Have Arthritis Or Crohn’s? It Might Be Because Your Ancestors Survived The Plague

Scientists now believe that descending from a survivor of the Black Death, the plague which wiped out one-third of Europe nearly seven hundred years ago, makes individuals more susceptible to certain medical conditions.

There are four particular DNA variants that were associated with surviving the plague as it first swept across the world in the mid-1300s, according to a new paper published in Nature. At least two of those mutations, which are carried by small mammals and the fleas that accompany them, are now linked to autoimmune disorders like Crohn’s disease and rheumatoid arthritis.

McMaster University professor Hendrik Poinar told The Washington Post the genes “provided tremendous protection during hundreds of years of plague,” but that they’re now linked to autoimmune conditions, as they contribute to hyperactive immune systems.

Poinar and his colleagues from the University of Chicago, Pasteur Institute and McMaster found that individuals who had the genetic mutations passed down from their parents were about 40% more likely to survive the plague. University of Chicago professor of genetic medicine Luis Barreiro said the study was “evidence that this one single disease event was enough to lead to selection in the human immune system.” (RELATED: Squirrel Tests Positive For Bubonic Plague In Colorado)

The researchers examined 200 DNA samples from individuals who lived in London or Denmark who lived before the plague, one to two generations after it, or died of it. DNA analyses suggest that today, about 45% of British people have the protective variants.

In all, the Black Death killed an estimated 75-200 million people, culling upwards of one-third the entire population of Europe and cutting the global population by around one-fifth over the course of less than a decade.

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