FXN and Friedreich ataxia: The 210 amino acids long human FXN precursor is imported into the mitochondrion where it undergoes a two-step proteolytic maturation: first into a 19 kDa (42–210) intermediate and then into the final 14 kDa (81–210) form1, in both healthy individuals and FA patients (Pastore and Puccio, 2013).