We hypothesized that (1) Plasma exosomal Aβ42, Aβ40, and P-T181-tau levels will be higher in PWS compared to NCs (similar to AD), and (2) Higher exosomal Aβ42, Aβ40, and P-T181-tau levels will be correlated with worse cognitive functioning in PWS and NCs. This evidence concerns the gene MAPT and Alzheimer disease.