CTSB and Alzheimer disease: Deletion of the CTSB gene in mice expressing human wild-type amyloid precursor protein (WT APP) has been shown to significantly impact AD pathology, resulting in a 67% reduction in cerebral levels of Aβ-40 and Aβ-42, as well as a decrease in the β-secretase-derived C-terminal fragment of APP (CTFβ).