Man's Semen Shows Donor's DNA After Bone Marrow Transplant

This rare scenario leads to big questions in the world of forensics.
Fabienne Lang
DNA test tubesAndy/iStock

Imagine not being able to trust the story your DNA is telling. The blueprint of what makes you you should be accurate, right? Chris Long from Reno, Nevada thought so too. 

But just three months after receiving a life-saving bone marrow transplant, some of Long's DNA had been replaced, portraying him as a German man 5,000 miles away. That man was his donor. 

The entire situation caused Long to question his own identity, baffled scientists, and brought up questions about potential criminal applications. 

What happened to Long's DNA?

According to The New York Times, Long needed a bone marrow transplant after he was diagnosed with acute myeloid leukemia and myelodysplastic syndromes— both of which stop the body from producing blood normally.

Of course, the goal of the transplant is to replace weak blood-forming cells with healthy ones – which explains why some of Long's DNA was his donors. But one of Long's colleagues at the Washoe County Sherriff's Department suggested that he should look into the possibility that the donor's DNA might travel to other parts of his body. With Long's consent, his colleagues in the crime lab took DNA samples and studied them.

It turns out Long's DNA had changed in places beyond just his blood. Swabs from his cheeks, lips, and tongue showed DNA from both men. Further, Long's semen only showed DNA from his donor. Long told the New York Times "I thought that it was pretty incredible that I can disappear and someone else can appear."

What does this mean for forensics?

Long's case raises a few questions, namely, what does this mean for the future of forensics?

DNA samples are sometimes used in court cases as evidence. If innocent people's DNA is showing up at crime scenes due to bone marrow transplants, forensic scientists have an interesting case on their hands. Tens of thousands of people get bone marrow transplants every year. Obviously, they all don't go on to commit crimes, but that leaves the potential for wrongful convictions. 

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It's happened before. When Abirami Chidambaram worked for the Alaska State Scientific Crime Detection Laboratory in Anchorage, said heard about one such scenario. As she told the NYT, a victim of sexual assault reported her attacker to the police. But the authorities were skeptical because the analysis showed DNA from two different attackers, not one. Eventually, the police determined that the second profile had come from her bone marrow donor.

Now, as in Long's case, if someone like him committed a sex crime, with investigators collecting semen samples — could the bone marrow donor be arrested for the crime if their DNA shows up positively?

Again, this case is incredibly rare. A donor's cells shouldn't be able to create new sperm cells. Dr. Mehrdad Abedi, the doctor at the University of California, Davis, who treated Long, believes his semen contained his donor's DNA due to Long's vasectomy. 

Still, future forensic scientists and detectives alike have a lot to consider, as our understanding of the capabilities of DNA evolves.