C9orf72 and amyotrophic lateral sclerosis: The unusual repeat-associated non-AUG (RAN) translation of the HRE into five toxic dipeptide repeat (DPR) species—poly-PA, poly-GA, poly-PR, poly-GR, and poly-GP—appears to be a key factor driving the pathophysiology of C9orf72-related ALS-FTD.