23 and No Longer Me;

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 It had all been replaced by the DNA of his donor, a German man he had exchanged just a handful of messages with.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.
 
[…]
 

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.
 
And it has misled them, Ms. Chilton learned once she began to research chimerism. In 2004, investigators in Alaska uploaded a DNA profile extracted from semen to a criminal DNA database. It matched a potential suspect. But there was a problem: The man had been in prison at the time of the assault. It turned out that he had received a bone marrow transplant. The donor, his brother, was eventually convicted.
 
Abirami Chidambaram, who presented the Alaska case in 2005, when she worked for the Alaska State Scientific Crime Detection Laboratory in Anchorage, said she had heard about another disconcerting scenario since then. It involved police investigators who were skeptical of a sexual assault victim’s account because she said there had been one attacker, though DNA analysis showed two. Eventually the police determined that the second profile had come from her bone marrow donor.
 
Similar scenarios could also create confusion around a victim’s identity — and in fact it has, said Yongbin Eom, a visiting research scholar at the University of North Texas Center for Human Identification. In 2008, he was trying to identify the victim of a traffic accident for the National Forensic Service in Seoul, South Korea. Blood showed that the individual was female. But the body appeared to be male, which was confirmed by DNA in a kidney, but not in the spleen or the lung, which contained male and female DNA. Eventually, he figured out that the victim had received a bone marrow transplant from his daughter.

But don’t worry. The same experts who assured this could never happen have also declared that the phenomenon is harmless.

From the comments: Oh great, we’re going to have to learn yet another set of pronouns.