Aβ, tau, and α-synuclein neuropathologies are reflected as neurochemical changes in the cerebrospinal fluid (CSF), and CSF Aβ42, total tau, and phosphorylated tau have been established as biomarkers for AD diagnosis.23 On a group level, amyloid species (Aβ42, 40, and 38) are lower than in controls and associated with CI in PD.24–29 In most studies, tau levels are reduced or unchanged in PD without dementia.25,29 CSF total α-synuclein (t-α-syn) is reduced or unchanged in PD,25,29 but its association with CI is not yet clarified.27–31. Here, MAPT is linked to Parkinson disease.