APOE and early-onset autosomal dominant Alzheimer disease: The alleles account for six genotypes: APOE ε2/ε2, ε3/ε3, ε4/ε4, ε2/ε3,ε2/ε4 andε3/ε4) (2).The APOE gene polymorphism is closely associated with Alzheimer’s disease (AD), the APOE ε2 allele is considered the most potent protective factor against AD (3, 4).