Fragile X Repeat Analysis

Fragile X syndrome is the most common inherited form of mental retardation. Affecting primarily males, this condition may also present with learning disabilities, behavioral problems, autism, or seizures. Other common features include a long face with a prominent jaw, large or protruding ears, a large head, large testicles in post-pubertal males, joint hyperextensibility, and mitral valve prolapse. Fragile X syndrome is caused by expansion of the FMR1 gene CGG triplet repeat. The molecular portion of the panel includes both PCR to assess for size of the CGG triplet repeat and Southern blot (positive cases and prenatal cases only) for the methylation status.

Due to the number of chromosome abnormalities which mimic the symptoms of Fragile X and are detected in patients referred for Fragile X testing, blood chromosome analysis is performed simultaneously unless it has been performed prior or the molecular analysis is ordered as an individual test. Please include a copy or statement regarding the chromosome analysis result if the testing was performed elsewhere.

Fragile X prenatal analysis is available for at-risk pregnancies. If the maternal Fragile X repeat analysis was not performed in this laboratory, please include a copy of her test result.

Indications for Testing

  • Confirmation of clinical diagnosis
  • Autistic-like behaviors and other behavioral problems
  • Family history of unexplained mental retardation or autism, especially showing a preponderance of affected males
  • Carrier testing
  • Premature ovarian failure
  • Pregnancy known to be at risk for Fragile X syndrome.

OMIM #: 300624

Sample Requirements

  • Infants: two to three mL whole blood in a purple top EDTA tube and two to three mL whole blood in a green top Sodium Heparin tube
  • Children (>2 years) and adults: five to seven mL whole blood in a purple top EDTA tube and five to seven mL whole blood in a green top Sodium Heparin tube
  • Amniotic fluid or cultured amniocytes

Contact laboratory genetic counselors or molecular director for specific sample requirements in advance.

Note: Maternal blood sample is also required for Maternal Cell Contamination studies for prenatal samples. Send five mL in a purple top EDTA tube along with prenatal sample.

Sample Handling

Blood samples stored overnight should be refrigerated or kept cold. Blood samples should never be frozen. Specimens being sent from outside facilities should be packaged with a cold pack according to standard medical safety practices. The specimen should be shipped by overnight priority (scheduled to arrive by Friday morning at the latest).

Shipping Address

Center for Human Genetics Laboratory
10524 Euclid Ave, Sixth Floor
Cleveland, OH 44106

For local samples, please call Client Service (216-844-5227) to arrange for sample pick-up.

Turnaround Time

14-21 days

CPT Codes

Fragile X Molecular Analysis: 81243
Southern Blot Analysis: 81244
Blood Chromosome Analysis: 88230, 88261, 88280, 88289

Please submit a completed Prenatal and Postnatal Cytogenetics and Molecular specimens requisition for each sample.

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