MAPT and hippocampal atrophy: In this study, we found that the CSF α-synuclein concentration (1) was associated with CSF t-tau and p-tau levels among the non-demented elderly adults, (2) was elevated in the AD dementia group and the Aβ/tau-positive group compared with the control group, and (3) could predict hippocampal atrophy and the conversion from MCI to AD dementia.