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– Scientists may have discovered the reason why some twins are born identical, an important step that could help develop treatments for the congenital disorders that affect identical twins more often. An international team of scientists from the Vrije Universiteit in Amsterdam have discovered a DNA signature shared by identical twins, the Guardian reports. They focused on epigenetic factors, which are external, in addition to genetics, and can turn genes on or off without affecting the sequence of genes. Switching affects the way cells read genes, according to Live Science. The reason why a fertilized egg divides into two embryos with exactly the same genes has never been known.
Scientists have examined the genomes of more than 6,000 people around the world: identical twins, fraternal twins, and family members who are not twins. Identical twins were found to have the same signature DNA tags at 834 points among 450,000 sites across their DNA, per Mashable. The researchers, who published their work in Nature Communications, said the method was so reliable that they could tell from the shared marks whether a person is an identical twin with 80% accuracy. This would tell people if they were separated from a twin at birth or if their twin was lost in the womb.
Discovery isn’t the last word on the twins. An American epigeneticist not involved in the study believes the epigenetic markers likely result from the process of separating twins, according to Science News. Another theory is that they are a cause factor, according to Popular Science; more research might help with this answer. The study is one more step towards understanding twins, experts said. A developmental psychologist at California State University said the findings are “very, very important” to understanding why identical twins more often have conditions such as spina bifida. In some cases, people with the condition may not know they are twins. (Read more stories of identical twins.)
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