GRN and frontotemporal dementia: Loss‐of‐function mutations in progranulin (GRN) are a major genetic cause of frontotemporal dementia (FTD) (Baker et al. 2006; Cruts et al. 2006), a neurodegenerative disorder characterized by behavioral, cognitive, and/or language impairments (Gorno‐Tempini et al. 2011; Rascovsky et al. 2011).