Proposed mechanisms of C9-ALS/FTD pathogenesis include loss of normal C9ORF72 function, RNA-related toxicity due to RNA foci formation, and proteotoxicity associated with dipeptide repeats (DPRs) translated from expanded sense- and antisense C9ORF72 transcripts (6, 7, 8, 9). Here, C9 is linked to frontotemporal dementia.