A man who had a bone marrow transplant to treat acute myeloid leukemia later found out that the DNA in his blood and semen had been replaced by that of his donor.

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Chris Long, who lives in Reno, Nevada had been urged to test his blood by a colleague working at the crime lab at the Washoe County Sheriff’s Department, where Long worked.

The colleague, Renee Romero, had suspected that Long’s blood DNA might change, given that the goal is to replace diseased blood with healthy blood, which would include the DNA it contains.

Romero also suspected that Long’s DNA may be affected elsewhere in his body and urged him to have DNA samples taken from various body parts before the procedure so they could be compared with samples taken afterward.

Four years after the procedure

Four years after the transplant had been carried out, the crime lab discovered that it was not only Long’s blood that contained his donor’s DNA. Samples taken from his lips and cheeks also did, and much to the team’s surprise, all of the DNA in his semen was his donor’s DNA.

I thought that it was pretty incredible that I can disappear, and someone else can appear.” Chris Long

Long had become what is known as a chimera - a person who has two sets of DNA. Clinicians and forensic experts have long known that certain medical procedures can lead to genetic chimerism, but exactly where in the body a donor’s DNA appears – beyond blood – has rarely been studied in terms of potential criminal implications.

Tens of thousands of people receive bone marrow transplants every year, and although it is unlikely any of them would be involved in crime, the possibility that they could be has long interested Long’s colleagues at the sheriff’s department’s crime lab.

The potential implications for forensic analysts

When investigating a crime, forensic analysts generally assume that any evidence gathered at a crime scene pertaining to a single perpetrator would have a single identifying set of DNA, rather than two.

When Romero heard that Long would be undergoing a bone marrow transplant, she saw an opportunity to investigate and told him: “We need to swab the heck out of you before you have this procedure to see how this DNA takes over your body,” which Long agreed to.

Within four months of the procedure, Long’s blood had been replaced with his donor’s blood, and of all the samples collected from other parts of his body, only the DNA in his chest and head was still long’s own.

The crime lab experiment persisted, and surprisingly, the researchers found that four years following the procedure, the DNA in Long’s semen had been completely replaced by his donor’s.

“We were kind of shocked that Chris was no longer present at all,” said criminal investigator Darby Stienmetz.

Colleague Brittney Chilton points out that if another patient who responded similarly to a transplant went on to commit a crime, it could mislead investigators.

Indeed, Chilton had already learned of such cases when she started her research into chimerism.

The issue came to light in 2004 after DNA left at a crime scene in Alaska matched that of a convict. However, at the time of the crime, the convict was in prison. It emerged that he had received a bone marrow transplant from his brother, who was eventually arrested and convicted.

Confusion also arose in 2008, following a road traffic accident in Seoul. The man involved was found to have blood that contained female DNA, kidneys containing male DNA, and a spleen that contained a mixture of the two. It was later discovered that the man had received a bone marrow transplant from his daughter.

All the people involved in Long’s case agree that he is a living, breathing case of a chimera and that it is impossible to say how many other people respond to bone marrow transplants the same way he did.

A curious possibility that forensic analysts may want to consider

This represents a curious possibility that forensic analysts may want to consider in cases where DNA results are not seeming to add up.

As far as Long is concerned, he is hoping to meet his donor (who lives in Germany) during an upcoming trip to the country so he can thank him for saving his life.