The identification of the ε4 allele of apolipoprotein E (APOE ε4) is a well-established genetic risk factor for both EOAD and LOAD [16], which has unfolded new findings of at least 21 extra genetic risk loci for the genetically complex form of AD, emerging from GWAS and massively parallel resequencing efforts. The gene discussed is APOE; the disease is Alzheimer disease.