PRNP and Alzheimer disease: One study found that the soluble Aβ assemblies derived from the brains of individuals with AD interacted with PrPC at the postsynaptic density to activate the Src kinase Fyn, which phosphorylates the NR2B subunit of NMDA receptor and causes a transient increase in NR2B on the cell surface with consequent excitotoxicity while rendering the destabilization of dendritic spines.