In Greek mythology, a chimera is a strange, monstrous creature having the body of a lion, the head of a goat arising from the spine, and a tail that ends with a snake’s head. Such a creature would perhaps be the only apt moniker of an anomaly that exists in real life. Chimeras are animals that have at least two different groupings of varying genetic cells. These groupings have their source in the different zygotes present during reproduction. More common among animals, human chimeras, however, do exist, albeit they are phenomena that is extremely rare.
Most human chimeras will never know that they are chimeras, unless, that is, a DNA test is involved. Only 35 Americans have been identified as having chimerism, and in only two cases involving DNA testing did chimerism become a head-scratching problem for scientists. Still, chimerism has caught our imagination, as it has been featured in CSI and other popular TV crime shows.
There exists two different types of human chimerism–microchimerism and tetragametic chimerism. In microchimerism, only a small part of the body has a different cell line, while the rest of the body is uniform. With tetragametic chimerism, there may result several patches of inconsistent sets of DNA. Human chimeras at times, but not always, manifest themselves as hermaphrodites.
The two cases in which chimerism became problematic involved DNA testing. In one case, a woman named Lydia Fairchild became pregnant with her third child. During a routine DNA test to determine the receipt of welfare funding, the results revealed that every relative was related to the newborn except the mother herself. Fairchild became involved in a suit that both denied her social support and accused her of fraud. Eventually, Fairchild’s lawyer discovered an article in The New England Journal of Medicine, in which a similar case was documented involving a chimera and a DNA test for a kidney transplant.
While human chimerism is a phenomenon that is so rare it’s almost negligible, the fact still remains that DNA testing, while extremely accurate in the crime lab, is not infallible. To learn more about chimerism, read Vivienne Lam’s article in the Science Creative Quarterly.
Note from DP Lyle: Want to know more about Chimerism?