This is the first reported case of a paternity test being fooled by what you might call a Human Chimera! Although this a unique reported case it could be that up to one in eight of people out there possess these Chimeric genes. How do we know this? One in eight of all single child births actually start out as a multiple pregnancy so there is the potential for this to happen again. It is unusual but the extra genes from the dead twin could be absorbed by the surviving one.
“Even geneticists are blown away by this,” Barry Starr, a geneticist at Stanford University, told BuzzFeed News.
Last year, a Washington couple came to Starr, who runs the “Ask a Geneticist”website at the Tech Museum of Innovation in San Jose, California looking for help with what appeared to be a mistake at a fertility clinic. The answer to their mystery points to a possible genetic loophole in standard paternity testing, Starr said, “one where we have no idea how big the problem is.”
In June of 2014, the parents (who have chosen to remain unnamed because of concerns for their privacy and confidentiality of medical records) had a son with the help of fertility clinic procedures. The boy was born healthy, but strangely, his blood type didn’t match that of his parents.
An at-home paternity test suggested an explanation: The man wasn’t actually the father of the child.
“You can imagine the parents were pretty upset,” said Starr, whose colleagues have presented the case at two scientific meetings this month. “They thought the clinic had used the wrong sperm.”
The parents hired a lawyer and sought a more precise paternity test from an accredited lab. Just like the at-home test, the new analysis relied on skin cells from a cheek swab to check the father’s genes against the child’s. Again, the test came back negative for paternity.
Accredited U.S. labs perform nearly 400,000 paternity tests every year in legal, immigration, and criminal cases, with more than 99% of them relying on cheek swab samples. About 24% find that the man is not the father of the child.
Concerned that the fertility clinic had made a mistake, the Washington couple approached them with the results of the paternity test. But the fertility clinic said that the 34-year-old father was the only white man to donate sperm at the facility on the day their son was conceived, and the child looked white.
That was when the couple approached Starr, who suggested they test the father and son with a direct-to-consumer genetic ancestry test sold by the startup firm 23andMe. The results of those tests came back late last year. Bizarrely, their results said that the man was his son’s uncle.
“That was kind of a eureka moment,” said Starr. At that point, he realized they might be dealing with a chimera.
“Chimera reports are very rare but they are real.”
People usually have just one set of genes, half of them from their mother and half from their father.
But in 2002, researchers reported the chimeric case of Karen Keegan in the New England Journal of Medicine, a rare case of maternity testing being fooled by a ghost’s genes.
Keegan needed a kidney transplant and her sons, as close relatives, were tested as possible donors. The gene tests, however, said the 52-year-old Boston woman wasn’t actually the mother of her children.
She was a chimera. Tests revealed that while her blood cells had one set of genes, her ovaries held distinctly different ones. Those ovaries had produced the eggs that led to two of Keegan’s sons holding genes different from her own, said Lynne Uhl, a pathologist at Beth Israel Deaconess Medical Center and co-author of the NEJMstudy. The researchers reported that these different genes most likely came from a lost twin of Keegan’s, one whose cells she had absorbed while she was an embryo in her own mother’s womb.
The true genetic mother was a twin sister that she never knew and who was never born—a ghost.