GGGGCC (G SB 4 sb C SB 2 sb ) repeat expansion in the first intron of I C9ORF72 i is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) [[6], [11]]. Thus, our proof-of-concept study suggests that CRISPR/Cas9-based targeting of the promoter region to eliminate sense repeat RNA and its toxic translation products may be a potentially useful therapeutic approach for I C9ORF72 i -ALS/FTD, especially before significant accumulation of DPR proteins. Expanded GGGGCC hexanucleotide repeat in noncoding region of C9ORF72 causes chromosome 9p-linked FTD and ALS. [Extracted from the article]