CTSB and Alzheimer disease: Activated caspase 3, which is a cysteine protease activated in apoptosis, was suggested to be a factor in the functional decline of those affected by AD, and the infection of human mesenchymal stem cells with ZIKV leads to enhanced expression of caspase 3, thereby implicating that caspase 3 is involved in neuronal cell death and plaque formation in AD brains [79,80].