Prions can be transmitted through contaminated food, surgical instruments and blood. Transmission of prions has caused the kuru epidemic in humans and bovine spongiform encephalopathy in cattle, which in turn has caused variant Creutzfeldt-Jakob disease in humans. Furthermore, injection of prion-contaminated hormones has caused hundreds of TSE cases.
In order to develop drugs to prevent the spread of prions into the brain after exposure via food or medical procedures, it is necessary to gain an understanding of how prions propagate from the site of entry to the brain. In the new study, the researchers tested whether prions in blood may enter the brain via blood vessels. To do so, they used genetically modified mice with a highly permeable blood-brain barrier -- a network of blood vessels and tissue that is made up of closely spaced cells and helps keep harmful substances from reaching the brain.
Both genetically modified and unmodified mice were similar in their survival rates after infection with prions. These surprising results suggest that passage of prions through the blood-brain barrier may not be relevant to the development of disease.
Scrapie is so named because the sheep scrape themselves against trees, fence posts, or other structures and tear their wool off. The disease causes sheep to behave in other bizarre ways, and it is fatal. Some of the newly formed prions resist being broken down by enzymes in the brain. Thus, they slowly accumulate. Prions also trigger other nearby PrP C to change into prions, and the process continues.
When prions reach a certain number, disease results. Prions never change back into normal PrP C. PrP C is present in all cells of the body but has a high concentration in the brain. Consequently, most prion diseases affect the nervous system predominantly or exclusively. The most common change caused by prions is the formation of tiny bubbles in brain cells, and the brain becomes filled with microscopic holes.
When samples of brain tissue are viewed through the microscope, they somewhat resemble Swiss cheese or a sponge hence, the term spongiform. After a period of time which can vary , the affected cells cease to function and die. Creutzfeldt-Jakob disease Creutzfeldt-Jakob Disease CJD Creutzfeldt-Jakob disease is a prion disease characterized by progressive deterioration of mental function, leading to dementia, involuntary jerking of muscles myoclonus , and staggering when Fatal insomnia Fatal Insomnia Fatal insomnia is a rare prion disease that interferes with sleep and leads to deterioration of mental function and loss of coordination.
Death occurs within a few months to a few years. Variably protease sensitive prionopathy Variably Protease-Sensitive Prionopathy VPSPr Variably protease-sensitive prionopathy is a prion disease that causes changes in mood and behavior, problems speaking, and impaired mental function.
See also Overview of Prion Diseases. Sporadic Creutzfeldt-Jakob disease is the most common type of the sporadic prion diseases. Worldwide, sporadic Creutzfeldt-Jakob disease occurs in about 1 in a million people each year. In sporadic prion diseases, how the first prion forms is unknown. But it is suspected that an error occurs in a cell's processes cell metabolism , and this error causes PrP C to spontaneously change its shape.
Familial prion diseases involve a mutation in the gene for PrP C , which can be inherited. The mutation makes PrP C more likely to change into prions. More than 50 mutations exist. Each mutation typically causes a different prion disease. Familial prion diseases are inherited as an autosomal dominant disorder Non—X-Linked Autosomal Inheritance Genes are segments of deoxyribonucleic acid DNA that contain the code for a specific protein that functions in one or more types of cells in the body.
Chromosomes are made of a very long strand That means that the mutation is not on the sex X or Y chromosomes and that only one gene for the disease, one from either parent, is required for the disease to develop. Familial Creutzfeldt-Jakob disease Creutzfeldt-Jakob Disease CJD Creutzfeldt-Jakob disease is a prion disease characterized by progressive deterioration of mental function, leading to dementia, involuntary jerking of muscles myoclonus , and staggering when Fatal familial insomnia Fatal Insomnia Fatal insomnia is a rare prion disease that interferes with sleep and leads to deterioration of mental function and loss of coordination.
The disease is fatal, usually in about 5 years Another familial prion disease has been recently discovered. It differs from other prion diseases because it causes diarrhea and affects nerves throughout the body years before symptoms of brain malfunction develop.
An epidemic of BSE among cows, dubbed 'mad cow disease', in Britain in the s, led to stringent controls on meat production and the use of surgical and dental instruments. Human cases of the disease, vCJD, were first seen in the mids. That sparked fears of a devastating human epidemic, but only around people have died from the disease since then, and cases have been tailing off.
But two recent surveys of tissue samples from removed appendixes suggest that as many as 1 in 4, people in the United Kingdom could be carriers 3 , 4. Science , Collinge, J. Hilton, D. Download references. You can also search for this author in PubMed Google Scholar.
Protein folding: The dark side of proteins Apr Prions jump species barrier Sep Prions' great escape Jul Prion disease: The shape of things to come Jan Prion research at INRA. John Collinge. Reprints and Permissions.
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