FXN and Friedreich ataxia: Frataxin knockdown had no effect on OXCT1 mRNA levels either in fibroblasts (Fig. 6C; n = 4) or in tissues from frataxin knockdown mice treated with doxycycline for 4W (Fig. 6D and E; n = 8) or KIKO mice (Fig. 6F; n = 8), consistent with the result from human skin fibroblasts derived from FRDA patients (19).