APOE and Alzheimer disease: Among an increasing number of genes implicated in AD, the APOE‐ε4 allele confers the strongest and most often replicated risk of AD; while the APOE‐ε2 allele appears to be protective (Corder et al., 1993, 1994; Holtzman, Herz, & Bu, 2012; Strittmatter et al., 1993).