November 19, 2009

Rare Gene Kept Cannibalistic Villagers From Getting Brain Disease

Researchers said on Wednesday that villagers in the highlands of Papua New Guinea who ritualistically ate human brains but did not die of a brain disease called kuru have a genetic mutation that protects them, Reuters reported.

The study, reported in the New England Journal of Medicine, said the unusual cannibalistic practice shows evolution in real time in the human population, and might lead to a treatment for similar brain-wasting conditions.

Entire generations of women in remote Papuan villages were once wiped out by kuru. Scientists traced the disease to a now-defunct mortuary ceremony in which women and children ate the brains of their dead relatives.

Women in these communities were more likely to live to an old age if they had the protective gene, whereas women without the gene died young of kuru, according to Dr. Simon Mead of the University College London and colleagues.

Mead called the discovery a classical example of evolution in humans.

The disease is caused by prions, the unusually folded brain proteins that also cause mad cow disease or bovine spongiform encephalopathy, Creutzfeldt Jakob disease, or CJD, chronic wasting disease in deer and elk and scrapie in sheep.

Each disease creates spongy holes in the brain and all are fatal and incurable. These diseases are transmittable by eating contaminated body parts.

BSE devastated British dairy herds in the 1980s and was traced to feeding sheep remains to cattle.

A more rare form of CJD killed 166 people in Britain and 25 in France after eating infected beef.

After studying more than 3,000 Papuans, including 709 who participated in cannibalistic mortuary feasts, Mead's team found that 152 of them died of kuru.

The researchers closely studied the genes for prions, ordinary brain proteins that take on a misfolded shape in prion disease such as CJD and kuru, and discovered a mutation called G127V that protected people from kuru.

They found that only people who ate brains and survived had the disease.

"It is not found in patients with kuru and in unexposed population groups worldwide," the researchers wrote.

Mead said they looked at both people who had CJD and those who did not and found they were unable to locate the mutation.

He explained that the gene itself is seen in many animals and almost never mutates.

"All the way back to frog there is the same amino acid in exactly this position in the prion protein gene. That tells us it is doing something very fundamental," Mead said.

Therefore, he believes the mutation must have evolved because of the selective pressure caused by eating brains.

"It is remarkable how few definite examples there are that we can really link with a clear history of a disease or an event. It was such a devastating disease and well documented ... and we can now see the effects of this genetically," Mead said.

He said that with prion diseases, the misfolded prion attaches to healthy prions, which for unknown reasons take on the misfolded shape. However, the mutation seems to block this attachment, and its discovery points researchers to the precise site.

Mead said this could even lead to treatments for CJD, which occurs randomly in about one in a million people.

"If you could find a drug or a molecule or an antibody that binds to that site, you could interfere with that process," he said.


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