Friedreich's Ataxia — the most common inherited ataxia, now with the first FDA-approved treatment after decades of supportive care, where expansion size determines disease course and repeat length guides treatment decisions.
Whole genome sequencing accurately sizes GAA repeat expansions in both FXN alleles — detecting compound heterozygous cases (GAA expansion + point variant) that standard PCR-based tests never identify, and providing the baseline expansion length that informs prognosis.
Friedreich's Ataxia
Friedreich's ataxia (FRDA) is the most common hereditary ataxia in individuals of European descent, affecting approximately 1 in 50,000, with a carrier frequency of approximately 1 in 100. It is caused by autosomal recessive loss-of-function of frataxin (encoded by FXN on chromosome 9q21.11), a mitochondrial protein involved in iron-sulfur cluster assembly. Frataxin deficiency leads to mitochondrial iron accumulation, oxidative stress, and progressive neurodegeneration. FRDA is characterized by progressive cerebellar and sensory ataxia, cardiomyopathy (present in >90% of cases and the leading cause of death), diabetes mellitus (developing in approximately 10-20%), and skeletal deformities (scoliosis, pes cavus).
The molecular cause of FRDA is unusual: approximately 96-98% of pathogenic alleles are GAA trinucleotide repeat expansions in intron 1 of FXN. Normal alleles contain 5-33 GAA repeats; full expansion alleles contain 66 to over 1,000 repeats, with premutation alleles in the 34-65 range conferring stability risk but not causing disease at that size. Expansion length correlates meaningfully with clinical phenotype: larger expansions in the shorter allele correlate with earlier age of onset and more severe cardiomyopathy. Approximately 2-4% of FRDA cases are compound heterozygous — one GAA expansion allele and one conventional pathogenic point mutation (missense, nonsense, splice site) on the other allele. These compound heterozygous cases are completely missed by PCR-based tests that detect only GAA expansion length.
The first disease-modifying therapy for FRDA was approved by the FDA in February 2023: omaveloxolone (Skyclarys), an Nrf2 activator that improves mitochondrial function and reduces oxidative stress. This approval marks a historic milestone after decades during which management was purely symptomatic. With an approved treatment available, early diagnosis and precise molecular characterization — including expansion sizing and compound heterozygous detection — becomes directly therapeutic in determining eligibility and monitoring treatment response.
2-4% of FRDA cases are compound heterozygous: one GAA expansion + one point mutation on the other allele. Standard GAA-PCR assays report the shorter allele as 'normal' in these cases, creating a false-negative result that leaves patients undiagnosed.
Standard GAA expansion testing by PCR detects homozygous expansion — the common case — but misses compound heterozygous FRDA (expansion + point mutation). Whole genome sequencing identifies both mechanisms simultaneously.
Compound heterozygous FRDA is invisible to standard PCR — leaving 2-4% of patients undiagnosed
PCR-based GAA repeat testing — the standard first-line FRDA diagnostic test — measures the size of GAA repeats on both alleles. In compound heterozygous patients (one expanded allele + one allele with a point mutation), the standard PCR assay detects the expansion on one allele but reports a normal repeat count on the other. This creates a result that appears to show heterozygous GAA expansion — often interpreted as 'carrier' rather than 'affected' — and leads to an incorrect or delayed diagnosis. FXN gene sequencing must be performed on all apparent 'heterozygous expansion' results to rule out compound heterozygosity. Whole genome sequencing performs both the repeat expansion measurement and complete FXN gene sequencing in a single analysis.
Precise GAA expansion sizing determines prognosis and guides omaveloxolone treatment decisions
GAA repeat length in the shorter (allele 1) expansion is the strongest predictor of age of onset in FRDA — each additional 100 GAA repeats is associated with approximately one year earlier onset. Patients with shorter alleles in the 66-400 repeat range tend toward later onset (teenage to adult) with slower neurological progression but may still have significant cardiomyopathy. Patients with allele 1 expansions above 700 repeats tend toward earlier onset and more severe disease. This expansion size information guides prognostic counseling, cardiac surveillance intensity, and — with omaveloxolone now approved — informs the benefit-risk discussion of initiating therapy at different disease stages.
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Common questions about whole genome sequencing.
What is the difference between whole genome sequencing and a targeted genetic test?
Targeted genetic tests — including standard hereditary cancer panels — read a pre-defined list of known variants in a specific set of genes. They are designed to find what they already know to look for. Whole genome sequencing reads your entire genome: all 6 billion base pairs, every gene, every region between genes. A Mayo Clinic study published in JAMA Oncology found that standard testing guidelines missed more than half of patients with inherited cancer mutations. Genome Test does not have a fixed list.
What will I receive when my results are ready?
Your Dante Genome delivers 200+ physician-ready reports organized by clinical category — hereditary cancer, cardiac conditions, rare diseases, pharmacogenomics, carrier status, and more. Reports are delivered to your secure Genome Manager and are formatted for direct clinical use. Your genome data is permanently retained and re-analyzed automatically as science advances.
What happens if a clinically significant variant is found?
If a pathogenic or likely-pathogenic variant is identified, it will be clearly flagged in your physician-ready report with clinical context, published evidence, and recommended next steps. We recommend sharing any clinically significant finding with your physician or a genetic counselor, who can guide decisions about surveillance, risk reduction, or cascade testing for family members.
How is this different from a consumer DNA test like 23andMe or AncestryDNA?
Consumer DNA tests use genotyping chips that read less than 0.1% of your genome — a tiny pre-selected set of common variants. They are optimized for ancestry and population-level traits, not clinical genetic findings. The Dante Genome Test sequences 100% of your genome at 30X coverage, the same standard used in clinical diagnostic settings. The two tests are not comparable in scope, methodology, or clinical utility.
How long does it take to get results, and how are they delivered?
Your collection kit ships within 48 hours of ordering. Once your sample arrives at our CLIA-certified laboratory, sequencing and analysis takes 6–8 weeks. Results are delivered securely to your Genome Manager, where you can access your reports, share them with your physician, and receive automatic updates as new findings are validated against your genome.
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