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O▪19 Embryo aneuploidies
Abstracts - 6th International Symposium on Preimplantation Genetics 2005
observed, based on fluorescence in-situ hybridization (FISH) analysis using specific probes for chromosomes 13, 16, 18, 21 and 22. The data further confirmed that chromatid errors represent the major source of aneuploidy in the resulting embryos. One-third of oocytes with meiosis I errors were prone to sequential meiosis II errors, half of the detected aneuploidies being of complex nature overall, with the involvement of two or more chromosomes, or the same chromosome in both meiotic divisions. The aneuploidy rates for individual chromosomes were dissimilar, with higher prevalence of chromosome 21 and 22 errors. The origins of aneuploidy for the individual chromosomes were also not random, with a shift of chromosome 16 and 22 error origin to meiosis II, and chromosome 18, 13 and 21 error origin to meiosis I. There was an age dependence not only for the overall frequency of aneuploidies, but also for each chromosome error, the errors originating from meiosis I, meiosis II, and both meiosis I and meiosis II, and different types of aneuploidies. The data further suggest the practical relevance of the oocyte aneuploidy testing for detection and avoidance from transfer of the embryos deriving from aneuploid oocytes, which should contribute significantly to the pregnancy outcomes of IVF patients of advanced reproduction age.
O 19 Embryo aneuploidies Magli MC, Gianaroli L, Ferraretti AP SISMeR Reproductive Medicine Unit, Via Mazzini 12, 40138 Bologna, Italy The occurrence of non-disjunction during meiosis is a rare event in most organisms, with the exception of the human species where approximately 40% of oocytes and 6% of spermatozoa are chromosomally abnormal. The level of aneuploidy varies in relation to the developmental time being considered, reaching the highest figure in early embryos. At this stage, the incidence of chromosomal abnormalities can be around 65% in patients with a poor prognosis of pregnancy. The contribution to aneuploidy by the oocyte depends strictly on maternal age, while for male gametes, the sperm sample profile is the determinant factor, the incidence of aneuploidy being higher in severe oligozoospermic samples and in testicular spermatozoa. This is reflected in the status of preimplantation embryos, where the incidence of aneuploidy increases proportionally to maternal age, whereas in embryos derived from testicular spermatozoa the presence of gonosomal aneuploidy is increased. Notably, errors at meiosis are chromosome specific and mostly involve chromosome 15, 21 and 22. Approximately 30% of preimplantation embryos carry complex abnormalities that are more frequent in some groups of patients, e.g. repeated IVF failures and embryos originating from testicular spermatozoa. In addition, the study of embryo morphology suggested that a correlation exists with chromosomal status, complex abnormalities being the major cause of irregular growth and cleavage arrest.
O 20 PGD for carriers of chromosome rearrangements Scriven PN Department of Cytogenetics, South Thames (East) Regional Genetics Centre and The Centre for Preimplantation Genetic Diagnosis, Guy’s and St Thomas’ NHS Trust, London, UK Couples with chromosome rearrangements such as Robertsonian translocations, reciprocal translocations, insertional translocations, pericentric inversions and deletions can have a significant genetic risk of affected liveborn offspring and may present with difficult reproductive histories, including termination of affected pregnancies, or a liveborn child with profound mental and physical disability that may have resulted in the early death of the child. However, many couples present with infertility or with a history of recurrent miscarriages, where a direct association with an abnormal karyotype may not have been established. Fluorescence in-situ hybridization (FISH) is the primary technique used to detect chromosome imbalance associated with chromosome rearrangements. Clinical application of preimplantation genetic diagnosis (PGD) has employed chromosome paints and locus specific probes using metaphase chromosomes (polar bodies, blastomere nucleus conversion) and interphase blastomere nuclei. Typically, FISH techniques are used to determine the copy number of target chromosome regions using target-specific DNA probes labelled with different fluorochromes or haptens. However, there are limitations associated with the FISH technique (e.g. probe availability, the analytical performance of the test) and sampling the genetic material of the embryo (e.g. the removal of one or more cells, chromosomal mosaicism), such that in conjunction with the challenges of assisted conception there can be a fine balance of priorities between establishing a successful pregnancy and minimising the risk of an affected outcome. PGD can have value in excluding chromosomally abnormal embryos from transfer for couples that require assisted conception, and provide a way forward for couples who don’t need assisted conception as such but are seeking to reduce their risk of miscarriage or where other reproductive options or prenatal diagnosis are unacceptable. The best practice guidelines that have emerged from the PGDIS (Reprod. BioMed. Online 2004, 9, 430–434) and the ESHRE PGD Consortium (Hum. Reprod. 2005, 20, 35–48) will provide a valuable aid to the good clinical practice of PGD for carriers of chromosome rearrangements.
O 21 CGH and microarrays for aneuploidy diagnosis Wilton L Melbourne IVF, East Melbourne, Australia Errors affecting all chromosomes exist in early human embryos. Aneuploidy testing in preimplantation genetic diagnosis (PGD) would be most effective and offer greatest benefit to patients if all chromosomes were analysed in the biopsied cell, rather than just the few that can be analysed by fluorescence in-situ hybridization (FISH).
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observed, based on fluorescence in-situ hybridization (FISH) analysis using specific probes for chromosomes 13, 16, 18, 21 and 22. The data further confirmed that chromatid errors represent the major source of aneuploidy in the resulting embryos. One-third of oocytes with meiosis I errors were prone to sequential meiosis II errors, half of the detected aneuploidies being of complex nature overall, with the involvement of two or more chromosomes, or the same chromosome in both meiotic divisions. The aneuploidy rates for individual chromosomes were dissimilar, with higher prevalence of chromosome 21 and 22 errors. The origins of aneuploidy for the individual chromosomes were also not random, with a shift of chromosome 16 and 22 error origin to meiosis II, and chromosome 18, 13 and 21 error origin to meiosis I. There was an age dependence not only for the overall frequency of aneuploidies, but also for each chromosome error, the errors originating from meiosis I, meiosis II, and both meiosis I and meiosis II, and different types of aneuploidies. The data further suggest the practical relevance of the oocyte aneuploidy testing for detection and avoidance from transfer of the embryos deriving from aneuploid oocytes, which should contribute significantly to the pregnancy outcomes of IVF patients of advanced reproduction age.
O 19 Embryo aneuploidies Magli MC, Gianaroli L, Ferraretti AP SISMeR Reproductive Medicine Unit, Via Mazzini 12, 40138 Bologna, Italy The occurrence of non-disjunction during meiosis is a rare event in most organisms, with the exception of the human species where approximately 40% of oocytes and 6% of spermatozoa are chromosomally abnormal. The level of aneuploidy varies in relation to the developmental time being considered, reaching the highest figure in early embryos. At this stage, the incidence of chromosomal abnormalities can be around 65% in patients with a poor prognosis of pregnancy. The contribution to aneuploidy by the oocyte depends strictly on maternal age, while for male gametes, the sperm sample profile is the determinant factor, the incidence of aneuploidy being higher in severe oligozoospermic samples and in testicular spermatozoa. This is reflected in the status of preimplantation embryos, where the incidence of aneuploidy increases proportionally to maternal age, whereas in embryos derived from testicular spermatozoa the presence of gonosomal aneuploidy is increased. Notably, errors at meiosis are chromosome specific and mostly involve chromosome 15, 21 and 22. Approximately 30% of preimplantation embryos carry complex abnormalities that are more frequent in some groups of patients, e.g. repeated IVF failures and embryos originating from testicular spermatozoa. In addition, the study of embryo morphology suggested that a correlation exists with chromosomal status, complex abnormalities being the major cause of irregular growth and cleavage arrest.
O 20 PGD for carriers of chromosome rearrangements Scriven PN Department of Cytogenetics, South Thames (East) Regional Genetics Centre and The Centre for Preimplantation Genetic Diagnosis, Guy’s and St Thomas’ NHS Trust, London, UK Couples with chromosome rearrangements such as Robertsonian translocations, reciprocal translocations, insertional translocations, pericentric inversions and deletions can have a significant genetic risk of affected liveborn offspring and may present with difficult reproductive histories, including termination of affected pregnancies, or a liveborn child with profound mental and physical disability that may have resulted in the early death of the child. However, many couples present with infertility or with a history of recurrent miscarriages, where a direct association with an abnormal karyotype may not have been established. Fluorescence in-situ hybridization (FISH) is the primary technique used to detect chromosome imbalance associated with chromosome rearrangements. Clinical application of preimplantation genetic diagnosis (PGD) has employed chromosome paints and locus specific probes using metaphase chromosomes (polar bodies, blastomere nucleus conversion) and interphase blastomere nuclei. Typically, FISH techniques are used to determine the copy number of target chromosome regions using target-specific DNA probes labelled with different fluorochromes or haptens. However, there are limitations associated with the FISH technique (e.g. probe availability, the analytical performance of the test) and sampling the genetic material of the embryo (e.g. the removal of one or more cells, chromosomal mosaicism), such that in conjunction with the challenges of assisted conception there can be a fine balance of priorities between establishing a successful pregnancy and minimising the risk of an affected outcome. PGD can have value in excluding chromosomally abnormal embryos from transfer for couples that require assisted conception, and provide a way forward for couples who don’t need assisted conception as such but are seeking to reduce their risk of miscarriage or where other reproductive options or prenatal diagnosis are unacceptable. The best practice guidelines that have emerged from the PGDIS (Reprod. BioMed. Online 2004, 9, 430–434) and the ESHRE PGD Consortium (Hum. Reprod. 2005, 20, 35–48) will provide a valuable aid to the good clinical practice of PGD for carriers of chromosome rearrangements.
O 21 CGH and microarrays for aneuploidy diagnosis Wilton L Melbourne IVF, East Melbourne, Australia Errors affecting all chromosomes exist in early human embryos. Aneuploidy testing in preimplantation genetic diagnosis (PGD) would be most effective and offer greatest benefit to patients if all chromosomes were analysed in the biopsied cell, rather than just the few that can be analysed by fluorescence in-situ hybridization (FISH).
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