C9orf72 and frontotemporal dementia: Microtubule-associated protein tau (MAPT) [4], granulin (GRN) [5,6] and chromosome 9 open reading frame 72 (C9orf72) [7,8] are the three most common genes causal of FTD and together account for 30–50% of familial FTD [9,10].