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Faulty proteins in your brain known as prions cause CJD. Proteins are chemical molecules that need to hold a specific shape to work (like how a lock opens for a key with the right shape).

Your cells can’t use proteins when they aren’t the right shape, and your body can’t break them down. With nowhere to go, those proteins slowly build up in your brain cells (neurons), ultimately damaging and destroying the neurons. When your body makes faulty proteins for any reason, those misshapen proteins can cause degenerative brain diseases, like Alzheimer’s disease.

But prion-based diseases have a key difference. Instead of a slow build-up of faulty proteins, prions convert normal proteins into more prions. As the number of prions grows, they turn more proteins into prions. The more prions there are, the faster the conversion happens. That’s why CJD goes from mild behavior changes to severe symptoms so quickly.

Prions are also dangerous because they’re more resilient than most microbes. Cooking temperatures don’t destroy prions like viruses or bacteria. Your immune system can’t stop prions, so there’s no way to develop an immunity to CJD or a vaccine to prevent it.

Types of CJD

Proteins can turn to prions in your body for multiple reasons. The different reasons are what determine the type of CJD you have. The different types are:

  • Sporadic CJD. This is the most common kind of CJD, making up about 85% to 90% of cases. It happens for unknown reasons.
  • Genetic CJD. This type happens because of a genetic mutation you inherit from one or both parents. It ranks second among the most common causes, making up between 10% and 15% of CJD cases.
  • Acquired CJD. This is CJD you “acquire” from various sources, such as medical procedures like organ or tissue transplants and grafts, contaminated surgical equipment, etc.
  • Variant CJD (vCJD). This happens after eating beef from a cow with bovine spongiform encephalopathy (BSE), another disease that happens because of prions. Prions that affect beef cattle with BSE can then pass it to humans and other species, causing vCJD.

Genetic CJD conditions

There are two specific genetic forms of CJD:

  • Gerstmann-Sträussler-Scheinker (GSS) syndrome. This condition is extremely rare and affects between 1 and 10 people out of every 100 million worldwide.
  • Fatal familial insomnia. This condition is even rarer than GSS syndrome. Researchers have only confirmed about two dozen cases.


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