Which condition is the most common autosomal recessive ataxia?

• A. SCA
• B. Ataxia Telangiectasia
• C. SCAN1
• D. Friedrich's Ataxia

Answer: (D)

Autosomal recessive ataxias appear when two mutated copies are present, and Friedrich's ataxia is by far the most common condition in this group. It comes from a GAA repeat expansion in the FXN gene, which reduces frataxin and disrupts mitochondrial function. This leads to progressive degeneration of the spinocerebellar tracts and dorsal columns, explaining the hallmark ataxia and sensory involvement. Clinically, it typically starts in childhood with gait ataxia and dysarthria, and features like pes cavus and scoliosis are frequently seen. Cardiac involvement, especially hypertrophic cardiomyopathy, is a major concern in Friedrich's ataxia. The other options are either autosomal dominant diseases (like many spinocerebellar ataxias) or, while autosomal recessive, much less common or have broader multisystem involvement, so Friedrich's ataxia is the most common autosomal recessive ataxia.