[Prion diseases--general aspect]

Prion diseases are characterized by the accumulation of prion protein(PrP) with abnormal configuration in the brain. PrP itself is a host gene-encoded glycoprotein composing cell membrane, and the PrP detected in prion diseases is its isoform. The function of normal PrP is not fully understood but may play a preventing role in the cell death mechanism. In human, prion diseases are divided into two types, hereditary (autosomal dominant) type and sporadic one. In hereditary prion diseases, 16 different pathogenic mutations of the PrP gene have been discovered and each mutation exhibits distinguishable clinical pictures. In sporadic prion diseases such as Creutzfeldt-Jakob disease(CJD) the abnormal PrP is highly infectious. Although routes of transmission are not clarified in most CJD cases, there are reports of iatrogenic CJD and, recently, 14 cases of atypical CJD probably transmitted from bovine spongiform encephalopathy. The mechanism of replication of the abnormal PrP, however, remains unknown in CJD.