What is the Origin of Embryonic Mosaicism?

The term combines "embryonic," referring to the preimplantation stage of development, with "mosaicism," a concept borrowed from art where diverse pieces form a single image. Its clinical significance became widely recognized with the refinement of preimplantation genetic testing (PGT) on trophectoderm biopsies. The clinical challenge lies in distinguishing true mosaicism from laboratory artifacts and predicting its impact on pregnancy outcome.

What is the Mechanism of Embryonic Mosaicism?

The underlying mechanism for embryonic mosaicism is a mitotic error, such as chromosomal non-disjunction or anaphase lag, occurring during the rapid, early cell divisions of the zygote. This error results in the propagation of both chromosomally normal and abnormal cell lineages as the embryo progresses toward the blastocyst stage. The developmental fate of the embryo is thought to be influenced by the specific chromosomes involved and the proportion of abnormal cells present in the inner cell mass versus the trophectoderm.

Embryonic Mosaicism ∞ Area

Embryonic Mosaicism

Meaning

Embryonic Mosaicism describes the presence of two or more distinct cell lines with different chromosomal compositions coexisting within the same early-stage embryo. This means that some cells are chromosomally normal (euploid), while others possess an abnormal number of chromosomes (aneuploid). The condition is a form of genetic variation that arises after fertilization, creating a mosaic pattern of genetic material within the developing organism. Understanding its prevalence is crucial for genetic counseling in assisted reproductive technologies.