decrement in the Compound Muscular Action Potential and the case-parents genetic study showed compound heterozygosity with the transmission of two different mutations in the rapsyn gene from both parents. The patient received pyridostigmine with great improvement, achieving optimal performance in school, sports, and daily life activities. Conclusions Weakness and fatigability with neonatal onset, mainly affecting the muscles with brain stem innervation and the decrement greater than 10 percent in the Compound Muscular Action Potential in the electromyographic studies, should make us suspect in a Congenital Myasthenic Syndrome. We review the literature and key clinical points to establish a timely diagnosis and effective treatment in some of these Syndromes.

  • novel synaptobrevin 1 mutation causes fatal Congenital Myasthenic Syndrome
    Annals of clinical and translational neurology, 2017
    Co-Authors: Xin Ming Shen, Joan M Brengman, Paulo José Lorenzoni, Rosana Herminia Scola, Duygu Selcen, Lineu Cesar Werneck, Andrew G Engel
    Abstract:

    OBJECTIVE: To identify the molecular basis and elucidate the pathogenesis of a fatal Congenital Myasthenic Syndrome. METHODS: We performed clinical electrophysiology studies, exome and Sanger sequencing, and analyzed functional consequences of the identified mutation. RESULTS: Clinical electrophysiology studies of the patient revealed several-fold potentiation of the evoked muscle action potential by high frequency nerve stimulation pointing to a presynaptic defect. Exome sequencing identified a homozygous c.340delA frameshift mutation in synaptobrevin 1 (SYB1), one of the three SNARE proteins essential for synaptic vesicle exocytosis. Analysis of both human spinal cord gray matter and normal human muscle revealed expression of the SYB1A and SYB1D isoforms, predicting expression of one or both isoforms in the motor nerve terminal. The identified mutation elongates the intravesicular C-terminus of the A isoform from 5 to 71, and of the D isoform from 4 to 31 residues. Transfection of either mutant isoform into bovine chromaffin cells markedly reduces depolarization-evoked exocytosis, and transfection of either mutant isoform into HEK cells significantly decreases expression of either mutant compared to wild type. INTERPRETATION: The mutation is pathogenic because elongation of the intravesicular C-terminus of the A and D isoforms increases the energy required to move their C-terminus into the synaptic vesicle membrane, a key step for fusion of the synaptic vesicle with the presynaptic membrane, and because it is predicted to reduce expression of either isoform in the nerve terminal.

  • neuromuscular junction acetylcholinesterase deficiency responsive to albuterol
    Pediatric Neurology, 2012
    Co-Authors: Sophelia H S Chan, Virginia Wong, Andrew G Engel
    Abstract:

    Abstract Congenital Myasthenic Syndrome caused by endplate acetylcholinesterase deficiency constitutes a rare autosomal recessive disease. We describe a child with early-onset ptosis, complete ophthalmoplegia, facial and proximal muscle weakness, easy fatigability, a decremental electromyographic response, and a repetitive compound muscle action potential not improved by anti-acetylcholinesterase medication. Mutation analysis of the collagenic tail of endplate acetylcholinesterase ( COLQ ) that encodes the collagenic structural subunit of acetylcholinesterase revealed two canonic splice-site mutations: a previously identified IVS15 + 1G>A mutation and a novel IVS2 − 1G>A mutation. Treatment with albuterol resulted in progressive improvement of muscle strength, exercise tolerance, and ophthalmoplegia. Further studies are needed of the efficacy of albuterol in different types of Congenital Myasthenic Syndrome and the physiologic basis of its beneficial effects.

  • beneficial effect of albuterol in Congenital Myasthenic Syndrome with epsilon subunit mutations
    Muscle & Nerve, 2011
    Co-Authors: Menachem Sadeh, Xin Ming Shen, Andrew G Engel
    Abstract:

    Mutations in the epsilon subunit of the acetylcholine receptor (AChR) are a common cause of Congenital Myasthenic Syndrome (CMS). Patients are usually treated with acetylcholinesterase inhibitors and 3,4-diaminopyridine with modest clinical benefit. We report 2 patients with CMS due to mutations in the AChR epsilon subunit. The first patient carries two heterozygous frameshift mutations, e127ins5 and e1293insG. The second patient is homozygous for the eC142Y mutation that curtails AChR expression to 22% of wild-type in HEK cells. Treatment with pyridostigmine and 3,4-diaminopyridine had a limited beneficial effect in the first patient, and the second patient became wheelchair-bound during therapy. The additional use of albuterol produced dramatic improvement in strength and in activities of daily living in both patients. The efficacy and safety of albuterol in patients who harbor identified low-expressor or null mutations in the epsilon or other subunits of AChR merits a well-designed clinical trial.

Ricardo A Maselli - One of the best experts on this subject based on the ideXlab platform.

  • recessive Congenital Myasthenic Syndrome caused by a homozygous mutation in syt2 altering a highly conserved c terminal amino acid sequence
    American Journal of Medical Genetics Part A, 2020
    Co-Authors: Ricardo A Maselli, Helio Van Der Linden, Michael J Ferns
    Abstract:

    Defects in the gene encoding synaptotagmin 2 (SYT2) have been linked to a presynaptic Congenital Myasthenic Syndrome (CMS) and motor neuropathies. However, to date only dominant forms of the disease have been described. We report here a consanguineous patient with a severe recessive form of presynaptic CMS and denervation atrophy caused by the homozygous mutation c.1191delG, p.Arg397Serfs*37 in SYT2. The affected 2-year-old girl had profound weakness and areflexia with moderate bulbar deficit. Repetitive nerve stimulation revealed an extreme reduction of compound muscle action potential amplitudes at rest, with a striking facilitation followed by a progressive decline at fast stimulation rates. These findings were reminiscent, but not identical to those seen in the Lambert-Eaton Myasthenic Syndrome. 3,4 diaminopyridine and pyridostigmine were effective to ameliorate muscle fatigue, but albuterol was ineffective. Modeling of the mutation using the rat Syt1 C2B x-ray structure revealed that Arg397Serfs*37 disrupts a highly conserved amino acid sequence at the bottom face of the C2B domain not directly involved in calcium binding, but crucial for synaptotagmin-SNARE interaction and exocytosis. Thus, this report describes a recessive form of synaptotagmin 2-CMS and highlights the importance of the synaptotagmin C-terminal on synaptic vesicle fusion and exocytosis.

  • choline acetyltransferase mutations causing Congenital Myasthenic Syndrome molecular findings and genotype phenotype correlations
    Human Mutation, 2015
    Co-Authors: Juan Arredondo, Constance M. Bowe, Marian Lara, Sidney M Gospe, Claudio Mazia, Maria Vaccarezza, Marcela Garciaerro, Celia H Chang, Michelle M Mezei, Ricardo A Maselli
    Abstract:

    Choline acetyltransferase catalyzes the synthesis of acetylcholine at cholinergic nerves. Mutations in human CHAT cause a Congenital Myasthenic Syndrome due to impaired synthesis of ACh; this severe variant of the disease is frequently associated with unexpected episodes of potentially fatal apnea. The severity of this condition varies remarkably, and the molecular factors determining this variability are poorly understood. Furthermore, genotype-phenotype correlations have been difficult to establish in patients with biallelic mutations. We analyzed the protein expression of phosphorylated ChAT of seven CHAT mutations, p.Val136Met, p.Arg207His, p.Arg186Trp, p.Val194Leu, p.Pro211Ala, p.Arg566Cys, and p.Ser694Cys, in HEK-293 cells to phosphorylated ChAT, determined their enzyme kinetics and thermal stability, and examined their structural changes. Three mutations, p.Arg207His, p.Arg186Trp, and p.Arg566Cys, are novel, and p.Val136Met and p.Arg207His are homozygous in three families and associated with severe disease. The characterization of mutants showed a decrease in the overall catalytic efficiency of ChAT; in particular, those located near the active-site tunnel produced the most seriously disruptive phenotypic effects. On the other hand, p.Val136Met, which is located far from both active and substrate-binding sites, produced the most drastic reduction of ChAT expression. Overall, CHAT mutations producing low enzyme expression and severe kinetic effects are associated with the most severe phenotypes.

  • Congenital Myasthenic Syndrome associated with epidermolysis bullosa caused by homozygous mutations in PLEC1 and CHRNE
    Clinical Genetics, 2010
    Co-Authors: Ricardo A Maselli, Juan Arredondo, Órla Cagney, Rr Davis, Salah Yousif, Jeffrey P Gregg, S Skinner, Tahseen Mozaffar, Mark Sivak, Thomas Konia
    Abstract:

    Maselli RA, Arredondo J, Cagney O, Mozaffar T, Skinner S, Yousif S, Davis RR, Gregg JP, Sivak M, Konia TH, Thomas K, Wollmann RL. Congenital Myasthenic Syndrome associated with epidermolysis bullosa caused by homozygous mutations in PLEC1 and CHRNE. Mutations in the plectin gene (PLEC1) cause epidermolysis bullosa simplex (EBS), which may associate with muscular dystrophy (EBS–MD) or pyloric atresia (EBS–PA). The association of EBS with Congenital Myasthenic Syndrome (CMS) is also suspected to result from PLEC1 mutations. We report here a consanguineous patient with EBS and CMS for whom mutational analysis of PLEC1 revealed a homozygous 36 nucleotide insertion (1506_1507ins36) that results in a reduced expression of PLEC1 mRNA and plectin in the patient muscle. In addition, mutational analysis of CHRNE revealed a homozygous 1293insG, which is a well-known low-expressor receptor mutation. A skin biopsy revealed signs of EBS, and an anconeus muscle biopsy showed signs of a mild myopathy. Endplate studies showed fragmentation of endplates, postsynaptic simplification, and large collections of thread-like mitochondria. Amplitudes of miniature endplate potentials were diminished, but the endplate quantal content was actually increased. The complex phenotype presented here results from mutations in two separate genes. While the skin manifestations are because of the PLEC1 mutation, footprints of mutations in PLEC1 and CHRNE are present at the neuromuscular junction of the patient indicating that abnormalities in both genes contribute to the CMS phenotype.

  • Mutations in MUSK causing Congenital Myasthenic Syndrome impair MuSK–Dok-7 interaction
    Human Molecular Genetics, 2010
    Co-Authors: Ricardo A Maselli, Juan Arredondo, Órla Cagney, Jarae J. Ng, Jennifer A. Anderson, Colette Williams, Bae J. Gerke, Betty Soliven, Robert L Wollmann
    Abstract:

    We describe a severe Congenital Myasthenic Syndrome (CMS) caused by two missense mutations in the gene encoding the muscle specific receptor tyrosine kinase (MUSK). The identified MUSK mutations M605I and A727V are both located in the kinase domain of MuSK. Intracellular microelectrode recordings and microscopy studies of the neuromuscular junction conducted in an anconeus muscle biopsy revealed decreased miniature endplate potential amplitudes, reduced endplate size and simplification of secondary synaptic folds, which were consistent with postsynaptic deficit. The study also showed a striking reduction of the endplate potential quantal content, consistent with additional presynaptic failure. Expression studies in MuSK deficient myotubes revealed that A727V, which is located within the catalytic loop of the enzyme, caused severe impairment of agrin-dependent MuSK phosphorylation, aggregation of acetylcholine receptors (AChRs) and interaction of MuSK with Dok-7, an essential intracellular binding protein of MuSK. In contrast, M605I, resulted in only moderate impairment of agrin-dependent MuSK phosphorylation, aggregation of AChRs and interaction of MuSK with Dok-7. There was no impairment of interaction of mutants with either the low-density lipoprotein receptor-related protein, Lrp4 (a co-receptor of agrin) or with the mammalian homolog of the Drosophila tumorous imaginal discs (Tid1). Our findings demonstrate that missense mutations in MUSK can result in a severe form of CMS and indicate that the inability of MuSK mutants to interact with Dok-7, but not with Lrp4 or Tid1, is a major determinant of the pathogenesis of the CMS caused by MUSK mutations.

  • Mutations in LAMB2 causing a severe form of synaptic Congenital Myasthenic Syndrome
    Journal of Medical Genetics, 2008
    Co-Authors: Ricardo A Maselli, Juan Arredondo, Órla Cagney, Jarae J. Ng, Jennifer A. Anderson, Colette Williams, H. B. Wessel, H. Abdel-hamid, Robert L Wollmann
    Abstract:

    Background: We describe a severe form of Congenital Myasthenic Syndrome (CMS) associated with Congenital nephrosis and ocular malformations caused by two truncating mutations in the gene encoding the laminin β2 subunit ( LAMB2 ). Methods and results: Mutational analysis in the affected patient, who has a history of a serious untoward reaction to treatment with acetylcholinesterase inhibition, revealed two frame-shifting heteroallelic mutations, a maternally inherited 1478delG and a paternally inherited 4804delC . An anconeus muscle biopsy demonstrated a profound distortion of the architecture and function of the neuromuscular junction, which was strikingly similar to that seen in mice lacking laminin β2 subunit. The findings included: pronounced reduction of the axon terminal size with encasement of the nerve endings by Schwann cells, severe widening of the primary synaptic cleft and invasion of the synaptic space by the processes of Schwann cells, and moderate simplification of postsynaptic folds and intact expression of the endplate acetylcholinesterase. The endplate potential quantal content was notably reduced, while the frequencies and amplitudes of miniature endplate potentials were only moderately diminished and the decay phases of miniature endplate potentials were normal. Western blot analysis of muscle and kidney tissue and immunohistochemistry of kidney tissue showed no laminin β2 expression. Conclusion: This case, which represents a new type of synaptic CMS, exemplifies the wide variability of phenotypes associated with LAMB2 mutations and underscores the fundamental role that laminin β2 plays in the development of the human neuromuscular junction.

Hanns Lochmüller - One of the best experts on this subject based on the ideXlab platform.

  • clinical variability of early onset Congenital Myasthenic Syndrome due to biallelic rapsn mutations in brazil
    Neuromuscular Disorders, 2018
    Co-Authors: Eduardo De Paula Estephan, Ana Topf, A A Zambon, P E Marchiori, Andre Macedo Serafim Da Silva, Vitor Marques Caldas, Cristiane De Araujo Martins Moreno, Umbertina Conti Reed, Rita Horvath, Hanns Lochmüller
    Abstract:

    Abstract Mutations in RAPSN are an important cause of Congenital Myasthenic Syndrome (CMS), leading to endplate acetylcholine receptor deficiency. We present three RAPSN early-onset CMS patients (from a Brazilian cohort of 61 CMS patients). Patient 1 and patient 2 harbor the mutation p.N88K in homozygosity, while patient 3 harbors p.N88K in compound heterozygosity with another pathogenic variant (p.V165M; c.493G ≥ A). At onset, patient 3 presented with more severe symptoms compared to the other two, showing generalized weakness and repeated episodes of respiratory failure in the first years of life. During adolescence, she became gradually less symptomatic and does not require medication anymore, presenting better long-term outcomes than patients 1 and 2. This case series illustrates the variability of RAPSN early-onset CMS, with patient 3, despite severe onset, revealing an almost complete reversal of Myasthenic symptoms, not limited to apneic episodes. Moreover, it suggests that RAPSN CMS may be underdiagnosed in non-European countries.

  • Congenital Myasthenic Syndrome with episodic apnoea clinical neurophysiological and genetic features in the long term follow up of 19 patients
    Journal of Neurology, 2018
    Co-Authors: Grace Mcmacken, Marina Dusl, Angela Abicht, Teresinha Evangelista, Roger G Whittaker, Hanns Lochmüller
    Abstract:

    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. 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. 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). 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.

  • drosophila studies support a role for a presynaptic synaptotagmin mutation in a human Congenital Myasthenic Syndrome
    PLOS ONE, 2017
    Co-Authors: Mallory C Shields, Hanns Lochmüller, Matthew R Bowers, Mckenzie M Fulcer, Madelyn K Bollig, Patrick J Rock, Bryan Sutton, Alysia D Vrailasmortimer, Roger G Whittaker
    Abstract:

    During chemical transmission, the function of synaptic proteins must be coordinated to efficiently release neurotransmitter. Synaptotagmin 2, the Ca2+ sensor for fast, synchronized neurotransmitter release at the human neuromuscular junction, has recently been implicated in a dominantly inherited Congenital Myasthenic Syndrome associated with a non-progressive motor neuropathy. In one family, a proline residue within the C2B Ca2+-binding pocket of synaptotagmin is replaced by a leucine. The functional significance of this residue has not been investigated previously. Here we show that in silico modeling predicts disruption of the C2B Ca2+-binding pocket, and we examine the in vivo effects of the homologous mutation in Drosophila. When expressed in the absence of native synaptotagmin, this mutation is lethal, demonstrating for the first time that this residue plays a critical role in synaptotagmin function. To achieve expression similar to human patients, the mutation is expressed in flies carrying one copy of the wild type synaptotagmin gene. We now show that Drosophila carrying this mutation developed neurological and behavioral manifestations similar to those of human patients and provide insight into the mechanisms underlying these deficits. Our Drosophila studies support a role for this synaptotagmin point mutation in disease etiology.

  • a 3 utr mutation creates a microrna target site in the gfpt1 gene of patients with Congenital Myasthenic Syndrome
    Human Molecular Genetics, 2015
    Co-Authors: Marina Dusl, Juliane S Muller, Johannes G Vogel, Anja Pertl, Rolf Stucka, Hanns Lochmüller, Jan Senderek, Robert David, Angela Abicht
    Abstract:

    Abstract Mutations in the gene encoding glutamine-fructose-6-phosphate transaminase 1 (GFPT1) cause the neuromuscular disorder limb-girdle Congenital Myasthenic Syndrome (LG-CMS). One recurrent GFPT1 mutation detected in LG-CMS patients is a c.*22C>A transversion in the 3'-untranslated region (UTR). Because this variant does not alter the GFPT1 open reading frame, its pathogenic relevance has not yet been established. We found that GFPT1 protein levels were reduced in myoblast cells of the patients carrying this variant. In silico algorithms predicted that the mutation creates a microRNA target site for miR-206*. Investigation of the expression of this so far unrecognized microRNA confirmed that miR-206* (like its counterpart miR-206) is abundant in skeletal muscle. MiR-206* efficiently reduced the expression of reporter constructs containing the mutated 3'-UTR while no such effect was observed with reporter constructs containing the wild-type 3'-UTR or when a specific anti-miR-206* inhibitor was added. Moreover, anti-miR-206* inhibitor treatment substantially rescued GFPT1 expression levels in patient-derived myoblasts. Our data demonstrate that the c.*22C>A mutation in the GFPT1 gene leads to illegitimate binding of microRNA resulting in reduced protein expression. We confirm that c.*22C>A is a causative mutation and suggest that formation of microRNA target sites might be a relevant pathomechanism in Mendelian disorders. Variants in the 3'-UTRs should be considered in genetic diagnostic procedures.

  • Congenital Myasthenic Syndrome due to choline acetyltransferase mutations in infants clinical suspicion and comprehensive electrophysiological assessment are important for early diagnosis
    Journal of Child Neurology, 2014
    Co-Authors: Robertino Dilena, Angela Abicht, Paola Sergi, Giacomo P Comi, Alessio Di Fonzo, Giovanna Chidini, Federica Natacci, S Barbieri, Hanns Lochmüller
    Abstract:

    Congenital Myasthenic Syndromes are inherited disorders caused by various defects in neuromuscular transmission. Although the typical presentation is fatigable weakness with prominent cranial involvement, neonates can lack these hallmark manifestations, and in those with choline acetyltransferase gene mutations, basal electrophysiological testing can yield negative findings. The authors report the case of a male infant presenting at birth with oculomotor and bulbofacial weakness, hypotonia, clubfoot, and severe respiratory insufficiency. Electromyography showed myogenic signs, and basal repetitive nerve stimulation yielded negative findings. Since age 6 months, the infant had progressively improved, acquiring autonomous respiration. Prolonged subtetanic repetitive nerve stimulation disclosed a marked decremental response compatible with suspected Congenital Myasthenic Syndrome with episodic apnea. Genetic testing identified 2 novel choline acetyltransferase mutations (R470X, F580C). Keeping a high clinical suspicion of this rare condition and undertaking early comprehensive electrophysiological assessments including prolonged repetitive nerve stimulation (10 Hz for 5 minutes) can expedite the diagnosis.

Kinji Ohno - One of the best experts on this subject based on the ideXlab platform.

  • hnrnp h enhances skipping of a nonfunctional exon p3a in chrna1 and a mutation disrupting its binding causes Congenital Myasthenic Syndrome
    Human Molecular Genetics, 2008
    Co-Authors: Akio Masuda, Xin Ming Shen, Kinji Ohno, Tohru Matsuura, Andrew G Engel
    Abstract:

    In humans and great apes, CHRNA1 encoding the muscle nicotinic acetylcholine receptor α subunit carries an inframe exon P3A, the inclusion of which yields a nonfunctional α subunit. In muscle, the P3A(−) and P3A(+) transcripts are generated in a 1:1 ratio but the functional significance and regulation of the alternative splicing remain elusive. An intronic mutation (IVS3-8G>A), identified in a patient with Congenital Myasthenic Syndrome, disrupts an intronic splicing silencer (ISS) and results in exclusive inclusion of the downstream P3A exon. We found that the ISS-binding splicing trans-factor was heterogeneous nuclear ribonucleoprotein (hnRNP) H and the mutation attenuated the affinity of hnRNP for the ISS ∼100-fold. We next showed that direct placement of hnRNP H to the 3′ end of intron 3 silences, and siRNA-mediated downregulation of hnRNP H enhances recognition of exon P3A. Analysis of the human genome suggested that the hnRNPH-binding UGGG motif is overrepresented close to the 3′ ends of introns. Pursuing this clue, we showed that alternative exons of GRIP1, FAS, VPS13C and NRCAM are downregulated by hnRNP H. Our findings imply that the presence of the hnRNP H-binding motif close to the 3′ end of an intron is an essential but underestimated splicing regulator of the downstream exon.

  • hnrnp h enhances skipping of a nonfunctional exon p3a in chrna1 and a mutation disrupting its binding causes Congenital Myasthenic Syndrome
    Human Molecular Genetics, 2008
    Co-Authors: Akio Masuda, Xin Ming Shen, Kinji Ohno, Tohru Matsuura, Andrew G Engel, Mikako Ito
    Abstract:

    In humans and great apes, CHRNA1 encoding the muscle nicotinic acetylcholine receptor alpha subunit carries an inframe exon P3A, the inclusion of which yields a nonfunctional alpha subunit. In muscle, the P3A(-) and P3A(+) transcripts are generated in a 1:1 ratio but the functional significance and regulation of the alternative splicing remain elusive. An intronic mutation (IVS3-8G>A), identified in a patient with Congenital Myasthenic Syndrome, disrupts an intronic splicing silencer (ISS) and results in exclusive inclusion of the downstream P3A exon. We found that the ISS-binding splicing trans-factor was heterogeneous nuclear ribonucleoprotein (hnRNP) H and the mutation attenuated the affinity of hnRNP for the ISS approximately 100-fold. We next showed that direct placement of hnRNP H to the 3' end of intron 3 silences, and siRNA-mediated downregulation of hnRNP H enhances recognition of exon P3A. Analysis of the human genome suggested that the hnRNPH-binding UGGG motif is overrepresented close to the 3' ends of introns. Pursuing this clue, we showed that alternative exons of GRIP1, FAS, VPS13C and NRCAM are downregulated by hnRNP H. Our findings imply that the presence of the hnRNP H-binding motif close to the 3' end of an intron is an essential but underestimated splicing regulator of the downstream exon.

  • E-box mutations in the RAPSN promoter region in eight cases with Congenital Myasthenic Syndrome
    Human molecular genetics, 2003
    Co-Authors: Kinji Ohno, Joan M Brengman, Menachem Sadeh, Ilan Blatt, Andrew G Engel
    Abstract:

    Myogenic determination factors are basic helix-loop-helix proteins that govern specification and differentiation of muscle cells, and bind to the E-box consensus sequence CANNTG in promoter regions of muscle-specific genes. No E-box mutation has been reported to date. RAPSN encodes rapsyn, a 43 kDa postsynaptic peripheral membrane protein that clusters the nicotinic acetylcholine receptor at the motor endplate. Transcriptional regulation mechanisms of RAPSN have not been studied. We here report two novel E-box mutations in the RAPSN promoter region in eight Congenital Myasthenic Syndrome patients. Patient 1 carries -27C-->G that changes an E-box at -27 to -22 from CAGCTG to GAGCTG. An allele harboring -27C-->G is not transcribed in patient's muscle. Patients 2-8 are of Oriental Jewish stock of Iraqi or Iranian origin with facial malformations, and harbor -38A-->G that changes another E-box at -40 to -35 from CAACTG to CAGCTG, which does not affect the consensus CANNTG sequence. Haplotype analysis shows that -38A-->G arises from a common founder. For each mutation, position +1 represents the major transcriptional start site that we determine to be 172 nucleotides upstream of the translational start site. Electrophoretic mobility shift assays reveal that -38A-->G gains, and -27C-->G looses, binding affinity for different components of nuclear extracts of C2C12 myotubes. Luciferase reporter assays show that both -38A-->G and -27C-->G attenuate reporter gene expression in C2C12 myotubes, and that -27C-->G additionally attenuates reporter gene expression in MyoD- or myogenin-transfected HEK cells. The -27C-->G mutation also markedly attenuates the enhancer activity of an E-box on an SV40 promoter. Impaired transcriptional activities of the RAPSN promoter region predict reduced rapsyn expression and endplate acetylcholine receptor deficiency.

  • fundamental gating mechanism of nicotinic receptor channel revealed by mutation causing a Congenital Myasthenic Syndrome
    The Journal of General Physiology, 2000
    Co-Authors: Hai Long Wang, Joan M Brengman, Kinji Ohno, Andrew G Engel, Margherita Milone, Amelia Evoli, Anna Paola Batocchi, Lefkos T Middleton, Kyproula Christodoulou, Steven M Sine
    Abstract:

    We describe the genetic and kinetic defects in a Congenital Myasthenic Syndrome due to the mutation eA411P in the amphipathic helix of the acetylcholine receptor (AChR) e subunit. Myasthenic patients from three unrelated families are either homozygous for eA411P or are heterozygous and harbor a null mutation in the second e allele, indicating that eA411P is recessive. We expressed human AChRs containing wild-type or A411P e subunits in 293HEK cells, recorded single channel currents at high bandwidth, and determined microscopic rate constants for individual channels using hidden Markov modeling. For individual wild-type and mutant channels, each rate constant distributes as a Gaussian function, but the spread in the distributions for channel opening and closing rate constants is greatly expanded by eA411P. Prolines engineered into positions flanking residue 411 of the e subunit greatly increase the range of activation kinetics similar to eA411P, whereas prolines engineered into positions equivalent to eA411 in β and δ subunits are without effect. Thus, the amphipathic helix of the e subunit stabilizes the channel, minimizing the number and range of kinetic modes accessible to individual AChRs. The findings suggest that analogous stabilizing structures are present in other ion channels, and possibly allosteric proteins in general, and that they evolved to maintain uniformity of activation episodes. The findings further suggest that the fundamental gating mechanism of the AChR channel can be explained by a corrugated energy landscape superimposed on a steeply sloped energy well.

  • new mutations in acetylcholine receptor subunit genes reveal heterogeneity in the slow channel Congenital Myasthenic Syndrome
    Human Molecular Genetics, 1996
    Co-Authors: Andrew G Engel, Joan M Brengman, Kinji Ohno, Margherita Milone, David O Hutchinson, Cecilia Bouzat, Hai Long Wang, S Nakano, Ned J Pruitt, Nina Bren
    Abstract:

    Abstract Mutations in genes encoding the epsilon, delta, beta and alpha subunits of the end plate acetylcholine (ACh) receptor (AChR) are described and functionally characterized in three slow-channel Congenital Myasthenic Syndrome patients. All three had prolonged end plate currents and AChR channel opening episodes and an end plate myopathy with loss of AChR from degenerating junctional folds. Genetic analysis revealed heterozygous mutations: epsilon L269F and delta Q267E in Patient 1, beta V266M in Patient 2, and alpha N217K in Patient 3 that were not detected in 100 normal controls. Patients 1 and 2 have no similarly affected relatives; in Patient 3, the mutation cosegregates with the disease in three generations. epsilon L269F, delta Q267E and beta V266M occur in the second and alpha N217K in the first transmembrane domain of AChR subunits; all have been postulated to contribute to the lining of the upper half of the channel lumen and all but delta Q267E are positioned toward the channel lumen, and introduce an enlarged side chain. Expression studies in HEK cells indicate that all of the mutations express normal amounts of AChR. epsilon L269F, beta V266M, and alpha N217K slow the rate of channel closure in the presence of ACh and increase apparent affinity for ACh; epsilon L269F and alpha N217K enhance desensitization, and epsilon L269F and beta V266M cause pathologic channel openings in the absence of ACh, rendering the channel leaky, delta Q267E has none of these effects and is therefore a rare polymorphism or a benign mutation. The end plate myopathy stems from cationic overloading of the postsynaptic region. The safety margin of neuromuscular transmission is compromised by AChR loss from the junctional folds and by a depolarization block owing to temporal summation of prolonged end plate potentials at physiologic rates of stimulation.