MAPT and frontotemporal dementia: Approximately one-third of cases are inherited on an autosomal dominant basis, with the majority being due to mutations in progranulin (GRN), chromosome 9 open reading frame 72 (C9orf72), or microtubule-associated protein tau (MAPT).1 Previous studies have shown that the heterogeneity of FTD is in part related to distinct clinical features and atrophy patterns between these different genetic groups.2,3 However, there can also be substantial phenotypic heterogeneity within each genetic group.4