MAPT and Parkinson disease: It’s worth noting that beyond α-syn, total tau (t-tau), threonine 181–phosphorylated tau (p-tau181), and β-amyloid 42 (Aβ42)—canonical Alzheimer-type markers—also show systematic alterations in PD cohorts: reduced Aβ42 and/or elevated tau levels are tightly associated with cognitive decline, coexisting Alzheimer pathology, and accelerated clinical progression (Mantovani et al., 2024; Montine et al., 2010; Siderowf et al., 2010).