Strict controls have been in place since 1996 to prevent BSE entering the human food chain, and the use of meat-and-bone mix has been made illegal. The prion then ended up in processed meat products, such as beef burgers, and entered the human food chain. In 2000, a government inquiry concluded that the prion was spread through cattle that were fed meat-and-bone mix containing traces of infected brains or spinal cords. There's clear evidence that variant CJD (vCJD) is caused by the same strain of prions that causes bovine spongiform encephalopathy (BSE, or "mad cow" disease). Sporadic CJD is more likely to occur in people who have specific versions of the prion protein gene.Īt present, nothing else has been identified that increases the risk of developing sporadic CJD. It's not known what triggers sporadic CJD, but it may be that a normal prion protein spontaneously changes into a prion, or a normal gene spontaneously changes into a faulty gene that produces prions. Sporadic CJDĮven though sporadic CJD is very rare, it's the most common type of CJD, accounting for around 8 in every 10 cases. But the reason why this happens is different for each type. The different types of CJD are all caused by a build-up of prions in the brain. Prions can survive in nerve tissue, such as the brain or spinal cord, for a very long time, even after death. The damage to the brain causes the mental and physical impairment associated with CJD, and eventually leads to death. Prion infections also cause small holes to develop in the brain, so it becomes sponge-like. This causes the brain cells to die, releasing more prions to infect other brain cells.Įventually, clusters of brain cells are killed and deposits of misfolded prion protein called plaques may appear in the brain. Prions are misfolded prion proteins that build up in the brain and cause other prion proteins to misfold as well. Normally, these misfolded prion proteins are recycled by the body, but they can build up in the brain if they aren't recycled. Mistakes sometimes occur during protein folding and the prion protein can't be used by the body. The exact role of normal prion proteins is unknown, but it's thought they may play a role in transporting messages between certain brain cells. Normal (harmless) prion proteins are found in almost all body tissues, but are at the highest levels in brain and nerve cells. This "protein folding" allows them to perform useful functions within our cells. They begin as a string of amino acids that then fold themselves into a 3-dimensional shape. Proteins are molecules made up of amino acids that help the cells in our body function. Creutzfeldt-Jakob disease (CJD) is caused by an abnormal infectious protein in the brain called a prion.
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