GRN and frontotemporal dementia: Frontotemporal dementia (FTD), as an early-onset neurodegenerative disease, is the second most common form of dementia and manifests clinically with progressive behavioral and personality disturbances including disinhibition, perseveration and emotional blunting, evolving into generalized cognitive impairment and eventual death, and mutations in PGRN has been proven to be a main cause during this process [36, 37].