Molecular biology and pathogenesis of prion diseases

Prions cause a group of human and animal neurodegenerative diseases, which are now classified together because their etiology and pathogenesis, involve modification of the prion protein (PrP)(1). Prion diseases are manifest as infectious, genetic and sporadic disorders. These diseases can be transmitted among mammals by the infectious particle designated 'prion'(2). Despite intensive searches over the past three decades, no nucleic acid has been found within prions(3,4); yet a modified isoform of the host-encoded PrP designated PrPSc is essential for infectivity(1,5-8). In fact, considerable experimental data argue that prions are composed exclusively of PrPSc. Earlier terms used to describe the prion diseases include transmissible encephalopathies, spongiform encephalopathies and slow virus diseases(9). The human prion disorders include kuru, Creutzfeldt-Jakob disease (CJD), Gerstmann-Straussler-Scheinker syndrome (GSS) and fatal familiar insomnia (FFI).