Increased cathepsin D levels have been linked with AD.44 Moreover, CYTC reportedly colocalizes with Aβ peptide in the AD brain,45 and inhibits the enzymes involved in the degradation of Aβ peptide into toxic Aβ aggregates.46 Genetic analyses have identified the CYTC haplotype CST3 B as a risk factor for AD.42 The role of CYTC in the AD brain is well-described in the literature, and it appears that the altered CYTC plays a role in AD progression. Here, CTSD is linked to Alzheimer disease.