In this study, we set out to examine the levels of neuronal DNase II and cytoplasmic damaged DNA in the brains of WT mice, Tau-P301S mice and AD patients, explore the roles of neuronal DNase II and cytoplasmic damaged DNA in tau phosphorylation, neuronal apoptosis and mouse cognition, and investigate the therapeutic effect in vivo by increasing DNase II expression. The gene discussed is MAPT; the disease is Alzheimer disease.