Friedreich ataxia (FRDA) is the most common hereditary ataxia disorder, with an estimated prevalence of 1 in 50,000. An autosomal recessive neurodegenerative disorder with a typical age of onset around 5-15 years, FRDA is characterized by progressive gait and limb ataxia, dysarthria, lower-limb areflexia, Babinski sign, loss of position and vibration senses. Cardiomyopathy and diabetes mellitus may also be observed.
Approximately 96% of individuals with FRDA have an abnormally expanded GAA repeat in intron 1 of FXN gene on both alleles (homozygous GAA repeat expansion). The remaining individuals with FRDA are compound heterozygotes for an abnormally expanded GAA repeat in the disease-causing range on one allele and another intragenic pathogenic variant on the other allele. Standard alleles in the FXN gene contain 5 to 60 repeats, while disease-causing alleles can range from 66 to approximately 1300 repeats.
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