After a bone marrow transplant, a man with leukemia found that his donor’s DNA traveled to unexpected parts of his body. A crime lab is now studying the case.
Three months after his bone marrow transplant, Chris Long of Reno, Nev., learned that the DNA in his blood had changed. It had all been replaced by the DNA of his donor, a German man he had exchanged just a handful of messages with.
He’d been encouraged to test his blood by a colleague at the Sheriff’s Office, where he worked. She had an inkling this might happen. It’s the goal of the procedure, after all: Weak blood is replaced by healthy blood, and with it, the DNA it contains.
But four years after his lifesaving procedure, it was not only Mr. Long’s blood that was affected. Swabs of his lips and cheeks contained his DNA — but also that of his donor. Even more surprising to Mr. Long and other colleagues at the crime lab, all of the DNA in his semen belonged to his donor. “I thought that it was pretty incredible that I can disappear and someone else can appear,” he said.
Mr. Long had become a chimera, the technical term for the rare person with two sets of DNA. The word takes its name from a fire-breathing creature in Greek mythology composed of lion, goat and serpent parts. Doctors and forensic scientists have long known that certain medical procedures turn people into chimeras, but where exactly a donor’s DNA shows up — beyond blood — has rarely been studied with criminal applications in mind.
Tens of thousands of people get bone marrow transplants every year, for blood cancers and other blood diseases including leukemia, lymphoma and sickle cell anemia. Though it’s unlikely that any of them would end up as the perpetrator or victim of a crime, the idea that they could intrigued Mr. Long’s colleagues at the Washoe County Sheriff’s Department, who have been using their (totally innocent) colleague in IT as a bit of a human guinea pig.
Where will the DNA go?
The implications of Mr. Long’s case, which was presented at an international forensic science conference in September, have now captured the interest of DNA analysts far beyond Nevada.
The average doctor does not need to know where a donor’s DNA will present itself within a patient. That’s because this type of chimerism is not likely to be harmful. Nor should it change a person. “Their brain and their personality should remain the same,” said Andrew Rezvani, the medical director of the inpatient Blood & Marrow Transplant Unit at Stanford University Medical Center.
He added that patients also sometimes ask him what it means for a man to have a woman’s chromosomes in their bloodstream or vice versa. “It doesn’t matter,” he said.
But for a forensic scientist, it’s a different story. The assumption among criminal investigators as they gather DNA evidence from a crime scene is that each victim and each perpetrator leaves behind a single identifying code — not two, including that of a fellow who is 10 years younger and lives thousands of miles away. And so Renee Romero, who ran the crime lab at the Washoe County Sheriff’s Office, saw an opportunity when her friend and colleague told her that his doctor had found a suitable match on a donor website and he would be undergoing a 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 recalled telling him.
Mr. Long agreed. He welcomed an intriguing distraction from his diagnosis of acute myeloid leukemia and myelodysplastic syndromes, both of which impair the production of healthy blood cells.
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