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Genetic differences between identical twins can start very early in embryonic development, according to a study Thursday which researchers say has implications for how these siblings help scientists disentangle the effects of nature from education.
Identical twins – or monozygotes – come from a single fertilized egg that splits in half.
These are important research topics because they are believed to have minimal genetic differences.
This means that when physical or behavioral differences appear, environmental factors are presumed to be the probable cause.
But the new research, published in the journal Genetics of nature, suggests that the role of genetic factors in the formation of these differences has been underestimated.
“The classic model is to use identical twins to help you separate the influence of genetics from the environment in analyzing disease,” said Kari Stefansson, Icelandic Genetics Manager atCODE, a subsidiary of the company. American pharmaceutical Amgen.
“So if you take identical twins raised apart and one of them developed autism, the classic interpretation has been that it is caused by the environment.”
“But this is an extremely dangerous conclusion,” he told AFP, adding that it is possible that the disease is due to an early genetic mutation that occurred in one of the twins but not in the other.
Stefansson and his team sequenced the genomes of 387 pairs of identical twins and their parents, spouses, and children in order to track genetic mutations.
They measured the mutations that occur during embryonic growth and found that identical twins differ on average by 5.2 mutations from early development.
In 15% of twins, the number of divergent mutations is higher.
When a mutation occurs in the first weeks of embryonic development, it is expected to be generalized in both an individual’s cells and those of their offspring.
In one of the pairs of twins studied, for example, a mutation was present in every cell in a sibling’s body – meaning it likely occurred very early in development – but not at all in the other twin.
Stefansson said that out of the initial mass that would continue to form individuals, “one of the twins is made up of the descendants of the cell where the mutation took place and nothing else,” while the other was not. not.
“These mutations are interesting because they allow you to start exploring how the match is going.”
Considering the genetic differences found, the same identical term can be misleading to describe siblings.
“I’m more inclined to call them monozygotic twins today than identical twins,” Stefansson said.
© Agence France-Presse
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