Chris Long of Reno, Nevada, recently received startling news. Four years after undergoing a bone marrow transplant for leukemia, Long learned that he now shares the DNA of his donor.

Not only is the donor’s DNA present in his blood, but it exists in swabs of his lips and cheeks. Even more startling, 100 percent of the DNA in Long’s semen now belongs to that of his donor, raising fascinating questions about everything from crime lab identification to heredity.

Here’s what we know so far about this fascinating case of a so-called “genetic chimera” and how it’s revolutionizing our understanding of DNA, donor/recipient relationships, and crime scene forensics.

The DNA of a Younger Man 5,000 Miles Away

After being diagnosed with acute myeloid leukemia and myelodysplastic syndromes, Long didn’t know how long he would live. Both conditions impaired his body’s ability to create new blood. He turned to a matching site to find a compatible bone marrow transplant donor.

After learning that Long would be receiving a transplant from a young man in Germany, Long’s colleague, Renee Romero, who ran the crime lab, was intrigued. She asked Long if she could take multiple swabs for DNA testing, and he agreed. She knew that the donor DNA he received would start to take over his body if the transplant worked. But nobody guessed how far the extent of this takeover would progress.

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Just three months after his bone marrow transplant, Long showed signs of an incredible and necessary metamorphosis. The DNA in his blood now belonged to that of his German donor, someone he’d only communicated with through a handful of messages.

It was encouraging news and proof that the procedure worked. The healthy blood cells of Long’s robust donor were replacing the weak ones sickening him—nothing surprising there. This result was the intended outcome of the procedure. But doctors, up to this point, had done little research beyond blood changes associated with transplants. That’s why the Washoe County Sheriff’s Department decided to dig deeper.

The Murky Waters of DNA Testing

About a year later, things took a decided twist when Long submitted to another round of DNA testing. From his cheeks to his lips and tongue, the results contained the genetic material of two men: Long and his donor. More shocking still, Long learned that the DNA in his semen now belonged exclusively to his donor; only his head and chest hair remained unaffected.

In the context of forensics, the findings are having a ripple effect. Crime scenes labs all over the world rely on DNA evidence to prosecute criminal cases. Using this DNA comes with the assumption that it belonged to the suspect or somebody else at the crime scene. Who would consider the possibility of a donor’s DNA muddying the forensic waters?

dna transfer

Another of Long’s colleagues, Brittney Chilton, dug into the possibility of genetic chimerism further. She uncovered startling cases of mistaken identity. For example, the Alaska State Scientific Crime Detection Laboratory in Anchorage reported a case in 2005, where the victim insisted assault by one person. But the DNA they extracted pointed to two different perpetrators. Further investigation revealed the second instance of DNA to be that of her bone marrow donor.

More Cases of Genetic Chimerism

Chilton found other cases where DNA pointed to the wrong culprit as a result of a bone marrow transplant. Along with these cases came accounts of fraternal twins acquiring each other’s DNA in the womb, fathers who feared infidelity due to confusing DNA results, and more. One mother almost lost custody of her kids as a result of DNA testing.

Although there’s still much to learn from Long’s case, one thing’s for sure. DNA represents a much more fluid identifier than previously thought. The complication of donor-recipient relationships is pushing the envelope when it comes to our understanding of genetics.

By Engrid Barnett, contributor for