About one in eight people had a twin embryo that didn’t survive to term, and in future there may be a simple cheek swab test that can reveal if you are in this group.
Jenny van Dongen at VU Amsterdam in the Netherlands and her colleagues have found that identical twins carry a characteristic pattern of alterations to their DNA, known as epigenetic changes, that isn’t seen in people who didn’t have twin embryos. These variations happen in early pregnancy and last into adulthood.
Epigenetic changes are chemical modifications of DNA that help keep genes turned on or off. In early pregnancy, embryos undergo swathes of such alterations to programme different cells to become the various parts of the body.
Van Dongen wondered if this process would work differently in multiple pregnancies. About one in 100 births globally are of twins, but studies have suggested that 12 per cent of people could have had a twin embryo at some point during pregnancy that didn’t survive. Although this may be referred to as vanishing twin syndrome, there can be visible remains.
The researchers looked at four existing epigenetic studies of twins from the UK, Australia, the Netherlands and Finland that had taken either blood samples or cheek swabs to get DNA samples. They found 834 areas of DNA where the epigenetic pattern was different in identical twins compared with single births.
Identical twins form when a very early embryo splits into two because the cells fail to adhere to each other, and some of the epigenetic changes found in this study affected genes involved in cell adhesion. “We may have identified a mechanism that causes cells to split,” says van Dongen. “It’s also possible that these changes arise after the cells separate.”
With further development, it should be possible to create a genetic test to identify if you once had a twin embryo, says van Dongen. Any companies wishing to commercialise the research need to improve its accuracy, as, for instance, if someone had an identical twin embryo at some point during pregnancy, the current test would be positive only 70 per cent of the time, says van Dongen. What’s more, any test based on this work wouldn’t pick up people who had a non-identical twin embryo.
“We don’t know yet if the association will be maintained as we get more data, but this is a very interesting way to start,” says Richard Meehan at the University of Edinburgh, UK.
Journal reference: Nature Communications, DOI: 10.1038/s41467-021-25583-7
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