A pathological hexanucleotide repeat expansion (GGGGCC), in the intronic region of the C9orf72 locus—exceeding 30 repeats—is the most common genetic cause of familial autosomal dominant amyotrophic lateral sclerosis (ALS) as well as frontotemporal dementia (FTD) with ALS [116]. This evidence concerns the gene C9orf72 and amyotrophic lateral sclerosis.