Evidence supports the idea that when PrP-sen comes into contact with PrP-res it is converted to PrP-res. The result is a chain reaction that multiplies copy after copy of the infectious prion. Because of their abnormal shape, PrP-res proteins tend to stick to each other. Over time, the PrP- res molecules stack up to form long chains called “amyloid fibers”. Amyloid fibers are toxic to cells, and ultimately kill them. Cells called astrocytes crawl through the brain digesting the dead neurons, leaving holes where neurons used to be. The amyloid fibers remain. As this process progresses, we begin to see the unique features that characterize all spongiform diseases: * Clumps of amyloid fibers (too small to see here) * Holes in the brain * Large numbers of astrocytes Prion disease represents a group of conditions that affect the nervous system in humans and animals. In people, these conditions impair brain function, causing changes in memory, personality, and behavior; a decline in intellectual function (dementia); and abnormal movements, particularly difficulty with coordinating movements (ataxia). The signs and symptoms of prion disease typically begin in adulthood and worsen with time, leading to death within a few months to several years. 9
The History of Prions 1730s Earliest written record of Scrapie in English sheep; already prevalent in central Europe. 1950s High levels of kuru ( appearance of a disease which means "trembling in fear." ) appear among the Fore people of New Guinea. ( victims of kuru lost the ability to swallow or chew. Drastic weight loss would inevitably lead to death. ) 1960s Scientists experimentally transmit Kuru and CJD to chimpanzees, demonstrating the transmissible nature of these diseases. 1980s 60 people die from CJD after being infected by contaminated surgical instruments. 85 people die after receiving prion-infected growth hormone injections. 1982 Dr. Stanley Prusiner coins the term "prion" (PROteinaceous INfectious particle). Highly purified PrP-res is shown to be infectious. He goes on to win the Nobel Prize in Medicine in 1997. 1985 Scientists identify the PrP gene and discover that uninfected people produce a normal form of the PrP protein. 11
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