The 3xTg-AD mice exhibited a low enrichment of H3K9bhb on the promoters of NMDA receptor subunits and Syn1 and axon-related genes together with impaired synaptic plasticity, all of which were rescued by 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2, a rate-limiting enzyme of β-OHB synthesis) upregulation. This evidence concerns the gene HMGCS2 and Alzheimer disease.