The Fore tribe of Papua New Guinea used to have a funeral rite in which mourners ate the brain of the deceased. In the process, some were unintentionally infected by a mad cow–like prion disease called kuru. By the 1950s, this practice was killing up to 2 percent of the tribe every year. But then something amazing—and yet totally natural—happened: some Fore evolved a genetic resistance to the disease that remains in place today, even though the Fore have largely abandoned the brain-eating ritual.

According to a new study published in the journal Nature, the genes of this tribe might help scientists unlock mysteries about neurodegenerative diseases, which could in turn lead to valuable insights on dementia.

Prions are infectious proteins that lead to brain diseases like Creutzfeldt-Jakob disease (CJD), kuru, and fatal familial insomnia in humans, scrapie in goats and sheep, mad cow disease in cattle, and chronic wasting disease in deer and elk. 

Previous research found that people like the Fore with a naturally occurring variant in the gene that codes for the prion protein seemed to be protected from these diseases. In this new study, John Collinge and colleagues analyzed this variant prion protein, called G127V, to see how it affects susceptibility to infectious prions. What has the researchers intrigued is that this particular prion resistance gene also guards against all other forms of CJD. 

On occasion, prions also cause dementia. This matters for scientists who say that the processes by which the prion diseases take hold are the same as the processes that lead to Alzheimer’s, Parkinson’s, and other brain-attacking diseases. Prions do this by essentially shape-shifting and then clumping together to form polymers that cause neurodegeneration.

Collinge told Reuters, “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 said the work will now be to understand the molecular basis of this effect, to examine more closely how misshapen proteins grow in the brain and lead to forms of dementia. In time, those findings could lead to new and better treatments of such diseases.

[h/t Guardian]