Genetics may protect against disease linked to eating human brains

A genetic study in an extraordinarily remote community in Papua New Guinea has uncovered new insights into a brain disease spread by people eating their dead relatives, which killed thousands of people in the 20^th century.

Strewn with mountains, gorges and fast-flowing rivers, the Eastern Highlands province of Papua New Guinea is so isolated from the rest of the world that it wasn’t until early in the 20^th century that outsiders realised it was home to around a million people.

Some of the tribes, known as the Fore, practised a form of cannibalism called “mortuary feasts”, where the bodies of deceased relatives were consumed as part of funeral rituals.

This sometimes meant they consumed abnormally folded proteins, called prions, that can cause a fatal neurodegenerative condition called kuru – which is related to Creutzfeldt-Jakob disease (CJD). Locals, however, believed that kuru was caused by sorcery. There were at least 2700 recorded kuru deaths in the Eastern Highlands.

Simon Mead from University College London and his colleagues examined the genomes of 943 people from the region, representing 68 villages and 21 linguistic groups. Although this part of Papua New Guinea covers only just over 11,000 square kilometres and is smaller than Jamaica, the different groups are as genetically distinct as people from Finland and Spain, which are around 3000 kilometres apart, say the researchers.

Not everybody who participated in the mortuary feasts succumbed to the disease, the study found. Mead and his colleagues say it appears the community had begun to evolve some resistance to kuru, which leads to tremors, loss of coordination and eventually death.

Some of the older women who survived the feasts carried variants in the gene that encodes prion proteins that probably made them resistant to kuru, the study found.

By the 1950s, the epidemic of kuru began to subside as mortuary feasts became illegal, but visitors noted that in some villages the number of females was depleted because so many had died from kuru. Mead says women and children were probably most susceptible to contracting the disease because they ate the brains of their dead relatives.

However, the genetic evidence shows that there was a large influx of women into Fore tribal areas, especially where there were the highest levels of kuru, in spite of fears about the disease.

“It seems likely to us that the sex bias caused by kuru led bachelors within kuru-affected communities to seek wives from further afield than usual due to the lack of availability of potential wives more locally,” says Mead.

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He says the team hopes to learn what factors confer resistance to prion diseases such as CJD, which caused a serious epidemic in the UK in the 1990s.

“[Our work sets] the scene to detect genetic factors that might have helped the Fore resist kuru,” says Mead. “Such resistance genes might hint at therapeutic targets.”

Ira Deveson at the Garvan Institute of Medical Research in Sydney, Australia, says the study provides new insights into the “rich and unique cultural, linguistic and genomic diversity” of the Eastern Highlands.

“It is a demonstration of how genomics can be used almost to look back in time – reading the genetic signatures of past epidemics, and to understand how these have shaped the populations of today.”