C9orf72 and amyotrophic lateral sclerosis: Hexanucleotide (GGGGCC) repeat expansions in a non-coding region of C9orf72 are found in patients with amyotrophic lateral sclerosis (ALS) and FTD (DeJesus-Hernandez et al., 2011; Renton et al., 2011; Majounie et al., 2012), providing the first genetic link between the two diseases, although it remains unclear how C9orf72 hexanucleotide expansion triggers ALS and FTD pathology.