Definition of Prion

Prion: A disease-causing agent that is neither bacterial nor fungal nor viral and contains no genetic material. A prion is a protein that occurs normally in a harmless form. By folding into an aberrant shape, the normal prion turns into a rogue agent. It then coopts other normal prions to become rogue prions.

Prions have been held responsible for a number of degenerative brain diseases, including scrapie (a fatal disease of sheep and goats), mad cow disease, Creutzfeldt-Jacob disease, fatal familial insomnia, kuru, an unusual form of hereditary dementia known as Gertsmann-Straeussler-Scheinker disease, and possibly some cases of Alzheimer's disease.

Dr. Stanley B. Prusiner received the 1997 Nobel Prize in Physiology or Medicine for his discovery of prions. See also: Prusiner, Stanley B..