Researchers say they've identified a genetic mutation that may make people resistant to the brain-destroying disease CJD, the human equivalent of "mad cow disease."

Creutzfeldt-Jakob disease (CJD) is a rare but fatal brain disorder, in a class of what is known as prion diseases, similar to bovine spongiform encephalopathy (BSE), or mad cow disease.

CJD is seen in three forms; sporadic CJD, which can occur naturally but rarely in humans; variant CJD, which can result from eating beef infected with BSE; and kuru, a type of CJD once common among a particular tribal community in Papua New Guinea that ate human brains of dead tribal members as a mark of respect during mortuary feasts.

Kuru became an epidemic among the community, known as the Fore people, reaching its height in the 1950s.

John Collinge of the Medical Research Council's Prion Unit at University College London, in the hope of finding treatments for the other forms of CJD, has been studying kuru among the tribe for some 20 years.

He was struck by the fact that some members of the Fore people seemed resistant to kuru.

Research showed they possessed a mutation in a single gene that provided resistance to kuru — and further study showed the mutation could provide protection against all of the types of CJD disease, the researchers report in the journal 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 says.

The findings could have applications in the search for treatments of other neurological conditions, the researchers point out.

The process involved in CJD and BSE — involving prion proteins that change their shape and form clumps that damage the brain — is found in other forms of dementia, including Alzheimer's, and in other neurodegenerative diseases such as Parkinson's.

In the 1990s, there were fears of an epidemic of variant CJD in people who ate beef infected with BSE.

It is estimated that one in 2,000 people in the United Kingdom may be carrying an infection, and although less than 200 people are believed to have died from variant CJD, "It is important that we don't drop our guard," Collinge says, noting that people with kuru take decades to develop the disease after being infected.

The same could be true of variant CJD, he says.

"Thirty thousand people are silently carrying the disease and we don't know whether they will carry on carrying the disease without developing symptoms or go on to develop the disease."

It may be decades before the full impact of the 1990s BSE exposure is known, he says.