In August 2018, a man and a woman arrived at the laboratory of the Population Genetics and Identification Group of the National University of Colombia to verify the paternity of two male twins who were supposed to be their children.
What should have been a normal process for researchers, who perform thousands of similar tests a year, turned into a strange and exciting case study. The results of the analyzes, published in the most recent edition of the scientific journal Biomedical , indicated that the genetic markers of the father only coincided with one of the children. Research confirms that the two twins have different biological parents.
Lilian Andrea Casas Vargas , master in Human Genetics, doctor in Biological Sciences and director of the work, tells by phone that she and her research group were so surprised to see the results of the DNA tests that they decided to start over and do all the process from the beginning.
“Due to the rarity of the case, we asked the four people (mother, father and the two children) to return to the laboratory to take their blood samples a second time,” says Casas. “In the end we got the same conclusion. That allowed us to be sure that there was no procedural error ”.
To take maternity and paternity tests and obtain the profile of study participants, scientists collate samples of DNA, the genetic material that contains the instructions used in the development and function of all living organisms.
“The first thing we did in this case was to confirm that the alleles of the children, which are the ways in which a gene can manifest itself, coincided with those of the mother to rule out a change in the babies in the hospital,” says Casas.
Once the bond with the mother was established, the genetic information that the father should provide was reviewed. In this comparison, 21 genetic markers were measured and it was shown that the man was only the father of the second twin.
Casas affirms that the scientific phenomenon that occurs in this case is called heteropaternal superfertilization. “It occurs when a second egg, released during the same menstrual cycle, is fertilized by a sperm from a different man in separate sex.”
In colloquial words, Casas continues, what happened was that the woman had sex with two different men in a short period of time, more or less seven to ten days, and one ovum was fertilized by a man and the other ovum by a man. different.
Casas explains that it is relatively common for women to produce two or more eggs in the same fertile cycle. “There are genetic, biological, or treatment factors with some hormones that can make this superovulation frequent.” In this case, the mother of the two twins had a genetic background because there were twins in her family.
Heteropaternal superfertilization is extremely rare in humans. At present, around 19 cases are known in the world, according to the investigation of Colombian scientists, who in addition to reporting the case, conducted a complete review of scientific literature on the phenomenon. “Three cases like this were found in 39,000 records from a database of paternity tests in the United States.”
Juan Ramón Ordoñana , director of the Murcia Twins registry , insists on the rarity of the case. “This type of superfertilization is more common in animals, such as cats and dogs. In people it is very strange ”, says Ordoñana. “We don’t know exactly how often it occurs. We only have estimates ”.
According to the Spanish researcher, professor of Genetics and Behavioral Evolution, only 2.4% of twins born from different ovules, whose parents had some type of paternity dispute, presented heteropaternal superfecundation. “It is a very low percentage, even among couples who had doubts about the paternity of their twins.”
Ordoñana says that despite the strangeness of the case, it has no implication in the development and healthy growth of babies. “8% of all twins are produced in superfertilization. That is, fertilized at different times, not in the same sexual relationship, but with the same father.
This is not a problem for children. They are simply two eggs, with two sperm. The only thing that changes in this case is that they are from different parents, but the biological process is the same. It does not have any special complications ”.
Casas and Ordoñana agree that although this case does not represent significant advances in scientific research, it is an interesting and necessary case report that will serve as a reference to establish comparisons in the future. “There is very little serious documentation on this phenomenon in humans. Therein lies the importance of our study ”, concludes Casas.
Professor William Usaquén Martínez, director of the Population and Identification Genetics Group of the Colombian university, affirms that “in the country 11,000 paternity tests are carried out per year, and until now no case of heteropaternal superfecundation has been documented in a scientific journal ”.
Martínez insists that, despite the fact that paternity tests are a simple procedure, “they have a very great emotional burden due to the type of social and cultural implications they have.”