APOE and Alzheimer disease: Two ABC transporters have been shown to play important roles in AD pathogenesis; (1) ABC transporter sub-family B member 1 (ABCB1; i.e., Multi Drug Resistance Protein; Mdr-1) that acts as an efflux pump of xenobiotic molecules, and (2) the ABC transporter sub-family A member 1 (ABCA1; i.e., Cholesterol Efflux Regulatory Protein; CERP) that acts as an efflux pump for cholesterol and phospholipids from cell membranes to Apolipoprotein E (ApoE) and ApoA-I (Wahrle et al., 2005; Kuhnke et al., 2007).