C9 and amyotrophic lateral sclerosis: We detected a significant increase in poly-(GP) levels in C9orf72 ALS/FTD iPSC-MGs compared to controls, including the isogenic pair C9–4 (Figure 3H), showing for the first time that the C9orf72 HRE translates into DPR proteins in endogenous C9orf72 HRE expressing microglial mono-cultures.