XPNPEP1 and neurodegenerative disease: Although Xpnpep1−/− mice exhibit neurodegenerative cell death and vacuolation in the hippocampal CA3 region, glial alterations in the Xpnpep1−/− hippocampus were quite different from those observed in common neurodegenerative diseases in that the density of astrocytes and expression levels of GFAP were reduced in the Xpnpep1−/− hippocampus, while the density of microglia was increased specifically in the CA3 subfields.