The widespread use of in vitro fertilization (IVF) throughout the world provides the opportunity to study human development at the very earliest stages before implantation. Nonetheless, the study of human embryos poses a series of unique ethical and moral implications. The unique totipotent nature of a human embryo and its potential to develop into a child necessitates a level of restriction and regulatory control that is not present when studying other cell types. Although some governments outlaw any experimental procedure on human embryonic material, others allow it under appropriate control. In the latter case (e.g., in the UK), experimentation can be justified on the basis of development of a diagnostic test and/or the goal of improving patient care. A further challenge to effective study is the paucity of material available. Much of the work reported in this chapter arises from the study of only single nuclei. For these reasons, research on interphase cytogenetics in human preimplantation embryos is less advanced than in other cell types. Despite this, a fundamental insight into chromosome copy number and nuclear organization can be gleaned from this material through collaboration with an appropriate clinical program. As attested by other chapters in this book, fluorescent in situ hybridization (FISH) was first adopted for research, but clinical applications rapidly followed. Prenatal and cancer diagnostics are the best examples of this,, but the increasing use of assisted reproductive technologies, namely IVF, precipitated the use of FISH in the field of preimplantation genetic diagnosis (PGD). PGD is defined as the diagnosis of genetic disorders in human preimplantation embryos. The purpose is selective implantation of unaffected embryos in the hope of establishing genetically normal ongoing pregnancies. PGD by interphase cytogenetics was first applied for sexing (to screen for sex-linked disorders), then for chromosome translocations, and later for chromosome copy number. In the latter case, termed preimplantation genetic screening (PGS), families at risk of adverse obstetrical outcomes (referral categories include advanced maternal age and recurrent miscarriage) are targeted, rather than families at risk of transmitting inherited disorders in a classical Mendelian fashion. Clinical application of interphase cytogenetics in the IVF world has allowed the subsequent study of chromosome copy number and nuclear organization. This chapter provides an overview of interphase cytogenetics in human embryos, highlighting the progress and the sometimes contentious pitfalls that it has encountered.
4Deep impact: sequencing embryo biopsy specimens at increasing depth
Deep impact: sequencing embryo biopsy specimens at increasing depth
154Selection of high potential embryos using time-lapse imaging: the era of morphokinetics
Selection of high potential embryos using time-lapse imaging: the era of morphokinetics
129Three-parent in vitro fertilization: gene replacement for the prevention of inherited mitochondrial diseases
Three-parent in vitro fertilization: gene replacement for the prevention of inherited mitochondrial diseases
1Gender does not impact the developmental rate of in vitro fertilization-derived human embryos as confirmed by day 3 blastomere biopsy and preimplantation genetic diagnosis (PGD)
Gender does not impact the developmental rate of in vitro fertilization-derived human embryos as confirmed by day 3 blastomere biopsy and preimplantation genetic diagnosis (PGD)
Read more324Chromosome mosaicism in human embryos.
In the human, mosaicism may occur before implantation; but, to determine when it first occurs, it is necessary to study the chromosomal complement of all blastomeres. Full karyotypes of blastomeres from 2- to 8-cell human embryos by conventional karyotyping of metaphase spreads are difficult to obtain. The aim of this study was to assess the stage at which mosaicism occurred in preimplantation human embryos through use of fluorescence in situ hybridization (FISH) with multiple probes. All or most blastomeres from 2- to 12-cell human embryos were analyzed by FISH using probes for gonosomes and chromosome 18. FISH was performed on blastomeres from 117 morphologically normal monospermic embryos that were not transferred after preimplantation diagnosis because of their risk of carrying X-linked disease; 20 (17.1%) of these embryos were mosaic. Another group of 163 arrested or morphologically abnormal monospermic embryos were also analyzed by FISH; 47 (28.8%) of these embryos were mosaic. In addition, 37 dispermic embryos were analyzed, and 28 (75.7%) of these were found to be mosaic. Mosaicism first occurred at the second cleavage division when the monospermic embryo was mostly diploid and at the first cleavage division when the embryo was mostly haploid, polyploid, or dispermic.
Read more13All 23 Chromosomes have Significant Levels of Aneuploidy in Recurrent Pregnancy Loss Couples
All 23 Chromosomes have Significant Levels of Aneuploidy in Recurrent Pregnancy Loss Couples
19Preimplantation genetic screening (PGS) for aneuploidy in embryos after in vitro fertilization (IVF) does not improve reproductive outcome in women over 35: a prospective controlled randomized study
Preimplantation genetic screening (PGS) for aneuploidy in embryos after in vitro fertilization (IVF) does not improve reproductive outcome in women over 35: a prospective controlled randomized study
Read moreAnalysis of the efficacy and safety of techniques used in pre-implantational genetic diagnosis in human embryos from in vitro Fertilization (IVF)
In vitro fertilization (IVF) represents an extraordinary advance in reproductive medicine, offering an alternative for couples who face difficulties in conceiving naturally, a condition that affects millions of people around the world. Despite all the advances in the technique, there is still concern about the possible transmission of hereditary genetic disorders to offspring, which can compromise the success of the treatment and impact the quality of life of future children. To this end, Preimplantation Genetic Diagnosis (PGD) was developed, a sophisticated technique that allows the identification of chromosomal anomalies and genetic mutations in embryos before their transfer to the patient's uterus, preventing aneuploidy, recurrent miscarriages, and especially providing specific care for women of advanced maternal age, who are at greater risk of generating embryos with chromosomal alterations. PGD uses several high-precision methodologies, such as next-generation sequencing and array comparative genomic hybridization, which provide a detailed and highly accurate analysis of embryonic genetic material. The aim of this review was to comprehensively evaluate the efficacy and safety of the different PGD techniques used in IVF procedures, examining their direct impact on embryo implantation rates, gestational success rates, and the possible adverse effects of these interventions on embryonic development. In view of the above, it is concluded that this technology ensures that embryos with the greatest potential for healthy development are selected, significantly increasing the chances of a successful IVF treatment.
Read moreNon-invasive preimplantationsexingusingRT-PCRon the spent embryo culture media
Non-invasive preimplantationsexingusingRT-PCRon the spent embryo culture media
13Next-generation sequencing: challenges in reproductive genetics
Next-generation sequencing: challenges in reproductive genetics
38Lineage segregation in human pre-implantation embryos is specified by YAP1 and TEAD1.
with details of the nature of the infringement. We will investigate the claim and if justified, we will take the appropriate steps.
Read more47Preimplantation diagnosis
Research towards preimplantation diagnosis of genetic disease was initiated in the UK in the mid 1980s with the aim of helping those couples who would prefer selection to occur at this stage rather than during pregnancy. Following in vitro fertilisation, (IVF), biopsy and removal of 1 or 2 of the totipotent cells from the cleavage stage 3 day old embryo provides the material for molecular genetic diagnosis without interfering with development. Earliest applications were in the avoidance of X-linked disease by sexing embryos and selecting females for transfer to the mother. Initially, polymerase chain reaction (PCR) amplification of DNA from the biopsied blastomeres was performed using primers specific for sequences derived from the Y chromosome and this led to the birth of several normal girls. To reduce the risk of misdiagnosis due to amplification failure, PCR based methods for sexing the embryo now employ both X and Y specific sequences, but the preferred method is currently considered to be fluorescent in situ hybridisation (FISH) with fluorochrome labelled DNA probes to the embryonic nuclei that have been fixed and spread on slides. Dual FISH with probes from X and Y chromosomes allows unequivocal diagnosis of sex and determination of chromosome copy number, avoiding transfer of embryos with abnormal numbers of sex chromosomes, including those with only the maternal X that would be at 50% risk for the X-linked disease. The application of FISH for preimplantation diagnosis has also led to the realisation that chromosomal mosaicism is common at the cleavage stage of development, a finding that has important implications for diagnosis of both dominant single gene disorders and trisomies, as well as for our understanding of early human development. Cloning and sequencing of the relevant genes has enabled the development of methods for the diagnosis of certain recessive single gene disorders in cleavage stage embryos. PCR based methods have to be developed for each condition, sometimes for each family if there is heterogeneity. Preimplantation diagnosis has been successful so far for cystic fibrosis, Tay Sachs disease, and Lesch-Nyhan syndrome. Worldwide, 32 pregnancies have been established following all types of preimplantation diagnosis and with 29 babies born, there is no evidence for any adverse effect on development.
Read moreThawing cryopreserved oocytes: genetic screening of thawed oocytes and ongoing pregnancy success rate
Thawing cryopreserved oocytes: genetic screening of thawed oocytes and ongoing pregnancy success rate
83Preimplantation Genetic Diagnosis—An Overview
Since the early 1990s, preimplantation genetic diagnosis (PGD) has been expanding in scope and applications. Selection of female embryos to avoid X-linked disease was carried out first by polymerase chain reaction, then by fluorescence in situ hybridization (FISH), and an ever-increasing number of tests for monogenic diseases have been developed. Couples with chromosome rearrangements such as Robertsonian and reciprocal translocations form a large referral group for most PGD centers and present a special challenge, due to the large number of genetically unbalanced embryos generated by meiotic segregation. Early protocols used blastomeres biopsied from cleavage-stage embryos; testing of first and second polar bodies is now a routine alternative, and blastocyst biopsy can also be used. More recently, the technology has been harnessed to provide PGD-AS, or aneuploidy screening. FISH probes specific for chromosomes commonly found to be aneuploid in early pregnancy loss are used to test blastomeres for aneuploidy, with the aim of replacing euploid embryos and increasing pregnancy rates in groups of women who have poor IVF success rates. More recent application of PGD to areas such as HLA typing and social sex selection have stoked public controversy and concern, while provoking interesting ethical debates and keeping PGD firmly in the public eye.
Read moreSpindle dynamics and chromosome segregation in human preimplantation embryos.
Spindle dynamics and chromosome segregation in human preimplantation embryos.
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