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Frataxin Protein Assessment: When is This Assay an Appropriate Option?



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March 2014

Friedreich ataxia (FRDA) has been historically diagnosed using a DNA-based molecular test to detect the presence of the trinucleotide (GAA) repeat expansion in intron 1 of  the FXN gene. While genetic testing is available for diagnosis of FRDA, measurement of frataxin protein concentration by immunoassay is faster, less costly, and may have greater utility to detect disease. In addition, an immunoassay to measure frataxin levels may also be more effective as a method to monitor treatment in individuals with FRDA and for future population screening.

The frataxin immunoassay1 developed at Mayo Clinic and now available from Mayo Medical Laboratories can be performed on blood spot specimens (FFRBS / Friedreich Ataxia, Frataxin, Quantitative, Blood Spot) or whole blood (FFRWB / Friedreich Ataxia, Frataxin, Quantitative, Whole Blood) and provides a simple, accurate, and reproducible method to measure frataxin protein concentrations. As therapies to increase frataxin concentrations in affected individuals enter clinical trials and, ultimately, clinical use, it will be necessary to accurately measure the concentrations of frataxin to monitor the efficacy of the drug candidates.

In pediatric patients younger than 18 years, normal frataxin levels are ≥19 ng/mL. In adults (≥18 years), normal frataxin levels are ≥21 ng/mL. Results within the normal reference range in properly submitted specimens are not consistent with a diagnosis of FRDA. An interpretation will be provided when results are outside the normal reference range.

Frataxin Protein Immunoassay

The immunoassay in use at Mayo Clinic is similar to the assay depicted in the figure. Frataxin-specific monoclonal antibodies are bound to Luminex microspheres (color-coded tiny beads) as capture antibodies and biotinylated frataxin-specific polyclonal antibodies are used as detection antibodies. The reporter dye, streptavidin-phycoerythrin conjugate, attaches to the biotin and when exposed to light at 352 nM emits a photon signal proportional to the frataxin in the patient specimen. (Image used with permission from BioRad Laboratories, Inc)

Reference

1. 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;59:1461–1469

 


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