[The mystery of prion proteins: from neurodegenerative diseases to the biology of reproduction].

Human prion diseases are rare neurodegenerative diseases, due to proteinaceous infectious particles, named prions. The most frequent of these rare diseases is Creutzfeldt-Jakob disease, which can be sporadic, inherited or acquired (iatrogenic or variant). The diagnosis is based on the post mortem examination of the brain. During the life of the patient, neuronal markers may be detected in CSF, the prion protein gene PRNP may be screened for pathogenic mutations linked to inherited prion disease forms, and the pathogenic prion protein may be evidenced in the tonsils of patients affected with the variant form of the disease. The agent responsible of the disease is still imperfectly known, and the recent discovery of the "prion like" proteins did not help at this point to elucidate the mystery.