What are Prions?
Proteins are three-dimensional biochemical compounds involved in several vital biological processes. Generally, a protein's structure determines what function it has. However, there are occasions where proteins may undergo a misfolding event that impacts structure. When this occurs, abnormal prion proteins capable of causing disease can form. Abnormal prion proteins are typically referred to simply as prions. [1, 2]
Development & Diseases
Infectious, abnormal prion proteins develop when typical prion proteins, which are associated with the cell surfaces in several cells in the body, undergo a misfolding event. Prions are capable of converting normal proteins into prions as well, which leads to the development of a collection of diseases, called prion diseases, that result from prions forming aggregates capable of causing physical damage. This collection of conditions typically impacts the brain, and diseases are found in both humans and animals. [2]
Prion diseases are rare and can be categorized into three groups: sporadic, familial/genetic, and acquired.
Sporadic: The onset of a prion disease occurs with no other coinciding risk or genetic factors. Examples include sporadic Creutzfeldt-Jakob Disease (sCJD), sporadic Fatal Insomnia (sFI), and variable protease-sensitive prionopathy.
Familial/Genetic: The onset of a prion disease occurs as a result of genetic factors, typically from mutations in the prion protein gene PRNP. Examples include familial Creutzfeldt-Jakob Disease (fCJD), Gerstmann-Sträussler-Scheinker Syndrome (GSS), and Fatal Familial Insomnia (FFI).
Acquired: The onset of a prion disease occurs from exposure to an external source, such as contaminated food or medical equipment. It is the least common way for a prion disease to develop. Examples include Iatrogenic and Variant Creutzfeldt-Jakob Disease (iCJD, vCJD), and kuru. [3,4]
Humans are not the only ones to experience prion diseases. They are also found in cows; deer and relative species; and sheep in the forms of bovine spongiform encephalopathy (BSE), Chronic Wasting Disease (CWD), and scrapie, respectively. BSE is also commonly known as mad cow disease, due primarily to a large outbreak that occurred in cattle in Europe during the later part of the 20th century. The consumption of cow meat contaminated with BSE is known to cause variant CJD in humans. While no such trend has been observed with deer meat contaminated with CWD, it is believed by health experts to be possibly transmissible to humans. [1,4]
Symptoms & Diagnosis
The symptoms experienced with prion disease result typically from progressive brain degeneration that is caused by the build-up of prion aggregates. As a result, these symptoms are neurologic in nature and get worse as the disease progresses. Common symptoms include memory issues; confusion; deteriorating physical coordination & movement; sudden personality changes; insomnia; hallucinations; loss of speech; dementia; and coma in the final stages of prion disease. [2,3]
There are a variety of methods that are used to diagnose prion disease without directly sampling brain tissue. These include:
MRI scans performed on the brain. This allows for visual analysis by healthcare professionals to look for evidence of prion disease.
Spinal tap & blood tests. This allows for the analysis of molecular indicators of disease or damage in both the blood and spinal fluid.
Electroencephalogram (EEG): A test that measures activity in the brain.
Physical examinations of both the eyes and nervous system to check for any damage or loss of function.
Genetic testing for known mutations linked to prion disease risk.
A test known as real-time quaking-induced conversion assay (RT-QuIC), allows for the identification of prions in cerebrospinal fluid. [2,3]
Current Treatments
Unfortunately, there are currently no cures to directly combat prion diseases. Because of this, prion diseases are always fatal. Treatments focus directly on mitigating the symptoms and slowing disease progression with an emphasis on ensuring the patient's comfort. Examples of such treatment methods include anti-seizure medication, muscle relaxants, and medication for pain. [2, 3]
Takeaways
While prions and prions diseases are not curable, they are incredibly rare and research is ongoing to better understand and treat them. Practices are put into place to prevent the onset of these diseases from contaminated food and medical devices. Genetic testing for mutations associated with genetic prion diseases should be considered if there have been people in your family who developed as a result of mutations. Be aware of possible symptoms to know whether further prion testing and diagnosis is needed.
References:
US Centers for Disease Control. (2024, April 22). About Prion diseases. CDC. https://www.cdc.gov/prions/about/index.html
John Hopkins Medicine. (2024, June 6). Prion diseases. Johns Hopkins Medicine. https://www.hopkinsmedicine.org/health/conditions-and-diseases/prion-diseases
Cleveland Clinic Medical. (n.d.). Prion Disease. Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/prion-disease
University of California San Francisco. (n.d.). Prion diseases. Memory and Aging Center. https://memory.ucsf.edu/dementia/rapidly-progressive-dementias/prion-diseases
Toxic Prion: Translation of a Genome's gene with a toxic change - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Conversion-of-a-helices-of-protein-into-b-sheets_fig2_366688090 (cover image) Assessed and Endorsed by the MedReport Medical Review Board