The elegant seminal experiments of grafting neural tissue overexpressing PrPC into the brain of PrP-deficient mice (Prnp0/0) demonstrated not only that after prion infection (scrapie RML strain), only the grafts were destroyed with PrPsc toxic accumulation but also that surrounding tissue devoid of PrPC remained healthy despite the diffusion of PrPsc aggregates from the grafts (Brandner et al., 1996). The gene discussed is PRNP; the disease is scrapie.