The APOE ε2 allele (encoded by the rs7412 SNP) is protective for incident Alzheimer’s disease, the APOE ε4 allele (encoded by rs429358) increases risk, and together the interplay between these two SNPs exerts an important influence on genetic susceptibility to Alzheimer’s disease [16, 17]. Here, APOE is linked to early-onset autosomal dominant Alzheimer disease.