APOE and Alzheimer disease: Of the three major APOE allelic variants, epsilon (ε) 2, ε3 and ε4, APOE ε4 is associated with an increased risk, while APOE ε2 has been reported as having a protective effect over the risk of AD (Saunders et al., 1993; Corder et al., 1994; Farrer et al., 1997; Liu et al., 2013).