Errors in chromosome segregation during oogenesis and early embryogenesis

Errors in chromosome segregation occurring during human oogenesis and early embryogenesis are very common. Meiotic chromosome development during oogenesis is subdivided into three distinct phases. The crucial events, including meiotic chromosome pairing and recombination, take place from around 11 weeks until birth. Oogenesis is then arrested until ovulation, when the first meiotic division takes place, with the second meiotic division not completed until after fertilization. It is generally accepted that most aneuploid fetal conditions, such as trisomy 21 Down syndrome, are due to maternal chromosome segregation errors. The underlying reasons are not yet fully understood. It is also clear that superimposed on the maternal meiotic chromosome segregation errors, there are a large number of mitotic errors taking place post-zygotically during the first few cell divisions in the embryo. In this chapter, we summarise current knowledge of errors in chromosome segregation during oogenesis and early embryogenesis, with special reference to the clinical implications for successful assisted reproduction

Technology requirements for preimplantation genetic diagnosis to improve assisted reproduction outcomes.

Preimplantation genetic diagnosis has been proposed as a method to improve assisted reproduction technology outcomes, but different techniques have produced conflicting results. The use of appropriate techniques may provide positive outcomes

Preimplantation genetic diagnosis of single-gene disorders: experience with more than 200 cycles conducted by a reference laboratory in the United States.

OBJECTIVE: To evaluate trends and outcomes from preimplantation genetic diagnosis (PGD) cycles. DESIGN: Retrospective data review. SETTING: A reference laboratory specializing in the provision of PGD services. PATIENT(S): One hundred sixty-two patients at risk of transmitting a serious monogenic disorder to their children. INTERVENTION(S): In vitro fertilization and PGD. MAIN OUTCOME MEASURE(S): Results of PGD cycles. RESULT(S): Two hundred twenty-four PGD cycles were referred by 59 different IVF centers. Forty-six different disorders were diagnosed, including several not previously diagnosed at the preimplantation stage. Cystic fibrosis was the most common reason for referral (73 cases). A diagnosis was obtained for 84.4% of tested embryos, with results available 6 to 36 hours from sample receipt. Only 10.7% of cycles had no transfer. The pregnancy rate per cycle with ET was 43.4%. CONCLUSION(S): Unlike previous reports of multiple PGD cycles, all of the cases in this study involved shipping of biopsied cells to a specialist reference laboratory for diagnosis. This approach, sometimes referred to as "transport PGD," accounts for the vast majority of PGD cycles in the United States. Preimplantation genetic diagnosis was shown to be an effective alternative to prenatal diagnosis for patients with an ethical or a religious objection to pregnancy termination and for infertile patients carrying a genetic disorder. Demand for this service at our center doubled in each of the last 4 years. Pregnancy rates per ET were encouraging, almost half of all patients undergoing their first PGD cycle achieving a birth or ongoing pregnancy

Preimplantation genetic diagnosis of single-gene disorders: experience with more than 200 cycles conducted by a reference laboratory in the United States.

OBJECTIVE: To evaluate trends and outcomes from preimplantation genetic diagnosis (PGD) cycles. DESIGN: Retrospective data review. SETTING: A reference laboratory specializing in the provision of PGD services. PATIENT(S): One hundred sixty-two patients at risk of transmitting a serious monogenic disorder to their children. INTERVENTION(S): In vitro fertilization and PGD. MAIN OUTCOME MEASURE(S): Results of PGD cycles. RESULT(S): Two hundred twenty-four PGD cycles were referred by 59 different IVF centers. Forty-six different disorders were diagnosed, including several not previously diagnosed at the preimplantation stage. Cystic fibrosis was the most common reason for referral (73 cases). A diagnosis was obtained for 84.4% of tested embryos, with results available 6 to 36 hours from sample receipt. Only 10.7% of cycles had no transfer. The pregnancy rate per cycle with ET was 43.4%. CONCLUSION(S): Unlike previous reports of multiple PGD cycles, all of the cases in this study involved shipping of biopsied cells to a specialist reference laboratory for diagnosis. This approach, sometimes referred to as "transport PGD," accounts for the vast majority of PGD cycles in the United States. Preimplantation genetic diagnosis was shown to be an effective alternative to prenatal diagnosis for patients with an ethical or a religious objection to pregnancy termination and for infertile patients carrying a genetic disorder. Demand for this service at our center doubled in each of the last 4 years. Pregnancy rates per ET were encouraging, almost half of all patients undergoing their first PGD cycle achieving a birth or ongoing pregnancy

Causes and estimated incidences of sex-chromosome misdiagnosis in preimplantation genetic diagnosis of aneuploidy

Preimplantation genetic diagnosis of aneuploidy (PGD-A) with comprehensive chromosome analysis has been known to improve pregnancy outcomes. Accuracy in detecting sex chromosomes becomes important when selecting against embryos at risk for sex-linked disorders. A total of 21,356 PGD-A cycles consisting of day-3 (cleavage) or day-5 (blastocyst) biopsies were received at the same laboratory for PGD-A via fluorescence in situ hybridization (FISH) or array comparative genome hybridization (aCGH) from multiple fertility centres. The misdiagnosis rates were 0.12% (Wilson 95% CI 0.05 to 0.25%) in day-3 FISH cycles, 0.48% (Wilson 95% CI 0.19 to 1.22%) in day-3 aCGH cycles and 0.0% (Wilson 95% CI 0 to 0.26) in day-5 aCGH cycles. Although rare, the likely causative biological event for true misdiagnosis is embryonic XX/XY mosaicism. Reanalysis of 1219 abnormal cleavage-stage research embryos revealed a 73% incidence of minor and major mosaicism. Only four (0.3%) embryos were found to be diploid and contained XX and XY cells that could potentially account for the misdiagnosis of sex. Our investigation identified errors leading to misdiagnosis and their attribution to specific events during PGD-A testing. The reported misdiagnosis rates suggest that PGD-A for sex determination is highly accurate, particularly when using aCGH applied to blastocyst biopsies

Protection of Overhead Lines Against Climatic Factors

Overhead power lines are devices on the transmission of electrical energy, which must resist the mechanical and electrical strain. The criterion for correct suggestion of overhead lines is the control of the limit level loads. This thesis aims to discuss the weather influences acting on the wires overhead. The first part focuses on the distribution of climatic factors influencing the wires overhead wires and calculations of strain for different weather factors. The second part is then focused on the protection of overhead against the negative effects caused by wind and icing. This thesis therefore deals primarily with the wals of de-icing of conductor overheads and with the calculations needed for the heating of wires. There are presented calculation procedures for determining basking current on de-icing from the conductors

The why, the how and the when of PGS 2.0: current practices and expert opinions of fertility specialists, molecular biologists, and embryologists

Study Question We wanted to probe the opinions and current practices on preimplantation genetic screening (PGS), and more specifically on PGS in its newest form: PGS 2.0? Study Finding Consensus is lacking on which patient groups, if any at all, can benefit from PGS 2.0 and, a fortiori, whether all IVF patients should be offered PGS. What is Known Already It is clear from all experts that PGS 2.0 can be defined as biopsy at the blastocyst stage followed by comprehensive chromosome screening and possibly combined with vitrification. Most agree that mosaicism is less of an issue at the blastocyst stage than at the cleavage stage but whether mosaicism is no issue at all at the blastocyst stage is currently called into question. Study Design, Samples/Materials, Methods A questionnaire was developed on the three major aspects of PGS 2.0: the Why, with general questions such as PGS 2.0 indications; the How, specifically on genetic analysis methods; the When, on the ideal method and timing of embryo biopsy. Thirty-five colleagues have been selected to address these questions on the basis of their experience with PGS, and demonstrated by peer-reviewed publications, presentations at meetings and participation in the discussion. The first group of experts who were asked about ‘The Why’ comprised fertility experts, the second group of molecular biologists were asked about ‘The How’ and the third group of embryologists were asked about ‘The When’. Furthermore, the geographical distribution of the experts has been taken into account. Thirty have filled in the questionnaire as well as actively participated in the redaction of the current paper. Main Results and the Role of Chance The 30 participants were from Europe (Belgium, Germany, Greece, Italy, Netherlands, Spain, UK) and the USA. Array comparative genome hybridization is the most widely used method amongst the participants, but it is slowly being replaced by massive parallel sequencing. Most participants offering PGS 2.0 to their patients prefer blastocyst biopsy. The high efficiency of vitrification of blastocysts has added a layer of complexity to the discussion, and it is not clear whether PGS in combination with vitrification, PGS alone, or vitrification alone, followed by serial thawing and eSET will be the favoured approach. The opinions range from in favour of the introduction of PGS 2.0 for all IVF patients, over the proposal to use PGS as a tool to rank embryos according to their implantation potential, to scepticism towards PGS pending a positive outcome of robust, reliable and large-scale RCTs in distinct patient groups. Limitations, Reasons for Caution Care was taken to obtain a wide spectrum of views fromcarefully chosen experts.However, not all invited experts agreed to participate, which explains a lack of geographical coverage in some areas, for example China. This paper is a collation of current practices and opinions, and it was outside the scope of this study to bring a scientific, once-and-for-all solution to the ongoing debate. Wider Implications of the Findings This paper is unique in that it brings together opinions on PGS 2.0 from all different perspectives and gives an overview of currently applied technologies as well as potential future developments. It will be a useful reference for fertility specialists with an expertise outside reproductive genetics.</p