These studies may also help addressing some unsolved questions in FRDA63 from the relatively high levels of frataxin in FRDA patients compared to other loss-of-function disorders, to the equivocal role of ROS production as main cause of cellular dysfunction and death and to the high sensitivity of a limited number of cell types despite the extensive distribution and expression of frataxin in the body. This evidence concerns the gene FXN and Friedreich ataxia.