Genetic differences between identical twins may begin very early in embryonic development, according to a study that researchers said has implications for how these siblings help scientists eliminate the effects of nature versus parenting.
Identical or monozygotic twins come from a single fertilized egg that divides into two.
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 shaping these differences has been underestimated.
“The classic model has been to use identical twins to help separate the influence of genetics from the environment on disease analysis,” said Kari Stefansson, head of Iceland’s deCODE genetics, a subsidiary of the company. American pharmaceutical company Amgen.
“So if you take identical identical twins and one of them developed autism, the classic interpretation has been that this is caused by the environment.”
“But this is an extraordinarily dangerous conclusion,” he told AFP, adding that there is a possibility that the disease may be due to an early genetic mutation that happened 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 trace genetic mutations.
They measured mutations that occur during embryonic growth and found that identical twins differ by an average of 5.2 early developmental mutations.
In 15 percent of twins, the number of divergent mutations is higher.
When a mutation occurs during the first weeks of embryonic development, it is expected to spread to both an individual’s cells and those of his offspring.
In one of the pairs of twins studied, for example, there was a mutation in every cell of a sibling’s body, that is, it probably happened very early in development, but not in the other twin.
Stefansson said that of the initial mass that would continue to form the 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.
“These mutations are interesting because they allow you to start exploring the way twinning occurs.”
Given 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 ones,” Stefansson said.
© France-Presse Agency