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Here it is. Some interesting facts in here. Parenthetical citations, too. Ignore them.
Chimerism
The body is a marvel which has continued to stupefy humanity and its scientists for generations. It is amazing the intricacy of the pathways (both neural and circulatory included) that make each organism the way that they are. Everyday doctors and biologists alike discover new anomalies which further our confusion of the way we are formed and the way we function. One such abnormality is chimerism. Chimerism is a fascinating phenomenon with odd, but often depressive effects on all involved.
A chimaera is one who’s “structure is made up of cells derived from more than one zygote or are otherwise genetically distinct.”(Chimera) This can be done either experimentally –through tissue grafting or mixing the cells of early embryos– or naturally, through blood vessel anastomosis –in other words, one twin dies, and the remaining twin absorbs them into their self, creating, as it were, two beings in one body.
The terms “chimerism” and “chimaera” come from a mythological creature: the chimaera. It was allegedly "a thing of immortal make, not human, lion-fronted and snake behind, a goat in the middle, and snorting out the breath of the terrible flame of bright fire,” and because of its menagerie of origins of body parts, the chimaera was deemed to have the best similarity to chimerism.(Chimera) Seeing a chimaera was a supposed signal of impending storms, shipwrecks, and natural disasters. The chimaera was believed to be defeated in the end by Bellerophon and his winged horse Pegasus.
Because of the having of more than one zygote in the cell, the DNA is affected by chimerism. In one part of the body a person may have cells with their own DNA, while in another part of the body that same person could have the DNA of the twin whose cells they absorbed as an embryo. DNA testing in numerous areas of the body is the one sure way to test for chimerism. “Affected persons are identified by the finding of two populations of red cells or, if the zygotes are of opposite sex, ambiguous genitalia and hermaphroditism alone or in combination.” (chimera)
With the DNA being affected so, it can cause problems where tests to show one’s biological parents come into play. In one famous case, the Lydia Fairchild Case, when a DNA test was given during a welfare support trial to prove that the children were indeed hers and her husband’s, it was found that while the kids DNA matched their father’s, it did not match their mother’s. The children were taken away and Fairchild was brought to court for claiming another’s child or taking part in a surrogacy scam, though at the time, they were not sure which it was. At the time, Fairchild was pregnant with her third child. When the time came for the child to be born, another DNA test was immediately undertaken after birth; but the results showed that that child was not hers either. (Lydia)
The courts and doctors, and no doubt the Fairchilds, were quite bewildered by these results until another case came up with a fifty-two year old teacher in Boston named Karen Keegan. She was in need of a kidney transplant, and so when she had tests done on her sons to see which, if any, could be a donor, it was found that of the three, two did not match her DNA. Confused, doctors conducted a great series of tests over two years until they finally concluded that Keegan was a tetragametic chimaera.(Ainsworth) Upon applying the same tests to Lydia Fairchild, they found that she was one also.
Chimerism can also affect a person’s outward appearance. Someone who is a chimaera may have patchy skin and/or hair. They may also have heterochromia, which is where a person has either two different colored irises or an iris with two different colors. Having one or more of these characteristics does not make someone a chimaera, they are simply common possible identifying factors.
Being a chimaera can have devastating effects psychologically too. After all, bonds are said to be made between twins even when they are merely embryos in their mother’s womb. According to author, colorologist, a single twin Caryl Dennis:
“Due to a deep longing for some undefined, missing part of themselves that, it seems, no mate can quite fulfill, single twins may experience problems with relationships, and/or with their sexual identity. They often suffer from feelings of guilt. They may be haunted by feelings that they’re ‘parasites’. I’ve heard from more than a few single twins who for one reason or another felt they’d ‘eaten’ or ‘killed’ their twin. Troubling, recurring dreams of their twin, fear of sleeping alone, fear of sudden loss or abandonment, profound loneliness, eating disorders, ‘hearing voices’, extreme emotional sensitivity and even schizophrenia or multiple personality disorder can afflict survivors.” (Dennis)
The parents can also be affected by this oddity, particularly on the mother’s part. A mother who has had the chimerism process go on inside her may suffer from cramps, bleeding, and/or decreased hormone levels during her first trimester of pregnancy, or she may even experience no symptoms at all. Afterward, like anyone who has lost a child, the parent may feel confusion and feelings of great loss, especially the mother, as the death and “rebirth” went on while the children were still in her womb.
Chimerism is not exactly something that you can prevent, as it is not actually a disease. However, the chances of a child becoming a chimaera increase if the baby is created invitro fertilization or if one or both of the parents is a chimaera themselves. Chances also are greater if there is a history of twins in the family or if the mother has already given birth to twins previously.
One in eight people start out as twins in the womb, but seventy-five percent of twins are not both borne. The facts behind chimerism are depths that have yet to be completely plumbed. Scientists will still be studying all the effects and causes of this phenomenon and others like it for years to come.
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