[Human spongiform encephalopathies. Diseases caused by prions]

Spongiform encephalopathies or prion diseases are common denominators for a group of diseases, all fatal, which show characteristic neuropathological changes. In man the group includes four diseases: kuru, Creutzfeldt-Jakob's disease (CJD), Gerstmann-Sträussler-Scheinker's disease (GSS) and fatal familial insomnia (FFI). In animals it comprises the following six: scrapie (sheep and goats), transmissible mink encephalopathy (mink), chronic wasting disease (mule/elk), exotic ungulate encephalopathy (antelopes) and feline and bovine spongiform encephalopathy (cats and cattle). The diseases can be transmitted to other animal species, including mice, hamsters, rats, monkeys and chimpanzees. The diseases show common histopathological changes in both animals and man, which are restricted to the CNS, in none of them are there signs of an inflammatory process or fever, and the cellcount in the CSF is normal. Disease symptoms are characterized by loss of higher levels of brain functions resulting in dementia and ataxia as the most pronounced symptoms. All prion diseases are associated with accumulation of an abnormal, partially proteinase-resistant isoform of a host-coded protein, the prion-protein (PrP), which is a cell surface sialoglycoprotein of unknown significance. PrP is highly conserved among mammals and is expressed in most tissues. Diseases caused by prions are exceptional as they can occur sporadically and are transmissible both genetically and infectiously. This review attempts to elucidate the present knowledge of the natural history of these diseases in man.