New Insights into the Nature of Embryo`s Aneuploidy, Arisen from PGD

Introduction

It is accepted that the majority of aneuploidies in the early developing embryos derive from errors occurring during oocyte meiosis .These anomalies, as deduced from analyses of miscarriage products, primarily involve chromosomes X, 16, 22, 21and 15. PGD analysis can be utilized to determine which chromosomes are prone to cause aneuploidy and their parental origin, at the earliest stages of embryo development.

Aim

To asses chromosomal aneuploidies as ascertained by PGD and to determine their parental origin by PCR-based haplotype analysis.

Materials &Methods

Aneuploidy rate was analyzed in 836 embryos by either PGD-CMA performed on day 5 (239 embryos), or by haplotype analyses performed on day 3 (597 embryos). The parental origin of aberrations in specific chromosomes, that were found to present the highest aneuploidy, was analyzed in the day 3 embryos.

Results: 33% of the embryos analyzed by CMA analyses were found to be aneuploid with mainly trisomies in chromosomes 16, 20, 21, 22, and 6. In contrast, haplotype analyses for genes located on the same chromosomes, demonstrated a higher frequency of monosomies (88.2%) compared to trisomies (11.2%). Unexpectedly, those monosomies originated similarly from both maternal and paternal gametes (46% and 54%, respectively).

Conclusion

Our detailed molecular analysis of preimplantation embryo`s aneuploidy emphasizes that monosomies have a significant contribution to chromosomal aberrations at day 3 embryos, compared to day 5 embryos and data from miscarriages. In addition, our results demonstrating the equivalent parental origin of the aneuploidy, appeal the dogma of the major maternal contribution to total aberrations.