Prion diseases are rare and occur due to proteins in the brain that “misfold.” Another name for prion disease is transmissible spongiform encephalopathies (TSEs). There are many types of prion diseases that affect both animals and humans.

Protein folding is an important process in the body — proteins must fold into specific three-dimensional shapes to function properly. When a protein misfolds, it loses its structure and is unable to function. Misfolded proteins may cause disease in people.

The brain contains high numbersTrusted Source of normally folded prion proteins, but scientists are yetTrusted Source to fully understand their function or why they misfold.

There is no cureTrusted Source for prion disease. However, scientists are looking into new approaches for treating this condition.

Read on to learn more about prion disease, including symptoms, diagnosis, and treatment.

Prion diseases are rare, uncurable brain diseases that affect mammals, including humans.

Sometimes, the terminology to describe prion diseases can be inconsistent. “Prions” are the disease-causing agentsTrusted Source that can stimulate the abnormal folding of “prion proteins.” In their usual, healthy state, prion proteins are typically present in the brain.

When prion proteins begin to fold abnormally and clump together — called amyloid plaquesTrusted Source — it leads to brain damage.

Disease-causing prions can transmit in various ways, for example, viaTrusted Source animal feed or unsterilized medical equipment. However, it is important to note that equipment-related cases occurred before healthcare facilities implemented routine sterilization techniques. According to the Centers for Disease Control and Prevention (CDC)Trusted Source, there have been no recorded medical equipment cases since 1976.

Some prion diseases have a rare genetic link, such asTrusted Source fatal familial insomnia.

When people start experiencing the effects of prion disease, their condition usually deterioratesTrusted Source at a fast rate. Prion diseases are always fatal.

Several types of prion disease can affect both humans and animals. Although experts have defined many types, it is not known for certain whether someone fits into one exact type. This is likely due to the absence of definite tests that could confirm diagnoses or rule out others.

Human prion diseases

Examples of the most common prion diseases includeTrusted Source:

  • Creutzfeldt-Jakob disease (CJD): This type of CJD is split into three types: familial, sporadic, and acquired. People inherit the familial type, but the sporadic type develops without any known causes. Sporadic CJD is the most common type of CJD and tends to affectTrusted Source those aged around 60 years. A person can develop acquired CJD after unsterilized medical equipment has introduced prions into the body, though this is rare.
  • Variant Creutzfeldt-Jakob disease (vCJD): This type of CJD is an infectious prion disease related to mad cow disease. People acquire it by eating meat containing proteins from the brain or spinal tissue of a sick cow. Unlike sporadic CJD, vCJD is more likelyTrusted Source to affect younger people.
  • Fatal familial insomnia: This type — typically hereditary — is linked to inheriting an atypical form of a gene that codes for prion proteins. Rarely, this disease occurs sporadically. Over the course of the disease, people sleep less and less. This can lead to mental deterioration and physical symptoms.
  • Gerstmann-Straussler-Scheinker syndrome: This is a genetic disease that affects prion proteins in the cerebellum. The cerebellum is the part of the brain that controls movement and balance, among other functions.

Animal prion diseases

Examples of common prion diseases in animals includeTrusted Source:

  • bovine spongiform encephalopathy, also known as mad cow disease, which affects cattle
  • chronic wasting disease, which affects deer and elk
  • scrapie, which affects sheep

Currently, scientists do not fully understandTrusted Source what causes prion proteins to misfold. Additionally, prion proteins can be misfolding for many years before a person experiences symptoms.

Risk factors

Prion diseases are rare. The CDCTrusted Source reports 1 case of CJD per million people annually.

However, risk factors for prion disease can include:

  • A family history of prion disease, especially with fatal familial insomnia.
  • Eating or coming into contact with meat that contains proteins from the brain or spinal tissue of a sick cow —especially with vCJD.
  • Transmission — for example, acquiring the disease via medical or surgical treatment.
  • Age, especially for CJD.

The symptoms of prion disease can vary, depending on the type of misfolded prion protein. Different prion proteins might target certain regions of the brain. Therefore, symptoms may be reflective of the brain areas prions are damaging.

For example, in instances of fatal familial insomnia, a person will not be able to sleep and usually experienceTrusted Source vivid daydreams in addition to changes in body temperature. As the disease progresses, they sleep less and less.

Alternatively, a person with CJD may firstTrusted Source develop dementia-like symptoms and experience issues with their balance. They may also report:

As prion diseases affect the brain, people generally tend to present with:

Usually, it takes a long time — even yearsTrusted Source — for symptoms to present after prion proteins begin to misfold.

Related conditions

Some symptoms of prion disease can overlapTrusted Source with other diseases, such as:

If a doctor suspects a person has prion disease, they usually also screen for the above conditions to rule them out. This is because they are more common than prion diseases.

Prion diseases are incredibly complex. Each disease has its own diagnostic criteria, usually consisting of various medical tests and physical examinations.

These can include:

  • Blood tests: Detects the presence of prions in the blood. People may also be able to get prototype tests since prion diseases are so rare.
  • Neurological exams: Screens for neurological damage.
  • Genetic tests: Detects whether someone has gene variants.
  • MRIs: Detects changes in brain structure.
  • Lumbar punctures: Screens cerebral spinal fluid for certain markers for CJD.
  • Electroencephalogram: Measures any changes in brain waves.

Some people may require a brain biopsy, where a doctor uses a small needle to collect a tissue sample. This is usually under a general anesthetic.

A brain biopsy is a high risk procedure as surgeons remove a part of the brain tissue. Additionally, in the case of prion disease, there are risks for anyone handling the removed sample. The best way to confirm the diagnosis for conditions such as CJD is by autopsy rather than biopsy.

Doctors can also request a sensitive diagnostic test to detect some prions or prion proteins. For example, in cases of CJD, they can useTrusted Source a Real Time-quaking Induces Conversion, or RT-QuIC assay. This technique can amplify undetectable levels of prions. Before this assay, the risk of a false-negative result was higher.

People should note that the RT-QuIC assay is not widely available.

There are currently no therapies that cure prion disease. Treatment approaches may focus on treating the symptoms instead.

However, scientists are investigating the effect of different molecules that can inhibit the formation of prions. Studies are still in their early stagesTrusted Source and limited to animal trials only.

Prion diseases are rare. They affect the brain by causing prion proteins to misfold.

Some types of prion disease run in families, which a person can inherit. People can contract other types by eating affected meat or being exposed to unsterilized medical equipment that doctors have used on another person with the disease.

Symptoms of prion disease typically take time to present. However, when a person begins experiencing symptoms, they deteriorate quite quickly. There is no cure for prion disease, but scientists are looking into new ways to treat this condition.