C9orf72 and amyotrophic lateral sclerosis: Expansions like the GAA repeat in FRDA [19, 94, 97, 162, 231], the CTG repeat in myotonic dystrophy type 1 (DM1) [25], the GGGGCC repeat in C9ORF72-associated frontotemporal dementia and amyotrophic lateral sclerosis (C9FTD/ALS) [108], and the CGG repeat in FXS (also known as FRAXA) [44, 285] have all been implicated in reduced or silenced transcription.