Moreover, over half of the patients with PD dementia (PDD) also have significant AD-related pathology with abnormally deposited α-synuclein, amyloid-β and tau proteins in the PDD brain, including in the hippocampus which correlates to the severity of cognitive decline in patients with PDD (Kalaitzakis and Pearce, 2009). Here, MAPT is linked to Alzheimer disease.