Aneuploid cells on embryos that lead to Miscarriages – a review of two studies

Jizaya Gary, Lauren Endres

Biology, College of Arts and Science, SUNY Polytechnic Institute, Utica, NY, USA

Most diploid/aneuploid mosaics arise during the cleavage stage of an embryo and are found with the help of karyotyping. Studies show the frequency of mosaic embryos increases from 15 percent at the 2-4 cell stage to 49 percent at the 5 to 8 cell stage. These two stages occur during day 1 to 3, respectively. On day 4, mosaicism is identified in about 58 percent of the embryos. The conclusion of the study was that mosaicism involving multiples aneuploidies occurs in a high proportion of cells at the blastocyst stage, interfering early embryonic development as a potential cause of implantation failure. It is also possible that these mosaic embryo arrest their cellular growth because and begin a cell death process (i.e., apoptosis). So, failure to implant and cell death are the cause of many miscarriages, of which females are not aware as these embryos are expelled as part of their normal menstrual cycle. Supporting evidence comes from several studies. Katz-Jaffe et al. [date?], developed single cell multiplex fluorescent PCR to distinguish between meiotic and mitotic division errors, and found 25 embryos aneuploidy for chromosome 21. Further analysis characterized 13 embryos as meiotic errors, and the remaining as mosaics; thus, a little over half (of the aneuploidies?) occurred during cell division. Munne et al. [04] published a study on over 2,000 cleavage stage embryos after PGS and FISH using 4 to 14 chromosome probes. The study showed the most frequency aneuploidy chromosomes were 22, 16, 21, and 15. As a mechanism to account for apoptosis, aneuploidy leads to an unbalanced protein pool and if left unresolved by activation of autophagy, involving CASP8/LC3B/p62, these proteins will interact to activate the apoptosis cascade (Regin et al., 2022). Also, Regin et al. mention that aneuploid results in replication stress and can lead to DNA-damage which results in p53 activation and apoptosis.