Intronic GGGGCC (G4C2) repeats are typically found within the C9orf72 gene between exon 1a and exon 1b.61 In healthy controls, the repeats occur <30 times62 but in some amyotrophic lateral sclerosis patients, the sequence repeats can be expanded up to hundreds of times.61 The C9-500 mouse harbours ∼500 G4C2 expansion repeats.63 This evidence concerns the gene C9orf72 and amyotrophic lateral sclerosis.