PRNP and Alzheimer disease: In vivo, 56-kD dodecameric assemblies of Aß1–42, dubbed Aß* (of note, PrP* has also been proposed as the biologically reactive form of PrP [25]), have been shown to be associated with memory deficits in a murine model of Alzheimer disease and to cause transient memory impairment after injection in the brains of rats [26].