Test Catalog

Test ID: FFRBS    
Friedreich Ataxia, Frataxin, Quantitative, Blood Spot

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosing individuals with Friedreich ataxia in blood spot specimens


Monitoring frataxin levels in patients with Friedreich ataxia


This test is not useful for carrier detection.

Genetics Test Information Provides information that may help with selection of the correct genetic test or proper submission of the test request

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.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

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 98% of individuals with FA have a homozygous expansion of the GAA trinucleotide repeat in intron 1 of FXN. The remaining 2% 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, though 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 those patients with point alterations or deletions. Moreover, a molecular-based analysis is not able to effectively monitor treatment. In contrast, a protein-based assay measuring concentration of frataxin is suitable for both diagnosis as well as treatment monitoring in individuals with FA.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Pediatric (<18 years) normal frataxin: > or =15 ng/mL

Adults (> or =18 years) normal frataxin: > or =21 ng/mL

Interpretation Provides information to assist in interpretation of the test results

Normal results (> or =15 ng/mL for pediatric and > or =21 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 Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

No significant cautionary statements

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Deutsch EC, Oglesbee D, Greeley NR, Lynch DR: Usefulness of frataxin immunoassays for the diagnosis of Friedreich ataxia. J Neurol Neurosurg Psychiatry. 2014 Sep;85(9):994-1002

2. Delaytycki MB, Bidichandani SI: Friedreich ataxia pathogenesis and implications for therapies. Neurobiol Dis. 2019; Dec;132:104606. doi: 10.1016/j.nbd.2019.104606

3. Boehm T, Scheiber-Mojdehkar B, Kluge B, et al: Variations of frataxin protein levels in normal individuals. Neurol Sci. 2011 Apr;32(2):327-30 doi: 10.1007/s10072-010-0326-1

4. Hanson E, Sheldon M, Pacheco B, et al: Heart disease in Friedreich's ataxia. World J Cardiol. 2019;11(1):1-12

Special Instructions Library of PDFs including pertinent information and forms related to the test