FXN and Friedreich ataxia: The etiologic determinant of FRDA is the lack of frataxin (FXN), the product of FXN gene [11], a 14 kDa mitochondrial protein involved, among additional functions still to be clarified, in iron–sulphur (Fe-S) cluster biosynthesis [12], iron metabolism and transport [13], and antioxidant defence [14].