Genetic differences between identical twins may begin very early in embryonic development, according to a study Thursday, according to which researchers have implications for how these siblings help scientists eliminate the effects of nature on food.
Identical twins – or monozygotes – come from a single fertilized egg that splits in two.
They are important research subjects because they are believed to have minimal genetic differences.
This means that when physical or behavioral differences occur, it is assumed that environmental factors are the probable cause.
But the new research, published in the journal Genetics of nature, suggests that the role of genetic factors in modeling these differences has been underestimated.
“The classic model was to use identical twins to help separate the influence of genetics from the environment in disease analysis,” said Kari Stefansson, head of genetic deCODE in Iceland, a subsidiary of US pharmaceutical company Amgen.
“So if you take identical twins raised outside and one of them has developed autism, the classic interpretation has been that it’s caused by the environment.”
“But this is an extraordinarily dangerous conclusion,” he told AFP, adding that there was a possibility that the disease was 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, wives and children to track genetic mutations.
They measured the mutations that occur during embryonic growth and found that identical twins differ on average by 5.2 early mutations of development.
In 15% of twins, the number of divergent mutations is higher.
When a mutation occurs in the first few weeks of embryonic development, it would be expected to spread to 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 all the cells in a brother’s body – which means that it probably happened very early in development – but not at all in the other twin.
Stefansson said that of the initial mass that was to form the individuals, “one of the twins is made up of the descendants of the cell in which the mutation took place and nothing else,” while the other was not.
“These mutations are interesting because they allow you to start exploring how twinning happens.”
Given the genetic differences found, even the identical term can be misleading to describe siblings.
“I’m more inclined to call them monozygotic twins today than identical ones,” Stefansson said.
© Agence France-Presse