Minute micro-organism thought to cause some diseases of the nervous system.
(acronym for proteinaceous infectious particle) Exceptionally small microorganism, a hundred times smaller than a virus. Composed of protein, and without any detectable amount of nucleic acid (genetic material), it is thought to cause diseases such as scrapie in sheep, and certain degenerative diseases of the nervous system in humans. How it can operate without nucleic acid is not yet known.
Researchers at the University of California 1982 first identified high protein in infected cells, concluded the protein was the infected particle, and named it prion.
The prion remains controversial but German researchers 1992 showed that it could be linked to a naturally occurring protein PrP. Mice lacking the gene that encodes for this protein are not susceptible to scrapie. The PrP protein exists in two forms: the normal form found in all cells and an abnormal form found only in diseased brain cells.