PARENT SESSION
Preimplantation Embryo/Fetal Development

IMBALANCES OF CHROMOSOMES 2 AND 7 IN THE HUMAN PREIMPLANTATION EMBRYO.

Bielanska, Magdalena¹, Bernier, Martin ¹, Adams, Erin ¹, Tan, Seang Lin¹, Ao, Asangla¹, ¹

ABSTRACT- Chromosomes 2 and 7 are the two most common autosomes involved in human confined placental mosaicism (CPM). We investigated the incidence of uniform and mosaic imbalances of chromosomes 2 and 7 in human preimplantation embryos. A total of 120 spare 2-cell to blastocyst stage embryos were analyzed using fluorescence in situ hybridization (FISH) probes for chromosomes 2, 7, and 18. Uniform aneuploidy for chromosomes 2 and 7 was detected in 3 (2.6%), 2(1.7 %) and 2(1.7%) of embryos respectively. Mosaic aneuploidy for chromosomes 2 and 7 and 18 was detected in eight (6.7%), ten (8.3%), and 7 (5.8%) of embryos. Aneuploidy was observed at the blastocyst stage. Majority of the aneuploid mosaic embryos had a higher proportion of diploid cells suggesting that mitotic gains and losses had occurred in a diploid zygote. This study showed that aneuploidy of chromosomes 2 and 7 is as frequent in preimplantation stages of human development as aneuploidy for chromosome 18. All three chromosomes are particularly susceptible to mitotic errors during cleavage divisions. Our data suggest that the discrepancy in the distribution of uniform and mosaic aneuploidy for chromosomes 2 and 7 between embryos and clinically recognized pregnancies is largely due to a high rate of embryo wastage at, or shortly after, implantation.

KEY WORDS: chromosomes 2 and 7, FISH, mosaicism, preimplantation embryo