L1CAM and Alzheimer disease: In parallel, previous studies have demonstrated that NEVs can transport key enzymes involved in the APP cleavage pathway, including β‐secretase.[26] Additionally, research has indicated that β‐secretase expression level and activity in other neurodegenerative diseases, such as Parkinson's disease and frontotemporal dementia, are significantly lower than in AD.[27] Leveraging these insights, we designed the NEV β‐secretase activity assay to assess β‐secretase activity from two subpopulations of NEVs: L1CAM(+)‐NEVs and NCAM(+)‐NEVs.