man has changed dna from donor
Sarah Biren
Sarah Biren
March 2, 2024 ·  5 min read

Man Who Had Transplant Finds Out Later That His DNA Changed To His Donor’s

Chimeras are monsters from Greek mythology that are part lion, part goat, and part serpent, but today, chimeras refer to people who possess more than one set of DNA. Forget Greek chimeras, this phenomenon sounds like horror stories where two beings share one body. Fortunately, it’s not dangerous, except perhaps when it comes to criminal investigation.

Chris Long from Nevada had a bone marrow transplant and his donor was a German man he had only a few conversations with. However, three months later, Long discovered that the DNA in his blood had changed to the DNA of his donor.

He may not have discovered this shift if it hadn’t been for a colleague at the Sheriff’s Office, Renee Romero. The colleague had suspected this might happen since the goal of his procedure was to replace weak blood with healthy blood.

Four years later, however, the German donor’s DNA has spread from Long’s blood. Now swabs from Long’s lips and cheeks show both men’s DNA. Most shocking was that all of the DNA in Long’s semen was his donor’s.

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

Long is now a chimera. Although doctors are aware that medical procedures can have this effect on their patients, but the implications of having another person’s DNA has not been largely studied when it comes to crime. Until Long.

Long already works in the defense force in the Washoe County Sheriff’s Department and has a clean criminal record, making him the perfect guinea pig as his colleagues began to study how a previous bone marrow transplant can confuse an investigation. After all, thousands of people who get bone marrow transplants to treat cancer and blood diseases every year. [1]

What are the Criminal Implications?

Long’s case was presented in September at an international forensic science conference, which made the idea popular among DNA analysts across the country.

In terms of medical procedures, most doctors do not need to consider a patient’s DNA because Long’s type of chimerism is unlikely to be harmful or change him in anyway.

“Their brain and their personality should remain the same,” said Andrew Rezvani, medical director of the inpatient Blood and Marrow Transplant Unit at Stanford University Medical Center. He also added that “it doesn’t matter” for a man to have a woman’s chromosomes in his bloodstream and vice versa.

For forensic scientists, DNA matters a great deal, especially among criminal investigators who rely on the fact that each victim and perpetrator have an individual identifying code: their DNA. The possibility that a person can contain two sets of DNA, one being of someone who can a be a vastly different age and live across the ocean. 

Renee Romero saw the opportunity to study this sort of case when Long prepared for his bone marrow transplant.

“We need to swab the heck out of you before you have this procedure to see how this DNA takes over your body,” she had told him.

Long embraced the experiment as a good distraction since he was suffering from acute myeloid leukemia and myelodysplastic syndrome, diseases that stunt blood cell production. His diagnosis was bleak. 

“I didn’t even know if I would live,” he said.

Fortunately, the transplant was a success and the lab team discovered that his blood had his donor’s DNA, which was also present in lip, cheek, and tongue swabs, although these percentages were inconsistent over the years. His chest and head hair were completely unaffected and maintained his DNA throughout the years. Yet the big surprise that at the end of four years post the procedure was that Long’s semen had only the DNA from his donor.

“We were kind of shocked that Chris was no longer present at all,” said Darby Stienmetz, criminalist at the Washoe County Sheriff’s Office.

“If another patient responded similarly to a transplant and that person went on to commit a crime, it could mislead investigators,” said Brittney Chilton, a criminalist at the Sheriff’s Office forensic science division. [2]

This scenario had actually occurred before. In 2004, criminal investigators in Alaska loaded a DNA profile taken from the semen of a criminal, and it matched the profile of a suspect, a known criminal. However, no other fact matched up. The suspect was in prison at the time of crime. It later turned away that the man had a bone marrow transplant and his donor, his brother, was the one who was guilty. [3]

Abirami Chidambaram, who had worked for the Alaska State Scientific Crime Detection Laboratory in Anchorage, presented the case, and had heard of a similar story. A sexual assault victim claimed there was only one attacker, but the DNA analysis insisted two were present. The police discovered that the second DNA profile was from the attacker’s bone marrow donor.

What Does Being a Chimera Mean for Long?

Long’s case brings up a major question: What happens if he father’s a child? Will the baby have Long’s or his German donor’s DNA. However, this question will never be answered since Long had a vasectomy after his second child.

However, does the possibility still stands from other patients? Three bone marrow transplant experts state that the question is intriguing but state that passing on another person’s genes from a transplant is impossible.

“There shouldn’t be any way for someone to father someone else’s child,” said Dr. Rezvani, Stanford medical director. [4]

The doctor who treated Long, Dr. Mehrdad Abedi at the University of California, agreed. He holds that Long’s vasectomy was the explanation for how his semen had his donor’s DNA. The forensic scientists involved still plan to investigate further. Long’s case is fascinating and it would be interesting for it to expand into a larger study to see how other bodies with a bone marrow transplant react. [5]

Meanwhile, Long is hoping to meet his donor to thank him in person during an upcoming trip to Germany. 


  1. Heather Murphy. Man who had transplant finds out months later his DNA has changed to that of donor 5,000 miles away. December 9, 2019
  2. Heather Murphy. When a DNA Test Says You’re a Younger Man, Who Lives 5,000 Miles Away. NY Times. December 7, 2019
  3. Peter Aldhous. Bone marrow donors risk DNA identity mix-up. New Scientist. October 26, 2005
  4. Andrew Rezvani, M.D. Stanford Medicine.
  5. Dr. Mehrdad Abedi.—cancer—hematology-oncology—internal-medicine-sacramento