chimärism

Chimärism, also known as chimerism, is the presence in a single organism of two or more genetically distinct cell populations that originate from different zygotes. The condition can occur naturally or arise after medical interventions.

Natural chimärism can result from dizygotic twinning, where two fertilized eggs develop within the same uterus, or from bidirectional transfer of cells between mother and fetus during pregnancy, producing fetal or maternal microchimerism. In rare cases, these cell populations persist in tissues and create a situation where two genetic lineages coexist in the same individual. Acquired chimärism occurs after medical procedures, most commonly following organ transplantation or hematopoietic stem cell transplantation, in which donor-derived cells engraft and persist as part of the recipient.

Detection and characterization rely on genetic analysis. Chimerism is typically identified by comparing DNA from different tissues or fluids; the presence of two distinct genotypes indicates chimerism. The proportion and distribution of the alternate cell lineage can vary, ranging from sporadic microchimerism to more widespread macrochimerism.

Clinical and forensic implications vary. Chimerism can complicate paternity testing and forensic DNA analyses when samples originate from different tissues. In transplantation, donor-derived cells can influence immune responses and tolerance, with potential effects on graft function and immunosuppression management. Natural chimärism has been studied for potential links to autoimmune phenomena and immune modulation, though such associations are not universally established.