DNA and Chimerism

We have all heard about the guy who served 25 years or so  for a crime he did not commit.  He was fortuitously saved from further incarceration by DNA testing. Released as an innocent man we all celebrate modern science and its amazing ability to reveal the truth in these cases and exonerate the poor guy.   But what if DNA wasn’t as cut and dried science as we think. What if your DNA can change?   Besides the normal things that can go wrong with testing, such as the testing process, the evidence collection and integrity of the sampling, they are weirder things that can happen.



26 year old Lydia Fairchild filed for public assistance in 2003. She had two children and another on the way. Washington State, where she filed, requires DNA samples for the family to prove they are related. It also helps the state pursue parental support and fraud if necessary.  The DNA samples came back and said that Lydia was not the mother of her children.


Cutting edge science in the field of Forensic DNA  is a topic found in essays in  many scientific journals.  Science is still learning about DNA testing, enhancing speed and sensitivity.  However, new advances are not always available immediately to everyone. The US government has built a DNA Library or database. Since the workings of a government machine turn slowly and is costly, it takes a long while before they can switch  to the latest test instruments. By the time they get there, there will be more advances.


boy-1300401_640Lydia was adamant that her children were, indeed, hers. In fact one was in her belly. The State concluded that she was as surrogate of sorts and denied her claim. Lydia tried to get a lawyer but those she approached told her the DNA was proof positive she was not the mother.



Scientists still do not totally know the nuances of DNA and how it affects us. For example, there is a thing called Chimerism.  It is the condition in which one person can have two sets of DNA.  One develops this condition through blood transfusions, organ transplants and the passage of DNA between a mom and her fetus while in utero.   It can also happen from the spontaneous termination of two zygotes into single embryo.  I have a niece who went through not one, but two bone marrow transplant. Her blood type changed and while I don’t know for sure, I would not be surprised if her DNA changed as well.


She was finally able to find an attorney, Alan Tindell. He believed her and went about trying to figure out what was happening. During his investigation he read an article in the New England Journal of Medicine. The article talked about another woman whose testing said her son was not her own. Since she was in need of a kidney transplant, the doctors took DNA from several spots in her body, finally finding her original DNA in her thyroid. The thyroid DNA matched the woman sons.  The lawyer requested the same type of DNA testing for Lydia. It was finally revealed that she was, in fact, the mother of her children. Lydia was the victim of Microchimerism.


Chimerism can play a part in criminal investigations as well. Police in Alaska inputted a semen sample into the computer and found a match in the DNA database. When they went to arrest the individual, he was incarcerated, the perfect alibi.  They were stumped. Until they learned that the suspect’s brother had donated bone marrow to him.  As his skin cells had not changed yet, they exonerated the accused.

Microchimerism is a little more common. It happens to pregnant women and is the result of the fluids that flow freely between mom and the fetus.  Most women find out about the DNA exchange when they go in for the blood tests at 10 weeks of pregnancy that is usually meant to detect genetic defects.  The blood test draws fetal cells from the mother’s blood. Studies have shown that the genes from her fetus migrate throughout the mother’s body. They have found traces of male DNA in women who have never given birth to sons. Scientists think that this exchange of DNA and genes may help to keep mom healthy during pregnancies.



Lydia Keegan had Tetragametric Chimerism. When pregnant she had two zygotes from four cells. (Two eggs and two sperms) Instead of having fraternal twins, they all fused into one baby. For Lydia that meant her blood cells contained one DNA and her other tissue contain a mix of the other two DNAs.



1 in 2400 people has chimerism. It is not as rare as thought.  In fact some think that with In Vetro techniques that implant several embryos, not all of them live, but their DNA do and typically shows up in the living fetuses.  Law enforcement perhaps should be aware of the fact that DNA testing is not a perfect science and that as we learn more, there will be more times that disputes and false arrests may arise. Others however, do say, that while Chimerism is more common than thought, it is still an exaggerated fear.



DNA At the Fringes: Twins, Chimerism, and Synthetic DNA  http://www.thedailybeast.com/articles/2015/10/07/dna-at-the-fringes-twins-chimerism-and-synthetic-dna.html