DISEASES TRANSMISSIBLE BY NONCONVENTIONAL AGENTS - NOSOLOGY AND DIAGNOSIS

Transmissible non conventional agents are currently called ''Prions''. This is not a neutral terminology: the attractive Prion hypothesis (t he infectious agent being a protein able to replicate in the absence o f DNA or RNA) due to Stanley Prusiner is the prevalent one, and has sh own to be heuristic, but has not been formally proven and does not eas ily explain all the data, unless modified and expanded. No simple acco unt has been given for the very unusual physical, chemical, and biolog ical properties of non conventional agents. These infectious agents ar e associated with degenerative diseases of the nervous system that are either the consequence of a genetic mutation or develop spontaneously in apparently normal individuals, and then can be transmitted to vari ous susceptible hosts, including man. Thus, non conventional agents ca nnot be considered only as fascinating biological enigmas. They consti tute a challenge for public health. The changing characteristics of pr ion-associated diseases has led to a renewing of their clinical and ne uropathological diagnostic criteria. A brief survey of the nosology an d neuropathology of prions diseases, with emphasis on new data and on difficulties, is provided. A simple classification based on the famili al, sporadic or infectious variety of the disease is suggested. Famili al diseases can be named according to the genetic disorder. Sporadic a nd infectious diseases can be classified following the main clinical s ymptoms and signs, and the presence or absence of amyloid plaques in t he brain, until new tools (analysis of the glycosylation pattern of Pr P, strain recognition) allow a more precise nomenclature. The new epid emiology of Prion disorders allowed by these new approaches relies on a full study of Prion diseases affected patients, which necessarily in volves their genetic study, and the analysis of brain tissue. This, fo r practical and ethical reasons, is better achieved by autopsy.