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Test ID: AFXN Friedreich Ataxia, Repeat Expansion Analysis, Varies


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. Call 800-533-1710 for instructions for testing patients who have received a bone marrow transplant.

 

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)/Refrigerated

 

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 Monday through Thursday and must be received by 5 p.m. CST on Friday in order to be processed appropriately. 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: Amniotic fluid

Container/Tube: Amniotic fluid container

Specimen Volume: 20 mL

Specimen Stability Information: Refrigerated (preferred)/Ambient

 

Specimen Type: Chorionic villi

Container/Tube: 15-mL tube containing 15 mL of transport media

Specimen Volume: 20 mg

Specimen Stability Information: Refrigerated

 

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

 

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 (formerly Ahlstrom 226) 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 of age is a fingerstick. See Dried Blood Spot Collection Tutorial for how to collect blood spots via fingerstick.

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 a Neurology Specialty Testing Client Test Request (T732) 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.

Method Name

Polymerase Chain Reaction (PCR)

Reporting Name

FXN, Repeat Expansion Analysis

Specimen Type

Varies

Specimen 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

Clinical Information

Friedreich ataxia (FA) is one of the most commonly inherited ataxias and is characterized by progressive gait and limb ataxia, dysarthria, dysphagia, and sensory loss. The phenotypic spectrum includes nonneurologic manifestations, particularly cardiomyopathy and diabetes mellitus. Onset typically occurs between the ages of 10 to 16 years; however, late-onset and early-onset variants have been reported. FA is autosomal recessively inherited. The majority of affected individuals (96%) have homozygous GAA trinucleotide repeat expansions in intron 1 of FXN. The remaining affected individuals have a heterozygous GAA trinucleotide repeat expansion and another pathogenic FXN variant detectable by sequencing or deletion and duplication analysis. Correlation exists between the size of the GAA repeat and disease onset and severity, with larger alleles associated with earlier onset and more severe disease presentation. GAA expansions may demonstrate instability during meiosis and mitosis. The GAA repeat size may expand or contract during transmission to offspring and GAA repeat size may vary in different tissues. The GAA trinucleotide repeat is polymorphic in the general population, with the number of nondisease-associated repeats ranging from 5 to 33. Repeats of 66, or greater, are fully penetrant disease-associated alleles; however, the majority of affected individuals have repeat sizes in the 600 to 1200 repeat range. Repeat sizes of 34 to 65 fall within a borderline range. Borderline alleles are of unclear significance and may be associated with clinical symptoms of FA and/or a risk for expansion to a full penetrance allele when transmitted to offspring.

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

14 to 21 days

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test 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
Mayo Clinic Laboratories | Neurology Catalog Additional Information:

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