Friedreich ataxia is inherited in which pattern?

• A. Autosomal recessive
• B. Autosomal dominant
• C. X-linked recessive
• D. Mitochondrial inheritance

Answer: (A)

Friedreich ataxia is caused by mutations in both copies of the FXN gene on chromosome 9, most commonly a GAA trinucleotide repeat expansion that reduces frataxin production. Because two defective alleles are needed for disease, it follows autosomal recessive inheritance. This means that men and women are affected in roughly equal numbers, and asymptomatic carriers can have affected children if both parents carry a mutant allele. It is not inherited through the X chromosome or through mitochondria, so the patterns seen with X-linked or mitochondrial inheritance don’t apply. The condition typically presents in childhood with progressive ataxia and signs such as pes cavus and hypertrophic cardiomyopathy, reflecting loss of frataxin function from the biallelic expansion.