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A prion is a type of pathogen and the name given to the first protein found that exhibits prion-like infectious properties. Prions are a misfolded form of a host expressed protein. The misfolding allows one protein to cause the misfolding of another (the first acting as a template for the second), which will itself cause the misfolding of other proteins in a chain reaction. Prions are mostly known for being the transmission mechanisms for diseases that cause neurological tissues to break down in animals and humans which are collectively known as transmittable spongiform encephalopathies (TSEs). While prions usually cause brain disease, but it has been shown that prions can ocassionally affect other areas as well (including peripheral nerves) as well as cause other diseases, such as Alzheimer's.
Pathology of prions
There are several known human diseases caused by prions:
- Cruetzfeldt-Jakob disease (CJD), and its variants
- Gerstmann-Strausler syndrome (GSS)
- Fatal familial insomnia (FFI)
- Kuru (transmitted by mortuary cannibalism of brain tissue)
- Variably protease-sensitive prionopathy
There are also several animal diseases caused by prions:
- Bovine spongiform encephalopathy (BSE, or "mad cow disease")
- Chronic wasting disease (CWD)
- Scrapie (sheep and (sobs) goats)
- Transmissible mink encephalopathy
- Feline SE (yep, your cat can get it!)
- Ungulate spongiform encephalopathy
- Camel spongiform encephalopathy
These diseases are known collectively as transmissible spongiform encephalopathies (SE) and they have varying symptoms. Proteins, when exposed to enzymes that break them down (proteases), are chopped up into small bits (technically, the protein is protease-sensitive.). However, when the normal prion protein (PrPC) folding occurs, the proteins may misfold into the pathogenic/infectious form (PrPSc), after which it then causes disease. This has two effects, one is that the protein is highly protease-resistant, and are also resistant to other forms of destruction. Once a misfolded prion protein (PrPSc) comes into contact with normal protein prion protein (PrPC) it converts the PrPC into PrPSc (a domino effect). Prion infections are currently untreatable, although some people seem to have evolved a degree of resistance (most notably the Fore people due to consistent encounters with Kuru over several generations, some of whom went 45 years after initial contact before becoming symptomatic); a person or animal infected will die and the proteins remain infectious.
Strangely enough, while synthetic mouse prions have been found to affect the brains of mice, synthetic human prions do not seem to be able to cause disease in vitro unless they are in the presence of certain co-factors such as specific forms of RNA, suggesting that the current picture of prion pathogenesis is incomplete.
Several prion-like proteins have also been identified in yeasts. However, these fungal prions appear to be benign or even positive in their effects, allowing them to function as a form of epigenetic inheritable that increases variation in phenotypes among a population that would otherwise be genetically homogenous.
There are three types of prion disease — infectious, sporadic and genetic.
- In the infectious form you get the disease by contact with infected materials or tissues. The nervous system tissue is the most infectious material. It is unknown whether prion disease can be transmitted by blood but blood banks often ban prion-infected people from donating blood (outside of the UK — there they just gave up checking due to the expected prevalence of non-clinical infections). Transmissible also covers iatrogenic transmission (getting the disease from infected medical instruments — don't think too hard about where that endoscope went last!).
- The sporadic form occurs at random when proteins just misfold for a reason not yet known to medical science (this is by far the most common form)
- For the genetic prion diseases, prions are caused by a mutation of the PRNP human protein gene. Genetic prion diseases are the rarest out of the three of them. The most notable genetic prion disease is fatal familial insomnia, a genetic disorder present in only 30 families worldwide. In animals it seems that corpses transmits prion disease and unlike in humans prions are 100% lethal.
Signs and symptoms of prion disease
Prion diseases are always degenerative, and eventually lead to death. Signs and symptoms vary among each disease but are very similar. This section will give lists of the symptoms of a few of these diseases.
- Memory loss
- Loss of motor function
- Slurred speech
- Vision loss
- Loss of motor function
- Trouble walking
- Memory loss
- Mood swings
- Trouble swallowing
- Slurred Speech
- Bouts of alternating between laughing (which is always quite mirthless) and crying, hence the common name laughing sickness
Fatal Familial Insomnia
- Insomnia, eventually to the extent where sleep is completely impossible
- Loss of motor skills
- Slurred speech
Many medical professionals have never even heard of prions because they are so rare.
As with any deadly disease, there are quacks who promote woo. Earth Clinic, which is a natural health website, claims that apple cider vinegar and caprylic acid can treat the symptoms. However, if someone ingests too much caprylic acid it may cause pain in the gastrointestinal tract. Caprylic acid is fairly safe if taken in small amounts; outside that it does nothing to help with symptoms.
- Prion Diseases National Institute of Allergy and Infectious Diseases'.
- A Novel Prion Disease Associated with Diarrhea and Autonomic Neuropathy New England Journal of Medicine
- Peripheral Neuropathy in Patients with Prion Disease Neurology
- Alzheimer’s Disease is a ‘Double-Prion Disorder,’ Study Shows. University of California San Francisco Research. Nicholas W, 1 May 2019.
- Prion Diseases Centers for Disease Control.
- Protein Aggregation in the Brain: The Molecular Basis for Alzheimer’s and Parkinson’s Diseases by G. Brent Irvine et al. (2008) Mol. Med. 14(7-8): 451–464. doi: 10.2119/2007-00100.Irvine.
- A View from the Top--Prion Diseases from 10,000 Feet by Suzette A. Priola (2003) Science doi:10.1126/science.1085920.
- Doppel: More rival than double to prion by Kefeng Qin et al. (2006) Neuroscience 141(1):1-8. doi:10.1016/j.neuroscience.2006.04.057.
- Epidemiological mechanisms of genetic resistance to kuru by Katherine E. Atkins et al. (2013) Journal of the Royal Society Interface 10(85): 20130331. doi:10: 20130331.
- Artificial strain of human prions created in vitro by Chae Kim, et. al. (04 June 2018) Nature.com. Nat Commun 9, 2166 (2018).
- Prions in Yeast by Susan W. Liebman & Yury O. Chernoff (2012) Genetics 191(4): 1041–1072. 10.1534/genetics.111.137760.
- Mad Cow Disease Remedies (Modified: Feb 17, 2017) Earth Clinic.