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Chimerism is a type of rare genetic alteration in which the presence of two different genetic materials is observed, which may be natural, occurring during pregnancy, for example, or be due to hematopoietic stem cell transplantation, in which the transplanted donor cells are absorbed by the recipient, with the coexistence of cells with different genetic profiles.
Chimerism is considered when the presence of two or more populations of genetically distinct cells with different origin is verified, unlike what happens in mosaicism, in which despite the cell populations being genetically distinct, they have the same origin. Learn more about mosaicism.
Scheme representing natural chimerism
Types of chimerism
Chimerism is uncommon among people and can be more easily observed in animals. However, it is still possible that there is chimerism between people, the main types being:
1. Natural chimerism
Natural chimerism happens when 2 or more embryos fuse to form one. Thus, the baby formed by 2 or more different genetic materials.
2. Artificial chimerism
It happens when a person receives a blood transfusion or a bone marrow or hematopoietic stem cell transplant from another person, with absorption by the body of the donor's cells. This situation was common in the past, however currently after transplants the person is followed up and performs some treatments that prevent the permanent absorption of the donor's cells, in addition to ensuring better acceptance of the transplant by the body.
This type of chimerism happens during pregnancy, in which the woman absorbs some cells from the fetus or the fetus absorbs cells from the mother, resulting in two different genetic materials.
4. Twin chimerism
This type of chimerism happens when during the gestation of twins, one of the fetuses dies and the other fetus absorbs some of its cells. Thus, the baby that is born has its own genetic material and the genetic material of its brother.
How to identify
Chimerism can be identified through some characteristics that the person can manifest as areas of the body with more or less pigmentation, eyes with different colors, occurrence of autoimmune diseases related to the skin or nervous system and intersexuality, in which there is variation in sexual characteristics and chromosomal patterns, which makes it difficult to identify the person as belonging to the male or female gender.
Furthermore, chimerism is identified through tests that assess the genetic material, DNA, and the presence of two or more pairs of DNA in red blood cells can be verified, for example. In addition, in the case of chimerism after hematopoietic stem cell transplantation, it is possible to identify this change through a genetic test that evaluates markers known as STRs, which are capable of differentiating recipient and donor cells.