The story of kuru, as classically told in biology textbooks, is a tragic one. The Fore population in Papua New Guinea ate the brains of their tribe members as an act of mourning, a ritual that allowed a misshapen protein to spread through the population. This caused the disease kuru, which killed as much as 10 per cent of the population in the mid-twentieth century.
Now, scientists have identified mutations in some of the survivors that makes them immune to kuru and possibly other similar brain diseases.
Kuru and Creutzfeldt — Jakob disease, the latter of which is also known as the human form of mad cow, are caused by a type of misfolded proteins called prions. Prions are poorly understood, but they spread by causing normal proteins to take on their misshapen form. As prions propagate through the brain, they cause microscopic holes, turning the brain "spongy". Confusingly, several different proteins can become prions, but the first protein ever discovered to take on this form is called the major prion protein, or PrP. The prion form of PrP causes both kuru and Creutzfeldt — Jakob disease.
The practice eating the brains of the dead was outlawed in Papua New Guinea in 1950s. In 2009, researchers went back to do a genetic analysis of elderly women who had survived the kuru epidemic. They ended up with two promising mutations in PrP, in the 127th and 129th amino acids of the protein.
The team has since followed up their findings with a new study in mice, published in Nature. They created mice with these two mutations and tested how they fared when exposed to kuru and Creutzfeldt — Jakob disease. Mice with only one copy of the mutation in 129 had some resistance to prion diseases. Mice with either one or two copies of the mutation in 127 were completely resistant.
Now, it's still unclear why a single amino acid change in PrP makes such a big difference. But this is an intriguing example of evolved immunity to a deadly disease, which could lead to better treatments in the future.