BACE1 and Alzheimer disease: It is worth noting that BACE1 protein levels, but not mRNA levels, remarkably increased in AD pathology (Holsinger, McLean, Beyreuther, Masters, & Evin, 2002; Yang et al., 2003), and BACE1 is also predominantly present in and plays roles in the endoplasmic reticulum, plasma membrane, and endosomes (Huse, Pijak, Leslie, Lee, & Doms, 2000).