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Human prion diseases may be sporadic, genetic, or acquired. The human prion protein gene (PRNP) is located to chromosome 20 (20p12-ter). Mutations and polymorphisms in the PRNP are associated with prion disease. Genetic prion diseases are inherited in an autosomal dominant trait, examination of the penetrance is restricted to mutation E200K (59-89%). Mutations can be substitutions or insertions. Genetic prion diseases are classified according to the clinicopathological phenotype and comprise genetic Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker disease and fatal familial insomnia. Base pair insertions may resemble Creutzfeldt-Jakob disease or Gerstmann-Sträussler-Scheinker disease phenotypes, however, their unique clinicopathological presentations are also emphasized. Among the polymorphisms of the PRNP, the one at codon 129 is the most important, where methionine or valine may be encoded. This polymorphism is known to influence the phenotype of disease forms. Molecular classification of sporadic Creutzfeldt-Jakob disease also depends on the codon 129 polymorphisms in addition to the Western blot pattern of the protease resistant prion protein. According to this at least six well characterised forms of sporadic Creutzfeldt-Jakob disease are known. Influence of other genes were also investigated. Contrasting results are reported regarding the role of apolipoprotein E allele epsilon4, but presence of allele epsilon2 seems to influence the prognosis. Polymorphisms in the doppel gene or ADAM10 could not be clearly associated with Creutzfeldt-Jakob disease. Polymorphisms in the upstream and intronic regulatory region of the PRNP gene may be a risk factor for Creutzfeldt-Jakob disease. The PRNP codon 129 polymorphism was examined in non-prion diseases. Some studies suggest that this polymorphism may have influence on the cognitive decline and early onset Alzheimer's disease. |
