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Friedreich ataxia — SCE Neurology MCQ

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HardNeurogeneticsFriedreich ataxiaSCE Neurology

A 17-year-old girl has progressive gait ataxia, dysarthria, scoliosis and pes cavus. Examination shows absent ankle jerks, extensor plantars and impaired vibration sense. ECG suggests hypertrophic cardiomyopathy. Genetic testing shows FXN GAA repeat expansion. What is the most likely underlying mechanism?

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Correct answer: D — Frataxin deficiency from intronic repeat expansion

Frataxin deficiency from intronic repeat expansion is the best answer. Friedreich ataxia is caused by GAA repeat expansion in FXN leading to frataxin deficiency, with ataxia, sensory loss and cardiomyopathy. NOTCH3 causes CADASIL; HTT causes Huntington's; dystrophin mutations cause dystrophinopathy; PMP22 duplication causes CMT1A. Clinical pearl: Mixed absent reflexes and extensor plantars point to combined peripheral and central pathway disease.

Reference: GeneReviews Friedreich ataxia; Neurology 2022 Curriculum