The mutation first arose about 200 years ago by accident in a single individual, who then passed it down to his or her descendants. “When the kuru epidemic peaked about 100 years back, there were maybe a couple of families who found that they and their children survived while all their neighbours were dying, and so on to today’s generation, who still carry the gene,” says Mead. “So it was a very sudden genetic change under intense selection pressure from the disease,” he says.
None of the 152 victims of kuru had the protective gene, suggesting that it provides almost complete resistance to the disease. But it’s not yet known whether the variant protects against other prion diseases. Mead said that experiments are already under way in mice deliberately given the new mutation, to see if they are protected against both kuru and vCJD.
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