[Prion diseases. The "prion" a remarkable infectious agents].

Prion diseases are a set of brain degenerative syndromes developed by many mammals. The epidemiological characteristics are remarkable, the origin of the disease is either infectious, genetics or sporadic. A protein synthesised by the host, the so-called prion protein (PrP), seems to be both the etiologic agent and it is also responsible for the induced pathology. This protein is found under two very different conformations. The normal cellular form (PrPC) is alpha-helix rich while the pathological (PrPSc) conformation is mainly composed of beta-sheet structures and resist proteinase-K attack. The conversion of the PrPC isoform to a structure resisting to proteinase-K has been demonstrated in vitro. In order to understand these phenomena, physico-chemical models have been proposed.