C9orf72 and frontotemporal dementia: After the discovery that a non-coding hexanucleotide repeat expansion in the chromosome 9 open reading frame 72 (C9orf72) gene could result in either FTD, amyotrophic lateral sclerosis (ALS), and FTD/ALS phenotypes, with common TDP-43 neuropathology, it became clear that these disorders are part of the same disease continuum [8].