Trace fetal stem cells often remain in a mother, long after she has given birth. These types of chimerism are commonly known as microchimerism, and one of the most frequent causes is pregnancy. The donor blood cells will live about 115 days in the host's body, and will eventually be completely replaced by red blood cells carrying their original genetic code. A blood transfusion, however, only produces a temporary chimera condition. For example, when someone undergoes a bone marrow transplant, they will carry blood cells that are identical to their donor for the rest of their lives, in addition to their own genetically distinct blood cells.
#WHATS A CHIMERA CODE#
In addition to genetic chimerism, the condition is commonly caused when another genetic code is introduced to the body by organ or tissue transplants, as well as blood transfusions. Randolph is a pediatrician at Children's Hospital in Los Angeles and author of a chimerism review published in The American Journal of Medical Genetics. These symptoms can occur not only in humans, but in other types of mammals, including mice.Ĭhimerism was once believed to be extremely rare, but such conditions are "commoner than we realized," Linda Randolph, M.D., told The New York Times in 2013.
Occasionally, chimeras are born with ambiguous genitalia, or possessing attributes of both male and female sex organs, though this is not the case with Muhl.
#WHATS A CHIMERA SKIN#
Often, babies born with chimerism have patchy skin or eye pigmentation, and sometimes they carry two distinct types of red blood cells. The result is a baby who is born a chimera. As the embryo's cells multiply and grow, so do the two different types of genetic material.
Then, the fertilized eggs, called zygotes, fuse to create a single organism with two genetically distinct types of DNA. It occurs when two eggs (ova) are each fertilized by a separate sperm (spermatozoa). Muhl's condition, tetragametic chimerism, is the most rare of all types of chimerism. The difference in skin pigmentation on Muhl's abdomen, the size discrepancies between her right and left sides - and a host of autoimmune symptoms - were caused by two warring sets of DNA. Muhl is a chimera (pronounced "ky-mer-a"), someone who carries two distinct sets of DNA, each with the genetic code to make a completely separate person.
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