PRNP and variant Creutzfeldt-Jakob disease: To investigate if PRNP point mutations would affect the propagation of vCJD prions and expression of characteristic pathology, we challenged Tg27, Tg23 and Tg49 transgenic mice (all of which are homozygous for 129M) with a previously characterized vCJD isolate designated I336 (Tables 2, 4 and 5).