The precise cause of sporadic CJD is unclear, but it's been suggested that a normal brain protein changes abnormally "misfolds" and turns into a prion. Most cases of sporadic CJD occur in adults aged between 45 and On average, symptoms develop between the ages of 60 and Since the link between variant CJD and BSE was discovered in , strict controls have proved very effective in preventing meat from infected cattle entering the food chain.
See preventing Creutzfeldt-Jakob disease for more information. But the average time it takes for the symptoms of variant CJD to occur after initial infection the incubation period is still unclear.
The incubation period could be very long more than 10 years in some people, so those exposed to infected meat before the food controls were introduced can still develop variant CJD. The prion that causes variant CJD can also be transmitted by blood transfusion , although this has only happened 5 times in the UK. Familial CJD is a very rare genetic condition where one of the genes a person inherits from their parent the prion protein gene carries a mutation that causes prions to form in their brain during adulthood, triggering the symptoms of CJD.
Strict controls have been in place since to prevent BSE entering the human food chain, and the use of meat-and-bone mix has been made illegal. Almost all definite cases of vCJD occurred in people with a specific version MM of the prion protein gene, which affects how the body makes a number of amino acids. It's estimated up to 4 in 10 of the UK population have this version of the gene. There have been no confirmed deaths from to Some experts believe that the food controls have worked and further cases of vCJD will continue to decline, but this doesn't rule out the possibility that other cases may be identified in the future.
It's also possible for vCJD to be transmitted by blood transfusion , although this is very rare and measures have been put in place to reduce the risk of it happening. We don't know how many people in the UK population could develop vCJD in the future and how long it'll take for symptoms to appear, if they ever will.
A study published in October that tested random tissue samples suggested around 1 in 2, people in the UK population may be infected with vCJD, but show no symptoms to date. Familial or inherited CJD is a rare form of CJD caused by an inherited mutation abnormality in the gene that produces the prion protein.
The altered gene seems to produce misfolded prions that cause CJD. Everyone has 2 copies of the prion protein gene, but the mutated gene is dominant.
This means you only need to inherit 1 mutated gene to develop the condition. As the symptoms of familial CJD don't usually begin until a person is in their 50s, many people with the condition are unaware that their children are also at risk of inheriting this condition when they decide to start a family.
Classic CJD is a human prion disease. It is a neurodegenerative disorder with characteristic clinical and diagnostic features. This disease is rapidly progressive and always fatal. Infection with this disease leads to death usually within 1 year of onset of illness. Creutzfeldt-Jakob disease CJD is a rapidly progressive, invariably fatal neurodegenerative disorder believed to be caused by an abnormal isoform of a cellular glycoprotein known as the prion protein.
Proteins are long chains of amino acids that have to fold together into a unique shape or conformation to gain function in the cells. Research findings indicate that the infectious prion originates from a normal protein whose conformation has changed to one that causes the disease. The normal prion protein is found throughout the body but is most abundant in the nervous system.
Its overall role is not fully understood. It is believed that the harmless to infectious protein conformational change is common to the all major forms of human prion disease, including CJD.
In the acquired form of the disease, the PrP Sc comes from the outside the body, for example, through contaminated meat as is seen in vCJD.
It then clings to and changes the conformation of the normal prion protein of the host and progressively spreads in domino-like fashion toward the brain where it causes lesions. As the mutated PrP C replicates itself, it spontaneously changes shape into the infectious form. Prions themselves do not contain genetic information and do not require genes to reproduce themselves.
Several different mutations in the prion gene have been identified. The particular mutation found in each family affects how frequently the disease appears and what symptoms are most noticeable. However, not all people with mutations in the prion protein gene develop CJD. In the sporadic form, the infectious prions are believed to be made by an error of the cell machinery that makes proteins and controls their quality.
These errors are more likely to occur with aging, which explains the general advanced age at onset of CJD and other prion diseases. Once they are formed, abnormal prion proteins aggregate, or clump together. Investigators think these protein aggregates lead to the nerve cell loss and other brain damage seen in CJD. However, they do not know exactly how this damage occurs. CJD cannot be transmitted through the air or through touching or most other forms of casual contact. Spouses and other household members of people with sporadic CJD have no higher risk of contracting the disease than the general population.
However, exposure to brain tissue and spinal cord fluid from infected persons should be avoided to prevent transmission of the disease through these materials. In some cases, CJD has spread to other people from grafts of dura mater a tissue that covers the brain , transplanted corneas, implantation of inadequately sterilized electrodes in the brain, and injections of contaminated pituitary growth hormone derived from human pituitary glands taken from cadavers.
Doctors call these cases that are linked to medical procedures iatrogenic cases. Since , all human growth hormone used in the United States has been synthesized by recombinant DNA procedures, which eliminates the risk of transmitting CJD by this route. Many people are concerned that it may be possible to transmit CJD through blood and related blood products such as plasma.
Some animal studies suggest that contaminated blood and related products may transmit the disease, although this has never been shown in humans.
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