Definition

A condition in which some cells or tissues in a person’s body contain at least two different sets of DNA. Chimerism can occur in different ways. One way it can occur is through an organ or stem cell transplant from another person (donor). After a stem cell transplant, the recipient has a mix of DNA from their own blood cells and DNA from the donor’s transplanted cells. Another way chimerism can occur is through pregnancy, when some fetal cells are absorbed into the bloodstream of the pregnant person. The DNA from the fetal cells may remain in that person’s body tissues for many years after childbirth. Chimerism can also occur during a twin pregnancy when cells and genetic material are exchanged between twins or during early development when one twin absorbs cells from another twin who does not survive. Most people with chimerism rarely show visible signs and are unaware they have the condition. Chimerism is usually diagnosed through genetic testing.