Post by JoannaL on Dec 9, 2019 12:20:42 GMT -5
Bone Marrow Recipient Now Has Donor's DNA
Three months after his bone marrow transplant, Chris Long of Reno, Nevada, learned the DNA in his blood had changed to that of his bone marrow transplant donor – a German man with whom he had exchanged a handful of messages.
He had been encouraged to test his blood by a colleague at the Washoe County Sheriff’s Department, where he was employed. His co-worker had an inkling this might happen because it is the goal of the procedure in which 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 Long’s blood that was affected: swabs of his lips and cheeks contained his DNA as well as that of his donor. Even more surprising to those in the crime lab, the DNA in his semen was also that of his donor. “I thought that it was pretty incredible that I can disappear and someone else can appear,” he observed.
Long had become a chimera, the technical term for the rare individual with two sets of DNA. The word takes its name from a fire-breathing female monster from Greek mythology with the head of lion, the body of a goat and the tail of a serpent. Doctors and forensic scientists have long known certain medical procedures turn people into chimeras, but precisely where a donor’s DNA shows up – beyond the 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. Although it is unlikely any of them would end up the perpetrator or victim of a crime, the idea they could intrigued Long’s colleagues, who have been using their (totally innocent) colleague as a human guinea pig.
The implications of Long’s case were presented at an international forensic science conference in September and 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 because this type chimerism is not likely to be harmful. Nor should it change a person: “Their brain and their personality should remain the same,” said Dr. Andrew Rezvani, 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 insisted.
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 perpetrator leaves behind a single identifying code – not two: in Long’s case, that of a fellow 10 years younger and thousands of miles away. Consequently, Renee Romero, who runs the crime lab at the Washoe County Sheriff’s Office, saw an opportunity when her friend and colleague told her 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 told him.
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. “I didn’t even know if I would live,” he remarked at the time.
Four years later, with Long in remission and back at work, Romero, asked by her crime lab colleagues, continued her experiments. Within four months of the procedure, Long’s blood had been replaced by his donor’s blood. Swabs collected from his lip, cheek and tongue revealed these contained his donor’s DNA, also, with the percentages rising and falling over the years. Of the samples collected, only his chest and head hair were unaffected. The most unexpected part was that four years after the procedure, the DNA in his semen had been entirely replaced by that of his donor. “We were kind of shocked that Chris was no longer present at all,” observed Darby Stienmetz, a criminalist at the sheriff’s department.
If another patient responded similarly to a transplant and that individual went on to commit a crime, it could mislead investigators, said Brittney Chilton, another Washoe County criminalist. Once she began researching chimerism, she learned that in 2004, investigators uploaded a DNA profile extracted from semen to a criminal DNA database and it matched a potential suspect. But there was a problem: the man had been in prison at the time of the crime and it turned out he had received a bone marrow transplant – the donor was his brother, who was eventually convicted of the assault.
The specifics of Long’s situation raise an inevitable question: What happens if he has a baby? Would he pass on the genes of his German donor or his own to future offspring? In this case, the answer will remain untested because Long had a vasectomy after the birth of his second child.
But what about everyone else? Three bone marrow transplant experts agreed it was an intriguing question. They also agreed that passing on someone else’s genes as a result of a bone marrow transplant was impossible. “There shouldn’t be any way for someone to father someone else’s child,” Rezvani, the Stanford medical director, explained.
This is not to say other forms of chimerism haven’t created comparably confusing scenarios. Fraternal twins sometimes acquire each other’s DNA in the womb and in at least one case, this led to unfounded fears of infidelity when a man’s child did not seem to be his. In another case, a mother almost lost custody of her children following a DNA test.
Nevertheless, a donor’s blood cells should not be able to create new sperm cells, Rezvani added. Dr. Mehrdad Abedi at the University of California, Davis, who treated Long, agreed: he is of the opinion Long’s vasectomy explained how his semen came to contain his donor’s DNA.
The forensic scientists involved plan to continue their investigation.
Sources: The Antelope Valley Press, December 8, 2019, and Heather Murphy, The New York Times, December 8, 2019.
