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Rett Syndrome: Review of Biological Abnormalities

Published online by Cambridge University Press:  02 March 2017

Henry G. Dunn*
Affiliation:
Division of Neurology, British Columbia's Children's Hospital, Vancouver, BC, Canada
Patrick M. MacLeod
Affiliation:
Division of Neurology, British Columbia's Children's Hospital, Vancouver, BC, Canada
*
Division of Neurology, British Columbia's Children's Hospital, 4480 Oak Street, Vancouver, BC, Canada V6H 3V4
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Abstract:

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The Rett syndrome (RS) is a peculiar, sporadic, atrophic disorder, almost entirely confined to females. After the first six months of life there is developmental slowing with reduced communication and head growth for about one year. This is followed by a rapid destructive stage with severe dementia and loss of hand skills (with frequent hand wringing), apraxia and ataxia, autistic features and irregular breathing with hyperventilation. Seizures often supervene. Subsequently there is some stabilization in a pseudo-stationary stage during the preschool to school years, associated with more emotional contact but also abnormalities of the autonomic and skeletal systems. After the age of 15-20 years, a late motor deterioration occurs with dystonia and frequent spasticity but seizures become milder. RS has generally been considered an X-linked disorder in which affected females represent a new mutation, with male lethality. Linkage studies suggested a critical region at Xq28. In 1999, mutations in the gene MECP2 encoding X-linked methyl cytosine-binding protein 2 (MeCP2) were found in a proportion of Rett girls. This protein can bind methylated DNA. Analyses are leading to much further investigation of mutants and their effects on genes. Neuropathological and electrophysiological studies of RS are described. Description of neurometabolic factors includes reduced levels of dopamine, serotonin, noradrenaline and choline acetyltransferase (ChAT) in brain, also estimation of nerve growth factors, endorphin, substance P, glutamate and other amino acids and their receptor levels. The results of neuroimaging are surveyed, including volumetric magnetic resonance imaging (MRI) and positron emission tomography (PET).

Résumé:

RÉSUMÉ:

Le syndrome de Rett (SR) est une maladie atrophique sporadique singulière qui touche presque exclusivement les filles. Après les premiers six mois de la vie, l'enfant présente un ralentissement du développement accompagné d'une diminution de la communication et de la croissance de la tête pendant à peu près un an, suivi d'une phase de destruction rapide avec démence sévère et perte de la dextérité manuelle (avec de fréquents épisodes de torsion des mains), de l'apraxie et de l'ataxie, des manifestations autistiques et une respiration irrégulière avec hyperventilation. Des crises convulsives s'ajoutent souvent au tableau. Par la suite, il y a une certaine stabilisation ou phase pseudo-stationnaire pendant la période préscolaire et scolaire, associée à plus de contacts émotifs mais aussi à des anomalies des systèmes autonome et squelettique. Après l'âge de 15 ou 20 ans, on observe une détérioration motrice accompagnée de dystonie et fréquemment de spasticité, et les crises convulsives s'atténuent. En général, on a considéré que le SR est une maladie liée à l'X où les filles atteintes sont porteuses d'une nouvelle mutation, une telle mutation étant léthale chez les garçons. Des études de liaison ont indiqué une région critique au niveau de Xq28. En 1999, des mutations dans le gène MECP2, le gène de la protéine de liaison de la méthyl cytosine2 lié au X (MECP2), ont été identifiées chez des filles porteuses du SR. Cette protéine peut lier l'ADN méthylé. Ces analyses ont mené à des investigations plus poussées des mutants et de leurs effets sur les gènes voisins. Des études neuropathologiques et électrophysiologiques du SR sont décrites. Parmi les facteurs neurométaboliques, on fait état de niveaux abaissés de dopamine, de sérotonine, d'adrénaline et de choline acétyltransférase (ChAT) dans le cerveau, et on rapporte également une évaluation des facteurs de croissance nerveux, des endorphines, de la substance P, du glutamate et d'autres acides aminés et des niveaux de leurs récepteurs. Les résultats de la neuroimagerie sont présentés, incluant la RMN volumétrique et le PET scan.

Type
Review Article
Copyright
Copyright © The Canadian Journal of Neurological 2001

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