MAPT and Alzheimer disease: Besides α-synuclein accumulation, AD copathology, including β-amyloid (Aβ) plaques12 and phosphorylated-tau (p-tau) neurofibrillary tangles (NFT),13 is often present in PD.14 Moreover, neuroaxonal15 and synaptic degeneration16 also occur across several cortical regions in PD.