Scientists have long used the study of identical twins to investigate the effects of nature on nurturing, as the accepted view is that because they have the same genes, any physical or behavioral differences between such siblings should be to outside influences.
Identical twins come from a single fertilized egg, or zygote.
In any embryo, cell division can lead to mutations, but this type of genetic difference has not been previously measured between identical twins.
The scientists sequenced the genomes of 387 pairs of identical twins and their parents, spouses and children mutation to detect divergence. The authors found that twins differed on average by 5.2 early developmental mutations.
In about 15% of twin pairs, one sibling has a large number of mutations that the other twin did not have.
A genetic mutation is a defect or a change in DNA. A mutation occurs when the genetic code somehow breaks or changes. Although most mutations are harmless, some can be serious and can lead to diseases such as cancer. Mutations can also affect physical characteristics such as hair color.
This is not the first study to suggest the differences between so-called identical twins. In a paper published in 2008 in The American Journal of Human Genetics, there are genetic differences between siblings. However, the new research goes a step further than the DNA of the extended family.
Genetic differences
Some researchers reveal striking differences, co-author of the study, Kari Stefansson, told CNN.
The implications of this, according to Stefansson, are significant, as the research led the team to conclude that “the role of genetic factors” in shaping the differences observed between monozygotic twins was “underestimated.”
He acknowledged that science and society at large were fascinated by identical twins, adding: “There is something magical about the connection between identical twins.”
However, his team’s research is more about what divides it than about uniting it.
“Imagine you have twins being raised apart. If one of them develops autism, the classical interpretation is that it is due to environmental factors. But our work shows that it comes before you to conclude that it is ’caused by the environment, you need the genome of the twin sequence to know what autism can explain,’ ‘Stefansson said.
The “mutation disorder,” he told CNN, could be responsible for a series of “devastating childhood diseases” such as severe epilepsy and a series of metabolic disorders.
“It is absolutely astonishing how large a percentage of such appalling syndromes from very early childhood stem from genome mutations,” he said.
“This is an extraordinary, exciting, and informative effort to point to early cellular mechanisms that explain genetic differences between MZ (monozygotic) twins,” said Nancy Segal, a writer and professor of psychology who taught twins at California State. University, Fullerton studied, said and was not involved in the research.
“It is well known that MZ twins do not have perfect similarity and that some differences may reflect genetic differences. The current study provides new information on the source of MZ twin differences,” said Segal, who is also director of CSU’s twin study center.
The research “did not deny environmental factors in the early and later development”, she added, but showed that “some twin models underestimate genetic effects and require revision.”
According to Segal, the study also raised questions about how the findings should be applied, such as whether action should be taken beforehand to correct certain genetic disorders.
“There are a lot of tantalizing questions raised by this extraordinary study,” she said.