Eating human brains helped some be disease-resistant
The Fore people, a once-isolated tribe in Papua New Guinea, had a long-standing tradition of mortuary feasts — eating the dead from their own community at funerals.
Men consumed the flesh of their deceased relatives, while women and children ate the brain. It was an expression of respect, but the practice wreaked havoc on the communities they left behind.
That’s because a deadly molecule that lives in brains was spreading to the women who ate them, causing a horrible degenerative illness called “kuru” that at one point killed two per cent of the population each year.
The practice was outlawed in the 1950s, and the kuru epidemic began to recede. But in its wake it left a curious and irreversible mark on the Fore: After years of eating brains, some Fore have developed a genetic resistance to the molecule that causes several fatal brain diseases, including kuru, mad cow disease and some cases of dementia.
The single, protective gene is identified in a study published this week in the journal Nature. Researchers say that the finding is a huge step toward understanding these diseases and other degenerative brain problems, including Alzheimer’s and Parkinson’s.
The gene works by protecting people against prions, a strange and deadly kind of protein. Though prions are naturally manufactured in all mammals, they can be deformed in a way that makes them turn on the body that made them, acting like a virus and attacking tissue.
The deformed prion is even capable of infecting the prions that surround it, reshaping them to mimic its structure and its malicious ways.
The prions’ impact on their hosts is devastating and invariably fatal. Among the Fore, the prions riddled their victims’ brains with microscopic holes, giving the muscle an odd, spongy texture. In cattle, prions cause mad cow disease — they are responsible for the epidemic in Britain of the late ’80s and ’90s that required hundreds of thousands of cattle to be destroyed.
They have been linked to a bizarre form of fatal insomnia that kills people by depriving them of sleep. And they’re the source of the degenerative neurological disorder Creutzfeldt-Jakob disease (CJD), characterized by rapid dementia, personality changes, muscle problems, memory loss and eventually an inability to move or speak.
The vast majority prion-diseases are “sporadic,” seemingly appearing without cause. But a lead author of the Nature study, John Collinge of University College London, said in an interview with Nature that a portion of cases are inherited from one’s parents, and an even smaller percentage are acquired from consuming infected tissue. Variant CJD, often called the “human mad cow disease,” is caused by eating beef from infected cows.
When the researchers looked at the part of the genome that encodes prion-manufacturing proteins, they found something completely unprecedented. Where humans and every other vertebrate animal in the world have an amino acid called glycine, the resistant Fore had a different amino acid, valine.
“Several individuals right at the epicentre of the epidemic, they have this difference that we have not seen anywhere else in the world,” Collinge told Nature.
“This is a striking example of Darwinian evolution in humans, the epidemic of prion disease selecting a single genetic change that provided complete protection against an invariably fatal dementia,” Collinge told Reuters.