Molecular origin of mitotic aneuploidies in preimplantation embryos.

Mitotic errors are common in human preimplantation embryos. The occurrence of mitotic errors is highest during the first three cleavages after fertilization and as a result about three quarters of human preimplantation embryos show aneuploidies and are chromosomally mosaic at day three of development. The origin of these preimplantation mitotic aneuploidies and the molecular mechanisms involved are being discussed in this review. At later developmental stages the mitotic aneuploidy rate is lower. Mechanisms such as cell arrest, apoptosis, active correction of the aneuploidies and preferential allocation of the aneuploid cells to the extra-embryonic tissues could underlie this lower rate. Understanding the mechanisms that cause mitotic aneuploidies in human preimplantation embryos and the way human preimplantation embryos deal with these aneuploidies might lead to ways to limit the occurrence of aneuploidies, in order to ultimately increase the quality of embryos and with that the likelihood of a successful pregnancy in IVF/ICSI. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.