Prion << PREE ohn >> is a microscopic particle that causes a group of fatal brain disorders called prion diseases. The term prion is an abbreviation for proteinaceous infectious particle. Brain tissue damaged by prions appears spongelike and riddled with holes when viewed under a microscope. Prion diseases include Creutzfeldt-Jakob disease in human beings, mad cow disease in cattle, scrapie in sheep and goats, and chronic wasting disease in deer and elk.
Scientists have not yet fully determined the structure of prions. But the particles consist largely—and possibly entirely—of a protein called prion protein. Most proteins are large molecules with complex three-dimensional shapes. Prion protein in its normal shape occurs naturally in the brains of all mammals and birds. Disease-causing prions contain abnormally shaped forms of prion protein. The leading explanation for prion diseases is that once the misshapen protein enters the brain, it transforms normal brain protein to an abnormal shape. Newly formed, misshapen prion protein then transforms more normal protein until brain function is destroyed.
Disease-causing prion protein can enter the brain as an infectious agent from outside the body. Abnormal forms can also arise within the brain. The transformation may begin by itself or occur due to an error in a gene. Infectious prions are unique because they have no genes of their own. All other known infectious agents, such as viruses and bacteria, contain genetic material.
There is no cure for prion disease. Death usually results from pneumonia or other diseases after the loss of brain function weakens the victim. Scientists continue to conduct research on prions in hope of developing successful treatments or a cure.
