For years, she was a woman like any other: typical female features, good health, and the ability to become pregnant. But a genetic test revealed something no one expected: her blood cells had XY sex chromosomes, the pattern normally associated with a man.
Her skin cells, by contrast, were 46,XX, the usual female profile. Doctors ordered more blood tests and studies of other tissues, and compared the genetic profile of her blood with that of her twin brother and her parents. The match with her twin confirmed the origin: during fetal development, her body incorporated DNA from her brother into her blood cell line, while the rest of her tissues retained the XX configuration.
This condition is called chimerism, a name that comes from the chimera of Greek mythology, a mix of lion, goat, and serpent. According to Cleveland Clinic, most people with chimerism feel healthy and discover it only through genetic or blood tests. And a karyotype, the test that detected it in this case, is not part of a standard medical visit.
