When BSE and scrapie were examined for their capability to convert human PrP with the three major polymorphic variants (PRNP codon 129 MM, MV and VV) expressed in the humanized transgenic mouse brain [5, 17], cattle BSE prions was able to trigger the efficient conversion of human PrP with a preference similar to that of human vCJD (MM > MV > VV) while scrapie failed to convert the human substrates [17]. The gene discussed is PRNP; the disease is scrapie.