Think about it, we all assume that every cell in your body has your own DNA, right? That's the basic thing we know about genetics. But, very rarely, a person's body can have cells with a second type of DNA that is not their own, and that is completely different. Sounds a bit strange, doesn't it? In medicine, we call this amazing condition 'Chimerism'. Don't worry, it's not a disease. Let's see what it really is.
What is 'Chimerism'?
Simply put, chimerism is the presence of two sets of cells within the same person's body that are descended from two genetically different individuals. This means that some cells in your body may have one type of DNA, while other cells may have a completely different type of DNA.
One of the main ways this can happen is with twin births. Imagine a mother carrying twins in her womb. During the first few weeks of pregnancy, one of the embryos may fail to develop and disappear for some reason. This is called Vanishing Twin Syndrome. When this happens, the cells from the missing embryo are absorbed by the healthy developing other embryo. So, the baby will have both its own cells and the cells from the missing sibling throughout its life.
The types of cells that come together in this way are different from each other. Most often, this difference is seen in the blood. It is called 'blood chimerism'. This is because the blood cells that are formed in the bone marrow are strong and can easily pass through the placenta. According to research, about 8% of normal twins may have this condition. Among triplets, this probability increases to 21%.
What are the causes of chimerism?
As we discussed earlier, some people are born with this condition. However, someone can develop chimerism during their lifetime. There are two main reasons for this. Let's break them down as follows.
| Cause | Description of how it happens |
|---|---|
| Congenital Chimerism | This is the 'Vanishing Twin Syndrome' we talked about earlier. One embryo is lost in the womb and its cells are absorbed by the other embryo, resulting in two types of cells remaining in the body throughout life. |
| Acquired Chimerism | This is done as a life-saving medical treatment. For example, consider an organ transplant . When a person receives a kidney from another healthy person, the new kidney works with the donor's DNA. The recipient then has both their own DNA and the donor's DNA. The same is true of a bone marrow transplant . In this case, the bone marrow of a healthy donor is transplanted instead of the diseased bone marrow. Then all the new blood cells are made from the donor's DNA. This can even change a person's blood type. |
Are there any symptoms of this?
The good news is that most people with chimerism have no symptoms. Many people go their entire lives without knowing they have the condition. Because there is no specific test for it, it is very rare to get a diagnosis.
However, sometimes this can lead to unimaginable problems, especially with DNA tests.
Imagine, a father does a DNA test to confirm the paternity of a child. But the result comes out that he is not the father of the child. He is 100% sure that it is his own child. What can happen here is that if the father is suffering from chimerism, the DNA is not in his blood or saliva, but in his reproductive cells (sperm). It is the DNA of the brother who was lost in the womb. Then genetically the child is related to him exactly as if it were the child of one of his brothers, that is, a nephew or a niece.
Similar things can happen to a mother, too. Therefore, most of the time, chimerism is diagnosed as a result of a random mismatch during a DNA test like this.
Can this situation cause serious problems?
Chimerism is not a disease or a dangerous condition, but it can cause some problems if you are not aware of it.
- Legal Issues: As mentioned earlier, incorrect paternity test results can lead to major legal issues regarding child custody. There have been several such incidents reported around the world.
- Mental problems:Some people may experience a bit of psychological shock and identity issues when they find out that they have parts of someone else's body.
- Medical significance: It may be important to be aware of this condition during tissue matching prior to an organ transplant.
But mothers don't need to worry about 'vanishing twin syndrome'. If it happens during the first three months of pregnancy, it won't harm the mother or the healthy baby. The mother may not notice any symptoms other than a little bleeding.
Take-Home Message
- Chimerism is the presence of two types of DNA in one organism. This often occurs through the absorption of cells from a twin in the womb or through an organ/bone marrow transplant.
- This is not a dangerous condition. Most people with chimerism have no symptoms.
- The main problem arises with DNA tests, especially in things like paternity tests, where the results can be inconsistent.
- If you ever have an unexplained problem with the results of a DNA test, talk to your doctor about the possibility of chimerism.
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