In contrast with elevated CSF t-tau and p-tau in Alzheimer disease, CSF tau were significantly lower in PD; (ii) CSF α-syn positively correlated with Aβ1–42 and tau levels in PD participants, and the correlation was more greater in the early-onset PDs; (iii) CSF Aβ1–42 and tau levels were inversely correlated with VMAT2 SUVRs in cortical brain areas associated with cognitive dysfunction. This evidence concerns the gene SLC18A2 and Alzheimer disease.