C9orf72 and amyotrophic lateral sclerosis: When the C9orf72 hexanucleotide expansion was discovered as the most common shared mutation in ALS/FTD disease spectrum in 2011(DeJesus-Hernandez et al., 2011; Renton et al., 2011), the fastest way to study disease mechanisms was via iPSCs, as the generation of the repeat expansion in mouse models proved to be difficult.