Mantzouratou, A.; (2008) Molecular cytogenetic investigation of the origin of chromosomal abnormalities arising in human preimplantation embryos and oocytes. Doctoral thesis , University of London.

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Abstract

Introduction: Advances in diagnosis and screening of preimplantation embryos or oocytes for chromosomal abnormalities have helped many couples achieve a normal pregnancy. They also pointed to the fact that numerical and structural chromosomal abnormalities are frequent in human preimplantation embryos and can arise at any point during gametogenesis and meiosis through to early embryonic development and mitotic division. However, information coming from studies in this area is far from complete and uniform.;Aim: To investigate aneuploidy and its mechanisms in human preimplantation embryos and oocytes. To develop protocols and improve on existing molecular cytogenetic techniques for the advance of preimplantation genetic diagnosis or screening (PGD/PGS) in routine clinical analysis. To evaluate the impact of PGD and PGS on the treatment of various types of infertility.;Methods: Fluorescent In situ Hybridisation (FISH) and Comparative genomic hybridisation (CGH) were the main methods used. I) Protocols were developed and implemented for the clinical PGD and PGS program. The PGD protocols included 2 couples with rare structural chromosomal abnormalities II) All untransferred embryos were studied and information was obtained for 101 PGS cycles (77 couples-935 embryos) and 18 PGD cycles for structural chromosomal abnormalities. III) Immature and undivided oocytes were studied using CGH from PGS, PGD and routine IVF couples.;Results and discussion: Specific and highly efficient methods and their clinical application to detect a variety of rare and common chromosomal abnormalities in PGD and PGS embryos were achieved. This study adds to the accumulating evidence showing the extent and mechanisms of genetic abnormalities in human oocytes and preimplantation embryos. It is one of the first studies to identify significant differences in the types of chromosomal abnormalities in embryos from couples with different reproductive history suggesting susceptibility to particular types of aneuploidy in these couples. The problems and effectiveness of PGS and PGD are also discussed.

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