GDNF and Alzheimer disease: Astrocyte-derived exosomes from patients with AD, patients with FTD, and healthy controls showed up to 20-fold higher levels of β-site amyloid β-protein precursor-cleaving enzyme 1, γ-secretase, Aβ42, soluble APPα and APPβ, glial-derived neurotrophic factor, pT181-tau, and pS396-tau compared to the concentrations measured in neuronal exosomes.