In 2011, a hexanucleotide GGGGCC (G4C2)n repeat expansion in the C9orf72 gene was found to be implicated in frontotemporal lobar degeneration and amyotrophic lateral sclerosis as the most common known genetic cause (DeJesus-Hernandez et al., 2011; Renton et al., 2011; Gijselinck et al., 2012). The gene discussed is C9orf72; the disease is frontotemporal dementia.