FRDA is the most common of the hereditary ataxias, affecting 1 in 50,000 children.4 It is an autosomal recessive GAA trinucleotide repeat disorder affecting the FRDA gene on chromosome 9q13 (which codes for frataxin protein). Triplet repeats greater than 100 result in accumulation of iron in mitochondria with gradually progressive dysarthria, ataxia, and posterior column signs. Presentation usually occurs between ages 2 and 16 years. Upper extremities are affected more than lower extremities. Deep tendon reflexes are usually absent on presentation; when reflexes are retained, the course may be milder. Plantar response may be upgoing. Most patients will have an axonal neuropathy, with small or absent sensory nerve action potentials, and relative sparing of motor nerve conduction. Brain MRI may show atrophic cerebellum, brainstem, and posterior columns, and the corticospinal tract may also be affected. A lipid panel with apolipoprotein levels would be helpful when hypobetalipoproteinemia or abetalipoproteinemia is suspected; however, in both of these conditions, there is generally some element of failure to thrive. Screening for metabolic disorders with amino and organic acids is more helpful when there is a history of lethargy, vomiting, or decompensations with minor illnesses. Most spinocerebellar ataxias are also trinucleotide repeat disorders, but most present in adulthood and are autosomal dominant. Management of FRDA includes screening for cardiomyopathy, scoliosis, and diabetes mellitus.
- Test for trinucleotide repeat of FRDA gene.
4. Pandolfo M. Friedreich ataxia. Semin Pediatr Neurol 2003;10:163-72.
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