On the surface, Taylor Muhl seems like a perfectly average person. She lives in California, works as a singer and a model, and has a lot of selfies on her Instagram page - many of which show the interesting birthmark on her torso.
However, unlike most people, Muhl knows exactly how and why she got the birthmark - which runs directly down the center of her body and covers half her stomach - because it isn't really a birthmark at all. In fact, Muhl isn't even a person. She's two people.
"I was born with a rare genetic condition called, Chimerism. I Am My Own Twin or I can say, I’m a Chimera," explains Muhl. "I’m a fraternal twin who fused together with my sibling in the womb and carry their genetic makeup within my own body. Not only that, I’ve been told I have two immune systems and two bloodstreams."
As cool as it sounds, though, being a Chimera has caused a lot of problems for Muhl.
As she explains on her blog:
"Everything on the left side of my body is slightly larger than the right side. I have a double tooth in the left side of my mouth and many sensitivities and allergies to foods, medications, supplements, jewelry, and insect bites. My body reacts to my twins DNA and cells as foreign matter, compromising my immune system to be much lower than an average person’s.
"Due to that, I unfortunately suffer with autoimmune and health challenges."
The model has a daily struggle with ongoing acid reflux, neuropathy, borderline fibromyalgia, and endometriosis. Fortunately, she can take birth control pills to ease the symptoms of this last illness; however, the medication makes her more susceptible to autoimmune flare-ups.
For years, she wondered what was wrong with her, and it was only in 2009 that one medical professional - Dr. Sean Nasseri - finally worked out the problem.
"I felt freedom [after the diagnosis] because for the first time in my life I knew why my stomach looks the way it does," Muhl said. "Prior to that, every doctor said my stomach must have just been a birthmark … Finally, this is making some sense."
Understandably, though, Muhl's discovery wasn't one of complete relief.
"My first reaction was shock," she said. "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 I hopefully could have been close to’. There was some sadness."
But Muhl isn't alone in her condition.
Dr. Brocha Tarshish, a clinical geneticist based in Florida, says that Chimerism often goes undiagnosed because of how difficult it is to identify. Without specific biomedical tests, it's impossible to tell whether someone is their own twin or not - and, obviously, those sorts of examinations aren't really performed without reason.
Having said that, there are subtle clues to the condition. Patchy or varying skin tones on an individual could be an indicator that they are a chimera, and different colored eyes are sometimes a symptom as well. However, Dr. Tarshish explained that it's very common for one cell line to become more dominant, so most chimeras will have a majority of one set of DNA, rather than an even split.
In one other case of Chimerism, a woman named Karen Keegan discovered she was her own twin after doctors told her she wasn't the biological mother of two of her three children. She had been seeking a kidney transplant, and somehow only one of her children fit her genetic profile. It eventually transpired that the other two children came from her twin's DNA.
Fortunately for Muhl, she is able to cope with most of the effects of her condition, and still leads a healthy and fulfilling life.
