[Prion diseases].

Prion is an ubiquitous membrane protein in mammals, which is mainly synthesized in central nervous system. Prion diseases are the result of an accumulation of prions having acquired a resistance to the physiological degradation and an infectious capacity. Human prion diseases are very rare diseases including sporadic Creutzfeldt-Jakob disease (the most frequent form manifesting as a presenile dementia), familial transmissible spongiform encephalopathies and two juvenile transmissible forms: iatrogenic Creutzfeldt-Jakob secondary to treatment with human extractive growth hormone and variant Creutzfeldt-Jakob disease resulting from bovine spongiform encephalopathy food transmission. Knowledge of the underlying prion biology has led to preventive measures which offer today a reasonable guarantee against the juvenile forms.