Identical twins bear distinctive epigenetic markings: study

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Sidentical twins have a lot in common with each other. In a Dutch study published on September 28 in Nature Communication, scientists find they also have something in common with other identical twins around the world: a set of matching marks on their DNA. The researchers studied around 6,000 pairs of twins of different ages from around the world, analyzing hundreds of thousands of sites on their genomes. Their discovery of 834 sites in the genome with distinct marks of identical, but not fraternal, twins could provide clues as to how identical twins occur, the researchers say.

While the basics of the origin of identical twins are clear, the mystery lies in why. Identical twins are born from a single fertilized egg, or zygote, dividing into embryos with duplicate DNA, but the cause of the split remains unknown. Zygote splitting was once considered completely random. The results of the new study challenge that idea, raising the possibility that certain epigenetic changes could lead to the split. Twin researcher and developmental psychologist Nancy Segal of California State University, Fullerton, tells Scientific news that the Study could lead to better understanding of “what could cause a fertilized egg to divide and form monozygotes [identical] twins.”

Alternatively, Baylor College of Medicine epigeneticist Robert Waterland relates Scientific news that epigenetic marks could be a consequence – and not the cause – of the division of the zygote. “They could be like a lingering molecular scar from the [splitting] process itself, ”he said, adding that more research is needed to find out if this is the case.

As part of their study, the researchers also designed a test using the brands they had identified and reported that it was 80% accurate in determining whether a given person is an identical twin. The Guardian reports that such a test could be used to reveal whether someone was separated from an identical twin early in life or suffered from ‘endangered twin syndrome’, which occurs when a twin is lost during pregnancy.

The work could also provide insight into certain disorders involving epigenetic changes, the Dutch research team writes in the article. For example, Beckwith-Wiedemann syndrome and spina bifida disproportionately affect twins. Twin researcher Jeffrey Craig tells Science that research could be useful in testing the idea that certain illnesses are unique to identical twins, which he said would be “great news if it turned out to be true.” Segal also expresses his optimism about the applicability of epigenetics in twin studies, recounting Scientific news, “This is a very, very important discovery that opens up many avenues for research. “


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