C9orf72 and amyotrophic lateral sclerosis: GGGGCC (G4C2) hexanucleotide repeat expansion (HRE) mutations in Chromosome 9 open reading frame 72 gene (C9orf72) are the most common genetic cause of FTD and ALS (abbreviated as C9FTD/ALS thereafter) (DeJesus-Hernandez et al., 2011; Renton et al., 2011).