Researchers at the Francis Crick Institute, working with University of Oxford, University of York and Oxford Archaeology, have developed a new technique to measure the number of chromosomes in ancient genomes more precisely, using it to identify the first prehistoric person with mosaic Turner syndrome (characterized by one X chromosome instead of two [XX]), who lived about 2,500 years ago.

As part of their research published in Communications Biology, they also identified the earliest known person with Jacob’s syndrome (characterized by an extra Y chromosome—XYY) in the Early Medieval Period, three people with Klinefelter syndrome (characterized by an extra X chromosome—XXY) across a range of time periods, and an infant with Down Syndrome from the Iron Age.