GRN and frontotemporal dementia: Whilst the majority of people with PPA have a sporadic disease, cases of familial PPA have been described for many years.5,6 Overall, between a third and a half of individuals with FTD have a familial disorder7 with mutations in progranulin (GRN), microtubule-associated protein tau (MAPT) and chromosome 9 open reading frame 72 (C9orf72) being the commonest genetic causes.