Scientists have diagnosed Down syndrome from DNA in the ancient bones of seven infants, one as old as 5,500 years. Their method, published in the journal Nature Communications, may help researchers learn more about how prehistoric societies treated people with Down syndrome and other rare conditions.
Down syndrome, which occurs in 1 in 700 babies today, is caused by an extra copy of chromosome 21. The extra chromosome makes extra proteins, which can cause a host of changes, including heart defects and learning disabilities.
Scientists have struggled to work out the history of the condition. Today, older mothers are most likely to have a child with the condition. In the past, however, women would have been more likely to die young, which might have made Down syndrome rarer, and the children born with it would have been less likely to survive without the heart surgery and other treatments that extend their lives today.
Archaeologists can identify some rare conditions, such as dwarfism, from bones alone. But Down syndrome — also known as trisomy 21 — is a remarkably variable disease.
People with it may have different combinations of symptoms, and they may have severe or milder forms. Those with the distinctive almond-shaped eyes caused by Down syndrome may have relatively ordinary skeletons, for example.
As a result, it’s hard for archaeologists to confidently diagnose ancient skeletons with Down syndrome. “You can’t say, ‘Oh, this change is there, so it’s trisomy 21,’” said Dr. Julia Gresky, an anthropologist at the German Archaeological Institute in Berlin who was not involved in the new study.
