An international study that has analysed the genome of nearly 10,000 ancient individuals to search for cases of chromosomal trisomies has identified six cases of Down syndrome, all from babies: five of them dating back to between 5,000 to 2,500 years ago, and one from a more recent period. Three of the prehistoric cases were found at sites dating back to the Early Iron Age in Navarre (ca. 2,800 to 2,500 years ago). Another less frequent and more severe case of Edwards syndrome was also found at one of the Navarrese sites, being the first in an archaeological population anywhere in the world. All of the babies died before or shortly after birth and were buried within the houses, some even accompanied by funerary offerings, demonstrating that they were appreciated members of their society. The study, published in Nature Communications, was led by the Max Planck Institute for Evolutionary Anthropology (MPI-EVA) in Leipzig and included the involvement of the Universitat Autònoma de Barcelona (UAB), the University of Alicante (UA) and the Public University of Navarre (UPNA).
The research is one of the first systematic studies using genetic screening in ancient human samples in search of uncommon genetic conditions, like chromosomal trisomies, characterized by the presence of three copies of a chromosome instead of the usual two. One of these conditions is Down syndrome, or trisomy 21, a genetic condition caused by an additional copy of chromosome 21 and occurring in approximately 1 out of every 1,000 births. The study was carried out on the basis of a new statistical method of genetic sequencing, complemented by an osteological review of the identified cases and the existing archaeological record.
Javier Armendáriz and Patxuka de Miguel, at UPNA.
Of the five prehistoric individuals with Down's syndrome, three were found in the Navarrese sites of Alto de la Cruz and Las Eretas, corresponding to Navarre’s Iron Age (ca. 2,800 to 2,500 years ago), and two more ancient cases dating back to the Bronze Age in Greece and Bulgaria (ca. 4,700 to 3,300 years ago). The sixth case was discovered in a church graveyard in Finland and dates back to the 17th or 18th century. Another case was discovered at the site of Alto de la Cruz and was identified as a baby with Edwards syndrome or trisomy 18, which occurs much less often than trisomy 21 and with more severe health issues that Down syndrome and affecting approximately 1 in every 3,000 births. This is the first ever case of Edwards syndrome identified in an archaeological population anywhere in the world.
According to the analysis of the skeletal remains, all individuals died before or shortly after birth. Only the case in Greece reached the age of one year.
One surprising aspect that all of the prehistoric cases share is that they were found to be buried inside their homes, within the settlements, and some of them with funerary offerings, as in the cases of Greece and Bulgaria and one female baby with Down syndrome found in Alto de la Cruz, who was buried in a rich funerary tomb (a bronze ring, a marine seashell and remains of three sheep or goats), possibly in what was once a place of worship.
"These burials seem to show us that these individuals were cared for and appreciated as part of their ancient societies", says Adam Ben Rohrlach, lead author of the study.
Left: skeleton of a baby boy with Down Syndrome in Las Eretas, Navarre, who died approximately with a gestational age of 26 weeks. Right: Skeleton of a baby girl with Down Syndrome who died with a gestational age of around 28 weeks. (© Foto J.L. Larrión, Gobierno de Navarra).
A surprising finding
The Iberian communities of the Iron Age had a particular funerary ritual: contrary to the dominant custom of cremation, some premature babies and newborns were buried inside the houses or in intramural spaces. Even so, the discovery of the four cases with genetic conditions in two closely located and contemporary settlements surprised the research team.
“For the moment, we cannot say what this could be due to, but we know that they belonged to the few children who received the privilege of being buried inside the dwellings after death. This is already a hint that they were perceived as special babies and valuable for their communities, but we will need to extend the research with individuals from the same period found at other sites to formulate a hypothesis on the rituals that led to this practice”, explains Roberto Risch, UAB archaeologist and co-author of the study.
Aerial photo of Alto de la Cruz, Navarre, belonging to the Early Iron Age (©Servicio Patrimonio Histórico Gobierno de Navarra).
“It is possible that only babies dying of natural causes, but perceived by the community as special beings, were buried in the living spaces”, says Javier Armendáriz from the UPNA. “It has to be noted, however, that not all newborns buried within the houses of the Iron Age were cases of genetic pathologies. In the settlement of Las Eretas we found a boy with Down syndrome and next to him a girl, a second-degree relative, who could have been his half-sister, buried in the same place”, Armendáriz adds.
As for the osteological study, researchers observed anomalies in some of the individuals, which could be compatible with their genetic condition, although other causes cannot be ruled out. "In any case, these first cases of trisomy in populations of the past offer the chance of identifying possible bone modifications related to this genetic anomaly, which would make it possible to identify them in large anthropological collections”, says Patxuka de Miguel, osteoarchaeologist at the UA.
The authors plan to continue to expand their research in the future as the number of DNA samples from ancient individuals continues to increase. “What we would like to know is how ancient societies reacted to individuals who might have needed a helping hand or were simply a bit different”, says Kay Prüfer, coordinator of the sequence analysis.