✅ Model Answer:
• Diagnosis: Friedreich ataxia (FRDA) — autosomal recessive, GAA trinucleotide repeat expansion in the FXN gene (frataxin). Progressive ataxia (gait, limb, speech), areflexia (loss of deep tendon reflexes), extensor plantars (upper motor neuron signs), pes cavus, scoliosis, and hypertrophic cardiomyopathy. Onset typically between 5-15 years.
• Any other test: Genetic testing for GAA repeat expansion in FXN gene (homozygous — gold standard), nerve conduction studies (sensory axonal neuropathy, absent sensory potentials), fasting glucose/diabetes screening, cardiac MRI (if echocardiogram abnormal), audiometry, bone density (osteoporosis), vitamin E levels.
• What to do next: Multidisciplinary care: cardiology (monitor cardiomyopathy — beta-blockers, ACE inhibitors if needed), endocrinology (diabetes screening), PT/OT (gait training, mobility aids), speech therapy. Start coenzyme Q10 and vitamin E (limited evidence — may provide modest benefit).
• Follow-up plan: Annual cardiac evaluation (ECG, echocardiogram), annual glucose monitoring (HbA1c, fasting glucose), genetic counseling for family. Prognosis: wheelchair by teens, death from cardiomyopathy (most common cause).

✅ Model Answer:
• Friedreich ataxia (FRDA) is the most common hereditary ataxia, affecting approximately 1 in 50,000 individuals.
• Gene: FXN gene located on chromosome 9q13.
• Mutation: GAA trinucleotide repeat expansion in intron 1 of the FXN gene (homozygous in 95% of cases).
• Normal: 5-33 GAA repeats.
• Pathogenic: >66 GAA repeats (full expansion).
• Protein: Frataxin — a mitochondrial protein essential for iron-sulfur cluster biogenesis and mitochondrial function.
• Pathophysiology: Frataxin deficiency → mitochondrial iron accumulation → oxidative stress → neuronal degeneration (dorsal root ganglia, spinocerebellar tracts, corticospinal tracts) and cardiomyopathy.
• Inheritance: Autosomal recessive (both parents are carriers).

✅ Model Answer:
• Core features:
- Progressive ataxia: Gait ataxia (wide-based, unsteady), limb ataxia (dysmetria, intention tremor), dysarthria (slurred, scanning speech).
- Loss of deep tendon reflexes (areflexia): Due to dorsal root ganglion degeneration.
- Extensor plantars (Babinski sign): Upper motor neuron involvement (corticospinal tract).
- Pes cavus: High-arched feet (due to muscle weakness).
- Scoliosis: Progressive spinal curvature.
- Cardiomyopathy: Hypertrophic cardiomyopathy (most common cause of death).
- Diabetes mellitus: Glucose intolerance/diabetes (due to pancreatic islet cell dysfunction).
- Other: Optic atrophy, hearing loss, nystagmus, sensory neuropathy (loss of vibration/proprioception).

✅ Model Answer:
• Key differentiating features:
- Areflexia + extensor plantars: Combination of lower motor neuron (areflexia) and upper motor neuron (extensor plantars) signs — characteristic of Friedreich ataxia.
- Loss of vibration and proprioception: Dorsal column involvement (sensory ataxia).
- Pes cavus + scoliosis: Skeletal deformities common in Friedreich.
- Cardiomyopathy: Hypertrophic cardiomyopathy is highly associated (not seen in most other hereditary ataxias).
- Optic atrophy + hearing loss: May occur but are not specific.
- Absent sensory nerve action potentials (SNAPs): On nerve conduction studies — hallmark of Friedreich (dorsal root ganglionopathy).
• Differentiation from other ataxias:
- Ataxia-telangiectasia: Telangiectasias, IgA deficiency, elevated AFP.
- Spinocerebellar ataxias (SCA): Variable presentation, no cardiomyopathy.
- Wilson disease: Kayser-Fleischer rings, low ceruloplasmin.

✅ Model Answer:
• Genetic testing is the gold standard for diagnosis.
• Method: PCR and Southern blot analysis to detect GAA repeat expansion in the FXN gene.
• Results:
- Homozygous expansion: Confirms Friedreich ataxia (95% of cases).
- Compound heterozygous: One expanded allele + one point mutation (5% of cases).
- Normal: 5-33 repeats.
- Premutation: 34-65 repeats (may cause mild symptoms).
- Pathogenic: >66 repeats (full expansion).
• Genetic counseling:
- Autosomal recessive: 25% recurrence risk for siblings.
- Carrier testing: Offered to at-risk family members.
- Prenatal testing: Available if both parents are carriers.
• Limitations: Genetic testing does not predict disease severity (the number of repeats correlates with earlier onset, but variability exists).

✅ Model Answer:
• Multidisciplinary care:
- Cardiology: Annual ECG and echocardiogram (monitor for hypertrophic cardiomyopathy). Beta-blockers or ACE inhibitors if cardiomyopathy is symptomatic.
- Endocrinology: Annual fasting glucose and HbA1c (monitor for diabetes). Insulin if diabetes develops.
- Physical therapy: Gait training, balance exercises, mobility aids (walkers, wheelchairs).
- Occupational therapy: Activities of daily living, adaptive devices.
- Speech therapy: Dysarthria management, communication aids.
- Orthopedics: Bracing for pes cavus, scoliosis monitoring/surgery if severe.
- Nutrition: Maintain healthy weight, prevent osteoporosis (calcium, vitamin D).
• Pharmacological:
- Coenzyme Q10 (ubidecarenone): 5-10 mg/kg/day — limited evidence, may provide modest benefit.
- Vitamin E: 400-800 IU/day — antioxidant, limited evidence.
- Idebenone: Synthetic CoQ10 analog (some studies show benefit, but not FDA-approved).
- Omaveloxolone: NRF2 activator — recently FDA-approved for Friedreich ataxia (improves neurological function).
• Genetic counseling: For family members.

✅ Model Answer:
• Complications:
- Cardiomyopathy: Hypertrophic cardiomyopathy (most common cause of death) — can lead to heart failure, arrhythmias, sudden death.
- Diabetes mellitus: 10-20% develop diabetes due to pancreatic islet cell dysfunction.
- Scoliosis: Progressive spinal deformity may require surgical correction.
- Pes cavus: High-arched feet may cause pain, difficulty walking.
- Osteoporosis: Increased risk of fractures (due to immobility and nutritional deficiencies).
- Swallowing difficulties (dysphagia): May lead to aspiration pneumonia.
- Hearing loss: Sensorineural hearing loss (20-30%).
- Optic atrophy: Vision loss (10-20%).
- Death: Usually from cardiomyopathy (heart failure) or arrhythmias; median survival 40-50 years.

✅ Model Answer:
• Prognosis:
- Progressive disease: Neurologic deterioration is inevitable.
- Wheelchair dependence: Usually by 15-20 years of age (average age 18 years).
- Life expectancy: Reduced — 40-50 years (most commonly due to cardiomyopathy).
- Variables: Number of GAA repeats (more repeats → earlier onset, more rapid progression).
- Cardiomyopathy: Main determinant of survival.
- Omaveloxolone: New FDA-approved therapy may slow disease progression.
• Long-term follow-up:
- Cardiology: Annual echocardiogram, ECG — monitor for arrhythmias, heart failure.
- Endocrinology: Annual glucose monitoring, HbA1c.
- Physical therapy: Maintain mobility as long as possible.
- Psychosocial support: Depression, anxiety, and social isolation are common — provide counseling and support groups.
- Palliative care: Consider early involvement for symptom management.
- Family support: Genetic counseling for siblings and extended family.