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  • Writer's picturePua E Rick

Prion diseases - A tale of cows and cannibals

Updated: Aug 20, 2022

What happens when proteins go rogue?


Edited by Sanaya Narula.


What does a disease that drives cows mad have in common with cannibalism and zombies? How about a disease that robs people of the ability to sleep, draining their mental acuity and physical strength until their inevitable death? In this case, they all happen to be caused by the same type of infectious particles—misshapen proteins known as prions.


Proteins play a part in most of our bodily functions, making up our antibodies and enzymes along with serving various structural and regulatory roles. Proteins are large molecules, consisting of chains of amino acids known as polypeptides. These polypeptides can fold into a three-dimensional structure, determined by the bonds and interactions between its amino acids.


However, proteins do not always fold correctly into fully functional shapes. It is believed that some misfolded proteins can bind to other proteins of the same type, inducing their normal neighbours to contort into their distorted state.¹ This triggers a chain reaction, causing more and more proteins to become “infected”, similar to the spread of pathogens such as bacteria or viruses.¹ These abnormal proteins then clump together, forming aggregates called amyloids.² When these aggregates accumulate on the axons of neurons, they lead to axon dysfunction and neuronal death³, ultimately manifesting as a set of diseases collectively known as transmissible spongiform encephalopathies (TSEs).



Prions are very stable—since they do not contain nucleic acids, they cannot be destroyed by ultraviolet radiation, unlike most other infectious agents.¹ A study by the National Institute of Allergy and Infectious Diseases found that a tissue sample from a prion disease patient managed to infect four out of eight mice even after being preserved in formaldehyde, embedded in wax, and kept on dry specimen slides for three years⁴. Worst of all, while some prion diseases have been linked to genetic and familial factors, some are believed to strike sporadically—suddenly and without warning.


There are many types of prion diseases, and not all of them affect humans. However, all prion diseases have one thing in common—their effects are devastating.


Towards the end of the 19th century, the Fore people in Papua New Guinea appeared to suffer from a bizarre ailment—tremors, speech problems and a staggered gait, which deteriorated to the point where eating or standing became impossible. Those who displayed these symptoms would inevitably end up comatose, dying after six to twelve months.⁵ This disease, named kuru from the Fore word for “trembling”, was later identified to be a prion disease. Today, it is believed that the cause of this outbreak was the practice of ritualistic cannibalism—during funerals, tribe members would cook and eat the body parts of their deceased family members, including the brain which contained the prions causing the disease.⁵ This was supported by the fact that intervention from the Australian government to discourage the practice in the 1950s was followed by a drop in kuru cases.⁶


Okay, that explains the cannibals. What about the cows?



In the 1990s, cattle in the United Kingdom began to show symptoms of a neurological disease which worsened over time, resulting in behavioural changes, trembling and eventual death. This was dubbed the “mad cow disease” after its bovine origins. A prion disease known as variant Creutzfeldt-Jakob disease (vCJD) began to manifest in a very small percentage of people following this. It is believed that this disease was tied to the consumption of nerve tissue from the infected cows.⁷ The timeline of these cases lent credence to one of the hypotheses surrounding prion diseases at the time—that it could take years after the initial infection for symptoms to materialise due to the long incubation periods of prion diseases.⁸


Perhaps the prion disease with the most nightmarish symptoms of all is Fatal Familial Insomnia. As its name suggests, those suffering from Fatal Familial Insomnia gradually lose the ability to fall asleep, eventually ending up in a state described as a “waking coma” before succumbing to the disease.⁹ This happens because prions damage the thalamus (the part of the brain that regulates sleep) until the patient is completely unable to sleep, resulting in a host of health complications such as excessive sweating, rapid heart rate and problems with memory and attention.⁹ These symptoms progressively worsen over months, lasting an average of 18 months between the onset of insomnia and eventual death.⁹ Though this disease largely affects those with a family history of fatal insomnia, sporadic cases with no genetic history of the disease have also been detected⁹.


Despite how disturbing some of this may sound, strides are being made in the treatment and study of prion diseases. At University College London, researchers recently uncovered a type of protein occurring naturally in the brain with the ability to “really throw a spanner into the works in terms of prion propagation,” according to neurologist and molecular biologist John Collinge.⁶ And in 2021, a team of researchers at Imperial College London and the University of Zurich were able to study the molecular mechanism behind the misfolding of prions and produce antibodies to successfully stop prions from transitioning into their infectious form.¹⁰


So at the end of the day, are prion diseases something worth losing sleep over? (Sorry.) On the bright side, prion diseases are incredibly rare—only around 300 cases are reported in the United States each year.¹¹ On a less cheerful note, the annual mortality rate of sporadic Creutzfeldt-Jakob disease (sCJD) seems to have increased in the past twenty years, especially in countries with ageing populations such as Japan.¹² According to Dr Yoshito Nishimura, a researcher from Okayama University, "CJD, albeit rare, will be more prevalent in the next 5-10 years." ¹²


Regardless, prions are just one of the many ways our bodies can go wrong, albeit one where there is still much we have yet to understand.


 

References:

  1. What Is a Prion? (1999, October 21). Scientific American. https://www.scientificamerican.com/article/what-is-a-prion-specifica/

  2. University of Massachusetts Amherst. (2020, May 5). Unraveling one of prion disease’s deadly secrets. ScienceDaily. https://www.sciencedaily.com/releases/2020/05/200505190552.htm

  3. Scripps Research. (2021, December 22). Scripps Research discovery illuminates how brain cells die in prion diseases. https://www.scripps.edu/news-and-events/press-room/2021/20211222-encalada-brain-cells-prion-diseases.html

  4. Chesebro, B. (2018, March 8). NIAID Scientists Assess Transmission Risk of Familial Human Prion Diseases to Mice. NIH: National Institute of Allergy and Infectious Diseases. https://www.niaid.nih.gov/news-events/niaid-scientists-assess-transmission-risk-familial-human-prion-diseases-mice

  5. Kuru Information Page. (2019, March 27). National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/Disorders/All-Disorders/Kuru-Information-Page

  6. Saey, T. H. (2019, August 8). A protein variant can provide protection from deadly brain-wasting. Science News. https://www.sciencenews.org/article/protein-variant-can-provide-protection-deadly-brain-wasting

  7. Healthwise Staff. (2020, September 23). Mad Cow Disease. University of Michigan Health. https://www.uofmhealth.org/health-library/tu6533

  8. Centers for Disease Control and Prevention (CDC). (2021, October 18). About BSE. https://www.cdc.gov/prions/bse/about.html

  9. Summer, J. (2021, October 29). Fatal Insomnia. Sleep Foundation. https://www.sleepfoundation.org/insomnia/fatal-insomnia

  10. Dunning, H. (2021, March 15). Crucial step in formation of deadly brain diseases discovered. Imperial News. https://www.imperial.ac.uk/news/217234/crucial-step-formation-deadly-brain-diseases/

  11. Johns Hopkins Medicine. (n.d.). Prion Diseases. https://www.hopkinsmedicine.org/health/conditions-and-diseases/prion-diseases

  12. Okayama University. (2020, October 20). ’Rare’ Brain Disorder May Not Be So Rare Anymore, Trends in Japan Reveal. http://www.okayama-u.ac.jp/eng/research_highlights/index_id115.html

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