Evrim Yazgin
Cosmos science journalist
DNA analysis has revealed a higher-than-expected number of cases of Down syndrome in past human societies going back as far as 5,000 years.
It also includes what could be the first identification of Edwards syndrome in prehistoric remains.
Approximately 10,000 samples were analysed in research which is published in Nature Communications.
Down syndrome is a genetic condition where an extra copy of chromosome 21 is inherited due to abnormal cell division. Therefore, it is also referred to as trisomy 21. Today, Down syndrome is seen in about 1 in 1,000 births.
“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,” says first author Dr Adam “Ben” Rohrlach, a statistician from the University of Adelaide. “We identified six cases of Down syndrome.”
“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.”
“The statistical model identifies when an individual has approximately 50% too much DNA that comes from one specific chromosome,” says co-author Dr Patxuka de Miguel Ibáñez of the University of Alicante in Spain.
She also says the research can help identify Down syndrome in other ancient individuals.
“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.”
One case from a church graveyard in Finland dated from the 17th to 18th century. But the other 5 cases were between 2,500 and 5,000 years old. They were found at Bronze Age sites in Greece and Bulgaria, and Iron Age sites in Spain.
Individuals with Down syndrome can live happy, long lives today – often with the help of modern medicine. But this would not always have been the case in the past.
All 6 individuals identified with Down syndrome in the study died at a very young age. Only one child reached the age of about one. The 5 prehistoric burials were accompanied by special items such as coloured bead necklaces, bronze rings and seashells.
“These burials seem to show us that these individuals were cared for and appreciated as part of their ancient societies,” says Rohrlach.
Another individual showed signs of a different kind of trisomy – trisomy 18, or Edwards syndrome.
Like in the past, Edwards syndrome today is less common than Down syndrome, showing up in 1 in 3,000 births. Edwards syndrome is also much more serious. The child found in the study had severe bone growth abnormalities and died approximately 40 weeks into gestation.
The ancient case was also found in one of the Spanish Iron Age sites.
“At the moment, we cannot say why we find so many cases at these sites,” says co-author Professor Roberto Risch, an archaeologist at the Autonomous University of Barcelona. “But we know that they belonged to the few children who received the privilege to be buried inside the houses after death. This already is a hint that they were perceived as special babies.”
