Fragile X syndrome (FXS) is a genetic disorder. Symptoms often include mild to moderate intellectual disability. Physical features may include a long and narrow face, large ears, flexible fingers, and large testicles. About a third of those affected have features of autism such as problems with social interactions and delayed speech. Hyperactivity is common and seizures occur in about 10%. Males are usually more affected than females. Fragile X syndrome is typically due to an expansion of the CGG triplet repeat within the Fragile X mental retardation 1 (FMR1) gene on the X chromosome. This results in not enough fragile X mental retardation protein (FMRP), which is required for normal development of the connection between neurons. Diagnosis is by genetic testing to determine the number of CGG repeats in the FMRI gene. Normal is between 5 and 40 repeats, fragile X syndrome occurs with more than 200, and a premutation is said to be present when a middle number of repeats occurs. Testing for premutation carriers may allow for genetic counselling.
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