MAPT and Parkinson disease: These neuropathology-related proteins, including amyloid-beta 42 (Aβ42), Aβ40, total Tau, phosphorylated Tau, and α-synuclein, are present in human body fluids, including CSF and blood plasma [10,11], which are good candidates for surrogate biomarkers for disease severity in patients with AD and PD.