A major breakthrough was made in the AD research field in 1993 when Allen D. Roses and colleagues first reported the strong genetic association of APOE ε4 with late-onset AD (LOAD), the most common form of the disease (representing 90–95% of AD cases) that does not involve a genetic cause and typically occurs in patients older than 65 years of age (Corder et al., 1993; Saunders et al., 1993; Strittmatter et al., 1993a; Roses, 2006). The gene discussed is APOE; the disease is Alzheimer disease.