The G4C2 hexanucleotide repeat expansion mutation (HREM) within C9orf72 [112,113] is perhaps the most significant genetic mutation associated with ALS thus far, and is estimated to be present in 34% of familial cases, and 5% of sporadic cases in Europe [19,114]. The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.