CTSB and early-onset autosomal dominant Alzheimer disease: Noticeably, the pathway via which TBI leads to tau pathology is dependent on I2PP2A (inhibitor 2 of PP2A, also called SET) cytoplasmic retention and the activation of asparaginyl endopeptidase (AEP), a lysosomal cysteine protease, which is activated under acidic milieu and is associated with the process of Alzheimer's disease (AD) [26].