The major success to emerge from these studies was perhaps the identification of SNP markers linked to the ApoE-ɛ4 allele as a risk factor for AD, hence replicating the association of the ApoE-ɛ4 allele with AD originally proposed long before the advent of the genomic era (Corder et al., 1993; Coon et al., 2007; Bertram and Tanzi, 2009). The gene discussed is APOE; the disease is Alzheimer disease.