By Sola Ogundipe
TWINS are special beings and ever since Taylor Muhl, a Los Angeles singer and model, was a little girl, she longed to have a twin sibling. She would often ask her mother whether she was a twin and became obsessed with dressing just like her friends.
Little did she realise she had a fraternal twin that she absorbed in the womb. It was not until several years later Muhl learned that her wish had already come true.
She grew up believing a discoloration on her stomach was simply a birthmark. And after years of battling autoimmune issues, Muhl went to a doctor who diagnosed her with Chimerism—a rare disorder in which a person has two sets of DNA—in Muhl’s case, she lives with the DNA of her fraternal twin whom she absorbed in her mother’s womb.
Each set of DNA has its genetic code to make a separate person. The rare condition can happen very early in embryonic development, according to People’s Magazine.
Muhl had fused with her sibling in the womb, unknown to her mother who opted for a “natural” pregnancy and never had an ultrasound, Now, she carries her twin’s DNA in her own body, with two different blood streams and immune systems. Muhl’s body is constantly working to fight off the twin’s cells, as it recognizes them as foreign.
“My first reaction was shock,” Muhl said when she recalled the moment she learned about her condition almost eight years ago.
“Then my second reaction was sadness because I was like, ‘Oh my gosh! I could’ve gone through life with a twin, with a sibling that hopefully I could’ve been close to.’ There was some sadness.
“I actually felt relief. I felt freedom because for the first time in my life I knew why my stomach looks the way it does. This is why I’ve had so many health challenges. I felt like for the first time I could really breathe. Prior to that, every doctor said my stomach must have just been a birthmark …. Finally, this is making some sense.”
One side has a different skin pigmentation colour than the other side—the result of her twin’s DNA.
But her mother, who didn’t have more children, was saddened by the news, viewing the situation as “losing a child.”
“I think, for her, it was really sad just to think about, ‘Wow, I could’ve had two babies.’ ”
Muhl has a type of chimerism called tetragametic chimerism. This can happen in cases of fraternal twins, where there are two separate eggs fertilized by two separate sperm, and the two zygotes “merge and form one human being with two different cell lines,” said Dr. Brocha Tarshish, a clinical geneticist at Nicklaus Children’s Hospital, in Miami.
Most of the time, people with chimerism probably go undiagnosed, Tarshish said. Indeed, without specific biomedical tests (such as genetic testing), it’s impossible for doctors to tell that a patient is a chimera, according to a 2009 about the condition.
But there may be subtle clues to this condition: Some people with chimerism have “patchy” skin coloration (like Muhl does) or different-colored eyes, the paper said. In some cases, chimerism is diagnosed when a person is found to have two different blood types.
It’s hard to predict how the condition will manifest or which tissues will be most affected, Tarshish said. But it’s common for one cell line to outgrow the other, so people end up having the majority of their cells come from one set of DNA, rather than a 50-50 split between the cell lines, Tarshish said.
In cases in which there are different sets of sex chromosomes (XX and XY), a person’s internal and external genital can be affected. For example, this could result in ambiguous genitalia, Tarshish said. (It was reported previously that Muhl’s fraternal twin was her “sister,” meaning both sets of DNA contained female chromosomes.)
Doctors have told Muhl that she has “two immune systems and two bloodstreams,” she wrote in a blog post published in March 2017, meaning cells in her immune system and her blood have two sets of DNA.
Her chimerism has also led to an autoimmune condition, because her body sees her twin’s DNA as “foreign” and reacts to it, she wrote. She has a number of allergies to foods, medications, supplements, jewelry and insect bites, she added.
Muhl was diagnosed with chimerism in 2009, but she went public with her diagnosis last year. She is now focused on living a healthy, active lifestyle to cope with her health challenges, according to People.
Now, Muhl focuses on living a healthy, active lifestyle to cope with her condition. Although she has known about her disorder for several years, she only went public with the news in 2017. She kept her condition private —and hid her stomach—in fear of losing opportunities in the entertainment industry.
“This has probably been the most freeing year that I have ever lived in my entire life. What was so hard for me was pretending that I wasn’t sick and it’s something that I did for the last seven-plus years. It really does start wearing on you. Now I don’t have to worry about any of it. It’s all out there.”
Muhl often shares information about her condition, and even shows off her stomach on Instagram, boldly writing, “I’m a fraternal twin who fused together with my sibling in the womb. I don’t have to hide who I am anymore and it’s a great feeling.”
Because chimerism is hard to diagnose, it’s probably more common than we think, Tarshish said, although overall, it’s still probably pretty rare.
Some cases of human chimerism have been reported before. For example, in 2002, a woman named Karen Keegan needed a kidney transplant, and doctors were puzzled when tests of possible family donors showed that she could not be the mother of two of her three sons, according to a report of the case. The mystery was solved when doctors discovered that Keegan was a chimera—the set of DNA in her blood cells was different from that in the other tissues in her body.