Previous methylome profiling studies, however, on purified neural cell populations [95] as well as in hundreds of bulk brain tissue samples [107,108,109] of AD patients, did not bring conclusive evidence to support epigenetic dysregulation in the gene body and/or the promoter regions of other key AD genes involved in the formation of neurofibrillary tangles (GSK3B, MAPT) and regulating the production of Aβ peptide (BACE1, PSEN1, PSEN2). Here, PSEN2 is linked to Alzheimer disease.