November 24, 2009
WASHINGTON (Reuters) - 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, researchers said Wednesday.
Their study of the unusual cannibalistic practice shows evolution in real time in the human population, and might lead to a treatment for similar brain-wasting conditions, the researchers reported in the New England Journal of Medicine.
Kuru once wiped out entire generations of women in remote Papuan villages. It was traced to a now-defunct mortuary ceremony in which women and children ate the brains of their dead relatives.
Dr Simon Mead of the University College London Institute and colleagues found that women in these communities were more likely to live to an old age if they had the protective gene. Women without the gene died young of kuru.
"This is just a classical example of evolution in humans," Mead said in a telephone interview.
Kuru 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.
All are fatal and incurable, creating spongy holes in the brain. They can be transmitted by eating contaminated body parts. BSE devastated British dairy herds in the 1980s and was traced to feeding sheep remains to cattle.
Some people developed a rare form of CJD from eating infected beef, and 166 people in Britain and 25 in France have died of it.
UNIQUE MUTATION
Mead's team studied more than 3,000 Papuans, including 709 who participated in cannibalistic mortuary feasts. They included 152 who died of kuru.
They looked at the genes for prions, ordinary brain proteins that take on a misfolded shape in prion disease such as CJD and kuru. They found a mutation called G127V that protected people from kuru.
Only people who ate brains and survived have it, they found. "It is not found in patients with kuru and in unexposed population groups worldwide," they wrote.
They have looked at people who had CJD and who did not have it, and have been unable to find the mutation, Mead said.
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.
So the mutation must have evolved because of the selective pressure caused by eating brains, he said.
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.
In prion diseases, the misfolded prion attaches to healthy prions, which for unknown reasons take on the misfolded shape.
The mutation seems to block this attachment, Mead said, and its discovery points researchers to the precise site.
That could lead to treatments for CJD, which occurs randomly in about one in a million people, Mead said.
"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.
(Editing by Philip Barbara)
