All identical twins may share a common set of chemical markers on their DNA

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Identical siblings are used to sharing a lot with their twin, including their DNA. But new research suggests all identical twins share a common signature of twinhood, not in their DNA, but on it.

This signature is part of the epigenome, chemical markers that dot many spots along DNA and influence the activity of genes without altering their sequence. Identical twins everywhere largely share a specific set of these marks that persists from birth to adulthood, researchers report September 28 in Nature Communications. These shared epigenetic tags could be used to identify people who were conceived as identical twins but lost their sibling in the womb or were separated at birth.

“This paper is absolutely fascinating,” says Nancy Segal, a developmental psychologist at California State University, Fullerton who has researched twins but wasn’t involved in the study. The research sets the groundwork for scientists to better understand “what might cause a fertilized egg to split and form monozygotic [identical] twins,” she says.

Despite humans’ age-old fascination with identical twins, the biological process that generates them, known as monozygotic twinning, “is an enigma,” says Jenny van Dongen, an epigeneticist at Vrije Universiteit Amsterdam.

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