Identification of Genetic Loci Affecting Mouse-adapted Bovine Spongiform Encephalopathy Incubation Time in Mice

Prion diseases are fatal neurodegenerative disorders of humans and animals, which include bovine spongiform encephalopathy (BSE) and its human form, variant Creutzfeldt-Jakob disease (vCJD). They are characterized by a prolonged incubation period, which is known to be influenced by polymorphisms in the prion protein gene. Previous studies of inbred mice have demonstrated that additional genetic loci also contribute to the observed variation in incubation period. However, a substantial transmission barrier between cow and mouse complicates studies using BSE. As a result, primary transmissions display large variations in incubation period and not all animals develop clinical signs of disease. To identify quantitative trait loci for BSE without the presence of a transmission barrier, we analysed 124 animals from an F2 intercross between CAST/Ei and NZW/OlaHsd mice and challenged them intracerebrally with a strain of BSE that was passaged twice through C57BL/6OlaHsd mice. Interval mapping identified two highly significant linked regions on chromosomes 2 and 11 with peak lod scores of 6.34 and 4.77, respectively. Composite interval mapping suggests that chromosome 2 includes three linked quantitative trait loci. Loci in the same position on chromosomes 2 and 11 were also identified in a previous study using the same mouse cross but infected with Chandler/RML scrapie prions. If these are the same loci, it suggests that these loci may be influencing incubation time independently of prion strain. This provides hope that it may be possible to identify human quantitative trait loci for prion incubation time using mouse models that may allow identification of at-risk individuals and the discovery of novel therapeutic targets.