Chromosome 9 open reading frame 72 (C9orf72) is usually considered one of the most common genetic causes, and the GGGGCC hexanucleotide repeat expansion (referred to as G4C2 HRE) in C9orf72 has been found to be associated with ALS and FTTD [219,220,221,222,223]. The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.