FXN Repeat Expansion Testing
Description
Pathogenic GAA repeat expansions within the first intron of the FXN gene have been associated with autosomal recessive Friedreich ataxia (FRDA).
Pathogenicity is dependent upon pathogenic variants in the FXN gene which include small sequence changes, structural variants and GAA repeat expansions according to the following ranges 1-2:
Normal Alleles | Mutable Normal Alleles | Intermediate/Uncertain Alleles | Reduced Penetrance Alleles | Full Penetrance Alleles |
5-33 | - | 34-65* | - | 66 or more |
*Individuals with unstable alleles (44-55) may manifest with later onset forms of FRDA 3. In addition, rare cases of repeats in the intermediate range (56 repeats) have been reported in earlier onset FRDA when accompanied by long repeats in the other allele 4.
Tests That Analyze FXN Repeats
- Genomic Unity® 2.0
- Genomic Unity® Whole Genome Analysis
- Genomic Unity® Lightning Genome Analysis – Pediatric
- Genomic Unity® Lightning Genome Analysis – Standard
- Genomic Unity® Exome Plus Analysis
- Genomic Unity® Exome Analysis
- Genomic Unity® Movement Disorders Analysis
- Genomic Unity® Comprehensive Ataxia Analysis
- Genomic Unity® Ataxia Repeat Expansion Analysis
- Genomic Unity® Cardiomyopathy and Arrhythmia Analysis
- Genomic Inform®
Additional Resources
Missed By Others, Found By Us
A 39-year-old female presented with a clinical Friedreich ataxia diagnosis. Variantyx testing identified a 2.7 kb FXN deletion missed by targeted gene sequencing, plus an expansion of 866 repeats in the other FXN allele.
Same Symptoms, Different Diagnoses
Five patients ranging in age from 59-70 presented with similar symptoms of progressive cerebellar ataxia, gait imbalance, progressive sensory neuropathy and dysphagia and/or dysarthria. Each received a different diagnosis with Variantyx testing.