Prion Diseases | Johns Hopkins Medicine

Prion Diseases | Johns Hopkins Medicine

What are prion diseases?

Prion diseases comprise several conditions. A prion is a type of protein that can trigger normal proteins in the brain to fold abnormally. Prion diseases can affect both humans and animals and are sometimes spread to humans by infected meat products. The most common form of prion disease that affects humans is Creutzfeldt-Jakob disease (CJD).

Prion diseases are rare. About 300 cases are reported each year in the U.S.

Types of prion diseases include:

• CJD. A person can inherit this condition, in which case it’s called familial CJD. Sporadic CJD, on the other hand, develops suddenly without any known risk factors. Most cases of CJD are sporadic and tend to strike people around age 60. Acquired CJD is caused by exposure to infected tissue during a medical procedure, such as a cornea transplant. Symptoms of CJD (see below) quickly lead to severe disability and death. In most cases, death occurs within a year.
• Variant CJD. This is an infectious type of the disease that is related to “mad cow disease.” Eating diseased meat may cause the disease in humans. The meat may cause normal human prion protein to develop abnormally. This type of the disease usually affects younger people.
• Variably protease-sensitive prionopathy (VPSPr). This is also extremely rare, it is similar to CJD but the protein is less sensitive to digestion. It is more likely to strike people around age 70 who have a family history of dementia.
• Gerstmann-Sträussler-Scheinker disease (GSS). Extremely rare, but occurs at an earlier age, typically around age 40.
• Kuru. This disease is seen in New Guinea. It’s caused by eating human brain tissue contaminated with infectious prions. Because of increased awareness about the disease and how it is transmitted, kuru is now rare.
• Fatal insomnia (FI). Rare hereditary disorder causing difficulty sleeping. There is also a sporadic form of the disease that is not inherited.

What causes prion disease?

Prion diseases occur when normal prion protein, found on the surface of many cells, becomes abnormal and clump in the brain, causing brain damage. This abnormal accumulation of protein in the brain can cause memory impairment, personality changes, and difficulties with movement. Experts still don’t know a lot about prion diseases, but unfortunately, these disorders are generally fatal.

Who is at risk for prion diseases?

Risk factors for prion disease include:

• Family history of prion disease
• Eating meat infected by “mad cow disease”
• Infection from receiving contaminated corneas or from contaminated medical equipment

What are the symptoms of prion diseases?

Symptoms of prion diseases include:

• Rapidly developing dementia
• Difficulty walking and changes in gait
• Hallucinations
• Muscle stiffness
• Confusion
• Fatigue
• Difficulty speaking

How are prion diseases diagnosed?

Prion diseases are confirmed by taking a sample of brain tissue during a biopsy or after death. Healthcare providers, however, can do a number of tests before to help diagnose prion diseases such as CJD, or to rule out other diseases with similar symptoms. Prion diseases should be considered in all people with rapidly progressive dementia.

The tests include:

• MRI (magnetic resonance imaging) scans of the brain
• Samples of fluid from the spinal cord (spinal tap, also called lumbar puncture)
• Electroencephalogram, which analyzes brain waves; this painless test requires placing electrodes on the scalp
• Blood tests
• Neurologic and visual exams to check for nerve damage and vision loss

How are prion diseases treated?

Prion diseases can’t be cured, but certain medicines may help slow their progress. Medical management focuses on keeping people with these diseases as safe and comfortable as possible, despite progressive and debilitating symptoms.

Can prion diseases be prevented?

Properly cleaning and sterilizing medical equipment may prevent the spread of the disease. If you have or may have CJD, do not donate organs or tissue, including corneal tissue.
Newer regulations that govern the handling and feeding of cows may help prevent the spread of prion diseases.

Living with prion diseases

As prion diseases progress, people with these diseases generally need help taking care of themselves. In some cases they may be able to stay in their homes, but they eventually may need to move to a care facility.

Key points about prion diseases

• Prion diseases are very rare.
• Symptoms can progress rapidly requiring help with daily needs.
• Prion diseases are always fatal.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your provider tells you.
• At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.
• Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your provider if you have questions.

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Related Topics

Prion Diseases as Transmissible Zoonotic Diseases

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How mad cow disease destroys the brain

Scientists have come close to unraveling the mechanism of action of prion diseases. This is a whole group of neurodegenerative diseases that destroy the human brain, leaving no chance for salvation. Scientists hope that the discovery will bring them closer to developing a treatment.

Author:

medical editor Maria Sotskova

2
minutes

Those strange prions

Prions are special proteins with an abnormal structure that, like viruses, can infect mammals, including humans. They multiply in living cells, cause the body’s own proteins to turn into prions, especially often they affect the brain. It is the only known infection that replicates without RNA and DNA.

Prions are very stable, they accumulate from the affected tissues, damaging and destroying them. However, they are very difficult to chemically or physically destroy. Because of this, there is still no cure for any prion disease, they are all fatal in 100% of cases. Collectively, prion diseases are referred to as transmissible spongiform encephalopathies.

1. Kuru is a neurodegenerative prion disease common among the aborigines of New Guinea. Basically, she dealt with cannibals who ate the brain of an enemy for ritual purposes. After the onset of the disease, the patient lives no more than a year, but the incubation period can last for decades.

2. Gerstmann-Straussler-Scheinker syndrome is rare. This is a hereditary disease that manifests itself in people from 20 to 60 years old. It starts with problems with coordination, and ends with deep dementia. The incubation period is from 5 to 30 years.

3. Fatal familial insomnia is perhaps one of the worst prion diseases. Patients literally lose the ability to sleep and die of insomnia within a few months. At this time, they are tormented by panic attacks and hallucinations.

4. Creutzfeldt-Jakob disease is also known as mad cow disease. Has several forms. The first – classical – occurs spontaneously in people over 50 years old, gradually destroys the brain, killing in 8 months. The second was called the “new version”, it appeared in the late 80s in the UK. Presumably, the first patients became infected from poorly processed meat from mad cows. There is an inherited form, and this disease can also be contracted, for example, during a medical intervention.

Prevent infection

Infecting the brain, prions accumulate in axons – long processes of neurons. As a result, they increase in size and lose their ability to conduct signals correctly. The development of other neurodegenerative diseases of a protein nature, for example, Alzheimer’s disease, proceeds in a similar way. If scientists manage to understand how and why this happens, then it will turn out, if not to rid people completely of these ailments, then at least learn to restrain them.

The researchers carefully observed the behavior of prions, proteins affect only axons, but do not touch the bodies of neurons themselves. It turned out that it was precisely in this feature that the solution lies. Usually, neurons are able to cleanse themselves of excess, including clumps of prions. However, things are more difficult with axons, the cells simply cannot cope with cleaning.

Apparently, neurons usually get rid of prions with the help of vesicles, small capsules that cells use to transport substances. Neurons send their vesicles along the microtubule systems to the axons, like on rails. If a prion is found in the capsule, then, once it enters the axon, it merges with others, forming aggregates, from which it is no longer possible to get rid of. As a result, these aggregates swell and block the paths for impulses, causing the rapid death of the neuron.

By understanding the mechanism, the scientists were able to counter it. They found four proteins that are responsible for sending prion vesicles into axons. When they suppressed the production of at least one of them, much fewer prions began to enter the axons. At the same time, neurons functioned normally or almost normally, and survived as well as healthy brain cells.

Results obtained in mice so far. However, it causes optimism among researchers, they hope that the method will, if not cure diseases associated with the accumulation of proteins, then at least slow down their development.

“We are very enthusiastic about discovering molecules that can inhibit this pathway of aggregate formation and studying the effects of such inhibitors in animal models of prions and other neurodegenerative diseases,” said study co-author Sandra Encalada, Ph.D.

Comments CACKL E

Brain tissue impurities

Stylab offers test systems for determining impurities of head and bone marrow tissue in meat raw materials, ready-made food products, as well as in equipment, tools and on working surfaces.

Prions can be transmitted from diseased carriers to healthy individuals with tissue particles. Since the PrP protein, the prion forms of which cause transmissible spongiform encephalopathies, is localized mainly in the cells of the central nervous system, the highest content of prions is found in the brain tissue. They are also found in the bone marrow, some parts of the intestines and tonsils.

The greater the amount of prion ingested, the faster the disease will develop. However, even a small dose of a prion can cause it. For example, in Romney and Suffolk sheep, the minimum effective oral dose of a prion that causes transmissible bovine spongiform encephalopathy was 0.05 g. Animals usually receive prions from a diet containing bone meal made from the bones of diseased individuals.

The hypothesis of the existence of disease-causing prions was formulated in 1960s, and they themselves were isolated in the 1980s. However, prion diseases were known before. These include scrapie (sheep scabies) – a disease of sheep and goats, described in 1732, Creutzfeldt-Jakob disease (1920), kuru (1957), etc.

Some prions are dangerous for both animals and humans. Thus, the prion that causes “mad cow disease” in humans causes an atypical form of Creutzfeldt-Jakob disease (vCJD). There have been cases of prion transmission from person to person during rituals involving cannibalism. This is how the kuru disease, previously common among the natives of New Guinea, spreads. It is characterized by ataxia, headaches, convulsions and trembling. Patients usually die within a year after the onset of the first symptoms. Prions enter the human body with the tissues of sick animals, especially their brains.

Brains are category 1 by-products. They are used for the production of pates, as well as canned food for baby food. In addition, brain tissue and bone marrow can contaminate animal meat and fat during carcass cutting. Prions are not destroyed during food preparation. They withstand high temperatures, freezing and acids. To destroy them, exposure to strong alkalis or sodium hypochlorite, autoclaving with a gravitational method of air extraction and subsequent sterilization by conventional methods is necessary. Thus, any product containing brain tissue that has not been analyzed can theoretically become a source of prions.

Some cosmetics are made with animal ingredients. They may also contain prions if they come from sick individuals. Thus, cosmetics are potentially a pathway for the spread of prions if they are applied to the mucous membranes of the eyes or lips, or to damaged skin.

Following the mad cow disease epidemic in the 1990s, the European Union banned the use of animal tissue in animal feed and the use of tissue potentially containing prions, especially brain tissue, in the food industry. These measures, together with the isolation of animals and the slaughter of sick animals, have led to a significant reduction in mortality from “mad cow disease” among animals: in 2012, no more than 10 animals died from this cause worldwide. The decision to undertake them was due to the long incubation period and the danger of prion diseases.

To analyze the content of impurities in brain and bone marrow tissues in raw materials and finished products, as well as on instruments and work surfaces, it is convenient to use the ELISA method.