In the year 2002, a single mother of three named Lydia Fairchild who was separated from her children’s father applied for government aid from the state of Washington for her children. Shockingly, the reports of the DNA test required for the application process revealed that Lydia was not the mother of her children since their DNA samples didn’t match. The DNA samples of a mother and a child should match about 50% to confirm their relationship. But in Lydia’s case, her DNA samples weren’t even close to 50% of any of her children. To confirm the results, multiple other DNA tests from different labs were taken. But every time the results showed that Lydia was not her children’s parent, but the children’s father was. For this, she had to face several legal allegations which took her to the family court as well and she was almost about to lose her children’s custody as the scientific proofs were all against her. After all, “a DNA test doesn’t lie”. What kept the case still going was the witness of Lydia’s children’s birth that included the doctors, nurses, and Lydia’s mother who were present during her children’s birth.

Coincidentally, in a similar time, another mother named Karen Keegan living in Boston needed a kidney transplant. When her children volunteered to donate their kidneys to their mother, the blood test revealed that the DNA samples in the blood of the mother didn’t match with any of her children, just like in the case of Lydia. To solve this mystery, several DNA samples from different organs of Karen were collected by the doctors from which the DNA from the thyroid tissue surprisingly matched with the children’s DNA. But how can one person have two different sets of DNA? 

This is due to a phenomenon called “Chimerism”. After Lydia’s attorney learned about Karen, she appealed that her client might have similar issues. And then, after investigation turns out Lydia had chimerism too for which she had two sets of DNA in her body of which one (of the blood) didn’t match with her children.

Coming to the main discussion, what is chimerism? And how does a person with chimerism have completely different sets of DNA inside their body? Human Chimerism is a very rare medical phenomenon with more or less 100 cases till now around the world where one person bears more than one set of DNA in the body. However, a comparatively common but minor form of chimerism that takes place in more than 80% of pregnancies is called microchimerism. In such forms of chimerism, the mother absorbs some DNA from the fetus during pregnancy or vice versa. In many cases, because of microchimerism, the mother passes away within a month of giving birth to a child due to autoimmune responses. Again, in several cases, after giving birth to a male child, the mother gets detected with the “Y” chromosome that exists only in men in different parts of her body. This is also a result of microchimerism. However, chimerism can cause people to have two different blood types and two different colors of eyes and skin as well. The first case of Human Chimerism was discovered in 1953 where a British woman had two different blood types in different organs of the body. Again, recently, a singer named Taylor Muhl from California was detected with Chimerism having two different skin pigments (half-white and half-red).

Circling back to the cases of the two mothers, Lydia and Karen, described above, the causes behind chimera in both cases is a result of a very rare disorder named “Vanishing Twin Syndrome”. Except for microchimerism, “Vanishing Twin Syndrome” is the only cause behind inborn chimerism. In the case of this syndrome, the individual bears an invisible twin inside his or her body. This might sound intriguing yet horrifying at the same time. But this happens when a person shares his or her mother’s womb with a non-identical twin which vanishes later. That means, two eggs fertilize at a time among which one either fuses together with the other forming one fetus with two sets of DNA, or the vanished one gets absorbed by the placenta leaving some DNA within the surviving fetus. Therefore, in the case of both Lydia and Karen, their germ cells weren’t their own, rather their unborn invisible twin’s that lived within their body. For which, the DNA samples of their children didn’t match with theirs. Astonishing, isn’t it? “Vanishing Twin Syndrome '' takes place in about 20% to 30% multiple pregnancies. But chimerism doesn’t take place in every case.

However, females aren’t the only victims of “Vanishing Twin Syndrome” causing chimerism. A similar case like Lydia and Karen were also found in a father living in Washington when his paternity test revealed that he isn’t the father of his children, rather uncle. Later, it turned out he too, had an invisible twin inside him that caused him to become a human chimera and his children were the product of his twin’s germ cells.

Though “Vanishing Twin Syndrome” has been very rare since it was discovered, the availability of Human Chimerism is increasing day by day. This is because chimerism can also occur in a human being artificially after an organ transplant. There are more possibilities in cases of “Bone Marrow Transplant”. Besides that, in very few cases, blood transfusion also results in chimerism. However, one of the main causes behind the rarity of both “Vanishing Twin Syndrome” and chimerism cases is the lack of detection. Till now, cases of getting detected with chimerism were all accidental. Hence, unless someone tests their DNA or requires a blood transfusion or organ transplantation, nobody would know they are human chimeras throughout their lifetime.

Therefore, something you should always remember is “Science can be very surprising”. And it is inconsistent. Things we claim to be impossible might become scientifically possible after a few or more years. That’s why it is not wise to always believe in all scientific explanations blindly as there can be many hidden scientific mysteries behind every explanation that hasn’t been revealed yet. Well, at least now we know that a DNA test doesn’t lie for sure but a person can be a biological parent without being a parent genetically. So, if you ever witness a case in your life where a parent claims their parentship but gets denied by the DNA tests, chances are that he or she might be a Human Chimera.