SNCA and Parkinson disease: α-synuclein and Aβ42 appear to be important markers of neuropathological staging, cognitive risk, and motor progression (as α-synuclein was significantly lower in the CSF of PD patients, not necessarily correlated with MDS-UPDRS part III scores, in line with previous literature [67]), but mood disturbances in PD appear to be driven chiefly by monoaminergic disruption, neuroinflammatory cascades, and psychosocial factors that operate on timescales and circuits only loosely related to bulk protein aggregation.