A hexanucleotide (GGGGCC) repeat expansion (HRE) in the first intron of the C9orf72 (Chromosome 9 open reading frame 72) gene is the most common genetic cause of both ALS and FTD, although its frequency varies according to geoancestry and is rare in Asian populations [6, 7]. The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.