C9orf72 and frontotemporal dementia: Hundreds to thousands of GGGGCC repeats in the first intron of the chromosome 9 open reading frame 72 (C9orf72) gene represent the most common genetic abnormality in C9ALS/FTD (DeJesus-Hernandez et al., 2011; Renton et al., 2011; Smith et al., 2013).