C9orf72 and amyotrophic lateral sclerosis: GGGGCC hexanucleotide repeat expansion (HRE) in the non-coding region of chromosome 9 open reading frame 72 (C9orf72) (C9-HRE) is the major genetic cause of familial FTLD (12–48%) and amyotrophic lateral sclerosis (ALS) (24–46%) cases and 6–20% of sporadic cases for both diseases (DeJesus-Hernandez et al., 2011; Renton et al., 2011; Majounie et al., 2012).