Taken together, our results demonstrate that the CRISPR/Cas13d system effectively and selectively targets the expanded GGGGCC repeat RNA of C9orf72 and reduces the production of poly-GP and poly-GA resulting from C9orf72 RAN translation in iPSCs and iMNs derived from C9-ALS patients. The gene discussed is C9; the disease is amyotrophic lateral sclerosis.