|MadSci Network: Neuroscience|
Lisa, you have asked an excellent question. Proteins are long linear chains of amino acids that fold up into specific shapes. Occasionally, proteins become folded into the wrong shapes. These misfolded proteins are unable to perform their natural functions in the body’s biochemical pathways. Usually this is harmless, and the body can do a little housekeeping to remove them, but in some cases, these misfolded proteins can actually cause damage. This is the case with Alzheimer’s disease. There is a protein found within neuronal cells called “amyloid beta.” The natural function of this protein is not well understood, but if this protein becomes misfolded, it can precipitate out of cellular solution. Essentially, the misfolded protein begins to form aggregates within and around brain cells. The aggregates build up and become the plaques that are found within the brains of Alzheimer’s patients. The damage to the brain cells caused by the plaques leads to the dementia that is so characteristic of Alzheimer’s disease. As people get older, the chance that their amyloid beta will become misfolded increases; therefore Alzheimer’s patients are primarily elderly. There are also inherited forms of Alzheimer’s disease in which an individual has a mutated form of amyloid beta that is much more prone to misfolding and the disease can strike at an early age. Alzheimer’s disease, however, is not contagious – it cannot be transmitted from one person to another. Creutzfeldt-Jakob disease (CJD) is one of a small group of fatal diseases caused by infectious agents called prions. The term prion comes from “proteinaceous infectious particle.” Prions are normal proteins that are misfolded. Unlike the amyloid beta protein, prions are infectious. In other words, if they are physically transported from one organism to another, the disease that they cause can be spread. Bovine spongiform encephalopathy (“mad cow disease,” another prion disease) was spread in Europe in the 1990’s when meat products from infected animals were fed to other animals. In another example, the prion disease kuru was spread among cannibalistic tribes in New Guinea when individuals ate the brains of others who were already infected with the disease. So to answer your question, you are correct in stating that both Alzheimer’s disease and CJD are caused by the same fundamental problem – misfolded proteins. But Alzheimer’s disease is not generally considered a prion disease because it is not infectious – it cannot be transmitted from one person to another. If you are interested in learning more about prion diseases, I found a good web page written by Stanley B. Prusiner who won the Nobel Prize for Medicine in 1997 for his pioneering research into prion diseases: http://www.nmia.com/~mdibble/prion.html I also found on this web page an excellent essay on protein folding: http://www.faseb.org/opar/protfold/protein.html
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