An expanded non-coding hexanucleotide repeat expansion [r(GGGGCC)exp] in the chromosome 9 open reading frame 72 (c9orf72) gene has been identified as the most common genetic cause underlying FTD and ALS (c9ALS/FTD) (DeJesus-Hernandez et al., 2011; Renton et al., 2011). The gene discussed is C9orf72; the disease is frontotemporal dementia.