Whether twins disappeared before birth, DNA knows

Identical twins are derived from eggs that divide to produce two embryos. In some cases, one of these two embryos disappears during development, and in this case, only one baby is born. This phenomenon is called vanishing twin. However, according to a recent study, the DNA records information to confirm whether the fetus was born as identical twins, and it is said that it is possible to determine if there were any missing twins.

In their latest paper, published in the scientific journal Nature Communications on September 28, the team focused on epigenetic targets in twin DNA. Epigenetics refers to factors that can switch genes on and off without changing the underlying DNA sequence. For example, a methyl group, one of epigenetics, attaches like a sticker to a specific gene, effectively disabling the gene so that cells cannot read these genes.

In this study, the DNA of identical twins found a characteristic pattern of sticky methyl groups. It has also been found that the characteristic pattern of sticky methyl groups spans 834 genes and is used to differentiate identical twins into fraternal twins and two non-twins.

The research team also succeeded in developing a computer algorithm that can reliably identify identical twins based only on the position of all methyl groups in DNA. Therefore, theoretically, it is possible to check whether there are siblings who have disappeared from their own twins. However, this study did not validate the loss of twins.

The research team explains that the characteristic pattern of sticky methyl groups is a kind of molecular scar left over from the early embryonic development of identical twins. Genes coated with methyl groups play a variety of roles in cell development, growth, and adhesion. To put it simply, it helps cells stick to each other. However, it is not clear how the methylation gene affects the growth, development and health of identical twins in the study.

According to a 1990 report, an estimated 12% of human pregnancies started with multiple pregnancies, but less than 2% of children are born with more than one twin. In other words, the remaining 10% will be the so-called loss of twins. It is also known that there are generally more fraternal twins than identical twins.

Fraternal twins are formed by fertilization of two eggs. Thus, there is evidence that genes play a role in fraternal twins. Research results have also been published that fraternal twins are related to genes related to excessive ovulation.

On the other hand, the birth rate of identical twins is 3 to 4 per 1,000 births worldwide. Therefore, it can be concluded that identical twins are not genetically responsible. So the question is what causes identical twins. The research team thought that there might be a secret to the methyl group that makes up DNA in investigating what causes identical twins. The methyl group serves to help control embryonic development at an early stage. It was also found that, thanks to a special protein called methyltransferase, the methyl group added to DNA during development is copied while the cell continues to divide and remains in adulthood. This is the characteristic pattern of sticky methyl groups.

The researchers analyzed blood and DNA samples from 6,000 identical and fraternal twins. In addition, since the dataset on which the analysis and investigation was based includes DNA samples collected at various times, it is also revealed that the characteristic pattern of sticky methyl groups can be confirmed over time.

In addition, this study did not reveal the effect on the human body by the characteristic pattern of sticky methyl groups. Therefore, the research team is planning to study the effect using experimental animal cells and human cells. Related information can be found here.