Prion disease is a rare and fatal neurodegenerative disorder caused by misfolded proteins known as prions. These abnormal proteins induce other normal proteins in the brain to also misfold, leading to brain damage and severe neurological symptoms. Common types of prion diseases include Creutzfeldt-Jakob disease and Bovine Spongiform Encephalopathy, also known as "mad cow disease." Symptoms of prion disease can include memory loss, personality changes, and difficulties with movement and coordination. The diseases are typically progressive, meaning they worsen over time, and there is currently no cure. Diagnosis often involves brain imaging and analysis of cerebrospinal fluid.