prion

1. (molecular biology) A self-propagating misfolded conformer of a protein that is responsible for a number of diseases that affect the brain and other neural tissue.Examples: "Prions retain deep mysteries, the foremost of which is what on earth they exist for."; "Five public research institutions in France have imposed a 3-month moratorium on the study of prions—a class of misfolding, infectious proteins that cause fatal brain diseases—after a retired lab worker who handled prions in the past was diagnosed with Creutzfeldt-Jakob disease (CJD), the most common prion disease in humans."