C9orf72 and amyotrophic lateral sclerosis: Among these, hexanucleotide repeat expansion in the C9orf72 gene has been shown to be the main cause of ALS/FTLD [13, 38, 51], for which three disease mechanisms have been proposed: toxicity of RNA foci formed by RNA repeats, toxicity induced by dipeptide repeat aggregation as a result of repeat associated non-ATG mediated RNA translation (RAN), and reduced expression of the C9orf72 gene [26, 39].