C9orf72 and frontotemporal dementia: Most familial cases of both ALS (~40%) and FTD (25%) are associated with hexanucleotide (G4C2) expansions in the Chromosome 9 open reading frame 72(C9orf72) gene (Dejesus-Hernandez et al., 2011; Renton et al., 2011; Bigio, 2012; Lee Y.-B.