C9orf72 and amyotrophic lateral sclerosis: A hexanucleotide repeat expansion (HRE), (GGGGCC)n, in the promoter or intron of the uncharacterized gene, chromosome 9 open reading frame 72 (C9orf72), has been found to be the most common cause of both ALS and FTD [1, 2] and has been linked to a number of other neurological disorders.