By analyzing brain tissues of AD patients and mouse models, they have found that the endo/lysosomal asparaginyl endopeptidase (AEP) or legumain is elevated and activated during ageing [10, 11], and that the activation of AEP is a crucial step that links ageing to tau cleavage and processing of amyloid precursor protein (APP) at the early stage of AD [10, 12]. Here, APP is linked to Alzheimer disease.