C9 and amyotrophic lateral sclerosis: To investigate the effects of HRE excision with AAV9-gRNA2,3 and gRNA2,4 on C9ORF72 pathology in human motor neurons, we used an iPSC line from an C9-ALS/FTD patient carrying a pathogenic C9ORF72 HRE or a control line derived from an individual with fragile x syndrome with a repeat expansion in the FMR1 gene61.