PSEN1 and Alzheimer disease: In summary, DNA methylation changes are present in AD-related genes; some of these genes are hypermethylated (MTHFR, Neprilysin, MAPT, APOE, SORB3), while others have been found to be hypomethylated (APP, BACE, PSEN1, PP2A, S100A2, CREB5) [14,17].