Therefore, we employed a CRISPR-Cas9 gene editing system to excise the GAA expansion mutation in the FXN intron 1 region of FRDA patient-derived iPSC lines (Figure 7C) following a previous report.40 We confirmed via PCR gel-electrophoresis that the guide RNAs (gRNAs) resulted in effective excision of the GAA mutated region as shown through shorter bands detected at 152 bp (Figure 7D). The gene discussed is FXN; the disease is Friedreich ataxia.