A group of scientists from the National University of Colombia documented a case of twins from different fathers , during the study of evidence requested by a man who inquired about the paternity of children.
The case began in August 2018, when a father who suspected his relationship with the children, asked the Population Genetics and Identification Group of the National University of Colombia (UNAL) for a test to establish the paternity of two male twins with markers. genetic
The results showed that the genetic profile of the father “coincided with the genetic profile of only one of them , that is to say, that for the other it was an exclusion of paternity”.
The doctor in Science-Biology from the National University Lilián Andrea Casas Vargas said that in this case a test known as “Y chromosome panel” was carried out, taking into account that the twins are male.
The Y chromosome is secreted only by the paternal line, and it does so en bloc from one generation to another, it never changes.
Therefore, those Y chromosome markers are expected to be completely identical to that of the father. But in this case, as the doctor explained, “the genetic profile coinciding with one of the twins is observed, while 14 out of 17 non-coincidences were identified with the other.”
The geneticist assured that the test had to be repeated several times, but then the case had to be confirmed, which due to its rarity was published in the Biomedical Journal of the National Institute of Health.
What is heteropaternal superfertilization?
In heteroparental multiple fertilization, heteroparental superfertilization , two or more eggs are fertilized during the same menstrual cycle by two different sperm , resulting in a dizygotic twin pregnancy, which we know as twins.
In this case, a second egg was fertilized by a sperm from a different man, the result of another sexual relationship, which is why it is called heteroparental.
The situation is as follows: the woman has sexual intercourse with a man and one of his eggs is fertilized by a sperm. In the same cycle, she ovulates again and has sex with another man. Then one of his sperm fertilizes a second egg from the woman. There is a pregnancy of twins from different fathers, who share the mother’s womb.
It is a rare situation that only occurs in one out of every 13,000 fertilizations, to which we must bear in mind that women must have sexual relations with different men within a maximum period of 5 days.
Difference with superfetation
Superfertilization, which occurs in the same menstrual cycle, should not be confused with superfetation . This is the fertilization of an egg released during the evolution of the pregnancy that results in the conception of twins of different gestational ages. That is, you get pregnant, being already pregnant.
Typically, when conception occurs, a woman’s reproductive system stops producing eggs. Only very rarely can the menstrual cycle repeat itself and a new egg is released while an embryo already exists. Even rarer is that this ovum is also fertilized: then superfetation occurs, when two embryos of different gestational ages come together . Having been conceived in different cycles, one of them could be born premature.
In superfetation it can also happen that each ovum is fertilized by a different parent.
Super-fertilization and super-feeding is very rare among humans , but it is very common among certain animal species (rodents, horses, sheep, dogs, cats), among whom the exchange of sexual partners in a short period of time is much more frequent. .
Other cases of hetero-parental superfertilization
It is estimated that there are about ten documented cases worldwide of twins who have different biological fathers, however, the number could increase since it is possible that many parents do not know it and have not realized the differences of their children. .
One of them happened in Denmark in 2004. Charlotte Hilbrandt became pregnant with twins and, having been with two different men in a very short time, admitted that she did not know who the father was. When the children were born, they all realized that they did not look like each other, and a doctor told them the remote possibility that they are children of different parents. A year after the children were born, the family performed a DNA analysis that confirmed that the babies were children of different parents.
Another happened in the city of Xiamen, China, where a woman gave birth to two twins from different parents in 2019. This was confirmed after performing a DNA test on the children, at the request of one of the biological parents.
In Babies and more | Rare cases of twins
