PRNP and neurodegenerative disease: Remarkably, disease transmission of brain extracts from Tg animals overexpressing the P101L mutation neither occurred to wild-type nor to Tg mice expressing MoPrP-P101L from two transgene copies that do not develop disease spontaneously in their natural lifespan [27], which is in full agreement with a previous study from Manson's group showing that PRNP gene-targeted 101LL mice expressing MoPrPP101L failed to develop the neurodegenerative disease spontaneously [28].