I bet you are thinking, this must be about a guy who birthed a child unbeknown to him. Guess what…you are wrong! Ever heard about the condition – Chimerism? Well, we will delve into that in a bit.

Sometime in October 2024, I did a piece titled “THIS DNA TEST” and received a comment that prompted me to research the condition referred to as Chimerism. Below are excerpts from an article found on The Royal Institution website – https://www. rigb.org titled – Human Chimeras: Why forensic DNA testing will never be the same.

Human chimeras are individuals that contain two different types of DNA and are named after the mythical creature made up of different animals including a lion and a goat. People can get a second set of DNA primarily in three ways : in the womb, through transplants, or when they are pregnant. 

CHIMERISM IN THE WOMB

Chimerism may result when a twin pregnancy exists, but one embryo dies and the survivor absorbs some of its twin’s cells thus exhibiting 2 sets of DNA. This was the case with Dubem who had a son outside wedlock. His wife however challenged his paternity because he was known to have low sperm count. To further complicate issues, the result of the Paternity test was negative. Muinat, the mother of the child was however convinced of the paternity and after Dubem was further tested, he was found to be a Chimera. He had actually fathered the boy.

This type of chimerism can result in failed maternity or paternity tests. For example, Karen Keegan needed a kidney transplant and family members’ blood was tested to see if they could be donors. The tests showed she wasn’t the biological mother of two of her three children—surprising since she’d given birth to them! Further studies showed that some of her tissue contained two different types of DNA. The type in her blood was different from the DNA two of her children inherited. This other DNA came from her deceased twin in the womb, so she was genetically her children’s aunt.  

CHIMERISM THROUGH TRANSPLANTS.

Chimerism can also occur through stem cell transplants.

For example, Chris Long received a bone marrow transplant as part of his treatment for leukaemia. Three months later, he learned that the DNA in his blood was no longer his. Chris continued testing other parts of his body. Four years later, swabs of his mouth contained both his and the donor’s DNA, whilst his semen only contained the donor’s DNA. 

DNA EXCHANGED FROM BABY TO MOTHER

A less dramatic form of chimerism occurs during pregnancy where foetal cells are transferred to the mother and can stay in the body for years. This is known as micro-chimerism, due to the low levels of foetal DNA in the mother. Research suggests this happens to all pregnant women. The simplest way to test for it is by searching for the Y chromosome in women who have given birth to sons. Micro-chimerism occurs during every pregnancy. In 2012 scientists found evidence of the Y chromosome in all 26 women sampled who had just given birth to a boy. 

CONSEQUENCES ON FORENSICS

After a car accident in 2008 police were trying to identify a body with blood and kidney tissue samples. The blood was determined to come from a woman and the kidney from a man, but there was only one person in the accident. This confusion was because the man in the accident had received a stem cell transplant from his daughter and his blood now contained her DNA.  

Also, during a sexual assault investigation in 2005, police collected semen samples which had a match in the DNA database. However, the suspect had a watertight alibi, being in jail at the time of the crime. The true perpetrator was chimeric, the incarcerated suspect had donated bone marrow years earlier. Therefore, when the chimeric perpetrator committed the crime, his semen contained DNA from someone else not at the scene. 

It is however hoped that with increasingly sophisticated equipment and testing methods, the error margins on DNA testing will be eliminated.

Love

Havilah