Ancient DNA Study Finds Evidence of Chromosomal Disorders

By analyzing ancient DNA, an international team of researchers have uncovered cases of chromosomal disorders, including what could be the first case of Edwards syndrome ever identified from prehistoric remains.

The team identified six cases of Down syndrome and one case of Edwards syndrome in human populations that were living in Spain, Bulgaria, Finland, and Greece from as long ago as 4,500 years before today.

The research indicated that these individuals were buried with care, and often with special grave goods, showing that they were appreciated as members of their ancient societies. 

The global collaborative study, led by first author Dr Adam "Ben" Rohrlach of the University of Adelaide, and senior author Dr Kay Prüfer of the Max Planck Institute for Evolutionary Anthropology, involved screening DNA from approximately 10,000 ancient and pre-modern humans for evidence of autosomal trisomies, a condition where people carry an extra (third) copy of one of the first 22 chromosomes. 

Using a new statistical model, we screened the DNA extracted from human remains from the Mesolithic, Neolithic, Bronze and Iron Ages all the way up to the mid-1800s. We identified six cases of Down syndrome."

Dr Adam "Ben" Rohrlach, statistician, University of Adelaide's School of Mathematical Sciences 

"While we expected that people with Down syndrome certainly existed in the past, this is the first time we've been able to reliably detect cases in ancient remains, as they can't be confidently diagnosed by looking at the skeletal remains alone."

Down syndrome occurs when an individual carries an extra copy of chromosome 21. The researchers were able to find these six cases using a novel Bayesian approach to accurately and efficiently screen tens of thousands of ancient DNA samples.

"The statistical model identifies when an individual has approximately 50 per cent too much DNA that comes from one specific chromosome," says Dr Patxuka de-Miguel-Ibáñez of the University of Alicante, and lead osteologist for the Spanish sites.

"We then compared the remains of the individuals with Down syndrome for common skeletal abnormalities such as irregular bone growth, or porosity of the skull bones, which may help to identify future cases of Down syndrome when ancient DNA can't be recovered."

The study also uncovered one case of Edwards syndrome, a rare condition caused by three copies of chromosome 18, that comes with far more severe symptoms than Down syndrome. The remains indicated severe abnormalities in bone growth, and an age of death of approximately 40 weeks gestation.

All of the cases were detected in perinatal or infant burials, but from different cultures and time periods.

"These individuals were buried according to either the standard practices of their time or were in some way treated specially. This indicates that they were acknowledged as members of their community and were not treated differently in death," says Dr Rohrlach. 

"Interestingly, we discovered the only case of Edwards syndrome, and a noticeable increase in cases of Down syndrome, in individuals from the Early Iron Age in Spain. The remains could not confirm that these babies survived to birth, but they were among the infants buried within homes at the settlement, or within other important buildings," says Professor Roberto Risch, co-author and archaeologist from The Autonomous University of Barcelona.

"We don't know why this happened, as most people were cremated during this time, but it appears as if they were purposefully choosing these infants for special burials."

The research has been published in the journal Nature Communications and was part of a large collaborative project involving researchers from the University of Adelaide, including Dr Adam "Ben" Rohrlach, Dr Jonathan Tuke and Associate Professor Bastien Llamas, as well as researchers from across the world, including at the Max Planck Institute for Evolutionary Anthropology in Germany where the data was generated.