• Test Code:
  • Department:
  • Test Synonyms:
    FMR1-Related Disorders FXTAS Fragile X Tremor Ataxia Syndrome
  • CPT Code(s):
    8124381244 (if expansion is found)

Fragile X-associated Tremor Ataxia syndrome (FXTAS) occurs in 40-45% of male FMR1 premutation carriers over the age of 50 and less frequently in female FMR1 premutation carriers.  FXTAS is the result of a premutation, >54 trinucleotide (CGG) repeats, in the FMR1 gene. Core features of FXTAS are intention tremor and/or ataxia; peripheral neuropathy, autonomic dysfunction, and gradual cognitive decline may be present as well. Common psychiatric features include anxiety, dysinhibition, depression, and apathy. 
Genetic counseling is recommended.

Reason for Referral
Testing is indicated for individuals with clinical features of FXTAS, particularly with a family history of Fragile X syndrome.


PCR and capillary electrophoresis  analysis is used to measure the number of CGG trinucleotide repeats in the 5’ untranslated region of the FMR1 gene at Xq27.3; additionally, CGG repeat size and methylation status is determined by Southern blot for large premutations (>CGG150) and for fully expanded alleles.

Allele Types #CGG Repeats:
     Normal: 5 - 44
     Intermediate: 45 - 54
     Premutation: 55 – 200
     Full mutation (i.e. disease-causing): >200

Specimen Requirements:

Blood: EDTA (purple-top) tube or ACD (yellow-top) tube

    • Adult: 6mL
    • Child: 3mL

DNA: 20ng at a minimum of 100ng/µL

A REQUISITION FORM MUST ACCOMPANY ALL SAMPLES.  Please include detailed clinical information, including ethnicity, clinical history, and family history

Test Performed (Days):


Turn Around Time:

7-10 days. If expansion found, add 14 days to turn around time.

Shipment Sensitivity Requirements:

  • Keep specimen cold during transit, but do not ship on dry ice. 
  • Contact Client Services at (855) 535-1522 for shipping kits and instructions. 
  • Please use the cold pack provided in the KDL shipping kit. 
  • Ship the specimen overnight express, using the FedEx priority overnight label provided.


NCBI GeneReviews: FMR1-Related Disorders by Robert A. Saul and Jack C. Tarleton (2012) http://www.ncbi.nlm.nih.gov/books/NBK1384/

Additional Info:

Related testing performed in our laboratory: 

  • Fragile X syndrome
  • FMR1-associated primary ovarian insufficiency (POI).

Prior to any genetic testing we recommend genetic counseling. To receive forms and information about prenatal diagnostic testing, please contact Client Services at (855) 535-1522. 

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