Of the three alleles of apolipoprotein E (APOE) (Mahley, 1988; Mahley and RallJr, 2000), APOE4 is the single most important genetic risk-factor for AD (Corder et al., 1993; Farrer et al., 1997; Bu, 2009; Liu et al., 2013). Here, APOE is linked to Alzheimer disease.