Disease-causing agent, discovered by
An abnormal form of a normally harmless protein found in mammals and birds, the disease-causing prion can enter the brain through infection, or it can arise from a {{link=mutation">mutation in the gene that encodes the protein. Once present in the brain it causes normal proteins to refold into the abnormal shape. As prion proteins multiply, they accumulate within nerve cells, destroying them and eventually causing brain tissue to become riddled with holes. Diseases caused by prions include Creutzfeldt-Jakob disease , mad cow disease , and scrapie. Prions are unlike all other known disease-causing organisms in that they appear to lack nucleic acid (DNA or RNA).