Scientists revealed why so many people have Alzheimer’s in Colombian town

The town of Yarumal in Colombia is famous for all the wrong reasons: it has the world’s largest population of people with Alzheimer’s disease.

In Yarumal and the surrounding state of Antioquia, 5000 people carry a gene mutation which causes early-onset Alzheimer’s – half of them will be diagnosed by the age of 45, and the other half will succumb by the time they are 65.

Locals call the disease La Bobera, “the foolishness”, and the village bears uncanny parallels with the fictional Macondo in Gabriel Garcia Marquez’s novel One Hundred Years of Solitude, where people suffer memory disorders and hallucinations. But while Yarumal’s “curse” is well known, no one knew how the mutation first appeared.

Now researchers have traced the ancestry of the mutation, concluding that it was probably introduced by a Spanish conquistador early in the 17th century.

Ken Kosik at the University of California, Santa Barbara, and colleagues collected blood samples from 102 people in Antioquia and sequenced their genomes. The mutation causing this form of early-onset Alzheimer’s is called E280A and is found in a gene on chromosome 14 – 74 people had the mutation.

Because Kosik’s team had information on the genome sequence around the mutation, they could use something called identity-by-descent analysis to determine how the people in the study were related. The analysis suggested the mutation arose from a common ancestor around 375 years ago.

The geneticists then compared the genetic profile of an Antioquian carrier of E280A against genetic profiles from three potential continents of origin, and the evidence pointed to Western Europe.

This is consistent with a Spanish origin for the 17th-century carrier of the initial mutation, the team say. The conquistadors – soldiers and explorers of the Spanish Empire – began colonising Colombia in the early 16th century, and Yarumal itself was founded in 1787.

“It’s hard to explain why all these people would share such a large chunk of DNA if there hadn’t been a common founder,” says Kosik.

“Putting the genetic data and the historical records together, the assumption that the mutation was introduced by one Spanish conquistador is very likely,” says Rita Guerreiro, a geneticist at University College London. “I think it is fair to conclude from this study that the history of Yarumal and the history of E280A are one and the same.”

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