C9orf72 and frontotemporal dementia: Abnormal expansions of the GGGGCC (G4C2) repeat sequence in the noncoding region of the C9orf72 gene have been found to be the most common genetic mutation responsible for ALS/FTD (DeJesus-Hernandez et al., 2011; Gijselinck et al., 2012; Renton et al., 2011).