A hexanucleotide repeat (GGGGCC, G4C2) expansion in chromosome 9 open reading frame 72 (C9orf72) [GenBank: JN681271] was discovered to likely be the most frequent genetic cause of bvFTD, FTD with motor neuron disease (FTD-MND), and amyotrophic lateral sclerosis (ALS) in some populations (60, 62). The gene discussed is C9orf72; the disease is behavioral variant of frontotemporal dementia.