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HelpTest Code AFXN Friedreich Ataxia, Repeat Expansion Analysis, Varies
Additional Testing Requirements
All prenatal specimens must be accompanied by a maternal blood specimen; order MATCC / Maternal Cell Contamination, Molecular Analysis, Varies on the maternal specimen as this must be a different order number than the prenatal specimen.
Shipping Instructions
Specimen preferred to arrive within 96 hours of collection.
Specimen Required
Patient Preparation: A previous bone marrow transplant from an allogenic donor will interfere with testing. For instructions for testing patients who have received a bone marrow transplant, call 800-533-1710.
Submit only 1 of the following specimens:
Specimen Type: Whole blood
Container/Tube:
Preferred: Lavender top (EDTA) or yellow top (ACD)
Acceptable: Any anticoagulant
Specimen Volume: 3 mL
Collection Instructions:
1. Invert several times to mix blood.
2. Send whole blood specimen in original tube. Do not aliquot.
Specimen Stability Information: Ambient (preferred) 4 days/Refrigerated
Prenatal Specimens
Due to its complexity, consultation with the laboratory is required for all prenatal testing; call 800-533-1710 to speak to a genetic counselor.
Specimen Type: Amniotic fluid
Container/Tube: Amniotic fluid container
Specimen Volume: 20 mL
Specimen Stability Information: Refrigerated (preferred)/Ambient
Additional information:
1. A separate culture charge will be assessed under CULAF / Culture for Genetic Testing, Amniotic Fluid.
2. All prenatal specimens must be accompanied by a maternal blood specimen; order MATCC / Maternal Cell Contamination, Molecular Analysis, Varies on the maternal specimen.
Specimen Type: Chorionic villi
Container/Tube: 15-mL tube containing 15 mL of transport media
Specimen Volume: 20 mg
Specimen Stability Information: Refrigerated
Additional Information:
1. A separate culture charge will be assessed under CULFB / Fibroblast Culture for Biochemical or Molecular Testing. An additional 3 to 4 weeks is required to culture fibroblasts before genetic testing can occur.
2. All prenatal specimens must be accompanied by a maternal blood specimen; order MATCC / Maternal Cell Contamination, Molecular Analysis, Varies on the maternal specimen.
Acceptable:
Specimen Type: Confluent cultured cells
Container/Tube: T-25 flask
Specimen Volume: 2 Flasks
Collection Instructions: Submit confluent cultured cells from another laboratory.
Specimen Stability Information: Ambient (preferred)/Refrigerated
Additional Information: All prenatal specimens must be accompanied by a maternal blood specimen; order MATCC / Maternal Cell Contamination, Molecular Analysis, Varies on the maternal specimen.
Specimen Type: Blood spot
Supplies: Card-Blood Spot Collection (Filter Paper) (T493)
Container/Tube:
Preferred: Collection card (Whatman Protein Saver 903 Paper)
Acceptable: Perkin/Elmer 266 filter paper, or Blood Spot Collection Card
Specimen Volume: 5 Blood spots
Collection Instructions:
1. An alternative blood collection option for a patient older than 1 year is a fingerstick. For detailed instructions, see How to Collect Dried Blood Spot Samples.
2. Let blood dry on the filter paper at ambient temperature in a horizontal position for a minimum of 3 hours.
3. Do not expose specimen to heat or direct sunlight.
4. Do not stack wet specimens.
5. Keep specimen dry.
Specimen Stability Information: Ambient (preferred)/Refrigerated
Additional Information:
1. For collection instructions, see Blood Spot Collection Instructions
2. For collection instructions in Spanish, see Blood Spot Collection Card-Spanish Instructions (T777)
3. For collection instructions in Chinese, see Blood Spot Collection Card-Chinese Instructions (T800)
4. Due to lower concentration of DNA yielded from blood spots, it is possible that additional specimen may be required to complete testing.
Forms
1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available:
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing-Spanish (T826)
2. Molecular Genetics: Neurology Patient Information
3. If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:
Useful For
Molecular confirmation of clinically suspected Friedreich ataxia
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| CULFB | Fibroblast Culture for Genetic Test | Yes | No |
| CULAF | Amniotic Fluid Culture/Genetic Test | Yes | No |
| MATCC | Maternal Cell Contamination, B | Yes | No |
Testing Algorithm
For prenatal specimens only:
If amniotic fluid (nonconfluent cultured cells) is received, the amniotic fluid culture will be added at an additional charge.
If chorionic villus specimen (nonconfluent cultured cells) is received, the fibroblast culture will be added at an additional charge.
For any prenatal specimen that is received, maternal cell contamination studies will be added. A maternal whole blood specimen is required to perform this test.
Special Instructions
- Informed Consent for Genetic Testing
- Hereditary Peripheral Neuropathy Diagnostic Algorithm
- Molecular Genetics: Neurology Patient Information
- Blood Spot Collection Card-Spanish Instructions
- Blood Spot Collection Card-Chinese Instructions
- Informed Consent for Genetic Testing (Spanish)
- Blood Spot Collection Instructions
Method Name
Polymerase Chain Reaction (PCR)
Reporting Name
FXN, Repeat Expansion AnalysisSpecimen Type
VariesSpecimen Minimum Volume
Amniotic fluid: 10 mL
Blood: 0.5 mL
Chorionic villi: 5 mg
Blood spots: 5 punches, 3-mm diameter
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Varies | Varies | ||
Reference Values
FXN
Normal alleles: <34 GAA repeats
Borderline alleles: 34-65 GAA repeats
Expanded alleles: >65 GAA repeats
An interpretive report will be provided.
Interpretation
An interpretive report will be provided.
Clinical Reference
1. Campuzano V, Montermini L, Molto MD, et al: Friedreich's ataxia: autosomal recessive disease caused by an intronic GAA triplet repeat expansion. Science. 1996 Mar 8;271(5254):1423-1427
2. Delatycki MB, Bidichandani SI: Friedreich ataxia-pathogenesis and implications for therapies. Neurobiol Dis. 2019 Dec;132:104606
3. Corben LA, Lynch D, Pandolfo M, Schulz JB, Delatycki MB, Clinical Management Guidelines Writing Group: Consensus clinical management guidelines for Friedreich ataxia. Orphanet J Rare Dis. 2014 Nov 30;9:184
4. Sharma R, De Biase I, Gomez M, Delatycki MB, Ashizawa T, Bidichandani SI: Friedreich ataxia in carriers of unstable borderline GAA triplet-repeat alleles. Ann Neurol. 2004 Dec;56(6):898-901
5. Montermini L, Richter A, Morgan K, et al: Phenotypic variability in Friedreich ataxia: role of the associated GAA triplet repeat expansion. Ann Neurol. 1997 May;41(5):675-682
Day(s) Performed
Monday, Wednesday
Report Available
21 to 28 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
81284
81265-Maternal Cell Contamination (if appropriate)
88233-Fibroblast Culture (if appropriate)
88235-Amniotic Fluid Culture (if appropriate)
88240-Cryopreservation (if appropriate)
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| AFXN | FXN, Repeat Expansion Analysis | 21762-0 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 609752 | Result Summary | 50397-9 |
| 609753 | Result | 21762-0 |
| 609754 | Interpretation | 69047-9 |
| 609755 | Reason for Referral | 42349-1 |
| 609756 | Specimen | 31208-2 |
| 609757 | Source | 31208-2 |
| 609758 | Method | 85069-3 |
| 609759 | Disclaimer | 62364-5 |
| 609760 | Released By | 18771-6 |