PPIB and Alzheimer disease: First, to measure the levels of the plasma biomarkers of neurodegeneration (p-tau181, Aβ42/40 ratio, NfL and GFAP) across a multicentre memory clinical cohort of older participants with PET-Αβ-positive MCI (MCI+) and AD (MCI+AD), LBD, FTD, PSP and controls.