C9orf72 and frontotemporal dementia: The GGGGCC (G4C2) hexanucleotide repeat expansion (HRE) in the first intron of the gene C9orf72, is the most common genetic abnormality associated with both ALS and frontal temporal dementia (FTD) (DeJesus-Hernandez et al., 2011; Renton et al., 2011).