Friedreich Ataxia
Friedreich ataxia (FRDA) is the most common inherited recessive ataxia, affecting approximately 1 in 20,000 to 1 in 50,000 people in populations of European ancestry. It is a progressive, multisystem neurodegenerative disease caused by homozygous GAA trinucleotide repeat expansions in intron 1 of the FXN gene (chromosome 9q21), leading to severe deficiency of frataxin — a mitochondrial protein essential for iron-sulfur cluster biogenesis and iron homeostasis. Cardiomyopathy is the leading cause of death, accounting for approximately 59% of mortality. In 2023, omaveloxolone (Skyclarys) became the first FDA-approved therapy for Friedreich ataxia, representing a landmark advance after decades without disease-modifying treatment.
Bottom Line
- Genetics: Homozygous GAA expansion in FXN intron 1 (~96%); compound heterozygotes (~4%) carry one expansion + one point mutation; pathologic repeats ≥66 (typically 600–1,200); the smaller allele correlates with age of onset and severity
- Onset: Typically 10–15 years (range 2–50+); wheelchair dependence by ~25 years; life expectancy ~40–50 years
- Core features: Progressive gait and limb ataxia, dysarthria, loss of deep tendon reflexes (with paradoxical Babinski sign), scoliosis (60–79%), cardiomyopathy (>60%), diabetes (8–32%)
- MRI hallmark: Cervical spinal cord atrophy (not cerebellar atrophy in early disease)
- Omaveloxolone (Skyclarys): FDA-approved Feb 2023; Nrf2 activator; MOXIe trial showed mFARS improvement of −2.40 vs placebo (p=0.014); 150 mg daily; EMA approved 2024
- Emerging therapies: Nomlabofusp (frataxin protein replacement, BLA planned Q2 2026), LX2006 (AAV cardiac gene therapy, registrational study 2026), CRISPR gene editing in development
Genetics
FXN Gene & Frataxin
The FXN gene was identified in 1996 by Campuzano et al. It encodes frataxin, a 210-amino acid nuclear-encoded mitochondrial protein involved in:
- Iron-sulfur cluster assembly — essential for mitochondrial respiratory chain complexes I, II, and III
- Iron homeostasis and transport within mitochondria
- Protection against iron-mediated oxidative stress
Frataxin deficiency leads to mitochondrial iron accumulation, impaired oxidative phosphorylation, increased reactive oxygen species (ROS), and progressive cellular damage particularly in neurons, cardiomyocytes, and pancreatic beta cells.
GAA Repeat Expansion
| Allele Status | GAA Repeat Range | Significance |
|---|---|---|
| Normal | 5–33 repeats | No disease; normal frataxin levels |
| Premutation | 34–65 repeats | Meiotic instability; may expand to pathologic range in offspring; carriers asymptomatic |
| Pathologic (full penetrance) | ≥66 repeats (typically 600–1,200) | Causes disease when biallelic; silences FXN transcription via heterochromatin formation |
Genotype-Phenotype Correlation
- ~96% of patients are homozygous for GAA expansions; ~4% are compound heterozygotes (one expansion + one point mutation/deletion)
- The smaller of the two expanded alleles is the strongest predictor of age of onset, disease severity, and rate of progression
- Larger expansions correlate with earlier onset, faster progression, higher risk of cardiomyopathy and diabetes, and more severe scoliosis
- GAA interruptions within the repeat tract delay age of onset in a location-dependent manner
- Somatic instability: GAA repeats tend to expand over time in affected tissues, potentially contributing to disease progression
Clinical Features
Neurological
| Feature | Prevalence | Details |
|---|---|---|
| Progressive gait ataxia | 100% | Usually the presenting symptom; clumsiness, frequent falls; wheelchair dependence typically by age ~25 (range 10–45) |
| Limb ataxia | >95% | Dysmetria, dysdiadochokinesia; upper limbs affected later than lower |
| Dysarthria | >90% | Slow, scanning speech progressing to severe unintelligibility |
| Areflexia | ~90% | Loss of deep tendon reflexes due to dorsal root ganglion degeneration; some patients retain reflexes (especially with smaller expansions) |
| Babinski sign (extensor plantar response) | ~80% | Paradoxical combination with areflexia reflects combined peripheral and central (corticospinal) degeneration |
| Loss of vibration/proprioception | >90% | Large-fiber sensory neuropathy (ganglionopathy); positive Romberg sign |
| Spasticity | ~40% (late) | May develop in advanced disease; pyramidal tract degeneration |
| Dysphagia | >50% (late) | Aspiration risk increases with disease duration |
| Optic neuropathy | ~30% | Subclinical in many; visual acuity loss in some; OCT shows retinal thinning |
| Hearing loss | ~13% | Sensorineural; auditory neuropathy pattern |
| Square-wave jerks | Common | Saccadic intrusions; fixation instability |
Systemic Manifestations
| System | Prevalence | Details |
|---|---|---|
| Hypertrophic cardiomyopathy | >60% | Leading cause of death (~59%); concentric LV hypertrophy; increased LVMI; fibrosis; arrhythmias (atrial fibrillation, supraventricular tachycardia); heart failure in advanced stages; annual echocardiography recommended |
| Scoliosis | 60–79% | Often progressive; may require surgical intervention; contributes to restrictive lung disease |
| Pes cavus | 55–75% | High-arched feet with hammer toes; may require orthotics or surgery |
| Diabetes mellitus | 8–32% | Impaired glucose tolerance in additional ~16%; results from beta-cell dysfunction + insulin resistance |
| Bladder dysfunction | ~40% | Urinary urgency, frequency, incontinence |
Cardiac Surveillance Is Essential
Cardiomyopathy is the leading cause of premature death in Friedreich ataxia. All patients should have annual echocardiography and 12-lead ECG. Cardiac MRI with late gadolinium enhancement can detect fibrosis. Elevated NT-proBNP and troponin levels may indicate progression. Early referral to a cardiologist experienced with neuromuscular cardiomyopathy is essential.
Diagnosis
Clinical Suspicion
Suspect Friedreich ataxia in a young patient (onset <25) with progressive ataxia, areflexia, and Babinski sign. The combination of absent reflexes + extensor plantar response is highly characteristic. Scoliosis, cardiomyopathy, and diabetes in a young person with ataxia should prompt testing.
Diagnostic Investigations
| Test | Findings |
|---|---|
| Genetic testing (GAA repeat analysis) | Confirmatory: biallelic pathologic GAA expansions (≥66 repeats); if only one expansion found, sequence FXN for point mutations |
| MRI brain and spine | Cervical spinal cord atrophy (decreased anteroposterior diameter); cerebellum typically normal or mildly atrophic early; dentate nucleus atrophy later |
| Nerve conduction studies | Absent or severely reduced sensory nerve action potentials (SNAPs); relatively preserved motor conduction; consistent with sensory ganglionopathy |
| Echocardiography | Concentric LV hypertrophy; increased interventricular septum and posterior wall thickness; diastolic dysfunction |
| ECG | T-wave inversions (widespread); LV hypertrophy pattern; ST changes; arrhythmias |
| Frataxin protein levels | Reduced to 5–30% of normal in lymphocytes or buccal cells; used in treatment trials as a biomarker |
| Glucose/HbA1c | Screen for diabetes and impaired glucose tolerance |
Assessment Scales
| Scale | Description |
|---|---|
| mFARS (modified Friedreich Ataxia Rating Scale) | Primary outcome measure in clinical trials; includes bulbar, upper limb, lower limb, and upright stability subscales; higher score = more severe |
| FARS (Friedreich Ataxia Rating Scale) | Comprehensive scale: functional staging, activities of daily living, neurologic assessment, timed activities (9-hole peg test, timed 25-foot walk) |
| SARA | 8-item ataxia severity scale; used across all ataxia types including FRDA |
| Timed 25-Foot Walk (T25FW) | Quantitative measure of gait speed; sensitive to change in ambulatory patients |
| 9-Hole Peg Test | Quantitative measure of upper limb coordination; useful even in wheelchair-bound patients |
Treatment
Omaveloxolone (Skyclarys) — First Approved Therapy
MOXIe Trial
A randomized, double-blind, placebo-controlled phase 2 trial in 103 patients with FRDA ages 16–40:
- Design: 150 mg oral omaveloxolone daily vs. placebo for 48 weeks
- Primary endpoint: Change in mFARS from baseline
- Results: Omaveloxolone −1.55 ± 0.69 vs. placebo +0.85 ± 0.64; difference −2.40 ± 0.96 (p=0.014)
- Extension data: Persistent benefit over 3 years compared with matched natural history cohort
- Mechanism: Activates nuclear factor erythroid 2-related factor 2 (Nrf2), a transcription factor regulating antioxidant gene expression; reduces mitochondrial oxidative stress
- Safety: Transient reversible aminotransferase elevations (most common), headache, nausea, fatigue, abdominal pain; no signs of liver dysfunction; hepatic monitoring recommended
- Regulatory: FDA approved February 28, 2023 (first drug for FRDA); EMA CHMP positive opinion December 2023, EU approval 2024
Emerging Therapies
| Agent | Mechanism | Status |
|---|---|---|
| Nomlabofusp (CTI-1601) | Recombinant fusion protein delivering frataxin directly to mitochondria | Phase 2: daily 50 mg SC dosing achieves frataxin levels ~50% of healthy controls (comparable to asymptomatic carriers); buccal and skin frataxin increases demonstrated. Open-label extension ongoing. Safety: Anaphylaxis in 7 participants (managed with modified dosing protocol: 5 mg test dose, then 25 mg with observation). BLA submission (accelerated approval) targeted Q2 2026 |
| LX2006 (AAVrh10-FXN) | Cardiac gene therapy: AAVrh10 vector delivering functional FXN gene to cardiomyocytes via IV infusion | Phase 1/2 SUNRISE-FA trial (NCT05445323): 3 dose cohorts; 100% (8/8) showed increased cardiac frataxin expression at 3 months; 115% mean increase at high dose; 5/6 patients with abnormal LVMI normalized by 12 months. Registrational study planned early 2026 |
| Antisense oligonucleotides (ASOs) | Target GAA repeat-induced heterochromatin to restore FXN transcription | Preclinical; multiple approaches under investigation |
| CRISPR-Cas9 gene editing | Delete expanded GAA repeats to restore FXN expression | Preclinical; demonstrated in iPSC models from FRDA patients (He et al. 2021, Ouyang et al. 2018) |
Supportive & Symptomatic Management
| Domain | Management |
|---|---|
| Physical therapy | Balance and coordination exercises; stretching; fall prevention; gait training; adapted exercise programs; transition to wheelchair when needed |
| Cardiomyopathy | Annual echocardiography and ECG; cardiology referral; ACE inhibitors/ARBs and beta-blockers for heart failure; antiarrhythmics as needed; ICD for high-risk arrhythmias |
| Scoliosis | Orthopedic monitoring; bracing in adolescents; surgical correction for curves >40° or progressive respiratory compromise |
| Diabetes | Annual glucose/HbA1c screening; standard diabetes management; insulin often required (beta-cell component) |
| Speech | Speech therapy; augmentative communication devices in advanced disease |
| Dysphagia | Swallowing evaluation; dietary modifications; thickened liquids; PEG tube in advanced cases |
| Foot deformities | Custom orthotics; surgical correction (tendon releases, osteotomies) for severe pes cavus |
| Bladder | Anticholinergics for urgency; intermittent catheterization if needed; urologic referral |
| Depression & QoL | Screen actively; SSRIs; psychological support; peer support groups; occupational therapy for ADL adaptation |
| Genetic counseling | Autosomal recessive: siblings have 25% risk; carrier testing for partners; reproductive options (PGT) |
Prognosis
- Age of onset: Typically 10–15 years; late-onset (>25) and very late-onset (>40) forms exist with generally slower progression
- Wheelchair dependence: Mean ~15 years after onset (typically by age ~25 in classic cases)
- Life expectancy: ~40–50 years; many patients surviving into their 50s–60s with optimal cardiac care
- Cause of death: Cardiomyopathy (~59%), followed by respiratory complications from scoliosis/aspiration
- Disease progression rate: Average mFARS worsening ~1.8–2.5 points/year in natural history studies; faster in younger onset and larger expansions
- Prognostic factors: Smaller GAA allele size is the strongest predictor; earlier onset and larger expansions predict faster progression and more systemic involvement
References
- Zesiewicz TA. Ataxia. Continuum (Minneap Minn). 2025;31(4, Movement Disorders):1093–1119.
- Campuzano V, Montermini L, Moltò MD, et al. Friedreich’s ataxia: autosomal recessive disease caused by an intronic GAA triplet repeat expansion. Science. 1996;271(5254):1423–1427.
- Lynch DR, Chin MP, Delatycki MB, et al. Safety and efficacy of omaveloxolone in Friedreich ataxia (MOXIe Study). Ann Neurol. 2021;89(2):212–225.
- Lynch DR, Goldsberry A, Rummey C, et al. Propensity matched comparison of omaveloxolone treatment to Friedreich ataxia natural history data. Ann Clin Transl Neurol. 2024;11(1):4–16.
- Clayton R, Galas T, Scherer N, et al. Safety, pharmacokinetics, and pharmacodynamics of nomlabofusp (CTI-1601) in Friedreich’s ataxia. Ann Clin Transl Neurol. 2024;11(3):540–553.
- Lexeo Therapeutics. Positive interim phase 1/2 data for LX2006 in Friedreich ataxia cardiomyopathy. Press release, April 7, 2025.
- Vankan P. Prevalence gradients of Friedreich’s ataxia and R1b haplotype in Europe co-localize. J Neurochem. 2013;126 Suppl 1:11–20.
- Payne RM, Peverill RE. Cardiomyopathy of Friedreich’s ataxia. Ir J Med Sci. 2012;181(4):569–570.