CTSD and Alzheimer disease: This list included several proteins that are explicitly linked to AD, including Aβ A4, adenosylhomocysteinase (AHCY), apolipoprotein (APO) E, A and C, cathepsin D, choline O-acetyltransferase, neuroendocrine protein 7B2, nicotinamide phosphoribosyltransferase (NAMPT), and presenilin 2 (Table 1).