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Etiology and pathogenesis of prion diseases.

Prions are self-propagating proteinaceous infectious agents capable of transmitting disease in the absence of nucleic acids. The nature of the infectious agent in prion diseases has been at the center of passionate debate for the past 30 years. However, recent reports on the in vitro generation of prions have settled all doubts that the misfolded prion protein (PrPSc) is the key component in propagating infectivity. However, we still do not understand completely the mechanism of prion replication and whether or not other cellular factors besides PrPSc are required for infectivity. In this article, we discuss these recent reports under the context of the protein-only hypothesis and their implications.

Identification of scrapie prion protein-specific mRNA in scrapie-infected and uninfected brain.

Prions are proteinaceous infectious particles, formed when normal proteins misfold and clump together. Biochemists Byron Caughey of the National Institute of Allergy and Infectious Diseases and Peter Lansbury of Brigham and Women’s Hospital were among the first to explore the analogy between Vonnegut’s ice-nine and prions in their 1995 review of scrapie, an infectious and deadly neurological disease of sheep. Like ice-nine, the particles that spread scrapie consist of highly stable crystals of a normally innocuous material found in the brains of sheep. Crystalline clumps of a misfolded version of this protein coax other molecules of the same protein to fold into the aberrant conformation. The process continues until virtually all of that protein in a cell or tissue has been converted to prions. In the case of scrapie and other mammalian prion diseases, the consequence of this self-amplifying cycle is an accumulation of toxic clumps of proteins that destroys neurons and invariably kills the organism.

Molecular neuropathology of prion diseases.

The chilling similarity between the modus operandi of ice-nine and prions is an apt illustration of the long-standing and well-deserved reputation of prions as catastrophic agents. Researchers are identifying more and more cases of prion-like protein misfolding that cause neurodegenerative diseases.

But a different side of prions is also coming to light. Many newly discovered prions and prion-like proteins do not appear to cause disease at all. On the contrary, some even protect against it. Still other prions are turning out to be key players in basic biological processes. (See .) These discoveries are driving a new appreciation for prions as versatile components in the machinery of life, a paradigm that has fostered conceptual advances in fields as diverse as signal transduction, memory formation, and evolution.

It's typicalof the priondiseases.

The protein that prions are made of (PrP) is found throughout the body, even in healthy people and animals. However, PrP found in infectious material has a different and is resistant to , the enzymes in the body that can normally break down proteins. The normal form of the protein is called PrP, while the infectious form is called PrP — the refers to 'cellular' PrP, while the refers to '', the prototypic prion disease, occurring in sheep. While PrP is structurally well-defined, PrP is certainly and defined at a relatively poor level. PrP can be induced to fold into other more-or-less well-defined isoforms in vitro, and their relationship to the form(s) that are pathogenic in vivo is not yet clear.

A systematic search of the Brookhaven data bank did not lead to the identification of other proteins with folds similar to PrP(121-231), and the relative orientation of the three helices in PrP(121-231) is clearly different from the proposed four-helix-bundle models. Mapping onto the three-dimensional structure of PrP(121231) of sequence variability in mammalian prion proteins of residues important for the species barrier of prion disease transmission and for predisposition to familial prion diseases, and of biochemical properties of the prion proteins shows the following:

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  • Prion diseases of human and animals.

    There are about 17,000 cases of primary malignant brain tumors in the US yearly; the majority prove fatal.

  • Regional mapping of prion proteins inbrain.

    Replication of distinct scrapie prion isolates is region specific in brains of transgenic mice and hamsters.

  • * Rocky Mountaindeer and elk have an epidemic prion disease.

    Abnormal isoform of prion protein accumulates in folliculardendritic cells in mice with Creutzfeldt-Jakob disease.

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GERSTMANN-STRÄUSSLER DISEASE is another hereditary prion disease.

Like other infectious particles, such as bacteria and viruses, prions can spread from one organism to another. Oral uptake is the most common natural form of transmission. Humans have also become infected through blood transfusions, human hormone injections, and surgery with contaminated instruments. Prions exhibit different variants, or strains, each with distinct molecular features and clinical manifestations. But what most fascinates scientists and the public alike is that, in contrast to viruses and all living organisms, prions lack the canonical information-storage molecules—DNA and RNA—yet are still able to copy and transmit biological information.

What's more, occasionally there ISa primary cause.

if [mice devoid of PrP] succumb to the disease or propagate infectivity, albeit without showing symptoms of neurological disease, the protein only hypothesis would be falsified.

Risk factors for brain tumors are, for the most part, obscure.

The idea that proteins could act in a manner previously ascribed only to nucleic acids was greeted with skepticism and ridicule when it was first championed by Stanley Prusiner in 1982. Even today there are those who maintain that prion diseases are actually caused by viruses. But as often seems to be the case in scientific discourse, what was once heretical is now dogma. The “protein-only” hypothesis, which posits that a string of amino acids is sufficient for disease transmission, steadily gained acceptance and, in the last three years, achieved irrefutable status when Jiyan Ma of Ohio State University College of Medicine and colleagues generated bona fide infectious particles from recombinant prion proteins.

In adults, 70% of primary brain tumors are supratentorial.

Prions are proteinaceous infectious particles, formed when normal proteins misfold and clump together. Biochemists Byron Caughey of the National Institute of Allergy and Infectious Diseases and Peter Lansbury of Brigham and Women’s Hospital were among the first to explore the analogy between Vonnegut’s ice-nine and prions in their 1995 review of scrapie, an infectious and deadly neurological disease of sheep. Like ice-nine, the particles that spread scrapie consist of highly stable crystals of a normally innocuous material found in the brains of sheep. Crystalline clumps of a misfolded version of this protein coax other molecules of the same protein to fold into the aberrant conformation. The process continues until virtually all of that protein in a cell or tissue has been converted to prions. In the case of scrapie and other mammalian prion diseases, the consequence of this self-amplifying cycle is an accumulation of toxic clumps of proteins that destroys neurons and invariably kills the organism.

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