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Asma Ben Ammar,
Payam Soltanzadeh,
Stéphanie Bauché,
Pascale Richard,
Evelyne Goillot,
Ruth Herbst, Karen Gaudon,
Caroline Huzé,
Laurent Schaeffer,
Yuji Yamanashi, [......],
Antoine Taly,
Jeanine Koenig,
Jean-Paul Leroy,
Fayçal Hentati,
Hossein Najmabadi,
Kimia Kahrizi,
Manouchehr Ilkhani,
Michel Fardeau,
Bruno Eymard,
Daniel Hantaï
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ABSTRACT: Congenital myasthenic syndromes (CMSs) are a heterogeneous group of genetic disorders affecting neuromuscular transmission. The agrin/muscle-specific kinase (MuSK) pathway is critical for proper development and maintenance of the neuromuscular junction (NMJ). We report here an Iranian patient in whom CMS was diagnosed since he presented with congenital and fluctuating bilateral symmetric ptosis, upward gaze palsy and slowly progressive muscle weakness leading to loss of ambulation. Genetic analysis of the patient revealed a homozygous missense mutation c.2503A>G in the coding sequence of MUSK leading to the p.Met835Val substitution. The mutation was inherited from the two parents who were heterozygous according to the notion of consanguinity. Immunocytochemical and electron microscopy studies of biopsied deltoid muscle showed dramatic changes in pre- and post-synaptic elements of the NMJs. These changes induced a process of denervation/reinnervation in native NMJs and the formation, by an adaptive mechanism, of newly formed and ectopic NMJs. Aberrant axonal outgrowth, decreased nerve terminal ramification and nodal axonal sprouting were also noted. In vivo electroporation of the mutated MuSK in a mouse model showed disorganized NMJs and aberrant axonal growth reproducing a phenotype similar to that observed in the patient's biopsy specimen. In vitro experiments showed that the mutation alters agrin-dependent acetylcholine receptor aggregation, causes a constitutive activation of MuSK and a decrease in its agrin- and Dok-7-dependent phosphorylation.
PLoS ONE 01/2013; 8(1):e53826. · 4.09 Impact Factor
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Karen Gaudon,
Isabelle Pénisson-Besnier,
Brigitte Chabrol,
Françoise Bouhour,
Laurence Demay,
Asma Ben Ammar,
Stéphanie Bauché,
Christophe Vial,
Guillaume Nicolas,
Bruno Eymard,
Daniel Hantaï,
Pascale Richard
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ABSTRACT: Congenital myasthenic syndromes (CMS) are a heterogeneous group of genetic disorders that give rise to a defect in neuromuscular transmission. We described here three patients with a characteristic phenotype of recessive CMS and presenting mutation in the gene encoding rapsyn (RAPSN). Familial analysis showed that one allelic mutation failed to be detected by direct sequencing. An allelic quantification on patient's DNA identified three novel multi-exon deletions of RAPSN. These three genomic rearrangements in RAPSN represent 15% of our CMS patients with RAPSN mutations and we emphasize that single-nucleotide polymorphism markers and a gene dosage method should be performed in addition to DNA direct sequencing analysis particularly when there is a genetic counselling issue.
Journal of Medical Genetics 10/2010; 47(12):795-6. · 6.36 Impact Factor
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Caroline Huzé,
Stéphanie Bauché,
Pascale Richard,
Frédéric Chevessier,
Evelyne Goillot, Karen Gaudon,
Asma Ben Ammar,
Annie Chaboud,
Isabelle Grosjean,
Heba-Aude Lecuyer, [......],
Nektaria Alexandri,
Thierry Kuntzer,
Michel Fardeau,
Emmanuel Fournier,
Andrea Brancaccio,
Markus A Rüegg,
Jeanine Koenig,
Bruno Eymard,
Laurent Schaeffer,
Daniel Hantaï
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ABSTRACT: We report the case of a congenital myasthenic syndrome due to a mutation in AGRN, the gene encoding agrin, an extracellular matrix molecule released by the nerve and critical for formation of the neuromuscular junction. Gene analysis identified a homozygous missense mutation, c.5125G>C, leading to the p.Gly1709Arg variant. The muscle-biopsy specimen showed a major disorganization of the neuromuscular junction, including changes in the nerve-terminal cytoskeleton and fragmentation of the synaptic gutters. Experiments performed in nonmuscle cells or in cultured C2C12 myotubes and using recombinant mini-agrin for the mutated and the wild-type forms showed that the mutated form did not impair the activation of MuSK or change the total number of induced acetylcholine receptor aggregates. A solid-phase assay using the dystrophin glycoprotein complex showed that the mutation did not affect the binding of agrin to alpha-dystroglycan. Injection of wild-type or mutated agrin into rat soleus muscle induced the formation of nonsynaptic acetylcholine receptor clusters, but the mutant protein specifically destabilized the endogenous neuromuscular junctions. Importantly, the changes observed in rat muscle injected with mutant agrin recapitulated the pre- and post-synaptic modifications observed in the patient. These results indicate that the mutation does not interfere with the ability of agrin to induce postsynaptic structures but that it dramatically perturbs the maintenance of the neuromuscular junction.
The American Journal of Human Genetics 07/2009; 85(2):155-67. · 10.60 Impact Factor
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[show abstract]
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ABSTRACT: Congenital myasthenic syndromes (CMSs) are rare hereditary disorders transmitted in a recessive or dominant pattern, and are caused by mutations in the genes encoding proteins of the neuromuscular junction. They are classified in three groups depending on the origin of the molecular defect. Postsynaptic defects are the most frequent and have been reported to be partly due to abnormalities of the acetylcholine receptor, and particularly to mutations in CHRNE, the gene encoding the acetylcholine receptor epsilon-subunit. In a Portuguese patient with a mild form of recessive CMS, CHRNE sequencing identified an unknown homozygous transition. This variation affects the third nucleotide of the glycine 285 condon, and leads to a synonymous variant. Analysis of transcripts demonstrated that this single change creates a new splice donor site located 4 nucleotides upstream of the normal site, leading to a deletion and generating a frameshift in exon 9 followed by a premature termination codon. This paper relates the identification of a synonymous mutation in CHRNE that creates a new splice donor site leading to an aberrant splicing of pre-mRNAs and so to their instability. This is the first synonymous mutation in CHRNE known to generate a cryptic splice site, and mRNA quantification strongly suggests that it is the disease-causing mutation.
Neuromuscular Disorders 06/2007; 17(5):409-14. · 2.80 Impact Factor
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Frédéric Chevessier,
Brice Faraut,
Aymeric Ravel-Chapuis,
Pascale Richard, Karen Gaudon,
Stéphanie Bauché,
Cassandra Prioleau,
Ruth Herbst,
Evelyne Goillot,
Christine Ioos, [......],
Shahram Attarian,
Jean-Paul Leroy,
Emmanuel Fournier,
Claire Legay,
Laurent Schaeffer,
Jeanine Koenig,
Michel Fardeau,
Bruno Eymard,
Jean Pouget,
Daniel Hantaï
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ABSTRACT: Congenital myasthenic syndromes (CMS) are rare genetic diseases affecting the neuromuscular junction (NMJ) and are characterized by a dysfunction of the neurotransmission. They are heterogeneous at their pathophysiological level and can be classified in three categories according to their presynaptic, synaptic and postsynaptic origins. We report here the first case of a human neuromuscular transmission dysfunction due to mutations in the gene encoding a postsynaptic molecule, the muscle-specific receptor tyrosine kinase (MuSK). Gene analysis identified two heteroallelic mutations, a frameshift mutation (c.220insC) and a missense mutation (V790M). The muscle biopsy showed dramatic pre- and postsynaptic structural abnormalities of the neuromuscular junction and severe decrease in acetylcholine receptor (AChR) epsilon-subunit and MuSK expression. In vitro and in vivo expression experiments were performed using mutant MuSK reproducing the human mutations. The frameshift mutation led to the absence of MuSK expression. The missense mutation did not affect MuSK catalytic kinase activity but diminished expression and stability of MuSK leading to decreased agrin-dependent AChR aggregation, a critical step in the formation of the neuromuscular junction. In electroporated mouse muscle, overexpression of the missense mutation induced, within a week, a phenotype similar to the patient muscle biopsy: a severe decrease in synaptic AChR and an aberrant axonal outgrowth. These results strongly suggest that the missense mutation, in the presence of a null mutation on the other allele, is responsible for the dramatic synaptic changes observed in the patient.
Journal de la Société de Biologie 02/2005; 199(1):61-77.
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Frédéric Chevessier,
Brice Faraut,
Aymeric Ravel-Chapuis,
Pascale Richard, Karen Gaudon,
Stéphanie Bauché,
Cassandra Prioleau,
Ruth Herbst,
Evelyne Goillot,
Christine Ioos, [......],
Shahram Attarian,
Jean-Paul Leroy,
Emmanuel Fournier,
Claire Legay,
Laurent Schaeffer,
Jeanine Koenig,
Michel Fardeau,
Bruno Eymard,
Jean Pouget,
Daniel Hantaï
[show abstract]
[hide abstract]
ABSTRACT: We report the first case of a human neuromuscular transmission dysfunction due to mutations in the gene encoding the muscle-specific receptor tyrosine kinase (MuSK). Gene analysis identified two heteroallelic mutations, a frameshift mutation (c.220insC) and a missense mutation (V790M). The muscle biopsy showed dramatic pre- and postsynaptic structural abnormalities of the neuromuscular junction and severe decrease in acetylcholine receptor (AChR) epsilon-subunit and MuSK expression. In vitro and in vivo expression experiments were performed using mutant MuSK reproducing the human mutations. The frameshift mutation led to the absence of MuSK expression. The missense mutation did not affect MuSK catalytic kinase activity but diminished expression and stability of MuSK leading to decreased agrin-dependent AChR aggregation, a critical step in the formation of the neuromuscular junction. In electroporated mouse muscle, overexpression of the missense mutation induced, within a week, a phenotype similar to the patient muscle biopsy: a severe decrease in synaptic AChR and an aberrant axonal outgrowth. These results strongly suggest that the missense mutation, in the presence of a null mutation on the other allele, is responsible for the dramatic synaptic changes observed in the patient.
Human Molecular Genetics 01/2005; 13(24):3229-40. · 7.64 Impact Factor
