PRNP and prion disease: Reconstituted Prnp0/0 mice by transgenic introduction of a mutant PrP with a deletion of the polybasic region residues 23–31, designated Tg(PrP∆23–31)/Prnp0/0 mice, were shown to develop prion disease with markedly elongated incubation times and delayed accumulation of PrPSc∆23–31 in their brains after inoculation with RML scrapie prions (Table 1) [63].