C9orf72 and frontotemporal dementia: Since the 2011 discovery that the expanded hexanucleotide repeat in C9ORF72 causes chromosome 9p-linked FTD and ALS [11, 30], several neuropathological features unique to c9FTD/ALS have been identified [1, 3, 5, 7, 11, 24, 25, 28].