Mai Thao Viou

Pierre and Marie Curie University - Paris 6, Lutetia Parisorum, Île-de-France, France

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Publications (8)28.09 Total impact

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    ABSTRACT: Cylindrical spirals are characteristic muscular inclusions consisting of spiraling double-laminated membranes. They are found in heterogeneous clinical conditions. We describe the presence of cylindrical spirals in muscle biopsies from 2 young sisters with severe congenital hypotonia, muscle weakness, and epileptic encephalopathy. We report an association of a congenital encephalomyopathy with cylindrical spirals. Through a detailed morphological and ultrastructural study, we speculate about the origin of these peculiar structures. This article is protected by copyright. All rights reserved. © 2015 Wiley Periodicals, Inc.
    Muscle & Nerve 05/2015; DOI:10.1002/mus.24699
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    ABSTRACT: Aldolase A deficiency has been reported as a rare cause of hemolytic anemia occasionally associated with myopathy. We identified a deleterious homozygous mutation in the ALDOA gene in 3 siblings with episodic rhabdomyolysis without hemolytic anemia. Myoglobinuria was always triggered by febrile illnesses. We show that the underlying mechanism involves an exacerbation of aldolase A deficiency at high temperatures that affected myoblasts but not erythrocytes. The aldolase A deficiency was rescued by arginine supplementation in vitro but not by glycerol, betaine or benzylhydantoin, three other known chaperones, suggesting that arginine-mediated rescue operated by a mechanism other than protein chaperoning. Lipid droplets accumulated in patient myoblasts relative to control and this was increased by cytokines, and reduced by dexamethasone. Our results expand the clinical spectrum of aldolase A deficiency to isolated temperature-dependent rhabdomyolysis, and suggest that thermolability may be tissue specific. We also propose a treatment for this severe disease.
    PLoS Genetics 11/2014; 10(11):e1004711. DOI:10.1371/journal.pgen.1004711
  • 19th International Congress of the World-Muscle-Society; 10/2014
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    ABSTRACT: Nemaline myopathy (NM) is a rare congenital myopathy characterised by hypotonia, muscle weakness, and often skeletal muscle deformities with the presence of nemaline bodies (rods) in the muscle biopsy. The nebulin (NEB) gene is the most commonly mutated and is thought to account for approximately 50% of genetically diagnosed cases of NM. We undertook a detailed muscle morphological analysis of 14 NEB-mutated NM patients with different clinical forms to define muscle pathological patterns and correlate them with clinical course and genotype. Three groups were identified according to clinical severity. Group 1 (n = 5) comprises severe/lethal NM and biopsy in the first days of life. Group 2 (n = 4) includes intermediate NM and biopsy in infancy. Group 3 (n = 5) comprises typical/mild NM and biopsy in childhood or early adult life. Biopsies underwent histoenzymological, immunohistochemical and ultrastructural analysis. Fibre type distribution patterns, rod characteristics, distribution and localization were investigated. Contractile performance was studied in muscle fibre preparations isolated from seven muscle biopsies from each of the three groups. G1 showed significant myofibrillar dissociation and smallness with scattered globular rods in one third of fibres; there was no type 1 predominance. G2 presented milder sarcomeric dissociation, dispersed or clustered nemaline bodies, and type 1 predominance/uniformity. In contrast, G3 had well-delimited clusters of subsarcolemmal elongated rods and type 1 uniformity without sarcomeric alterations. In accordance with the clinical and morphological data, functional studies revealed markedly low forces in muscle bundles from G1 and a better contractile performance in muscle bundles from biopsies of patients from G2, and G3.In conclusion NEB-mutated NM patients present a wide spectrum of morphological features. It is difficult to establish firm genotype phenotype correlation. Interestingly, there was a correlation between clinical severity on the one hand and the degree of sarcomeric dissociation and contractility efficiency on the other. By contrast the percentage of fibres occupied by rods, as well as the quantity and the sub sarcolemmal position of rods, appears to inversely correlate with severity. Based on our observations, we propose myofibrillar dissociation and changes in contractility as an important cause of muscle weakness in NEB-mutated NM patients.
    04/2014; 2(1):44. DOI:10.1186/2051-5960-2-44
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    ABSTRACT: Lipin-1 deficiency is associated with massive rhabdomyolysis episodes in humans, precipitated by febrile illnesses. Despite well-known roles of lipin-1 in lipid biosynthesis and transcriptional regulation, the pathogenic mechanisms leading to rhabdomyolysis remain unknown. Here we show that primary myoblasts from lipin-1-deficient patients exhibit a dramatic decrease in LPIN1 expression and phosphatidic acid phosphatase 1 activity, and a significant accumulation of lipid droplets (LD). The expression levels of LPIN1-target genes (PPARδ, PPARα, PGC-1α, ACADVL, CPT1B and CPT2) were not affected while lipin-2 protein level, a closely related member of the family, was increased. Microarray analysis of patients' myotubes identified 19 down-regulated and 51 up-regulated genes, indicating pleiotropic effects of lipin-1 deficiency. Special attention was paid to the up-regulated ACACB (acetyl-CoA carboxylase beta), a key enzyme in the fatty acid synthesis/oxidation balance. We demonstrated that overexpression of ACACB was associated with free fatty acid accumulation in patients' myoblasts whereas malonylcarnitine (as a measure of malonyl-CoA) and CPT1 activity were in the normal range in basal conditions accordingly to the normal daily activity reported by the patients. Remarkably ACACB invalidation in patients' myoblasts decreased LD number and size while LPIN1 invalidation in controls induced LD accumulation. Further, pro-inflammatory treatments (TNF1α+IL-1ß) designed to mimic febrile illness, resulted in increased malonylcarnitine levels, reduced CPT1 activity and enhanced LD accumulation, a phenomenon reversed by dexamethasone and TNFα or IL1-ß inhibitors. Our data suggest that the pathogenic mechanism of rhabdomyolysis in lipin-1-deficient patients combines the predisposing constitutive impairment of lipid metabolism and its exacerbation by pro-inflammatory cytokines.
    Biochimica et Biophysica Acta 08/2013; 1832(12). DOI:10.1016/j.bbadis.2013.07.021
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    ABSTRACT: Autosomal dominant centronuclear myopathy (AD-CNM) is due to mutations in the gene encoding dynamin 2 (DNM2) involved in endocytosis and intracellular membrane trafficking. To understand the pathomechanisms resulting from a DNM2 mutation, we generated a knock-in mouse model expressing the most frequent AD-CNM mutation (KI-Dnm2(R465W)). Heterozygous (HTZ) mice developed a myopathy showing a specific spatial and temporal muscle involvement. In the primarily and prominently affected tibialis anterior muscle, impairment of the contractile properties was evidenced at weaning and was progressively associated with atrophy and histopathological abnormalities mainly affecting mitochondria and reticular network. Expression of genes involved in ubiquitin-proteosome and autophagy pathways was up-regulated during DNM2-induced atrophy. In isolated muscle fibers from wild-type and HTZ mice, Dnm2 localized in regions of intense membrane trafficking (I-band and perinuclear region), emphasizing the pathophysiological hypothesis in which DNM2-dependent trafficking would be altered. In addition, HTZ fibers showed an increased calcium concentration as well as an intracellular Dnm2 and dysferlin accumulation. A similar dysferlin retention, never reported so far in congenital myopathies, was also demonstrated in biopsies from DNM2-CNM patients and can be considered as a new marker to orientate direct genetic testing. Homozygous (HMZ) mice died during the first hours of life. Impairment of clathrin-mediated endocytosis, demonstrated in HMZ embryonic fibroblasts, could be the cause of lethality. Overall, this first mouse model of DNM2-related myopathy shows the crucial role of DNM2 in muscle homeostasis and will be a precious tool to study DNM2 functions in muscle, pathomechanisms of DNM2-CNM and developing therapeutic strategies.
    Human Molecular Genetics 12/2010; 19(24):4820-36. DOI:10.1093/hmg/ddq413
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    ABSTRACT: Neuromuscular diseases with perinatal or neonatal onset are usually very severe and the diagnostic approach requires multiple and complex tests to determine their cause with the shortest delay. We studied all the muscle biopsies from newborns referred to our laboratory over a period of 40 years (1970–2010); they represented 309 biopsies (2.6% of the total series). The infants’ ages ranged from 0 to 12 weeks, including children born from 28 weeks of gestational age. The objective of this retrospective study was to evaluate the frequency of the different muscle disorders in the newborn population and the relevance of the muscle biopsy analysis for the diagnosis. The clinical, biological and molecular data were collected and the muscular biopsies were reviewed. The patients, 141 female (45.6%) and 168 male (54.4%), were separated in 5 categories, on the basis of themain clinical features:Group 1 Hypotonia/amyotrophy with arthrogryposis/ dysmorphy (with or without mechanic ventilation); Group 2 Hypotonia/amyotrophy without limb deformations (with or without mechanic ventilation);Group3Cardiac involvement;Group4Multi systemic involvement and Group 5 Central nervous system involvement. A morphological diagnosis was established in 215 patients (69.6%): metabolic myopathies in 108 (35%) cases, congenital myopathies in 55 (17.8%), spinal muscular atrophy and neuropathic disorders in 28 (9%), congenital myotonic dystrophy in 12 (3.9%), congenital muscular dystrophies in 10 (3.3%) and inflammatory myopathies in 2 (0.6%). In 94 (30.4%) cases no significant abnormalities were seen in the muscle biopsies and additional investigations are necessary to establish or to orientate the diagnosis. All the patients with congenital myopathies, spinal muscular atrophy and congenital myotonic dystrophy corresponded to Groups 1 and 2, while patients with metabolic myopathies showed a wide spectrum of clinical presentation.
    WMS Congress 15th 2010; 10/2010
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    ABSTRACT: INTRODUCTION Les dystrophies musculaires présentant un déficit en a-DG constituent un groupe hétérogène. Certaines alphadystroglycanopathies sont associées à des mutations des gènes FKRP, POMT1, POMT2, POMGnT1, FKTN, LARGE. OBJECTIFS Présentation de l’analyse précise en immunochimie sur muscles squelettiques, en immunofluorescence et au Western blot, et corrélation avec les phénotypes cliniques et les différentes anomalies moléculaires observées. MÉTHODES Nous avons analysé, en histoenzymologie et en immunochimie (IF & Western blot), les biopsies musculaires de 81 patients. Les analyses en biologie moléculaire des gènes FKRP, POMT1, POMT2, POMGnT1, FKTN, LARGE ont été réalisées sur la grande majorité des patients. Certains sont encore en étude. RÉSULTATS Parmi 81 patients étudiés, 40 d’entre eux ont une identification moléculaire : 34 présentaient une mutation dans le gène FKRP, 5 dans le gène POMT1 et 1 dans le gène FKTN. Chez 34 patients, soit aucune mutation dans ces 6 gènes n’a été trouvée, ou soit sont en cours d’étude. Pour les 7 derniers patients, la déficience en a-DG s’avérait être secondaire. DISCUSSION La déficience en alpha dystroglycane est un groupe très hétérogène de dystrophies musculaires. Ce déficit en alpha-DG nous permet d’envisager des études moléculaires ciblées sur les 6 gènes connus de la glycosylation. De plus, les cas de déficit non associés à ces 6 gènes identifiés ouvrent des perspectives à la recherche de nouveaux gènes candidats. CONCLUSION Cette étude démontre les larges spectres phénotypiques des alphadystroglycanopathies et le rapport entre l’expression immunochimique de l’alpha dystroglycane, phénotypes cliniques et les gènes mutés.
    VII Journées Annuelles de la Societé Francaise de Myologie 2009; 10/2009

Publication Stats

49 Citations
28.09 Total Impact Points

Institutions

  • 2013–2014
    • Pierre and Marie Curie University - Paris 6
      • Département de Pharmacologie
      Lutetia Parisorum, Île-de-France, France