In the late 1990s, a 52-year-old patient was admitted to the Boston Medical Center (BIDMC) in need of a kidney transplant. In search of a suitable donor, the doctors first turned to the woman's closest relatives and took blood samples from her husband and her three sons. To the patient's surprise, genetic analysis showed that she is the biological mother of only one, the other two sons are strangers. The woman believed that an error crept into the data, since she gave birth to all three children personally. However, a repeated test showed that there was no error - the haplotype of the two sons did not match the haplotype of the mother.
Doctor Margot Kruskall was taken aback. She turned to colleagues from around the world for help. They sent various versions of detective properties, from changing babies in a maternity hospital to secret fertilization, in which the woman does not want to admit. Nobody offered a scientific explanation. Then Margot decided to do additional research. Instead of a blood test, she took a test from other tissues of the patient (thyroid gland, mouth, hair, etc.). The results amazed everyone: some of the tissues had one haplotype, and some had a completely different one, confirming the relationship of the sons. In other words, a woman's body consisted of two genetically dissimilar cell types.
More than 50 years ago, a very rare event occurred in this woman's mother's womb: two embryos, two fraternal female twins fused at an early stage of pregnancy, forming one embryo. In medical terminology, the patient is a tetragametic chimera, that is, an organism that has arisen on the basis of four germ cells - two eggs and two spermatozoa.
No one can know exactly how common chimeras are. They cannot be detected without special tests. Recently, there has been growing evidence that some of the mother's cells can move into the child's body and continue to function and divide there for decades. This phenomenon is called microchimerism.