Man’s Unborn Twin Fathered His Son – What is Chimerism?

Chimera, an organism that contains at least two different sets of DNA

Rare case of chimerism

A chimera is a single organism made up of cells of two or more individuals, therefore, it contains two sets of DNA and makes two separate organisms. One of the ways through which chimeras happen naturally is when the fetus absorbs its twin. This is a common scenario with fraternal twins. If an embryo dies early in the pregnancy, the other twin absorbs the the cells. The fetus now has two sets of cells including its own and one from its twin. This phenomenon is referred to as chimerism.

This case describes a similar scenario in which a man’s unborn twin unknowingly fathered his child. The birth revolves around a failed paternity test and genetic chimerism. The baby boy was born to an anonymous couple after they underwent a number of fertility treatments. The birth was without any complications. However, when the baby’s blood test results came back, there was a discrepancy in the blood type of the parents and baby. Due to the discrepancy in the initial findings, doctors advised a follow up paternity test. The test showed that the man was not the father of the baby.

However, this was a miracle of science, not a case of infidelity.

The case was neither a blunder at the end of the fertility clinic. The child’s genes were actually from the DNA of the man’s unborn twin lost in early pregnancy. Genetic testing further revealed that the man and the child only shared 25% of their DNA. This is the same amount of DNA shared between an uncle and niece or nephew. Whereas a full biological parent shared 50% of their DNA with a child. The findings led to the conclusion that this was a case of chimerism.

Currently, there are only 100 documented cases of chimerism. Although, this case was more unusual because the man’s unborn twin gave rise to two distinct cell lines, incorporating into his reproductive line. In simpler words, some of the sperm cells were his and some contained genetic material of the unborn twin. Therefore, the unusual test results when a paternity test was carried out using the father’s cheek cells.

What’s more, when the man conceived a second son with the same partner, the paternity tests showed that the two shared 50% of their DNA. Technically, making the two children neither full nor half siblings.


A Man’s Unborn Twin Fathered His Son Thanks To Genetic Chimerism

Previous articleRare case of Splitting Headaches caused by Subarachnoid Hemorrhage
Next articleNirvana – A new testing method for COVID-19
Dr. Aiman Shahab is a dentist with a bachelor’s degree from Dow University of Health Sciences. She is an experienced freelance writer with a demonstrated history of working in the health industry. Skilled in general dentistry, she is currently working as an associate dentist at a private dental clinic in Karachi, freelance content writer and as a part time science instructor with Little Medical School. She has also been an ambassador for PDC in the past from the year 2016 – 2018, and her responsibilities included acting as a representative and volunteer for PDC with an intention to make the dental community of Pakistan more connected and to work for benefiting the underprivileged. When she’s not working, you’ll either find her reading or aimlessly walking around for the sake of exploring. Her future plans include getting a master’s degree in maxillofacial and oral surgery, settled in a metropolitan city of North America.


Please enter your comment!
Please enter your name here