APA Dictionary of Psychology

any of a group of fatal neurodegenerative diseases caused by self-replicating abnormal prion proteins in the brain. Symptoms include gait disturbance, lack of coordination, muscle tremors and jerks, and difficulty in swallowing. Human varieties include Creutzfeldt–Jakob disease, fatal familial insomnia, Gerstmann–Straussler–Scheinker syndrome, and kuru. Prion diseases are also known as spongiform encephalopathies because of the postmortem appearance of the brain.