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Fragile X Syndrome

Fragile X syndrome (FXS) is the most common known inherited form of intellectual disability and autism spectrum disorder (ASD). This entry addresses the clinical and genetic manifestations and the neurobehavioral phenotype associated with FXS, as well as the interventions.

Clinical and Genetic Manifestations

The syndrome is caused by loss of function in the FMR1 (fragile X mental retardation) gene on the X chromosome. This gene encodes for the FMRP (fragile X mental retardation protein), which is found in all cells and at particularly high levels in cells that make up the central nervous system. Everyone has the FMR1 gene; however, this gene is stable in the vast majority of people. In FXS, FMR1 mutation expansions are caused by too many CGG trinucleotide repeats within the gene, although ...

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