Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey
Speaker 1: brain Stuff Lauren Vogelbaum here with a classic brain Stuff episode. Today,
Speaker 1: we're looking at a number of conditions in which different
Speaker 1: cells in a person's body might be operating using a
Speaker 1: different person's DNA, including one in which you can be
Speaker 1: your own twin. Hey brain Stuff, Lauren vogel bam Here.
Speaker 1: Gwen Taylor Mall, a California based singer, asked a doctor
Speaker 1: to investigate the birthmark that stretched across the whole left
Speaker 1: side of her torso. She wondered what role the ruddy
Speaker 1: patch might play, if any, in a series of seemingly
Speaker 1: disparate health conditions she had experienced for most of her life.
Speaker 1: Mole says, everything on the left side of my body
Speaker 1: is slightly larger than the right side. I have a
Speaker 1: double tooth in the left side of my mouth, and
Speaker 1: many sensitivities and allergies to foods, medications, supplements, jewelry, and
Speaker 1: insect bites. While Mole says she hoped for answers, she
Speaker 1: was shocked by what the doctor told her. Her birthmark
Speaker 1: wasn't a birthmark at all. She actually carried the genetic
Speaker 1: code of her twin a sister Mall had absorbed while
Speaker 1: still in the womb. Mal is a chimera, someone who
Speaker 1: carries two distinct sets of DNA, each with the genetic
Speaker 1: code to make a completely separate person. The difference in
Speaker 1: skin pigmentation on Mall's abdomen, these sized discrepancies between her
Speaker 1: left and right sides, and a host of autoimmune symptoms
Speaker 1: are caused by two warring sets of DNA. In Greek mythology,
Speaker 1: a chimera is a fire breathing female monster that's part lion,
Speaker 1: part goat, and part dragon. As remarkable as this creature sounds,
Speaker 1: real life chimeras are perhaps even more astounding and probably
Speaker 1: more common than we realize. Mall's condition, tetracomedic chimerism is
Speaker 1: the most rare of all types of chimerism. It occurs
Speaker 1: when two separate eggs or ova, are each fertilized by
Speaker 1: a separate sperm. Then the fertilized eggs, called zygoats, fused
Speaker 1: together to create a single organism with two genetically distinct
Speaker 1: types of DNA. As the embryo cells multiply and grow,
Speaker 1: so do the two different types of genetic material. The
Speaker 1: result is a baby who is born a chimera. Often,
Speaker 1: baby is born with chimerism have patchy skin or eye pigmentation,
Speaker 1: and sometimes they carry two distinct types of red blood cells. Occasionally,
Speaker 1: chimeras are born with ambiguous genitalia or possessing attributes of
Speaker 1: both male and female sex organs. These symptoms can occur
Speaker 1: not only in humans, but in other types of mammals,
Speaker 1: including mice. Chimerism was once believed to be extremely rare,
Speaker 1: but such conditions are commoner than we realized, as Linda Randolph,
Speaker 1: m d. Told The New York Times. Randolph is a
Speaker 1: pediatrician at Children's Hospital in Los Angeles, an author of
Speaker 1: a chimerism review published in the American Journal of Medical Genetics.
Speaker 1: In addition to genetic chimerism, the condition is commonly caused
Speaker 1: when another genetic code is introduced to the body by
Speaker 1: organ or tissue transplants, as well as by blood transfusions.
Speaker 1: For example, when someone undergoes a bone marrow transplant, they'll
Speaker 1: carry blood cells that are identical to their donor for
Speaker 1: the rest of their lives, in addition to their own
Speaker 1: genetically distinct blood cells. A blood transfusion, however, only produces
Speaker 1: a temporary chimera. Condition, The donor blood cells will live
Speaker 1: about a hundred and fifteen days in the host's body
Speaker 1: and will eventually be completely replaced by red blood cells
Speaker 1: carrying their original genetic code. These types of chimerism are
Speaker 1: commonly known as microchimerism, and one of the most frequent
Speaker 1: causes is pregnancy. Trace fetal stem cells often remain in
Speaker 1: a mother long after she has given birth. Some of
Speaker 1: these stem cells have even been found to reside in
Speaker 1: women's brains. Likewise, a pregnant woman's cells can cross the
Speaker 1: placenta and become part of their child's liver, heart, thymus, gland,
Speaker 1: and bloodstream. Many people may not ever suspect that microchimerism
Speaker 1: is part and parcel of their existence, but it's probably
Speaker 1: more frequent than we realize. In fact, chimerism, both tetragametic
Speaker 1: and micro may someday challenge how medicine, forensics, and even
Speaker 1: the legal system contend with DNA. DNA testing, which is
Speaker 1: done by collecting small amounts of human saliva, semen, hair, bone, blood,
Speaker 1: or skin tissue, relies on the notion that every cell
Speaker 1: in an individual body contains identical DNA, and that each
Speaker 1: person has different DNA chimerism challenges the notion of a
Speaker 1: one DNA to one person system. In one complex assault case,
Speaker 1: for example, evidence at the scene matched a DNA blood
Speaker 1: sample from a criminal already profiled in a law enforcement database. However,
Speaker 1: this person was in jail when the assault occurred. To
Speaker 1: make matters even more confusing, the DNA blood sample also
Speaker 1: matched the DNA profile of another person who could also
Speaker 1: have been implicated in the crime. After investigating, it was
Speaker 1: determined that the two men were brothers. The man in
Speaker 1: jail had previously received a bone marrow transplant from his brother.
Speaker 1: This means that the jailed man was a chimera. His
Speaker 1: blood DNA profile matched that of his brother's blood DNA,
Speaker 1: while his saliva DNA profile was distinctly his own. In
Speaker 1: the end, investigators used a blood sample and cheek swab
Speaker 1: to make a d n A match from the crime
Speaker 1: scene and charged the correct brother with the crime. Today's
Speaker 1: episode is based on the article calimerism you Can be
Speaker 1: your Own twin on how stuff Works dot Com, written
Speaker 1: by Laur L. Dove. Brain Stuff is production of I
Speaker 1: Heart Radio in partnership with how stuff works dot Com,
Speaker 1: and it is produced by Tyler Clang four more podcasts
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