MAPT and Parkinson disease: The quantification and characterization of EV-associated biomarkers – such as phosphorylated tau (p-tau181, p-tau217) in AD, oligomeric α-synuclein in PD, or neurofilament light chain (NfL) across disorders – provide a minimally invasive “liquid biopsy” tool for early diagnosis, patient stratification, and objective monitoring of therapeutic efficacy [11], 12].