MAPT and Alzheimer disease: The goal of the present study was to tackle the conundrum of cognitive impairment due to DD by analyzing patients with DD in whom comorbid AD has been excluded with use of AD-biomarkers (amyloid- and tau-proteins in cerebrospinal fluid, 18F-fluordesoxyglucose-PET (FDG-PET), or amyloid-PET (Am-PET)).