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HelpTest Code FFRWB Friedreich Ataxia, Frataxin, Quantitative, Blood
Reporting Name
Frataxin, Quant, WBUseful For
Diagnosing individuals with Friedreich ataxia in whole blood specimens
Monitoring frataxin levels in patients with Friedreich ataxia
This test is not useful for carrier detection.
Method Name
Immunoassay
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
Whole bloodNecessary Information
Provide a reason for testing with each specimen.
Specimen Required
Collection Container/Tube:
Preferred: Lavender top (EDTA)
Acceptable: Green top (sodium or lithium heparin)
Specimen Volume: 2 mL
Collection Instructions: Send whole blood specimen in original tube. Do not aliquot.
Specimen Minimum Volume
1.25 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Whole blood | Frozen (preferred) | 70 days | |
| Ambient | 70 days | ||
| Refrigerated | 70 days |
Reject Due To
| Gross hemolysis | OK |
| Gross lipemia | OK |
| Gross icterus | OK |
Special Instructions
Reference Values
Pediatric (<18 years) normal frataxin: ≥19 ng/mL
Adults (≥18 years) normal frataxin: ≥21 ng/mL
Day(s) Performed
Twice per month, Thursday
CPT Code Information
83520
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| FFRWB | Frataxin, Quant, WB | 80979-8 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 32253 | Reason for Referral | 42349-1 |
| 32254 | Method | 85069-3 |
| 32255 | Frataxin | 80979-8 |
| 32256 | Interpretation | 59462-2 |
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.Clinical Information
Friedreich ataxia (FA) is an autosomal recessive disease affecting approximately 1:50,000 individuals in the white population. The disease is clinically characterized by progressive spasticity, ataxia, dysarthria, absent lower limb reflexes, sensory loss, and scoliosis. Cardiac involvement occurs with the development of myocardial fibrosis due to mitochondrial proliferation and loss of contractile proteins. It tends to be correlated with the clinical neurologic age of onset and the GAA triplet repeat length, but not the duration of disease or the severity of neurologic symptoms. Although most individuals begin experiencing initial symptoms between 10 and 15 years of age, atypical late-onset forms with initial symptoms presenting after age 25 do occur.
FA is caused by variants in the FXN gene encoding a mitochondrial protein, frataxin. Variants in this gene lead to a reduced expression of frataxin, which causes the clinical manifestations of the disease. Approximately 96% of individuals with FA have a homozygous expansion of the GAA trinucleotide repeat in intron 1 of FXN. The remaining 4% of FA patients have the trinucleotide expansion on 1 allele and a point alteration or deletion on the second allele. Normal alleles contain between 5 to 33 GAA repeats. Disease-causing alleles typically range from 66 to 1700 repeats, although the majority of individuals with FA have repeats ranging from 600 to 1200.
Historically, FA has been diagnosed by use of a DNA-based molecular test to detect the presence of the GAA expansion. Unfortunately, testing for the triplet repeat expansion will miss patients with point alterations or deletions. Moreover, a molecular-based analysis is not able to effectively monitor treatment. In contrast, this protein-based assay measuring concentration of frataxin is suitable for both diagnosis as well as treatment monitoring in individuals with FA.
For patients with a low frataxin level, molecular repeat expansion analysis of the FXN gene (AFXN / Friedreich Ataxia, Repeat Expansion Analysis, Varies) allows for detection of disease-causing expansion alleles.
Interpretation
Normal results (≥19 ng/mL for pediatric and ≥23 ng/mL for adult patients) in properly submitted specimens are not consistent with Friedreich ataxia.
For results outside the normal reference range an interpretative comment will be provided.
Cautions
No significant cautionary statements
Method Description
The immunoassay utilizes frataxin-specific monoclonal antibodies bound to Luminex microspheres as capture antibodies and biotinylated frataxin-specific polyclonal antibodies as detection antibodies. Streptavidin-phycoerythrin attaches to the biotin and when exposed to light at 352 nM emits a photon that is measured and that signal is used to determine the amount of frataxin in the sample.(Oglesbee D, Kroll C, Gakh O, et al. High-throughput immunoassay for the biochemical diagnosis of Friedreich ataxia in dried blood spots and whole blood. Clin Chem. 2013;59(10):1461-1469. doi:10.1373/clinchem.2013.207472; Cowan T, Pasquali M. Laboratory investigations of inborn errors of metabolism. In: Sarafoglou K, Hoffman GF, Roth KS, eds. Pediatric Endocrinology and Inborn Errors of Metabolism. 2nd ed. McGraw-Hill; 2017:1139-1158)
Report Available
2 to 14 daysSpecimen Retention Time
1 monthForms
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. Biochemical Genetics Patient Information (T602)
3. If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:
Genetics Test Information
Friedreich ataxia (FA) presents most commonly between 10 to 15 years of age with progressive neurologic changes including spasticity and ataxia.
Decreased frataxin protein levels are diagnostic of FA and can also be utilized for ongoing medical monitoring.