C9orf72 and frontotemporal dementia: The pathogenic mechanisms resulting in FTD remain largely unknown, but current knowledge suggests that genetic, epigenetic and environmental factors contribute to disease development.2 Approximately 40% of patients with FTD have a positive family history of dementia3 and about 25% of patients with FTD have an identified genetic form of the disease.1 The vast majority of genetic FTD is inherited in an autosomal dominant pattern caused by mutations in one of three genes: chromosome 9 open reading frame 72 (C9orf72), progranulin (GRN) or microtubule-associated protein tau (MAPT).