A GGGGCC hexanucleotide repeat expansion (HRE) in the intronic region of the chromosome 9 open-reading frame 72 (C9orf72) gene is the most common genetic cause underpinning both FTLD, ALS, and combined FTLD-ALS (11–14). The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.