C9orf72 and frontotemporal dementia: Recent studies indicate that an expanded hexanucleotide GGGGCC repeat located in the first intron of the C9orf72 gene represents the most common genetic abnormality for familial cases of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) with European ancestry, both of which constitute an overlapping continuum of a multisystem disorder affecting the central nervous system (CNS) [1-4].