APOE and Alzheimer disease: APOE ε4 confers the highest known genetic risk for developing sporadic AD in older age, with 30%–60% of those diagnosed with AD carrying 1 or 2 copies of the APOE ε4 allele (Myers et al., 1996, Sando et al., 2008, Saunders et al., 1993, Winblad et al., 2016).