FXN and Friedreich ataxia: The mean concentrations (± SD) of mature frataxin in healthy controls and homozygous FRDA cases in blood samples taken at year-1 were significantly different (p < 0.0001) at 7.5 ± 1.5 ng/mL and 2.1 ± 1.2 ng/mL, respectively (Figure 4A).