A hexanucleotide expansion consisting of GGGGCC (G4C2) nucleotides in the first intron of the C9orf72 gene is the most frequent genetic cause of ALS and is found in about 40–50% of familial ALS cases and 5–10% of sporadic ALS cases (Umoh et al., 2016). The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.