APOE and Alzheimer disease: They mainly investigated the DNA methylation and histone modification differences between AD cases and unaffected controls using candidate gene or genome-wide analysis approaches (e.g., pyrosequencing and array hybridization) which revealed AD-associated epigenetic modifications in some well-known AD genes, such as amyloid-β precursor protein (APP), Microtubule Associated Protein Tau (MAPT) [14], and Apolipoprotein E (APOE) [15], as well as in other genes [12].