It is noteworthy that folic acid administration in mice protects against Aβ accumulation by enhancing DNMT1 methyltransferase activity in a dose-dependent manner and reducing PSEN1 and APP expression through methylation of their promoter regions [184], although the association of APP gene methylation with AD pathogenesis needs further validation, since several studies have reported non-significant changes [177,185]. Here, PSEN1 is linked to Alzheimer disease.