Anticipating advances in genome-wide analysis, candidate gene studies conducted in AD patients and control subjects have compared the frequency of genetic variants and identified the protein-coding genes of the amyloid-β precursor protein (APP), and the subunits PS1 and and PS2 of presenilins (PSEN1, PSEN2), and ApoE [32,33] as important susceptibility factors for AD. This evidence concerns the gene APOE and Alzheimer disease.