Expansion of a hexanucleotide repeat (HRE) GGGGCC (G4C2) in an intronic region of chromosome 9 open reading frame 72 (C9orf72) is the most common genetic cause of both ALS and FTD (DeJesus-Hernandez et al, 2011; Renton et al, 2011). Here, C9orf72 is linked to amyotrophic lateral sclerosis.