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Eur J Clin Invest. 1994 Jan;24(1):1-10.

The fragile X syndrome: implications of molecular genetics for the clinical syndrome.

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Unité de Recherche en Génétique Humaine et Moléculaire, Centre de Recherche de l'Hôpital, St-François-d'Assie, Québec, Canda.


The fragile X syndrome of mental retardation is one of the most common genetic diseases. Characterization of the mutations involved has greatly improved our knowledge of the transmission of fragile X syndrome and new DNA-based diagnostics tools significantly outperform cytogenetic testing both for establishing the diagnosis and for determining carrier status. Fragile X mutations consist of an expansion of a CGG trinucleotide repeat localized in a gene (FMR-1) that is abnormally methylated in all affected individuals. They are classified as premutations (asymptomatic) and full mutations (associated with the disease). Several different DNA analysis protocols are used for fragile X genotyping but only a few have been tested on large samples of individuals. There are several clinical indications for direct DNA genotyping for fragile X including mental retardation, learning disability or hyperactivity in children with or without a family history of mental retardation, the establishment of carrier diagnosis in fragile X families and prenatal screening of children from carrier women.

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