Fragile X Syndrome

Fragile X syndrome is the most common form of inherited intellectual and developmental disabilities (IDDs).  Fragile X syndrome is the result of an expansion of a trinucleotide repeat (CGG) in the Fragile X Mental Retardation 1 (FMR1) gene located on the X chromosome.  Full size repeat expansions result in methylation of the FMR1 gene and the lack of a gene product.  Fragile X is inherited as an X-linked disorder and affects both males and females. All mothers of males affected with fragile X syndrome are premutation carriers, and all full mutations arise from premutations.  Premutation carriers may be affected with Fragile X-associated Tremor Ataxia Syndrome (FXTAS), which is generally found in older premutation male carriers and consists of tremor and ataxia.  Premutation female carriers may be affected with FMR1-associated primary ovarian insufficiency (POI), and occasionally with tremor and ataxia.  Genetic counseling is recommended for all premutation and full mutation carriers.

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