Test Id : AFXN

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.

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.

Specimen preferred to arrive within 96 hours of collection.

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.

• 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

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:

-Neurology Specialty Testing Client Test Request (T732)

-Biochemical Genetics Test Request (T798)

Amniotic fluid: 10 mL

Blood: 0.5 mL

Chorionic villi: 5 mg

Blood spots: 5 punches, 3-mm diameter

Molecular confirmation of clinically suspected Friedreich ataxia

This test assesses for GAA trinucleotide repeat expansions within the FXN gene to confirm a molecular diagnosis of Friedreich ataxia.

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.

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 disease-causing 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.

FXN

Normal alleles: <34 GAA repeats

Borderline alleles: 34-65 GAA repeats

Expanded alleles: >65 GAA repeats

An interpretive report will be provided.

An interpretive report will be provided.

For familial testing, it is important to first document the molecular etiology of disease in an affected family member to confirm that a repeat expansion is the underlying mechanism of disease in the family. Specifically, this assay will not detect nonrepeat expansion variants (eg, sequence variants, deletions, and duplications).

It is strongly recommended that patients undergoing genetic testing receive genetic counseling.

Test results should be interpreted in the context of clinical findings, family history, and other laboratory data, such as frataxin concentrations (see FFRWB / Friedreich Ataxia, Frataxin, Quantitative, Blood and FFRBS / Friedreich Ataxia, Frataxin, Quantitative, Blood Spot). Errors in test interpretation may occur if the provided information is inaccurate or incomplete.

Rare variants (ie, polymorphisms) may exist, such as intron 1 deletions, which could lead to false-negative results. If GAA-repeat expansion results do not match clinical findings, additional testing should be considered.

Due to somatic mosaicism, GAA repeat-sizes in peripheral blood specimens may not reflect GAA repeat-sizes in other tissues (eg, central nervous system).

Bone marrow transplants from allogenic donors will interfere with testing. Call Mayo Clinic Laboratories at 800-533-1710 for instructions for testing patients who have received a bone marrow transplant.

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

A polymerase chain reaction-based assay is used to amplify across the region of FXN containing GAA repeats.(Unpublished Mayo method)

Monday, Wednesday

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• Clients without access to Test Prices can contact Customer Service 24 hours a day, seven days a week.
• Prospective clients should contact their account representative. For assistance, contact Customer Service.

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.

81284

81265-Maternal Cell Contamination (if appropriate)

88233-Fibroblast Culture (if appropriate)

88235-Amniotic Fluid Culture (if appropriate)

88240-Cryopreservation (if appropriate)