Accounting for over 40% of fALS cases and up to 7% sALS, the repeat expansion of the noncoding hexanucleotide GGGGCC (G4C2) in intron 1 of the c9orf72 gene [7,93], originally identified in 2011, is the most frequent genetic mutation associated with ALS. Here, C9orf72 is linked to amyotrophic lateral sclerosis.