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:
211. S Main Street
Orange, CA 92868
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’s: 81244, G0452