Every person is born with unique strands of DNA, proteins that contain our genetic code. As a natural ‘social security number,’ DNA tests can help the police catch criminals during investigations. Although these tests are highly regarded, one man threw the entire science into question.
Chris Long, a resident of Reno, Nevada, had his DNA become identical to a German man who was ten years younger than him. How did this happen? And what does this mean for future DNA tests? Read the story that has baffled scientists from around the world.
The Life-Threatening Diagnosis
In 2015, specialists diagnosed Chris Long with acute myeloid leukemia and myelodysplastic syndrome. But to Chris, those scientific terms translated to blood cancer. The father of two had abnormal tumor growth in his bone marrow, which infected his blood cells.
Those who have acute myeloid leukemia (AML) have a 24% chance of survival. The only treatment is to combine chemotherapy with a bone marrow transplant. While Chris considered his options, he understood that his future seemed bleak.
What Is A Bone Marrow Transplant?
During a bone marrow transplant, cancerous bone marrow is replaced with healthy marrow. Because bone marrow creates red and white blood cells, patients require an operation before their blood becomes too unhealthy.
Before Chris could receive the transplant, he had to undergo chemo to destroy the harmful cells. Then, he had to find a donor whose cells would not attack his body. Doing so was difficult, but fortunately, there are plenty of donors around the world.
Finding The Right Donor Is Harder Than It Sounds
However, finding a bone marrow donor is more complicated than finding a blood donor. To find a match, doctors examine donors’ human leukocyte antigen (HLA). HLA is a protein that the immune system uses to know which cells are yours and which are not.
Each person has six different HLA markers. Doctors can pinpoint your HLA through a DNA test by swabbing the inside of your cheek. If the six markers line up, the donor’s cells will not be "foreign" to the patient’s immune system.
An Unusual Bargain
Fortunately, Chris found his donor quickly–an anonymous man from Germany. At the time, Chris worked as an information technology employee at the Washoe County sheriff’s department in Reno, Nevada. They were a world apart.
Chris’s sad diagnosis spread around his office. When the news reached them, forensic scientists of Washoe County took an interest in his case. They offered Chris an unusual opportunity that would challenge the scientific community only a couple of years later.
Can Your DNA Change?
Renee Romero, who led the crime lab at Washoe County, heard about Chris’s situation through a colleague. The situation raised a question that Renee had been mulling over: would a bone marrow transplant change Chris’s DNA?
Renee spoke to Chris about the opportunity to partake in an experiment. "We need to swab the heck out of you before you have this procedure to see how this DNA takes over your body," she remembered telling him.
A Human Guinea Pig
After hearing Renee’s proposal, Chris agreed. He welcomed the distraction from his fatal diagnosis and his difficult path to recovery. During the conversation, he reportedly told Renee, "I don’t even know if I will live."
Regardless, Chris began the joint experiment. Acting as a human guinea pig, Chris allowed the scientists to take samples of his DNA before he underwent surgery. The scientists would continue to monitor Chris’s DNA throughout his remission and recovery.
Results Came Faster Than Expected
After his bone marrow transplant, Chris spent four years in remission. But Renee and her crime lab colleagues monitored him throughout his journey. Four months in, they analyzed Chris’s blood. His German donor’s DNA had replaced the genetic code in his blood.
The scientists also swabbed Chris’s cheek, lip, and tongue. The DNA in these areas was replaced by the donor’s as well. The DNA swapping was already accelerating faster than the forensic scientists had expected.
How Chris Transformed Into Another Person
The forensic scientists tracked Chris’s DNA samples over four years. Within months, swabs of his arms, legs, body, and face had been replaced by his donor’s DNA. Oddly, these findings fluctuated throughout the study. Some swabs contained both Chris’s and his donor’s DNA.
An even more surprising find was that Chris’s semen had its DNA replaced. By the end of the four years, every area of his body had new DNA except for his chest and head hair.
The Shock Of A Lifetime
These findings baffled the forensic scientists at the Washoe County sheriff’s office. No one expected Chris’s DNA to be entirely overtaken by his donor. As criminalist Darby Steinmetz said, "We were kind of shocked that Chris was no longer present at all."
Chris was also shocked about the findings–but not to the point of despair. He told the New York Times, "I thought it was pretty incredible that I can disappear and someone else can appear."
He Is A Real-Life Chimera
So what happened to Chris? The bone marrow transplant had made Chris a chimera–the scientific term for people with two sets of DNA. The term stems from the monster in Greek mythology that was a hybrid of three animals.
Before Chris’s study, forensic scientists knew that specific medical procedures cause chimerism. But they never researched where the donor’s DNA replaced the patient’s in the body. The fact that 99% of Chris’s DNA had changed raised questions among the medical community.
This Has Been Studied Before
Chimerism from bone marrow transplants has been researched before. In 2004, research in Bone Marrow Transplantation reported that marrow transplants replace at least some of the patient’s blood DNA. Even blood transplants temporarily replace DNA in the patient’s blood.
However, these studies have only analyzed DNA changes in blood. Before the study on Chris, scientists have not tested how a patient’s DNA changes in the rest of their body. In this sense, his case defied all expectations.
Will Chris Remain The Same Person?
The implications of Chris’s case reached scientists far beyond Nevada. One nagging question was: would Chris remain the same person with someone else’s DNA? Dr. Andrew Rezvani, the blood and marrow transplant professional at Stanford University, says yes.
"Their brain and their personality should remain the same," he told the Independent. He added that, if Chris’s donor were female, it would not convert him to the female sex. "It doesn’t matter," Dr. Rezvani stated simply.
For The Doctors, This Isn’t An Issue
Although medical doctors understand the DNA change, they don’t see it as an issue. As long as the transplant is successful, the change does not create any medical problems. The patient’s medical history and mind do not change. So what’s the issue?
For Renee and her colleagues, the DNA change does matter. As forensic scientists, they viewed Chris’s case from the perspective of combating crime, and they knew that the DNA change could mean life or death for some.
…But It Could Throw Off Criminal Investigations
For forensic scientists, Chris’s DNA change uncovered a new host of problems. When criminal investigators hunt down criminals, they rely on DNA swabs to lead to one person. What will happen if the DNA links to two people, one in Nevada and one ten years younger in Germany?
According to Brittney Chilton, a criminalist of the forensic science division, says that this DNA change could mislead investigators. It could result in someone being falsely accused of a crime they didn’t do.
This Mix-Up Has Happened Before
In 2004, criminal investigators in Alaska thought they had caught a criminal when they uploaded a DNA sample to a database. There was just one problem: the man was in jail at the time of the crime. But DNA samples are flawless, right?
It turned out that the criminal’s brother had received a bone marrow transplant. He was convicted, and a year later, crime detection scientist Abirami Chidambaram presented the case in 2005. It’s the exact dilemma that Chilton was talking about.
But That’s Not The Only Problem
According to Chilton, chimeras create another issue for the medical community. In 2008, research scholar Yongbin Eom tried to identify a victim of a car accident in Seoul, South Korea. His DNA showed that he was female–but his body was male.
It turned out that the victim received a bone marrow donation from his daughter. Chimeras have two sets of DNA: their original DNA and their donor’s DNA. This may prevent medical investigators from properly identifying a body.
How Have Scientists Not Caught This Before?
Every year, thousands of people receive bone marrow transplants. The surgery is commonly recommended for patients with leukemia, sickle cell anemia, and lymphoma. Then how did this dilemma not surface before? Here’s the thing: it has.
Bone marrow transfusions have interrupted criminal investigations before. Renee’s study was the first in-depth research to explore DNA changes from a scientific perspective. The team presented Chris’s case at the international forensic science conference in September of 2019.
Chimeras May Be Common (And In Trouble)
Studies suggest that chimerism may occur in 21% of triplets and 8% of twins. But these results don’t explain how common the condition may be. If these chimera news stories hadn’t come out, many people wouldn’t know that chimerism even exists.
Most people don’t take a paternity test to make sure that they’re related to their biological family. As a result, many people could be chimeras and never know it. It only becomes an issue when a person’s life is on the line.
Parents Could Lose Their Children
In some instances, chimerism may separate families. In 2002, Lydia Fairchild applied for child support. But the DNA tests said that she wasn’t related to her children. During the case, she became pregnant with her third child–and the child still exhibited different DNA while in the womb!
Even though a judge arranged for a witness to be present for her third child’s birth, the courts held her DNA tests above her doctor’s testimony. Luckily, she was diagnosed as a chimera; otherwise, she would have lost her children.
What About Their Offspring?
Long’s case raised another question. If a patient’s DNA changed, and they had a child, would they create someone else’s child? Renee surveyed three bone marrow transplant specialists for the answer to this question.
Although the experts agreed that it is an intriguing question, they highly doubted that a child’s DNA would change. "There shouldn’t be any way for someone to father someone else’s child," reported Dr. Rezvani. After all, a donor’s blood cells should not create new sperm cells.
Could Chris Have His Donor’s Child?
If sperm isn’t usually affected by transplants, why did Chris’s change? According to Mehrdad Abedi, the doctor who treated Chris, his semen change likely resulted from his vasectomy. The fact that sperm couldn’t move meant that their DNA would change.
If Chris hasn’t had a vasectomy, would the same result occur? We don’t know, and the scientists can’t test this on Chris. DNA analyses of sperm have shown the donor’s DNA instead of the patient’s before. Time will tell.
Chimeras Can Occur Naturally
Human chimeras don’t only result from bone marrow transplants. For instance, there’s a case of a “vanishing twin,” where one fraternal embryo dies early on. The remaining embryo absorbs the twin’s DNA, resulting in two sets of DNA in the child.
During pregnancy, some women may retain some DNA from their baby. This phenomenon, called microchimerism, occurs in around 63% of women, even those over 94 years old. The New York Times says that microchimerism is “very common, if not universal.”
But Identifying Chimeras Is Very Difficult
To make matters worse, it’s not easy to tell if someone is a chimera. In 2015, parents discovered that their newborn’s blood type and DNA did not match their parents’. They assumed that the clinic had used the wrong sperm.
Stanford geneticist Barry Starr recommended that the couple take a genetics test. Oddly, the test said that the father was the child’s uncle. "Human chimerism is very common, but exquisitely difficult to identify, coming to light almost exclusively by accidents like this," biologist Charles Boklage told Buzzfeed News.
How This Study Impacted The Future
Chris’s case has changed many peoples’ opinions about DNA tests. Before, DNA tests were considered infallible in the courtroom. But the study suggests that common conditions may make DNA exams less foolproof than we assumed.
Chimeras have no issues in terms of health or medicine, but they create stumbling blocks for criminal investigators who rely on DNA tests to catch a perpetrator. With chimera cases coming to light, forensic scientists will have to redefine how they analyze DNA evidence.
Where Is Chris Now?
Chris Long recovered from his AML. He is now healthy and experiences no issues as a chimera (he is completely innocent!) He told the Independent that he planned a trip to Germany to thank his donor for saving his life.
Chris has not reported whether or not he’ll continue working with the forensic scientists. However, Renee and her colleagues have suggested that they will continue to research the effects of chimerism — specifically how it affects a patient’s offspring.