APOE and Alzheimer disease: Many studies have reported epigenetic changes in the brains of AD patients, for example, changes in DNA methylation levels in COASY, SPINT, BRCA1, and PLD3 promoter regions, APOE CpG islands and HOXA gene clusters, an overall reduction in DNA methylation in the cortex and hippocampus, increased histone deacetylase (HDAC) 6, decreased class III HDACs, changes in miRNAs (miR-29 family, miRNA-7, miRNA-9-1, miRNA-23a/miRNA-27a, miRNA-34a, miRNA-125b-1, miRNA- 146a, and miRNA-155) and long noncoding RNA (BC200 RNA) levels in the AD brain.