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Fragile X Syndrome

Fragile X syndrome is one of the most common inherited causes of cognitive impairment. This condition is known to be caused by a trinucleotide (CGG) repeat expansion in the 5’ untranslated region of the FMR1 gene located on the X chromosome.

FMR1 repeat expansion mutations are classified as follows:

<40 CGG repeats: Normal.

59-199 CGG repeats: Premutation

>200 CGG repeats: Full Mutation.

As this is an X-linked condition, males with a full mutation expansion nearly always have features of mild to severe cognitive impairment, autistic-like behavior, ADHD, speech delay and characteristic facial features. Females with a full mutation may exhibit a spectrum of clinical findings from mild to moderate cognitive impairment, which can be variable due to X-inactivation. Males with premutation range expansions are at increased risk of fragile X-associated tremor/ataxia syndrome (FXTAS). Female premutation carriers are at increased risk for premature ovarian failure.

Reasons for Referral

  • Child with unexplained developmental delay, cognitive impairment or a diagnosis of autism.
  • Carrier testing for at-risk relatives.
  • Women with unexplained premature ovarian failure.
  • Prenatal carrier testing for women with a family history of fragile X syndrome.

Specimen Requirements and Shipping/Handling

Blood: A single tube with 1-5 mL whole blood in EDTA (lavender top).

Saliva: To request a DNA Mouthwash Collection Kit please contact Genetics Center at (714)288-3500.


Store blood at 4°C until shipment. Ship at ambient temperature in an insulated container via overnight delivery within 96 hours of collection.

Send Specimen(s) to:

Genetics Center
211. S Main Street
Suite AA
Orange, CA 92868
Tel: (714)288-3500


Test Limitations

The test interpretation is based on the clinical and family information provided and the current understanding of the molecular genetics of fragile X syndrome. The more rare forms of mutations (deletion or single nucleotide substitution) in the coding region of the FMR1 gene are not examined in this assay.

CPT Codes

CPT’s: 81244, G0452

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