Bronze and Iron Age graves of five babies with Down syndrome revealed by ancient DNA

A study of DNA sequences from nearly 10,000 ancient individuals has revealed six children with Down syndrome. By following the trail to records of their remains and burial sites, scientists can map the history of these children and the positions they took within their communities.

Most people are born with 46 chromosomes – 22 pairs of autosomes, plus XX or XY sex chromosomes. However, occasionally people are born with missing or extra copies of certain chromosomes, a condition called aneuploidy.

People with Down syndrome have an extra copy of chromosome 21. In the vast majority of cases, all cells in their bodies have three copies of chromosome 21 instead of two, known as a trisomy. The condition affects about one in a thousand births today, but scientists knew less about how common the condition was among our ancient ancestors.

Adam “Ben” Rohrlach of the Max Planck Institute for Evolutionary Anthropology, together with colleagues from around the world, planned the first systematic study of rare genetic disorders in ancient human genomes. Among nearly 10,000 DNA samples tested, they were surprised to identify six individuals with unusually large amounts of chromosome 21 DNA, something they said could only be explained by having an extra copy of the chromosome.

One of the samples came from a child buried in a cemetery in Finland sometime in the 17th centurye or 18e centuries, but the other five were much older. These samples come from Bronze Age sites in Greece and Bulgaria, and Iron Age sites in Spain, and all date from between 5,000 and 2,500 years ago. In addition to the six new cases, the team was also able to verify a previous report of Down syndrome in a baby from Ireland born between 3629 and 3371 B.C. died.

aerial view of the early Iron Age settlement of Alto de la Cruz

An aerial view of the Early Iron Age settlement at Alto de la Cruz, Navarre, Spain.

Image credit: Government of Navarre and JL Larrion

But probably even more exciting than the genetic findings was the wealth of information the researchers were able to obtain about the individuals’ graves and remains.

They were able to confirm for the first time that all the children had died in infancy, and that only one appeared to have reached their first birthday. This is perhaps not surprising, as Down syndrome comes with a range of potential medical complications – these can be treated well with modern medicine, but may have been an insurmountable challenge for the doctors of the ancient world.

The cemeteries themselves provided some clues as to how these children may have been treated by the adults around them.

“These burials seem to show us that these individuals were cared for and valued as part of their ancient societies,” Rohrlach said in a statement. This was evident from the special grave goods such as jewelry, shells and even animal remains that were buried with some bodies. The five oldest burials were all located within settlements, a privileged position for the deceased.

partially buried human bones

Remains of a child with Down syndrome buried in one of the houses in the Iron Age settlement.

Image credit: Government of Navarre and JL Larrion

Down syndrome wasn’t the only rare genetic condition shown in the data. Another individual was also flagged for having unexpectedly high levels of DNA sequences from chromosome 18, indicating there was an extra copy of that chromosome. Trisomy 18 is also called Edwards syndrome. Most fetuses with the condition do not survive to term, and those born have a severely shortened life expectancy.

It is puzzling that the child with Edwards syndrome was also found in one of the Spanish Iron Age cemeteries. “At this time we cannot say why we find so many cases at these sites,” says co-author Roberto Risch, “but we know that they were among the few children who were given the privilege of being buried in the houses after their death . This is already an indication that they were seen as special babies.”

Evidence from even older burials has suggested that prehistoric societies were friendlier to people with disabilities than we might have thought. These findings seem to reinforce that idea, and the authors hope to expand their research to shed even more light on it.

Senior author Kay Prüfer explains: “What we would like to learn is how ancient societies responded to individuals who might need a helping hand or were just a little different.”

The research has been published in Nature Communications.

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