CTSD and early-onset autosomal dominant Alzheimer disease: [18] Of relevance to this study cathepsin D has been shown to exhibit a beta-secretase-like role [19], and could therefore cleave beta amyloid precursor protein (APP) and promote the cascade leading to deposition of extracellular amyloid beta-peptide (Aβ), the senile plaques found in Alzheimer's disease.