Prion diseases are a group of rare, progressive neurodegenerative disorders 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 prion diseases include Creutzfeldt-Jakob disease, Bovine Spongiform Encephalopathy (commonly known as "mad cow disease"), and Kuru. Prion diseases are transmissible, meaning they can spread between individuals, often through contaminated tissue or medical procedures. Symptoms typically include memory loss, personality changes, and coordination difficulties. There is currently no cure, and the diseases are usually fatal within months to a few years after onset.