Frataxin, the protein produced by the FXN gene, works in mitochondria to help to create energy. Normally, frataxin works to regulate iron and sulfur molecules in the mitochondria while also working as an antioxidant to reduce oxidative stress. Both of these processes allow the mitochondria to efficiently produce ATP, the source of cellular energy. The nervous and cardiac systems require high levels of ATP, and these two systems are predominantly affected in symptoms of F A.
In people with two fully functioning FXN genes, frataxin is made at maximum levels. In those with only one functioning gene (carriers), only 50% of the normal amount of frataxin is made, but they remain asymptomatic. However, in those with two affected FXN genes, very minimal amounts of frataxin protein is made. With limited frataxin, iron-sulfur clusters in mitochondrial proteins cannot form properly, causing a reduction in energy production. Additionally, insufficient frataxin makes mitochondria especially sensitive to free radicals, causing increased damage and destruction of cells. Cells in the brain, spinal cord and muscles that are damaged or have low energy supplies degenerate over time, causing the signs and symptoms associated with F A.