Chimerism: understanding the genetic condition of the character Brisa, from the soap opera Travessia

In the storyline, Lucy Alves’ character must prove that she is Tonho’s mother after two DNA tests are negative; it is estimated that there are only 40 proven cases worldwide

Rare genetic condition that results in the individual having two distinct types of DNA in your body, the chimerism it is a phenomenon that can have an impact in the legal field. In the soap opera Intersectionfrom the television Globo, the character Brisa (Lucy Alves) lives the drama of being able to lose custody of her son, after two trials of DNA give negative. It is estimated that there are only 40 proven cases worldwide.

The plot revolves around trying to explain why tests failed to prove that she is the boy’s biological mother. It is speculated that the young woman may have been the result of a twin pregnancy, in which only Brisa was born. The other fetus, even if it did not survive, would have its genetic material fused with that of Tonho’s mother. According to experts, the chimerism can affect the result of a test DNA.

What is chimerism?

“Chimerism is a rare genetic condition, which determines that the individual has two different types of DNA in his body,” says Danyelle Oliveira Toledo, neonatologist and professor of medicine at the University of Franca (Unifran). It is the presence of cells from two or more zygotes (primordial cell formed by the fusion of sperm and egg) in the same individual. It’s like there are two people inside the same body.

In turn, DNA is responsible for the genetic information of an individual, which will be passed on to his descendants.

Although genetic, the condition is not hereditary. That is, it is related to genes and DNA, however, it is not necessarily passed on from parents to children.

What are the causes?

“Human chimeras can be born naturally – the carrier can spend long years of his life or his entire life without knowledge or diagnosis of the condition – or artificially, through medical or scientific interventions,” says the neonatologist and professor of the Medicine course of the University of France (Unifran).

“Natural human chimerism occurs between the uterus, before birth, and the degree of variation in DNA differ from case to case”.

According to her, natural chimeras can present themselves in three ways:

• Microchimerism (or fetomaternal).
• Parthenogenetic chimerism (formed when an egg that has not undergone meiosis is fertilized by two sperm).
• Tetragametic chimerism (two eggs are fertilized by two sperm, resulting in two separate embryos that fuse to form a single person).

There are also non-embryonic chimerisms (technically they are cases of microchimerisms), which occur in the case of organ donation or even blood transfusion.

How many people in the world does the rare genetic condition affect?

According to Danyelle, the bibliographic references indicate that it is a very rare phenomenon, the proven incidence of which affects only 40 individuals worldwide. The first documented case of a human chimera was published in British Medical Journalin 1953. See below for more info..

How does the person know about the condition? Are there any symptoms or signs?

The carrier of the human chimera can go their entire life or years unaware that they have the genetic condition, which is why a diagnosis is considered difficult. “Genetic tests on various types of body tissue can diagnose chimeras. However, such tests are not easy to perform. Diagnostic tests are performed in rare cases of the appearance of symptoms, which characterize the condition,” says the professor of Medicine.

Characteristic physical symptoms include: genital ambiguity, hermaphroditism, uneven skin color or different colored eyes, or difficulty determining blood groups, as previously described by Clive N.Svendsen AND Allison D. Ebert in the publication “Encyclopedia of Stem Cell Research”.

“When there is no clinical manifestation, diagnosis becomes more difficult, depending on the occurrence of a specific event that can raise suspicion of the condition,” adds Danyelle.

Does someone with the diagnosis need to have any treatment, or does the condition affect the person’s health?

Treatment depends on whether or not there are clinical manifestations and on which, for example in cases of hermaphroditism, a holistic approach to the patient and family should occur.

“The approach depends on the age of diagnosis and the functionality of the genitalia, as in any case of genital ambiguity,” says the specialist.

Where does the term chimerism come from?

As published in SciELO, virtual health library, in 2016, the term chimera originates in mythology as a massive and terrifying monster that “breathed fire” through its mouth and nostrils. The front of its body was a combination of a lion and a goat and the back that of a dragon. While not a frequently discussed issue, studies have already addressed the genetic condition.

“For years the figure of the chimera inhabited only the ancient world, however, today the scientific community has maintained the terminology to characterize individuals who have one or more distinct types of DNA, as will be analyzed later”, reads the article .

second SciELOthe first documented case of a human chimera has been published British Medical Journalin 1953. “The case involved a British woman, who allegedly had different blood types. Her test results indicated that she had blood types O and A. Deeming this to be an impossible phenomenon, the English clinic where the woman had performed the examination repeated the procedure, in order to discard any errors resulting from the analysis of the original sample.”

According to the publication, however, the new result confirmed the old one: The woman had two blood types, O and A. Later, the doctor learned that the woman had a twin brother who died months after birth.

“A new test was carried out, this time using the patient’s saliva, which confirmed O blood. With this, the doctors concluded that the patient originally had O blood, having received type A blood from her twin brother, being considered , therefore, the first human chimera”, reads the article.

How does chimerism relate to legal issues?

With the evolution of science, the term ceased to be known only in the mythological sphere and began to cover the scientific one as well. It is also part of the legal environment.

“In cases of criminal investigations, for example, using DNA tests for human identification, to blame or exonerate individuals, it can also be influenced by human chimera, being necessary to demonstrate the condition of chimerism,” says Danyelle, of Unifran.

That is, although it is a very rare and specific condition, in addition to issues related to DNA testing, chimerism is also related to legal issues, as DNA is commonly used in situations where identification of the person is not possible by other means . , such as, for example, in the case of an investigation into paternity or for the investigation of a crime.

“Chimerism can raise a question regarding the technical evidence of DNA testing. DNA testing is considered, by criminal and civil law, family law, it is considered a very robust and strong evidence. In the case of chimerism, this evidence it will not be considered valid. In this case, it will be necessary to evaluate other evidence that makes up the case,” says Matheus Falivene, Doctor and Masters in Criminal Law at the Faculty of Law of the University of São Paulo (USP).

“However, it is important to underline that despite these possibilities, chimerism is a rare condition and that it does not call into question the reliability of DNA tests”, reads the article published on SciELO.

Source: Terra

Ben

Ben Stock is a lifestyle journalist and author at Gossipify. He writes about topics such as health, wellness, travel, food and home decor. He provides practical advice and inspiration to improve well-being, keeps readers up to date with latest lifestyle news and trends, known for his engaging writing style, in-depth analysis and unique perspectives.