iPSC-MG carrying the endogenous C9orf72 HRE recapitulate pathological hallmarks of C9orf72 ALS/FTD disease, such as the formation of HRE-associated RNA foci, expression of poly (GP) DPRs, and reduced C9orf72 protein levels. The gene discussed is C9orf72; the disease is frontotemporal dementia.