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Prion diseases are a related group of rare, fatal brain diseases that affect animals and humans. Also known as transmissible spongiform encephalopathies (TSE). They include bovine spongiform encephalopathy (BSE, or "mad cow" disease) in cattle; Creutzfeldt-Jakob disease (CJD) in humans; scrapie in sheep; and chronic wasting disease (CWD) in deer and elk. The brain disorders are characterized by tiny holes that give the brain a "spongy" appearance. These holes can be seen when brain tissue is viewed under a microscope.
BSE ("mad cow" disease)
Creutzfeldt-Jakob disease (CJD)
Fatal familial insomnia (FFI)
Variant CJD (vCJD)
Research suggests that TSEs are caused by an abnormal version of a protein called a prion (prion is short for proteinaceous infectious particle). Prion proteins occur in both a normal form, which is a harmless protein found in the body's cells, and in an infectious form, which causes disease. The harmless and infectious forms of the prion protein are nearly identical, but the infectious form takes on a different folded shape from the normal protein.
Human TSEs can occur three ways: sporadically; as hereditary diseases; or through transmission from infected individuals. Sporadic TSEs may develop because some of a person's normal prions spontaneously change into the infectious form of the protein and then alter the prions in other cells in a chain reaction. Inherited cases arise from a change, or mutation, in the prion protein gene that causes the prions to be shaped in an abnormal way. This genetic change may be transmitted to an individual's offspring. Transmission of TSEs from infected individuals is relatively rare. TSEs cannot be transmitted through the air or through touching or most other forms of casual contact. However, they may be transmitted through contact with infected tissue, body fluids, or contaminated medical instruments. Normal sterilization procedures such as boiling or irradiating materials do not prevent transmission of TSEs.
Symptoms of TSEs vary, but they commonly include personality changes, psychiatric problems such as depression, lack of coordination, and/or an unsteady gait. Patients also may experience involuntary jerking movements called myoclonus, unusual sensations, insomnia, confusion, or memory problems. In the later stages of the disease, patients have severe mental impairment and lose the ability to move or speak.
There is currently no treatment that can halt progression of any of the TSEs. Treatment is aimed at alleviating symptoms and making the patient as comfortable as possible.