The most common of these is a -(G4C2)n- nucleotide repeat expansion (NRE) in a non-coding region of the C9orf72 gene (C9), which accounts for up to 20% of all ALS cases, as well as a subset of frontotemporal dementia (FTD) cases (DeJesus-Hernandez et al, 2011; Renton et al, 2011). The gene discussed is C9; the disease is amyotrophic lateral sclerosis.