This week, I have been researching three specific diseases (two of which are hereditary and found in humans and the other in cows). I will be referring to terms that I used in my previous round of research; I will provide short explanations for some of them as a recap, but refer to my 1st round if confused. My inquiry question is:
How influential is the role of prions in evolution and is it more beneficial or detrimental?
Before we begin, I will do a quick revision to clarify.
Prion protein (PrP): this is a protein that is encoded in a host and is non-infectious.
PrPc: a normal prion, formed of prion protein (the c stands for cellular) and that is the form that PrP normally exists as.
PrPsc: this is a mutated prion; it is abnormal and not all prions mutate into it. This is the infectious form that causes the diseases I'll be focusing on below. (sc stands for scrapie, which was the original disease primarily observed in goats). (1)(2)
Otherwise known as CJD, there are three forms of this disease: sporadic, familial and acquired infection.
Sporadic: most cases of CJD are documented as sporadic and occurs for unknown reasons (it appears in people who have no known risk factors). This type accounts for 85% of cases and is normally found in people over 65. (3)(4)
Familial: occurs when person inherits an abnormal prion from a descendant. These cases account for about 10% of the population. (4)
Acquired infection: this disease is transmitted through the nervous system, usually by another medical operation (blood product transfusion, contaminated surgical instruments). This is also the rarest of the three types of CJD. This form includes variant CJD (vCJD), which is related to mad cow disease. This can be caused by eating infected meat. (3)(4)(5)
These three forms of the disease share the same symptoms, visible both mentally and physically. Mood swings, depression and apathy are common as well as impaired memory, judgement and thinking. Many subjects develop increasing confusion and disorientation as well. Physically, people begin to develop difficulty walking and often develop involuntary jerky muscle movements. As the illness progresses, mental impairment becomes severe and individuals will, not uncommonly, enter a coma. Patients diagnosed with CJD most often die within the year of diagnosis. (3)(4)(6)
Mad Cow Disease
Mad cow disease (or BSE) is another neurodegenerative disease that infects the central nervous system of adult cattle. (7)(8) This infection leads the tissue in the brains of cattle to develop tiny, sponge-like holes when viewed under a microscope. These holes cause a slow mental deterioration in the cow. The reason why it was named "mad" cow disease is because months after diagnosis, cattle begin to have "mad" seizures because of their mental deterioration. Symptoms of this disease are very similar to symptoms found in CJD, including depression, impaired thinking and involuntary jerky movements.
Lastly, Fatal Familial Insomnia.
This hereditary disease mainly affects the thalamus. The thalamus is the part of the brain that controls our sleep cycles but is also considered the "relay center" of the brain because it communicates messages to other parts of the brain. FFI is another progressive degenerative disease.
Symptoms for this disease can begin as early as 18 and as late as 72, but the mean age to develop it is 53. Evidently, as the name suggests, one of the defining symptoms is progressive insomnia. Weight loss, lack of appetite and extreme body temperatures are also common symptoms as well as the similar symptom in all prion diseases, dementia and increasing mental deterioration. (9)(10)
That's it for this round! To quickly recap, I summarized three different prion diseases. All of these diseases are categorized as progressive neurodegenerative diseases (which means over time there are fewer neurons) and although are quite rare, are deadly and as little is known about why prions cause these diseases, it makes them all the more dangerous. Thanks for reading, comment feedback and questions below!