Thursday , December 9 2021

Identical twins are not always genetically identical, a new study finds


Scientists have long used the study of identical twins to examine the effects of nature versus feeding, as the accepted view was that because they share the same genes, any physical or behavioral differences between such siblings must depend on outside influences.

However, that may not be the case, the new research, published in the journal Nature Genetics on Thursday, suggested.

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 had not been previously measured between identical twins.

During a four – year study, a team of Icelandic researchers at DeCode Genetics, a biopharmaceutical company in Reykjavík, found that monozygotic or identical twins have genetic differences that begin in the early stages of embryonic development

Scientists have sequenced the genomes of 387 pairs of identical twins and their parents, wives and children to track mutational divergence. The authors found that twins differed on average by 5.2 early developmental mutations.

In about 15% of the twin pairs, one brother carried a large number of mutations that the other twin did not have.

A genetic mutation is an error or a change in DNA. A mutation occurs when the sequence of the genetic code breaks or changes in some way. While most mutations are harmless, some can be serious and can lead to diseases such as cancer. Mutations can also affect physical attributes, such as hair color.

This is not the first study to suggest differences between so-called identical twins. A paper published in The American Journal of Human Genetics in 2008 revealed some genetic differences between siblings. However, the new research goes beyond this step by including the DNA of the extended family.

Genetic differences

Some of the subjects of the research revealed amazing differences, study co-author Kari Stefansson told CNN.

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“We found a pair of identical twins in which a mutation was found in all the cells in the body of one of them, but it was not present at all in the other twin. Then we found twins in which a mutation was found in all the cells in the body in a twins, but in only 20% of each other’s cells, “said Stefansson, founder and CEO of DeCode Genetics, which is a subsidiary of US pharmaceutical company Amgen.

The implications of this are significant, according to Stefansson, because 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 both science and society are fascinated by identical twins, adding: “There is something magical about the connection between identical twins.”

His team’s research, however, is more about what divides them than unites them.

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“Imagine you have identical twins who are raised outside. If one of them develops autism, the classic interpretation is that it is only environmental factors. But our paper shows that before we come to the conclusion that it is caused by the environment, you have to sequence the genome of the twins to know what could explain autism, “Stefansson said.

“Mutational divergence,” he told CNN, could explain a number of “devastating childhood illnesses,” such as severe epilepsy and a number of metabolic disorders.

“It’s absolutely amazing how high a percentage of such horrible syndromes are from very early childhood, to genome mutations,” he said.

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“This is an extraordinary, interesting and insightful effort to identify early cellular mechanisms that explain the genetic differences between MZ (monozygotic) twins,” said Nancy Segal, an author and professor of psychology studying twins at California State University, Fullerton. , and was not involved in the research.

“It is well known that MZ co-twins do not have perfect similarities and that some differences may reflect genetic differences. This study provides new information on the source of MZ co-twin differences,” said Segal, who is also the director. at the Twin Studies Center of the CSU.

The research “did not deny environmental factors in early and later development,” she added, but showed that “some twin models underestimate genetic effects and need revision.”

The study, according to Segal, also raised questions about how the findings should be applied, such as whether to intervene prenatally to correct certain genetic disorders.

“There are many tempting questions raised by this extraordinary study,” she said.

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