Petkau and Leavitt reviewed data on progranulin in neurodegenerative diseases and suggested that GRN variants resulting in decreased progranulin expression might be risk factors for both FTLD and other dementias and that common GRN variants can act as modifying factors for age of onset, disease duration, and risk of disease in ALS, AD, multiple sclerosis, bipolar disorder, and schizophrenia [59]. Here, GRN is linked to Alzheimer disease.