PRNP and scrapie: After intracerebral (i.c.)administration of 3 x 105 ID50 units of prions (Rocky Mountain Laboratory strain, passage 6, henceforth denoted RML), both wt and Tg(MoPrP169F) mice developed signs of scrapie with similar latencies (Fig 2A), whereas Prnp-/- mice died of intercurrent disease without developing scrapie.