[Human prion diseases]

Prion diseases are rare neurodegenerative transmissible fatal diseases affecting humans and mammals. The causative agent is a novel pathogen termed the prion. Unlike classical infectious agents such as bacteria or viruses, prions lack an independent genome and consist largely of an abnormal form of the host-encoded prion protein. Creutzfeldt-Jakob disease (CJD) is the main representative of human prion diseases that may be sporadic in most cases, hereditary, or acquired. Clinical examination yields only a suspected diagnosis with formal criteria for probable or possible. Definite diagnosis relies on autopsy and neuropathology findings. This is also true for the new variant CJD (vCJD), a previously unknown prion disease of humans that is connected with the same strain of prions as found in bovine spongiform encephalopathy (BSE). The autopsy and handling of laboratory material for histopathological examination requires specific precautionary measures and decontamination. For definite histopathological diagnosis of a human prion disease, immunohistochemical detection of the prion protein deposits is the gold standard. Furthermore, molecular and genetic investigations are necessary for classification because a close correlation could be established between distinct CJD phenotypes, codon 129 genotypes of the prion protein gene, and the prion protein type.