Kuru prions most similar to sporadic CJD prions
4 March 2008
In the early 20th century the prion disease kuru gripped the Fore people of the Eastern Highlands of Papua New Guinea killing many women and children.
The spread of kuru through ritual cannibalism is well documented, but what caused the disease to arise in these isolated people in the first place has been more difficult to determine. By comparing kuru prions to those that cause other kinds of human prion disease, researchers at the MRC Prion Unit have been able to show that kuru probably originated from an individual with sporadic Creutzfeldt-Jakob disease (CJD).
Prion diseases are unique in that they can arise in one of three ways: by an inherited mutation in the gene that gives instructions for the normal version of prion protein, infection with tissue that contains prions or by rare sporadic creation of an abnormal prion protein that then corrupts the other normal versions present in the brain. Worldwide sporadic CJD occurs in one or two in a million people each year.
In 1995 the first case of variant CJD (vCJD) appeared in the UK. It was later confirmed that vCJD is caused by the same strain of prion that causes bovine spongiform encephalopathy (BSE) in cattle. BSE prions were passed on when people consumed infected meet. When one of the Fore people died, their relatives honoured them by eating their remains. Studying the incubation period before the signs of kuru developed and individual genetic susceptibility to the disease has helped scientists to learn more about how vCJD might affect the UK population.
By comparing if, and how, kuru and other prions that infect humans cause disease in mice scientists have shown that kuru prions are most similar to those that cause sporadic CJD, rather than vCJD prions.
Two groups of mice were used. The first group was genetically modified to carry a human version of the prion gene making it susceptible to infection; the second group consisted of unaltered ‘wild type’ mice.
Kuru prions were found to have the same rates of transmission to the transgenic mice as sporadic CJD prions but it did not cause disease in the wild type mice.
In comparison only half of the transgenic mice developed prion disease when given vCJD prions. This suggests that kuru prions are more similar to sporadic CJD prion types than those that cause vCJD and in turn indicates that the kuru epidemic originated from chance consumption of one individual who had sporadic CJD.
This conclusion is further supported by the pattern of brain disease kuru prions cause in the transgenic mice. Comparison of the changes to brain tissue caused by kuru prions showed that these are most similar to changes caused by sporadic CJD prions and distinct to the changes caused by variant CJD prions.
Although kuru and vCJD are caused by different strains of prions, the route of infection (through consumption) is the same. Kuru remains the only known epidemic of a human prion disease that is passed on in this way making it important to continue to study the disease.
The research was led by Professor John Collinge, Director of the Medical Research Council Prion Unit at the Institute of Neurology, University College London. Results are published online in the journal PNAS.
Original research paper: Kuru prions and sporadic CJD prions have equivalent transmission properties in transgenic and wild type mice: PNAS 3 March 2008.
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