After optimizing electroporation conditions in healthy donor LCLs (Supplementary Fig. 1, top), we verified that HDR efficiencies in FA LCLs were extremely low compared to wild-type LCLs, especially in the FANCA–/– background (for example, 0.3 ± 0.2% FANCA–/– versus 2.3 ± 0.6% FANCD2–/– versus 9.1 ± 0.7% wild-type) (Fig. 1a). This evidence concerns the gene FANCD2 and Friedreich ataxia.