The Case of the Vanishing Twin

A couple in Washington state used a fertility clinic to have their youngest son.  When they had a blood test run on their newborn child, the child’s blood type did not coincide with that of his parents.  A paternity test was then run and the results were grim, the child was not the man’s son.  The couple immediately blamed the clinic, because the only reasonable explanation was a mistake on their part.  

In reality, the explanation was a lot more complicated than just mistakenly using the wrong sperm cells.  The son’s DNA was not completely foreign, there was significant resemblance between the son and father’s DNA, approximately 25% similarity.  The genetic testing company 23andme determined the true father of the child was the man’s fraternal twin, making the man the child’s uncle.  However, the man had no twin brother.  So who was the actual father of this child?

The genetic phenomenon, chimerism or often referred to as the “vanishing twin” phenomenon, explains what happened in this very interesting situation.  This phenomenon refers to one fetus not surviving through the entire pregnancy, and the other fetus absorbing its genetic material.  The man had a twin in the womb, but the two zygotes fused into one, producing solely the man and not both offspring.  However, this man still had his twin’s DNA and this is the DNA that went on to produce his child.  

This is extremely interesting.  A genetic study found that one in every eight single births, begin as two or more zygotes at conception.  This is a high ratio for something that seems so rare, which means many people whose DNA have been affected by this, most likely do not even know.  It is interesting to think that you may only have around 25% of one of your parent’s DNA, and the other 25% from an unborn uncle or aunt.  It sounds more like a science fiction novel than reality, making it quite shocking.

Click here to read another case of the “vanishing twin” phenomenon.

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