In normal brain cells, a normal gene (the PRNP gene, on chromosome 20) produces a normal prion protein, PrPC. But in , this somehow changes into an abnormal protein, PrPSc. Either the loss of the normal protein or the accumulation of the abnormal protein, or both, leads to disease in the brain resulting in progressive and, eventually, fatal neurological disease. The trigger for the protein change is unknown. But there are two popular theories. Firstly, PrPC might, rarely, spontaneously change to PrPSc. Secondly, a copy of the PRNP gene in a brain cell might spontaneously mutate and produce abnormal PrPC, which then turns into PrPSc. While no environmental source has yet been identified, spCJD might result from infection. vis related to BSE in cattle. Scientific studies have shown that the agent strain that caused BSE in cattle is the same as that in vCJD. Secondly, there is strong evidence to suggest the agent is passed from cattle to man. There is no reasonable theory to suggest another source of infection that led to disease in both. The strongest (but unproven) theory is that infection passed from cattle to man in food, most probably in MRM (mechanically recovered meat) in cheaper, pre-prepared foodstuffs. Until 1995, it was permitted to use backbones in MRM. This posed the risk that the product could have contained potentially infective spinal cord tissue. There is currently no evidence that muscle from BSE cattle (that would be eaten as beef, steak, etc) poses a risk. A genetic mutation of the PRNP gene is inherited from one of the individual's parents. The abnormal gene produces a different form of PrPC, which then becomes PrPSc and causes disease. No other forms of are inherited. If you inherit one abnormal PRNP gene from both parents, then you will usually develop the disease. If you inherit the gene from only one of your parents, then you have a 50:50 chance of developing the disease. You also have a 50:50 chance of passing it on to your children. The individual is infected with PrPSc from someone with and this acquired PrPSc causes their normal PrPC to change into PrPSc. There are common and rare recognised means of infection. Common Human growth hormone (hGH) injections, ie human growth hormone extracted from human cadaver brain tissue and used in the treatment of short stature. This type of hGH has been replaced by synthetic hGH, which has no risk of contamination. Human dura mater grafts: dura mater is the tough membrane covering the brain which can be recovered from human cadavers and used as a patching material in some types of surgery.
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