Prion proteins (PrP) are proteins that every individual has, located on the surfaces of cells. The instructions for the synthesis of this protein are located on chromosome 20; on the prion protein gene (PRNP). However, sometimes these proteins are folded abnormally, and can cause diseases in animals. These abnormal versions of the protein are called prions, and they cause prion diseases as they infect surrounding proteins by also causing them to fold abnormally.
Prion diseases are neurodegenerative diseases, as the prions spread across the brain and damage nerve tissues. These diseases have a long incubation period – often of around 5-20 years, but sometimes as long as 50 years – where there are no symptoms. After the incubation, symptoms begin to show and cognitive deterioration is rapid.
Prion diseases can be spread in three different ways. The first way is through genetics; if the PRNP gene develops a random mutation, then the RNA transcripted from the DNA will be faulty, and the polypeptide chain translated from the mRNA will code for an abnormal version of the protein. This gene can then be inherited by offspring of the individual, however 60% of genetic causes of prion diseases have no prior history of the disease. A small percentage of prion diseases are sporadic, and the cause is unknown.
The least common way of obtaining a prion disease is by acquiring it from an individual. However, this transmission was very common in the kuru epidemic in Papua New Guinea which was at its peak in the mid 20th century. In this culture, the practice of transumption – eating dead relatives – was very common at this time. Eating the cooked flesh of a dead human bared no more risk than eating a cooked joint of meat such as beef or pork…except the eating of the human brain. If the brain was infected with prions, then the cannibal would acquire the kuru disease.
The symptoms of kuru varied between the three stages of the disease after the initial, asymptomatic period. The ambulant stage had symptoms including headaches, shaking and decreased muscle control. The sedentary stage had symptoms including loss of the ability to walk, severe tremors and loss of emotional stability, including bursts of pathological laughter which gave the disease its nickname of ‘laughing sickness’. The final stage – the terminal stage – had symptoms including virtually no muscle control, inability to speak and inability to respond to surroundings. Usually, the individual died within 3 months to 2 years of obtaining symptoms. The last case of kuru was thought to have been in 2005.
So the lesson is, if you are going to indulge in the practice of cannibalism, under no circumstances should you eat the brain!
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