Prions in the Body and Human Disease

BSE, a prion disease, affects many different breeds of cattle. It can also trigger disease in humans.
BSE, a prion disease, affects many different breeds of cattle. It can also trigger disease in humans. | Source

Prions are misfolded proteins that can cause some very serious diseases in our bodies. Unfortunately, their formation and behaviour isn't completely understood. Researchers are trying to unlock the mysteries of these small but potentially deadly particles.

The normal proteins in our body are essential molecules with complex, folded shapes. The shape of a protein enables it to do its job. If a protein is folded incorrectly or becomes unfolded it can no longer function.

A prion (pronounced "preeon") is a misfolded protein with a special ability. It can change other protein molecules into prions. These can then alter the shape of even more proteins in a chain reaction.

Prions are the causal agents of some horrible illnesses known as prion diseases. These often progress rapidly once symptoms appear and (at the moment) are always fatal.

The most common prion disease is Creutzfeldt-Jakob disease, or CJD. A variant of this disease has appeared in people who have eaten contaminated meat from a cow suffering from bovine spongiform encephalopathy, or BSE. BSE is a prion disease in cattle. It's also known as Mad Cow disease.

Scientists have recently discovered that about 1 in 2000 apparently healthy people in the United Kingdom have prions in their body. The question that scientists cannot answer is whether these people will stay healthy or whether the prions will eventually trigger an illness. There is still a great deal to learn about these mysterious particles and their role in health and disease.

An illustration showing myoglobin (a muscle protein) and the complex, folded structure of a functional protein; the folds are held in place by chemical bonds
An illustration showing myoglobin (a muscle protein) and the complex, folded structure of a functional protein; the folds are held in place by chemical bonds | Source

Pathogens - Infectious Agents That Cause Disease

Most infections are caused by viruses, bacteria and fungi, including yeasts. Infectious agents that cause disease are known as pathogens.

Like human cells, pathogens contain DNA (or, in the case of some viruses, a similar chemical called RNA). DNA and RNA belong to the nucleic acid family.

Nucleic acids contain genes. The genes contain a code that controls a pathogen's structure and behavior and enables it to cause an infection.

A prion consists of protein and has no nucleic acid or genetic code. The discovery that prions could reproduce in our body and cause disease was at first very hard for scientists to accept. Although they now know that this happens, they still have many questions about how and why prions form.

Scrapie in sheep was the first prion disease to be discovered.
Scrapie in sheep was the first prion disease to be discovered. | Source

What are Prion Proteins and Prions?

Prion proteins are common in our body and occur in two varieties. One is a normal and necessary part of our cells while the other (the prion) is dangerous. Prions not only transform useful proteins into harmful ones but also form protein clumps.

Cellular or Normal Prion Proteins

A cellular prion protein (PrPc) is a normal constituent of cells and is folded correctly. Cellular or normal prion proteins are located throughout the body but are especially abundant in the brain. They seem to be very important in the life of cells, although their exact function isn't known. They may play a role in preventing cells from being damaged.

Abnormal Prion Proteins or Prions

An abnormal prion protein that is folded incorrectly and has the ability to cause other proteins to become misfolded is often known as simply a "prion". It's symbolized by PrPsc. The "sc" stands for scrapie, the first prion disease to be discovered. Scrapie damages the nervous system of sheep.

Prion Formation and Activity

Prion Formation

How are Prions Made?

Prions may appear in our body for several reasons.

  • They may enter the body from another organism.
  • They may be made in our bodies due to altered genes. Genes contain instructions for making proteins. Some inherited genes may contain a mutation (a change in a gene) that alters the structure of the gene and causes it to code for a misfolded prion protein, or prion.
  • Normal prion proteins may spontaneously change into prions.

The "holes" that are visible in the brain of a cow with BSE;  similar holes develop in a person with a TSE, or Transmissible Spongiform Encephalopathy
The "holes" that are visible in the brain of a cow with BSE; similar holes develop in a person with a TSE, or Transmissible Spongiform Encephalopathy | Source

Prion Diseases

Prion diseases are quite rare in humans (as far as we know), but they are very unpleasant for the sufferers. They affect the brain more than any other body part and cause neurodegeneration.

Prion diseases are also known as Transmissible Spongiform Encephalopathies, or TSEs. They are known as spongiform diseases because they cause nerve tissue to break down and make the brain look as though it has spaces resembling the pores of a sponge.

Classic Creutzfeldt-Jakob Disease, or CJD

About 1 in a million people develop Creutzfeldt-Jakob Disease or CJD every year. In the United States, the incidence of CJD is about 200 to 300 cases per year.

Symptoms of CJD include a personality change, depression, vision problems, loss of muscle coordination, balance problems, jerky movements, slurred speech, memory loss and impaired thinking and judgement. Eventually patients are unable to walk or feed themselves and lose awareness of their surroundings. Death is usually due to pneumonia, respiratory failure or heart failure.

Since there is no cure for CJD, the goal of treatment is to relieve pain and make the patient feel as comfortable as possible. Research into finding an effective treatment or cure is continuing. The website of the National Prion Clinic in the United Kingdom provides information to help patients and describes the latest research.

Creutzfeldt-Jakob Disease Information

Types of Creutzfeldt-Jakob Disease

There are three types of classic Creutzfeldt-Jakob Disease.

  • Sporadic CJD is the most common type. It develops when normal prion proteins in the patient's body spontaneously change into abnormal prions. The cause of this change is unknown. The prions that are made can transform other normal prion proteins.
  • Sporadic CJD generally develops in people aged 45 or older. The disease usually lasts for six or seven months after the first symptom appearance, but some people have died after only a few weeks while others have lived for a year or more.
  • Familial CJD develops due to inherited genes. The genes produce abnormal prion proteins in people aged about 50 or older. This form of CJD is much rarer than the sporadic form.
  • A very rare disease called iatrogenic CJD is spread by a transplant of contaminated tissue from an infected person or by the use of contaminated surgical equipment.

BSE and Humans

Stained clumps of prions in tonsil tissue from a vCJD patient
Stained clumps of prions in tonsil tissue from a vCJD patient | Source

Variant Creutzfeldt-Jakob Disease or vCJD

Creutzfeldt-Jakob disease and variant Creutzfeldt-Jakob disease are both prion diseases. Although the diseases have similar names, there are major differences between them.

  • vCJD was discovered in the United Kingdom in 1996. It's a relatively new disease compared to CJD, which was discovered in 1920.
  • All people who have developed variant Creutzfeldt-Jakob disease have lived in a country inhabited by cows with BSE. CJD hasn't been linked to BSE.
  • Researchers believe that with the exception of three people, everyone to date who has become ill with vCJD became infected by eating contaminated beef. The three exceptions are thought to have become infected by receiving contaminated blood during a transfusion.
  • Cow meat is the muscle of a cow. It can become contaminated with BSE prions when material from the brain or nervous system enters the meat. This could happen when processing equipment cuts through the spinal cord and then touches the meat, for example.
  • Median age of death from CJD in the United States is 68 while median age of death from vCJD in the United Kingdom is 28.
  • Each disease causes specific differences in the appearance of brain tissue.
  • The first symptoms of vCJD are generally psychiatric or sensory problems. The patient develops the dementia that is typical of CJD later.
  • People with variant Creutzfeldt-Jakob disease tend to live longer than patients with classic Creutzfeldt-Jakob disease.

Prion Disease Incubation Period

In October 2013 an interesting report was published in the British Medical Journal. The researchers collected data which suggests that 1 in 2000 people in the UK could have the vCJD prions in their body, even though they aren't sick. The data was obtained by examining appendices removed from people around the country.

The number of vCJD cases in the UK peaked in 2000 and has fallen since then. Prion diseases seem to have an incubation period, which sometimes lasts for many years. During the incubation period no symptoms are present. Once the symptoms appear, the disease progresses rapidly. Some researchers suggest that vCJD might have an incubation period of about ten years, given that UK cases peaked about ten years after a recent BSE outbreak. Others suggest that the incubation period may be much longer.

The data described in the British Medical Journal is interesting, but scientists are cautious about their interpretation of the data. They say that infected people could remain asymptomatic for the rest of their lives. On the other hand, the prions could be in their incubation period and the infected people could eventually develop a prion disease. Not enough is known about prion biology to predict the outcome of the infection.

Gene Mutations and Prion Formation

Prion Biology

Prion biology is fascinating and important. Even though prion diseases are quite rare, they are devastating for patients and their families. In addition, some other serious human diseases involve misfolded and misbehaving proteins and seem to operate in a similar way to prion diseases. These diseases include Alzheimer's disease and Parkinson's disease. Understanding prion diseases could help us understand these health disorders and even help us to treat them more effectively.

It may be that the effects of prions in our bodies are more widespread and common than we realize. We certainly don't understand prion biology very well yet. For example, a few experimental drugs have been created that slow prion replication in the lab. A recent report has described the development of drug resistance in prions. Drug resistance normally develops in cells with nucleic acid, such as bacterial cells. The puzzle of how it could develop in protein molecules is one of the many aspects of prion biology that needs to be explained.

© 2013 Linda Crampton

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Comments 30 comments

Sue Bailey profile image

Sue Bailey 3 years ago from South Yorkshire, UK

Thanks Alicia that was so interesting and although a complicated subject, the way you presented the information was easy to understand. Voted up, pinned and shared.


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Thank you very much for the comment, Sue. I appreciate your vote and shares as well!


Faith Reaper profile image

Faith Reaper 3 years ago from southern USA

Alicia, you always come up with fascinating topics for hubs indeed! As Sue stated above, you have written it so that all are able to understand the information. We do not eat much red meat at all any longer, and may not at all after reading all of this information! Pretty scary stuff to say the least.

Thank you for always writing such excellent hubs! Up and more and sharing

Blessings, Faith Reaper


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Thank you so much for the kind comment and the support, Faith. I always appreciate your visits and blessings!


billybuc profile image

billybuc 3 years ago from Olympia, WA

You do know your stuff, Alicia! If I had been taught this in high school I would have zoned out halfway through the lecture. This was interesting enough to keep me going all the way. Well done!


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Thank you very much for the visit and the lovely comment, Bill!


CraftytotheCore profile image

CraftytotheCore 3 years ago

What an amazing article! You obviously spent a lot of time and effort in to this and I find it so educational. I've heard of this but never read so much about it before.


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Thank you very much, Crafty! I think we may be hearing a lot more about prions in the future. They are fascinating - but very worrying - particles. I hope researchers learn how to treat prion diseases and other protein folding disorders very soon.


DDE profile image

DDE 3 years ago from Dubrovnik, Croatia

Prions in the Body and Human Disease very important information, a useful and well researched hub.


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Thank you for the visit and the comment, DDE.


drbj profile image

drbj 3 years ago from south Florida

Absolutely, positively fascinating discourse about prions, Alicia. Thank you for your research and expertise. Though I think I felt better when I was less prion-educated!


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Thank you very much, drbj. Prions are scary to think about, especially since they can be so dangerous. It would be so good if we knew how to prevent their formation or how to stop them from becoming active!


FlourishAnyway profile image

FlourishAnyway 3 years ago from USA

What a fascinating but also scary hub. With all of this Mad Cow Disease I am so glad I don't eat red meat any longer. Voted up and more, plus pinned.


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Thank you very much for the votes and the pin, FlourishAnyway. I appreciate your visit and comment!


Nell Rose profile image

Nell Rose 3 years ago from England

Hi Alicia, that was really interesting, I never knew what a prion was, but of course had heard of 'mad cow disease' which is the illness with the cows, great information, voted up and shared! nell


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Thank you very much, Nell. I appreciate your comment as well as the vote and the share!


CMHypno profile image

CMHypno 3 years ago from Other Side of the Sun

Informative hub as always Alicia. There is still so much more to learn about the human body and what causes disease. Hopefully research will continue and some kind of treatment/cure will be found for sufferers.


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Thanks for the comment, Cynthia. I hope that a cure will be found for prion diseases soon, too. They are horrible disorders.


aviannovice profile image

aviannovice 3 years ago from Stillwater, OK

Now I finally know what happens regarding meat ingestion of animals afflicted with mad cow disease. Thanks for bringing this up.


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Thanks for the visit and the comment, Deb. It's sad that mad cow disease still occurs, both for the cows and for us.


Minnetonka Twin profile image

Minnetonka Twin 3 years ago from Minnesota

Wow Alicia~This is a very scary disease and I had never heard the term 'prions.' I have heard of mad cow disease and how dangerous it is to humans. I sure hope they learn more about this disease. I feel so sad for the woman in the video, not knowing if and when she will get the disease. At least she has the right attitude about how to live her life. Great article!


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Thank you very much for the comment, Minnetonka Twin. I'm sorry for the woman in the video, too. It must be frightening for her to know that she could get such a horrible disease.


bdegiulio profile image

bdegiulio 3 years ago from Massachusetts

Hi Linda, Sadly we know all too well about prion disease and CJD. A very good friend of ours died from this a few years ago. To say that this is scary is an understatement. What happened to our friend in just 3 to 4 months was so sad and heart-wrenching, and as you know, there is nothing that can be done. Great job explaining this.


AliciaC profile image

AliciaC 3 years ago from British Columbia, Canada Author

Bill, that is so sad. I am very sorry that you lost your friend, and I'm sorry for his or her family, too. I hope that an effective treatment or cure for prion diseases is discovered very soon.


AudreyHowitt profile image

AudreyHowitt 2 years ago from California

This is such an informative hub on the subject--I have been a vegetarian for many years, and so do not worry so much about this disease--but I worry for others


AliciaC profile image

AliciaC 2 years ago from British Columbia, Canada Author

Thank you very much for the visit and the comment, Audrey. The existence of prions is certainly worrying. Hopefully researchers will soon discover better ways of dealing with the problem.


jhamann profile image

jhamann 2 years ago from Reno NV

Well researched and well written hub. I work in Pathology and I remember back about ten years ago if we got suspected brain tissue we would spend half the day decontaminating. Jamie


AliciaC profile image

AliciaC 2 years ago from British Columbia, Canada Author

Thanks for the kind comment and for sharing the interesting information, Jamie. It can't be easy or pleasant to work with tissue that may be infected with prions!


Arachnea profile image

Arachnea 2 years ago from Texas USA

I recall this topic from my Biology class. I swore off fast food for a very long time as a result. This is a very informative hub. Great job.


AliciaC profile image

AliciaC 2 years ago from British Columbia, Canada Author

Thank you very much, Arachnea. I appreciate your visit. The existence of prions certainly is scary. I hope scientists learn more about them soon.

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