Several years ago, Chris Long, an IT specialist at the Sheriff’s Office in Nevada (USA), received a bone marrow transplant as a leukaemia treatment. He received the donation from an unknown man from the other continent, Germany.
The disease Chris suffered from was a type of cancer, and the new bone marrow of the donor and healthy cells were supposed to help him resume normal blood production. Researchers expected Chris’ blood to contain the donor’s DNA.
A colleague of Chris, who is a forensic scientist, and works with Chris in the Sheriff’s office, knew about the treatment procedure and out of curiosity, she suggested Chris take a sample of his DNA, prior to the bone marrow transplantation to determine whether it would change following the transplantation.
The results were astounding. The DNA, collected from various parts of Chris’ body after the transplantation, was disparate, with it occasionally being changed. For example, on Chris’ mouth, cheeks and tongue, both Chris’ and the donor’s DNA were collected. The chest hair, as well as his head hair, contained exclusively Chris’ DNA every time.
However, four years later, to the surprise of forensic scientists and his doctors, Chris’ semen repeatedly contained only the donor’s DNA.
As the New York Times, which covered this case extensively, reported, numerous experts asserted this situation to be theoretically completely unexpected. Chris’ physician Dr Mehrdad Abedi stated that it was probably somehow connected to the fact that Chris had had a vasectomy after his two children had been born.
What currently confounds Chris’ forensic scientist friend and her colleagues across the globe is that bone marrow transplantation could become a major conundrum in their line of work, and DNA use as forensic evidence can turn very questionable. If Chris is not an isolated case, innocent people’s DNA (along with donors’ bone marrow) could appear in various criminal reports. If, for example, Chris committed a felony, who would the police search for, based on the DNA evidence?
Even more problematic is the possibility of Chris not being some rare singular case. Annually, several thousands of bone marrow transplantations are carried out as leukaemia and lymphoma treatments – what if only one per cent of patients have similar effects as Chris? It is recognized that there were several cases in forensic science which implied similar problems, and now after Chris’ case having been presented at the International Conference on Forensic Sciences, the question of DNA analysis reliability is being put to the test.
In Alaska, 15 years ago, a case of sexual assault was under investigation. The DNA profile based on a man’s semen suggested a person who, at the time of the assault, was in prison. It later emerged that the crime was committed by his brother, who had donated bone marrow to the brother in prison, thus they both had the same DNA profile.
There was also a case of sexual assault in which the victim claimed there had been one attacker, while the DNA evidence suggested two – in this case also it was later revealed, that the perpetrator received bone marrow transplantation, therefore he had two sets of DNA.
When, 11 years ago, police investigators from Seul, South Korea, tried to identify the victim of a traffic accident, the DNA blood sample kept pointing to the victim being a woman, while the body was male. The DNA samples were collected from various body parts – the DNA from a kidney showed it was a male DNA sample, while the spleen and lungs DNA pointed to a female – in the end, it turned out that the man had received a bone marrow transplant from his daughter.
Medicine classifies the cases such as these as chimaeras. In Greek mythology, a chimaera is an unusual creature, Cerberus and Hydra’s cousin, whose body consists of lion, goat and snake parts. Natural-born chimaera humans can be twins who somehow, in rare cases, get their DNA mingled – there are less than 100 such documented cases. Alternatively, chimaera humans have acquired different DNA following some specific transplantations. However, scientists have not investigated where donors’ DNA pops up.
Doctors claim that people with two DNAs are completely healthy and that everything is all right with them since other people’s DNA does not change them in any way. Nevertheless, what if they want to have a child? Would it be their child? Will this discovery become something to consider for potential bone marrow donors, and the reason to possibly drop out? If Chris were to be involved in a crime, he would leave traces of not one, but two people, one of which is an innocent German benefactor from the other side of the planet.
M.Đ.
The image shows a Chinese sculpture of a Chimera, from the Han Dynasty period. Photo: Los Angeles Museum of Art/Wikimedia Foundation