Fundamentals of prion biology and diseases.

One of the most remarkable changes in medicine during the last 20 years of the 20th century was the shift from the clinical-neuropathological classification of Creutzfeldt-Jakob disease (CJD) and related disorders as 'transmissible spongiform encephalopathies' to a molecular-etiologic classification as 'prion diseases'. We now know that these diseases are caused by abnormalities of the prion protein (PrP). Specifically, CJD is caused by the conversion of the normal, protease-sensitive PrP isoform, designated PrP(C), to a protease resistant isoform, designated PrP(Sc). PrP(Sc) forms into an infectious particle, named a 'prion', that can transmit the disease. Accumulation of PrP(Sc) in the brain causes neurodegeneration. The main goals of this review are to summarize our understanding of the attributes of the PrP molecule that give it the properties of an infectious agent and to describe how different alterations of the PrP molecule cause the multiple known prion disease variants. Finally, the emergence of a new variant of CJD in Great Britain and to a lesser extent in Europe and its relationship to the emergence of a particularly virulent form of bovine spongiform encephalopathy will be discussed.