Friedreich's Ataxia Repeat Expansion Analysis


Abbrev Code:MMMISC   
Order Code:LAB4909Order Name:Laboratory Miscellaneous Order
Order Instructions:All prenatal specimens must be accompanied by a maternal blood specimen. Order MATCC/Maternal Cell Contamination, Molecular Analysis, Varies on maternal specimen.
Methodology:Polymerase chain reaction (PCR)
CPT Codes: 81284 x1, 81284 x1, 81265 x1, 81265 x1, 88233 x1, 88233 x1, 88235 x1, 88235 x1, 88240 x1, 88240 x1
Turnaround Time:Testing performed Mon and Wed; results are available within 8-16 days.
Special Instructions:A previous bone marrow transplant from an allogenic donor will interfere with testing. Call 800-533-1710 for instructions for testing patients who have received a bone marrow transplant.

Due to its complexity, prenatal testing will not be accepted without approval from the laboratory. Call 800-533-1710 for prenatal testing consultation. Prenatal specimens can be sent Mon-Thur, and must be received by 5 pm Friday in order to be processed appropriately. Prenatal specimens must be accompanied by a maternal blood specimen.
Associated Links:

Genetic Testing Consent Form


Collection Instructions

Specimen:Whole blood
Optimal Volume:5 mL
Minimum\Peds Volume:3 mL
Container:Purple (EDTA)
Alternate Containers: Yellow (ACD, Solution A) tube available from laboratory
Collection Instructions:Collect only one of the following specimens:
  • Whole blood: 3 mL, 0.5 mL minimum in purple (EDTA) or yellow (ACD) preferred; any anticoagulant accepted. Invert several times to mix blood Store at room temperature.
  • Amniotic fluid: 20 mL, 10 mL minimum in amniotic fluid container. Store at room temperature.
  • Chorionic villi: 20 mg, 5 mg minimum in 15 mL tube containing 15 mL transport media. Refrigerate.
  • Confluent cultured cells (from another laboratory): 2 flasks, each in T-25 flask. Store at room temperature.
  • Blood spot: Collect blood spots on preferred collection card (Whatman Protein Saver 903 Paper); alternatively, collect on Perkin/Elmer 266 (formerly Ahlstrom 226) or blood spot collection (T493) filter.
    • An alternative option for patients older than 1 year of age is fingerstick. See Dried Blood Spot Collection Tutorial at https://vimeo.com/508490782
   
Causes for Rejection:Frozen specimen


Processing and Shipping

Specimen Processing:
  • Whole blood, amniotic fluid, confluent cultured cells: Do NOT process. Send collection container. Store at room (preferred) or refrigerated temperature.
  • Chorionic villi: Do NOT process. Send in collection container. Refrigerate.
  • Blood spot filter paper: Let blood dry on filter paper at room temperature in a horizontal position for 3 hours minimum. Do not expose to heat or direct sunlight. Do not stack wet specimens. Keep specimens dry. Store at room temperature.
Shipping Instructions:
  • Whole blood, amniotic fluid, confluent cultured cells, blood spots: Ship at room temperature.
  • Chorionic villi: Ship at refrigerated temperature.
Test Performed at or Referral Lab Lab Sendouts  (Mayo)
Referral Lab number:AFXN


Interpretive

Reference Range:
Normal alleles <34 GAA repeats
Borderline alleles 34-65 GAA repeats
Expanded alleles >65 GAA repeats
An interpretive report will be provided.
Limitations:For familial testing, first document the molecular etiology of the disease in an affected family member to confirm that a repeat expansion is the underlying mechanism of disease in the family. This assay will not detect nonrepeat expansion variants (e.g., sequence variants, deletions, and duplications). Genetic counseling is highly recommended prior to genetic testing.

Interpret test results in the context of clinical findings, family history, and other laboratory data to avoid errors to inaccurate or incomplete information.

Rare variants, e.g., polymorphisms, such as intron 1 deletions, may exist which could lead to false negative results. If GAA-repeat expansion results do not match clinical findings, consider additional testing.

Dur to somatic mosaicism, GAA repeat sizes in peripheral blood specimens may not reflect GAA repeat sizes in other tissues, e.g., central nervous system.
Use:Molecular confirmation of clinically suspected Friedreich Ataxia.


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