PRNP and Alzheimer disease: However, a subsequent report found no effect on Aβ or APP levels when the PrP gene (Prnp) was deleted from an AD mouse model that expresses APPswe and the exon 9 deletion of presenilin-1 (PS-1ΔE9), although they did find that synaptic degeneration was reduced and spatial memory was better preserved compared with the parental line4, suggesting a disease-enhancing effect of PrPC.