BACE1 and Alzheimer disease: Protein expression of BACE1 is increased in the brains of patients with AD and transgenic AD mice (Yang et al., 2003; Li et al., 2004; O’connor et al., 2008), and there is no corresponding increase in BACE1 gene transcription (Holsinger et al., 2002; Preece et al., 2003).