A method for the diagnosis or prognosis of Alzheimer's disease (AD), includes the steps of placing a sample isolated from a person suspected of having AD onto a substrate labeling the sample to identify at least one epigenetic marker and/or genetic variation and determining a state of AD. One of the epigenetic markers is PM20D1 promoter DNA methylation and/or one of the genetic variation is in at least one of PM20D1 mQTL-associated SNPs. PM20D1 is used as a therapeutic target and viral vectors encoding PM20D1 are used in the therapy of AD. Moreover, a kit for diagnosing AD includes reagents for detecting the SNPs rs708727, rs947211, rs708730, rs708724 or rs823130.