C9orf72 and frontotemporal dementia: Frontotemporal dementia (FTD) is a common cause of early-onset dementia.1 Clinically, patients present with either changes in personality (behavioral variant FTD [bvFTD]) or impaired language (primary progressive aphasia [PPA]), although overlap with motor neuron disease (FTD-MND) is not uncommon.1 FTD has an autosomal dominant genetic cause in around a quarter of people, with mutations in the progranulin (GRN), chromosome 9 open reading frame 72 (C9orf72), and microtubule-associated protein tau (MAPT) genes being commonest.2