In a study conducted Thursday, researchers said these siblings helped scientists overcome the effects of nature versus nutrition.
Identified – or monozygotic – twins come from a single fertilized egg that splits into two.
They are important research topics because they think there are at least genetic differences.
This means that when physical or behavioral differences emerge, environmental factors are considered as possible causes.
But new research published in the journal Nature genetics, Suggests that the role of genetic factors in shaping these differences is underestimated.
“Classic models use identical twins to help differentiate genetics vs. environmental influences in disease analysis,” said Kari Stephanson, head of Decode Genetics, Iceland, a subsidiary of US pharmaceutical firm Amgen.
“So if you take equally grown twins and one of them has developed autism, the classic interpretation is that it is caused by the environment.”
“But this is an exceptionally dangerous conclusion,” he told AFP, adding that there is a possibility that the disease may have been caused by an early genetic mutation that occurred in one of the twins but not in the other.
Stephenson and his team sequenced the genome of identical twins and 387 pairs of their parents, spouse and children to track genetic mutations.
They measured mutations occurring during fetal development and found that identical twins differ from an average of 5.2 early developmental mutations.
In 15 percent of twins, the number of mutation mutations is high.
When a mutation occurs in the first few weeks of fetal development, it would be widely expected to occur in both a person’s cells and those in their offspring.
For example, in one of the twins studied, a mutation was present in all cells in a sibling’s body – meaning that it probably occurred long before development – but not at all in the other twin.
Stephenson said that of the initial mass that tends to form individuals, “one of the twins is made up of descendants of the cell where the mutation occurred and nothing else”, while the other did not.
“These mutations are interesting because they allow you to begin to explore how to be a twin.”
Given the genetic differences found, similar terms can be misleading to describe siblings.
“I’d be more inclined to call them monozygotic twins today than equals,” Stephanson said.
© Agnes France-Presse