The Fragile X Syndrome is a genetic disorder involving the long arm of the X chromosome that results in developmental disability. Affected patients are usually male but women may also be affected.

Affected persons have an increased number of repeats for the trinucleotide sequence cytosine-guanine-guanine (CGG) in the FMR1 (Fragile X Mental Retardation 1) gene.


Patient Type

Number of CGG Repeats


6 - 50

unaffected carriers with premutation

50 - 200

affected patients

> 200


Diagnostic testing includes cytogenetics and PCR amplification.


Indications for testing:

(1) any male or female with intellectual impairment, developmental delay or learning disabilities of unknown cause, no matter how subtle

(2) any male or female with autism or autistic-like characteristics

(3) a person with a family history of Fragile X syndrome

(4) a person with a family history of undiagnosed intellectual disability

(5) an individual with a previous Fragile X cytogenetic test that was inconclusive

(6) the fetus of a woman who is known to be a Fragile X carrier

(7) women with a family history of premature menopause

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