Healthy deliveries from biopsied human embryos

On the origins and fate of chromosomal abnormalities in human preimplantation embryos: an unsolved riddle

About 8 out of 10 human embryos obtained in vitro harbour chromosomal abnormalities of either meiotic or mitotic origin. Abnormalities of mitotic origin lead to chromosomal mosaicism, a phenomenon which has sparked much debate lately as it confounds results obtained through preimplantation genetic testing for aneuploidy (PGT-A). PGT-A in itself is still highly debated, not only on the modalities of its execution, but also on whether it should be offered to patients at all.

We will focus on post-zygotic chromosomal abnormalities leading to mosaicism. First, we will summarize what is known of the rates of chromosomal abnormalities at different developmental stages. Next, based on the current understanding of the origin and cellular consequences of chromosomal abnormalities, which is largely based on studies on cancer cells and model organisms, we will offer a number of hypotheses on which mechanisms may be at work in early human development. Finally, and very briefly, we will touch upon the impact our current knowledge has on the practice of PGT-A. What is the level of abnormal cells that an embryo can tolerate before it loses its potential for full development? And is blastocyst biopsy as harmless as it seems?

Comparison of pregnancy outcomes following preimplantation genetic testing for aneuploidy using a matched propensity score design

STUDY QUESTION

Does preimplantation genetic testing for aneuploidy (PGT-A) increase the likelihood of live birth among women undergoing autologous IVF who have fertilized embryos?

SUMMARY ANSWER

PGT-A is associated with a greater probability of live birth among women 35 years old and older who are undergoing IVF.

WHAT IS KNOWN ALREADY

Previous studies evaluating the association between PGT-A and the incidence of live birth may be prone to confounding by indication, as women whose embryos undergo PGT-A may have a lower probability of live birth due to other factors associated with their increased risk of aneuploidy (e.g. advancing age, history of miscarriage). Propensity score matching can reduce bias where strong confounding by indication is expected.

STUDY DESIGN, SIZE, DURATION

We conducted a retrospective cohort study utilizing data from women who underwent autologous IVF treatment, had their first oocyte retrieval at our institution from 1 January 2011 through 31 October 2017 and had fertilized embryos from this retrieval. If a woman elected to use PGT-A, all good quality embryos (defined as an embryo between Stages 3 and 6 with Grade A or B inner or outer cell mass) were tested. We only evaluated cycles associated with the first oocyte retrieval in this analysis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Our analytic cohort included 8227 women. We used multivariable logistic regression to calculate a propensity score for PGT-A based on relevant demographic and clinical factors available to the IVF provider at the time of PGT-A or embryo transfer. We used the propensity score to match women who did and did not utilize PGT-A in a 1:1 ratio. We then used log-binomial regression to compare the cumulative incidence of embryo transfer, clinical pregnancy, miscarriage and live birth between women who did and did not utilize PGT-A. Because the risk of aneuploidy increases with age, we repeated these analyses among women <35, 35–37 and ≥38 years old based on the Society for Assisted Reproductive Technology’s standards.

MAIN RESULTS AND THE ROLE OF CHANCE

Overall, women with fertilized embryos who used PGT-A were significantly less likely to have an embryo transfer (risk ratios (RR): 0.78; 95% CI: 0.73, 0.82) but were more likely to have a cycle that resulted in a clinical pregnancy (RR: 1.15; 95% CI: 1.04, 1.28) and live birth (RR: 1.21; 95% CI: 1.08, 1.35) than women who did not use PGT-A. Among women aged ≥38 years, those who used PGT-A were 67% (RR: 1.67; 95% CI: 1.31, 2.13) more likely to have a live birth than women who did not use PGT-A. Among women aged 35–37 years, those who used PGT-A were also more likely to have a live birth (RR: 1.27; 95% CI: 1.05, 1.54) than women who did not use PGT-A. In contrast, women <35 years old who used PGT-A were as likely to have a live birth (RR: 0.91; 95% CI: 0.78, 1.06) as women <35 years old who did not use PGT-A.

LIMITATIONS, REASONS FOR CAUTION

We were unable to abstract several potential confounding variables from patients’ records (e.g. anti-Mullerian hormone levels and prior IVF treatment), which may have resulted in residual confounding. Additionally, by restricting our analyses to cycles associated with the first oocyte retrieval, we were unable to estimate the cumulative incidence of live birth over multiple oocyte retrieval cycles.

WIDER IMPLICATIONS OF THE FINDINGS

Women aged 35 years or older are likely to benefit from PGT-A. Larger studies might identify additional subgroups of women who might benefit from PGT-A.

STUDY FUNDING/COMPETING INTEREST(S)

No funding was received for this study. D.S. reports that he is a member of the Cooper Surgical Advisory Board. The other authors report no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Single-cell DNA and FISH analysis for application to preimplantation genetic diagnosis

Preimplantation genetic testing, which includes preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS), is a form of a very early prenatal testing. The goal of this method is to avoid transfer of embryos affected with a specific genetic disease or condition. This unit describes the steps involved in amplifying DNA from a single blastomere and specific assays for detecting a variety of DNA mutations. For some assays, whole-genome amplification by primer-extension preamplification (PEP) is performed prior to analysis. Support protocols describe the biopsy of one or two blastomeres from the developing preimplantation embryo, isolation for further investigation of all blastomeres from embryos shown to have the mutant allele, and isolation of single lymphocytes or lymphoblastoid cells as models for single-cell DNA analysis. A procedure for FISH analysis on single interphase blastomeres is provided along with support protocols for probe preparation and probe validation, which is recommended as a preliminary step before performing any PGD or PGS FISH analysis.

Single-cell DNA and FISH analysis for application to preimplantation genetic diagnosis

The goal of preimplantation genetic diagnosis (PGD) is to avoid transfer of embryos affected with a specific genetic disease or condition. This unit describes the steps involved in amplifying DNA from a single blastomere and specific assays for detecting a variety of DNA mutations. For some assays, whole-genome amplification by primer-extention preamplification (PEP) is performed prior to analysis. Support protocols describe the biopsy of one or two blastomeres from the developing preimplantation embryo, isolation for further investigation of all blastomeres from embryos shown to have the mutant allele, and isolation of single lymphocytes or lymphoblastoid cells as models for single-cell DNA analysis. A procedure for FISH analysis on single interphase blastomeres is provided along with a support protocol for probe validation that is recommended as a preliminary step before performing any PGD FISH analysis.

Ten-year experience with preimplantation genetic diagnosis (PGD) at the New York University School of Medicine Fertility Center

We describe our experience of over 300 cycles of preimplantation genetic diagnosis (PGD) and report clinical pregnancy rates (35%-67%) that support using this technology to screen for genetic disorders and chromosomal abnormalities. In clinical practice for over ten years, PGD offers couples the earliest form of genetic screening and may help improve ongoing pregnancy rates in poor-prognosis patients.

Preimplantation genetic diagnosis: present and future

PURPOSE

Preimplantation genetic diagnosis (PGD) was developed more than a decade ago and aims to identify embryos free of genetic disease attributed either to gene mutations or chromosome errors. The purpose of this article is to provide an update on the current status and future prospects of PGD.

METHODS

Review of studies employing different strategies for the detection of single gene defects, and chromosome abnormalities, both structural and numerical in the context of PGD.

RESULTS

Amplification of several DNA fragments is feasible via multiplex PCR for the PGD of single gene disorders, whilst current FISH protocols employ up to 10 probes to identify embryos with a normal chromosome complement. New methods are being developed which will enable the assessment of the entire chromosome complement of embryonic blastomeres.

CONCLUSIONS

PGD has come a long way since its first application, and has become very accurate and reliable. Technical advances in the field of preimplantation genetics mean that PGD holds great promise for the future.

The "spanning protocol": a new DNA extraction method for efficient single-cell genetic diagnosis

PURPOSE

We evaluated methods of preparation of DNA from single cells for amplification and preimplantation genetic diagnosis (PGD), including our "spanning protocol."

METHODS

Dystrophin gene exons 45 and 51 were amplified by nested polymerase chain reaction (PCR) from a single lymphocyte or blastomere. Amplification efficiencies were compared between DNA extraction by (A) lysis in distilled water with freeze-thawing and boiling; (B) two-step lysis involving potassium hydroxide and dithiothreitol; and (C) the spanning protocol, using N-lauroylsarcosine.

RESULTS

With method A, amplification efficiency was 66/120 (55%) and false-positive such as amplification failure or allele drop out was 42/120 (35%); with B, 96/120 (80%) and 21/120 (17.5%); and with C, 111/120 (92%) and 5/120 (4.2%), using single blastomeres and unaffected lymphocytes from male. Occurrence of false-negative such as contamination of another DNA with method A was 4/120 (3.3%); with B, 10/120 (8.3%); and with C, 2/120 (1.7%) from using single lymphocytes from affected males.

CONCLUSION

The spanning protocol was most efficient for extracting DNA from a single cell and should be particularly useful for preimplantation genetic diagnosis.

Advances in preimplantation genetic diagnosis

Strategies for preimplantation genetic diagnosis (PGD) have become increasingly complex. For single gene disorders it is now usual for several DNA fragments to be simultaneously amplified using multiplex-PCR. This allows redundant diagnostic loci to be analyzed, reducing the chance of misdiagnosis due to allele dropout (ADO). Additionally, hypervariable 'fingerprinting' loci can be amplified, revealing the presence of DNA contaminants. Chromosomal screening has also increased in complexity. Current FISH techniques investigate up to nine chromosomes per cell and are offered to an increasingly wide range of patients, including women of advanced reproductive age and those with a history of repeated spontaneous abortion. Technical limitations, which preclude a full assessment of all chromosomes using FISH, have encouraged the development alternative tests. These include nuclear conversion, comparative genomic hybridization (CGH) and the use of DNA microarray 'chip' technology. This paper discusses technical innovations that have improved the scope and accuracy of PGD, as well as the emergence of new indications for PGD that are sometimes considered controversial (e.g. HLA-typing).

Preimplantation genetic diagnosis for the treatment of failed in vitro fertilization–embryo transfer and habitual abortion

OBJECTIVE

To apply preimplantation genetic diagnosis (PGD) for the treatment of patients with a history of failed IVF-ET or habitual aborters.

DESIGN

Prospective clinical study.

SETTING

Tertiary center for assisted reproduction.

PATIENT(S)

Ninety-four couples with failed IVF-ET after >2 IVF cycles and 64 couples with >2 spontaneous abortions.

INTERVENTION(S)

Patients were prepared for oocyte retrieval using standard controlled ovarian hyperstimulation protocols after standard laboratory techniques. Blastomeres from 6- to 8-cell embryos were analysed using fluorescence in situ hybridization with commercial chromosomal probes, and normoploid embryos were transferred on day 3 after fertilization.

MAIN OUTCOME MEASURE(S)

Pregnancy and implantation rates and live births.

RESULT(S)

Both 3- and 5-probe PGD resulted in a significantly higher outcome than controls for failed IVF-ET. Five-probe PGD appeared to be more suitable for habitual aborters.

CONCLUSION(S)

This pilot study suggests that 3-probe PGD is a valid option for failed IVF-ET patients. The use of five or more probes is indicated for habitual aborters.

Issues and concerns of couples presenting for preimplantation genetic diagnosis (PGD)

BACKGROUND

The use of preimplantation genetic diagnosis (PGD) to select genetically 'normal' human embryos and to transfer them to the uterus of a woman has generated considerable controversy. Debate has occurred over the implications of PGD, sex selection, safety of embryonic manipulation and eugenics. This study evaluates a range of social and moral concerns of couples towards PGD and assisted reproductive technologies (ART) prior to treatment to obtain unbiased authentic attitudes independent of the treatment cycle and the outcome.

METHODS

A total of 121 subjects were administered a structured questionnaire after each couple's in vitro fertilization (IVF) or genetic counselling session. Group A consisted of 41 subjects presenting for PGD of single gene disorders (PGD-SG) and group B consisted of 48 subjects undertaking PGD for aneuploidy screening (PGD-AS). A control group consisted of 32 subjects that were about to commence their first IVF cycle.

RESULTS AND DISCUSSION

All groups found PGD to be a highly acceptable treatment. They expressed little concern about its extension to testing non-disease states such as sex and they were strongly in favour of a shared decision-making model in which couples have considerable autonomy over decisions about the embryo(s) to transfer. Differences between the groups included issues surrounding the transfer of embryos, restrictions to PGD and the destruction of embryos.

Birth of MHC-defined rhesus monkeys produced by assisted reproductive technology

One of the best animal approaches for testing HIV vaccines is the challenge of vaccinated rhesus macaques with SHIV or SIV. Production of rhesus macaques in which all of the MHC class I and II alleles are known represents an opportunity to characterize the entire immune response to SIV and should be an invaluable resource for understanding pathogenesis and vaccine-induced immune responses. Unfortunately, there are few MHC-defined rhesus macaques available for vaccine research. Selective breeding supports the production of limited numbers of macaques that express particular MHC class I alleles. If both parents express the allele of interest, only three quarters of the offspring will express the same allele. However, assisted reproductive technologies, such as in vitro fertilization (IVF) and embryo transfer, can be used for production of MHC-defined macaques, expressing multiple MHC class I and II molecules for which SIV peptides, tetramers and ELISPOT assays exist. Here, we report the birth of MHC-defined rhesus monkeys produced by assisted reproductive technology. Continued improvements in assisted reproductive technologies in rhesus monkeys will enable us to develop a unique prototypic animal production program for the creation of MHC-defined and genetically-identical monkeys for vaccine research.

Aspects of biopsy procedures prior to preimplantation genetic diagnosis

Today, preimplantation genetic diagnosis (PGD) is offered in over 40 centres worldwide for an expanded range of genetic defects causing disease. This very early form of prenatal diagnosis involves the detection of affected embryos by fluorescent in situ hybridization (FISH) (sex determination or chromosomal defects) or by polymerase chain reaction (PCR) (monogenic diseases) prior to implantation. Genetic analysis of the embryos involves the removal of some cellular mass from the embryos (one or two blastomeres at cleavage-stage or some extra-embryonic trophectoderm cells at the blastocyst stage) by means of an embryo biopsy procedure. Genetic analysis can also be performed preconceptionally by removal of the first polar body. However, additional information is then often gained by removal of the second polar body and/or a blastomere from the embryo. Removal of polar bodies or cellular material from embryos requires an opening in the zona pellucida, which can be created in a mechanical way (partial zona dissection) or chemical way (acidic Tyrode's solution). However, the more recent introduction of laser technology has facilitated this step enormously. Different biopsy procedures at different preimplantation stages are reviewed here, including their pros and cons and their clinical applications. The following aspects will also be discussed: safety of zona drilling by laser, use of Ca2+/Mg2+-free medium for decompaction, and removal of one or two cells from cleavage-stage embryos.

Embryo implantation after biopsy of one or two cells from cleavage-stage embryos with a view to preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) can be offered as an alternative to prenatal diagnosis (PND) to couples at risk of having a child with a genetic disease. The affected embryos are detected before implantation by fluorescent in situ hybridisation (FISH) for sexing (X-linked diseases) and chromosomal disorders (numerical and structural) or by polymerase chain reaction (PCR) for monogenic disorders (including some X-linked diseases). The accuracy and reliability of the diagnosis is increased by analysing two blastomeres of the embryo. However, the removal of two blastomeres might have an effect on the implantation capacity of the embryo. We have evaluated the implantation of embryos after the removal of one, two or three cells in 188 PGD cycles where a transfer was done. The patients were divided into five groups: a first group which received only embryos from which one cell had been removed, a second group which received only embryos from which two cells had been removed, a third group which received a mixture of embryos from which one and two cells had been taken, a fourth group where two and three cells had been removed, and a fifth group where three cells had been removed. The overall ongoing pregnancy rate per transfer was 26.1%, the overall implantation rate per transfer was 15.2% and the overall birth rate was 14.2%. Although pregnancy rates between the groups cannot be compared because the second group (two cells removed) contains more rapidly developing and therefore 'better quality' embryos, an ongoing pregnancy rate of 29.1% and an implantation rate of 18.6% per transferred embryo in this group is acceptable, and we therefore advise analysing two cells from a > or =7-cell stage embryo in order to render the diagnosis more accurate and reliable.

Expression of apoptosis-related genes in human oocytes and embryos

PURPOSE

The objective was to study whether apoptosis occurs in human embryogenesis.

METHODS

Human viable, arrested, and nonviable embryos and immature, and nonfertilized oocytes donated by our patients were used to detect apoptosis by Tunel labeling, annexin staining, and single-cell reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

DNA fragmentation and phosphotidylserine translocation, the two markers for apoptosis, were detected frequently in fragmented human embryos derived from in vitro fertilization-embryo transfer (IVF-ET). Using RT-PCR, apoptotic genes also were detected in these embryos. The frequencies of gene expression in viable embryos, arrested embryos, nonviable embryos, immature oocytes, and non-fertilized oocytes were: 7/8, 5/5, 5/6, 0/6, 0/3, for Bax; 8/8, 5/5, 7/7, 0/4, 0/5 for Fas; 2/8, 0/2, 0/3, 0/5, 0/3 for BCL-2; 0/8, 1/3, 0/2, 0/3, 0/2 for Fas-ligand; and 8/8, 17/17, 21/21, 24/24, 15/15 for actin, respectively.

CONCLUSIONS

Our preliminary data did not show a significant difference in the expression frequency of all studied genes between viable embryos and nonviable or arrested embryos. However, the expression of Bax and Fas was noticeably higher in nonviable embryos than in viable embryos as judged by the intensities of amplicons visualized after ethidium bromide staining. In addition, BCL-2 was only detected in viable embryos. Whether embryos quality is related to the regulation of BCL-2, Bax, and Fas expressions requires further study.

Ultrarapid detection of sex chromosomes with the use of fluorescence in situ hybridization with direct label DNA probes in single human blastomeres, spermatozoa, amniocytes, and lymphocytes

OBJECTIVE

To assess the ultrarapid fluorescence in situ hybridization (FISH) procedure with a 1-minute hybridization time for gender determination.

DESIGN

Fluorescence in situ hybridization with direct label fluorescence DNA probes for chromosomes X and Y were tested with the use of different hybridization times and different cell types.

SETTING

Hospital-based IVF program.

INTERVENTION(S)

The efficiency of the FISH procedure with different hybridization times was compared with the use of male lymphocytes. The same FISH procedure, but with only 1-minute hybridization, was carried out in human blastomeres, spermatozoa, uncultured amniocytes, male lymphocytes, and female lymphocytes.

MAIN OUTCOME MEASURE(S)

Percentages of nuclei with positive signals.

RESULT(S)

The percentages of nuclei with positive signals in lymphocytes with hybridization times of 1, 3, 4, 10, 30, and 45 minutes were 97%, 97%, 98%, 98%, 98%, and 98%, respectively. The percentages of nuclei with positive signals after FISH with a 1-minute hybridization time in single blastomeres, spermatozoa, amniocytes, male lymphocytes, and female lymphocytes were 94%, 96%, 96%, 98%, and 97%, respectively.

CONCLUSION(S)

Chromosomes X and Y of human blastomeres. spermatozoa, uncultured amniocytes, and lymphocytes can be detected rapidly with the use of this ultrarapid FISH procedure with a 1-minute hybridization time.

Comparison of FISH PRINS, and conventional and fluorescent PCR for single-cell sexing: suitability for preimplantation genetic diagnosis

PURPOSE

Although conventional polymerase chain reaction (PCR) was the first method used for sexing in preimplantation genetic diagnosis, fluorescent in situ hybridization (FISH) has become the method of choice. Recently two new techniques, primed in situ synthesis (PRINS) and fluorescent PCR, have been developed. This study compares the reliability and accuracy of these four techniques in single cells.

RESULTS

In buccal cells, fluorescent PCR and FISH had similar reliability (94 and 93%) and accuracy (97 and 96%) rates. The reliability and accuracy of PRINS (91 and 25%) and conventional PCR (79 and 89%) were lower. In human blastomeres, FISH and fluorescent PCR had similar reliability (100%, 717; 95%, 190/201) rates. Accuracy rates were 71% (517) and 99% (188/190) for FISH and fluorescent PCR, respectively, however, too few blastomeres were analyzed by FISH for meaningful comparison. However, when these data are compared with published data, the method of choice for blastomere sexing appears to be fluorescent PCR.

CONCLUSIONS

Flouroscent PCR has major implications for PGD.

Rapid sexing of murine preimplantation embryos using a nested, multiplex polymerase chain reaction (PCR)

The objective of this study was to develop a rapid and efficient means of sexing murine preimplantation embryos at the 4- to 8-cell stage of development. To achieve this goal, a nested, multiplex polymerase chain reaction (PCR) was optimized using DNA from male and female mice and primers specific for X- (DXNds3)- and Y- (Sry,Zfy) gene sequences. Sensitivity of the assay was measured using groups of 4, 2, or 1 blastomere from dissociated embryos. Efficiency was evaluated using single blastomeres obtained by embryo biopsy. Accuracy of sexing was determined by comparing single-cell results with those of matched blastocysts. Robust amplification of male (XY) and female (XX) gene sequences was obtained in less than 6 hours. The percentage of male (3 bands) and female (1 band) reactions for groups of 4, 2, or 1 blastomere was 100% (6/6), 100% (15/15), and 94.4% (17/18), respectively. Assay efficiency for single, biopsied blastomeres from 4 to 8 cell embryos was 95.8% (207/216). For male and female embryos, sexing of single blastomeres accurately predicted results of matched blastocysts, 100% (10/10) and 100% (13/13), respectively. Simultaneous amplification of one X- and two Y-gene sequences ensured correct interpretation of sexing reactions. Short thermal cycling times and minimal tube handling increased the assay speed and decreased the potential risk of contamination.

The simplified two-pipette technique is more efficient than the conventional three-pipette method for blastomere biopsy in human embryos

OBJECTIVE

To evaluate the efficiency and efficacy of a simplified two-pipette technique in comparison to the conventional three-pipette method; in the two-pipette method, a single, larger drilling/biopsy pipette is used to perform zona pellucida (ZP) drilling and blastomere aspiration for embryo biopsy.

DESIGN

A preclinical, prospective, randomized, in vitro experiment.

SETTING

The reproductive unit of a university teaching hospital.

PATIENT(S)

Ninety-five excess embryos at the two- to four-cell stage were obtained from 35 patients undergoing IVF.

INTERVENTION(S)

At the six- to eight-cell stage, 88 embryos were allocated randomly to three groups: group I for the conventional method (n = 29), group II for the simplified technique (n = 30), and group III for controls (n = 29). The embryos then were cultured in vitro. The retrieved blastomeres were fixed and examined with fluorescence in situ hybridization using X and Y probes simultaneously.

MAIN OUTCOME MEASURE(S)

Biopsy time, successful retrieval of a blastomere, fixation of the cell, signals developed from fluorescence in situ hybridization, and growth potential and hatching capacity of the biopsied embryos were evaluated.

RESULT(S)

The mean time (+/- SD) for biopsy of each embryo in group I (435 +/- 137 seconds) was significantly longer than that in group II (126 +/- 32 seconds). The success rates for obtaining an intact blastomere were not different between group I (93%) and group II (97%). The growth capacity to the blastocyst stage was similar among the three groups (34%, 37%, and 38%, respectively). However, the ZP-drilled and biopsied embryos of groups I and II had higher percentages of hatching (34% and 37%, respectively) and complete hatching (17% and 20%, respectively) than did those of group III (10% and 0, respectively). The blastomeres obtained by biopsy in groups I and II were equally fixed (90% vs. 90%, respectively) and shown in fluorescence in situ hybridization (79% vs. 80%, respectively).

CONCLUSION(S)

Compared with the conventional method, the simplified technique is more efficient and equally efficacious for blastomere biopsy in preimplantation genetic diagnosis.

Update in preimplantation genetic diagnosis. Age, genetics, and infertility

PGD has been successfully used for several years. Over 40 babies have been born worldwide by use of these techniques. Unfortunately, a number of misdiagnoses have been made, a distressing consequence of a new frontier. Significant advances have been made to improve the efficiency and accuracy of PCR and FISH. The widespread use of this technology awaits further documentation of safety and accuracy. Other issues must also be addressed. First, the cost-effectiveness of the techniques relative to the traditional alternatives must be evaluated. A number of ethical issues regarding embryo screening must be addressed including what diseases are serious enough to warrant the procedure. Another concern is the use of this technology for nongenetic disorders such as gender selection. Finally, the experimental nature of these procedures must continually be discussed with patients, and long-term follow-up studies must be undertaken. Development of more accurate and less expensive assays coupled with improved IVF success rates may make PGD a more widely used clinical tool. The future awaits these developments.

A simplified technique for embryo biopsy: use of the same micropipette for zona drilling and blastomere aspiration

PURPOSE

Using different micropipettes for zona drilling and blastomere aspiration for embryo biopsy is prevalent at centers of preimplantation genetic diagnosis. The purpose of our study was to simplify the technique by using only one micropipette.

METHODS

In this animal model, ICR mouse embryos at the four-cell stage (n = 446) were randomly allocated into two groups; a biopsied group (n = 224) for blastomere aspiration and a control group (n = 222) without micromanipulation. We used a drilling/biopsy micropipette to drill a hole in the zona by expulsion of acidified Tyrode's solution and to aspirate the blastomere by gentle suction with the same micropipette and pull it out of the zona. One blastomere was biopsied from each embryo.

RESULTS

In all, 222 (99.1%) intact blastomeres were successfully biopsied from 224 embryos. Only two blastomeres were damaged during aspiration. The capacity for blastocyst development (92.4 vs 93.7%) was not different between the two groups, but the percentages of embryos hatching (51.8 vs 18.0%) and hatched (29.9 vs 8.1%) were significantly higher in the biopsied group than in the control group.

CONCLUSIONS

This simplified technique of embryo biopsy is safe and highly efficient for obtaining blastomeres for preimplantation genetic diagnosis and may also facilitate hatching of the blastocysts.

The use of embryo genotyping in the propagation of genes involved in the immune response

Multiple ovulation and embryo transfer (MOET) now enables researchers to produce identical twin animals, to obtain progeny from pre-pubertal females and to obtain more offspring from valuable animals. MOET and sexed semen have produced genetic progress of up to 60% of milk production. The oestrous cycles of animals are synchronized with progestagens before superovulation with gonadal hormones, pregnant mare serum gonadotrophin and follicle stimulating hormone. Surgical, non-surgical and laparoscopic methods are applied to recover and transfer embryos. Sexing and genotyping of the pre-implantation embryos is a key step in improving the management and breeding programmes for livestock, as well as in the human for the prenatal diagnosis of genetic disorders. Several serological and physiological methods have been used to determine the sex of the pre-implantation embryos; none has had satisfactory results in terms of time and accuracy. Sexing by polymerase chain reaction (PCR) using male-specific chromosome sequences alone or with female-specific chromosomal DNA probes simultaneously has been sufficient to identify the sex of the embryos with 100% accuracy. However, caution should be taken against sources of the contamination. The MHC class I, class II and background genes have been implicated in resistance to internal parasites in animals. Biotechnological methods such as screening of embryos prior to transfer using PCR and primer extension pre-amplification have already made it possible to detect transgenic or genetically disordered embryos and could be applied to select those embryos bearing immunological genotypes of interest, such as resistance to internal parasites. Ultimately, cloning and nuclear transplantation would provide the possibility of isolating these resistance genes and to transfer them to livestock pre-implantation embryos to propagate these desirable traits.

Polymerase chain reaction amplification specificity: incidence of allele dropout using different DNA preparation methods for heterozygous single cells

PURPOSE

The purpose was to evaluate methods of DNA preparation in a single cell to determine the ability to amplify and correctly diagnose a targeted gene.

METHODS

One- or two-cell lymphoblasts (n = 100/group), heterozygous for the normal and 4-base pair insertion on exon 11 of the beta-hexosaminidase A gene, were collected and prepared under the following conditions: (1) freeze-thaw liquid nitrogen, then boiling (LN2); (2) potassium hydroxide/dithiothreitol, heated to 65 degrees C, followed by acid neutralization (KOH); (3) boiling only (Bl); and (4) water only (H2O). Cells were analyzed by polymerase chain reaction using nested primers.

RESULTS

The total number of cells amplifying [in brackets] and the cells with amplification for both alleles (heterozygous), the normal allele, or the mutant allele were as follows, respectively: LN2 [38], 11, 16, 11; KOH [97], 91, 5, 1; Bl [41], 17, 13, 11; and H2O [85], 41, 16, 28. With two cells per reaction tube the results were as follows: LN2 [85], 53, 14, 18; and KOH [97], 96, 1, 0.

CONCLUSIONS

KOH lysis was significantly greater than with all other methods (P < 0.006) and should be used for single cells. This study also demonstrates the importance of using heterozygous cells to determine the ability to amplify both alleles as a method of quality control for single-cell analysis.

Reduction in signal overlap results in increased FISH efficiency: implications for preimplantation genetic diagnosis

BACKGROUND

In the absence of mosaicism, one of the problems of preimplantation genetic diagnosis with FISH is the occurrence of false-negative hybridization results. It has been hypothesized that missing signals are produced by spatial overlap of signals.

METHODS AND RESULTS

To investigate the relation among cell density, signal overlap, and hybridization signal detection, 371 blastomeres and 4556 lymphocytes were fixed in different cellular concentrations and analyzed by FISH using probes for chromosomes X, Y, and 18, and their nuclear diameters and FISH results scored. The results showed that the lower the diameter of fixed nuclei, the higher the number of signal overlaps and missing signals. The minimum number of missing signals was obtained when lymphocyte and blastomere nuclei had 40 or more microns in diameter after fixation and FISH. Since blastomeres were fixed individually, results with blastomeres were invariably better than with lymphocytes.

Fluorescent PCR: a new technique for PGD of sex and single-gene defects

BACKGROUND

For single-cell diagnosis, particularly preimplantation genetic diagnosis to be successful four main criteria must be achieved: sensitivity, reliability, accuracy, and identification/elimination of contamination.

METHODS AND RESULTS

Fluorescent PCR achieves all four necessary criteria and, in addition, currently allows genes on up to nine chromosomes to be simultaneously investigated. Fluorescent PCR has high sensitivity (approximately 1000 x conventional analysis systems), high reliability (97%), and high accuracy (97%) rates for both sex and CF diagnosis in single somatic cells. The low detection threshold allows allelic dropout (one of the main causes of misdiagnosis) to be easily distinguished from PCR phenomena such as preferential amplification. High reliability (90%) and accuracy (97-100%) have been achieved in sex and CF diagnosis in human blastomeres. Fluorescent PCR can also be used to DNA fingerprint (STR profiling) single cells to identify the source/origin of the cell and determine if contamination has occurred.

CONCLUSIONS

Fluorescent PCR is therefore a suitable method for PGD.

Preimplantation diagnosis of inherited disease by embryo biopsy: an update of the world figures

PURPOSE

Cleavage stage embryo biopsy and preimplantation diagnosis was first reported five years ago. The annual collation of the world figures for centres offering this procedure is important to continually assess the efficiency and success of the biopsy, diagnosis and pregnancies obtained.

MATERIALS AND METHODS

Data was collected from 14 centres worldwide. The largest series of diagnosis has been performed for those patients carrying X-linked disease where the embryos have been sexed either by PCR or FISH. PCR has also been used for the specific diagnosis of a number of single gene defects, mainly for cystic fibrosis but also for the diagnosis of Lesch Nyhan syndrome, Fragile X, Duchenne muscular dystrophy, Tay Sachs, haemophilia and RhD blood typing.

RESULTS

For PCR sexing, a total of 62 cycles have been performed with 14 pregnancies, 8 deliveries and 11 babies born. For FISH sexing, 70 cycles have resulted in 15 pregnancies, 8 deliveries and 11 babies born. For the specific diagnosis of single genes defects, a total of 65 cycles resulted in 21 pregnancies, 12 deliveries and 12 babies born. Overall, 197 cycles were performed, with 171 embryo transfers (86%), 50 pregnancies (25% per cycle, 29% per transfer), 28 deliveries and 34 babies born.

CONCLUSIONS

New methods are being developed to increase the scope of preimplantation diagnoses that can be offered. From next year, the biochemical and miscarriage rates will also be recorded.

Birth of a healthy girl after preimplantation gender determination using a combination of polymerase chain reaction and fluorescent in situ hybridization analysis. Preimplantation Genetics Group

OBJECTIVE

To perform preimplantation gender determination by a combination of polymerase chain reaction (PCR) sexing and fluorescent in situ hybridization technique using the directly labeled fluorescent alpha-satellite centromeric DNA probes for X and Y chromosomes.

SETTING

The IVF program of Illinois Masonic Medical Center.

PATIENTS

A couple requested preimplantation diagnosis because the mother is a carrier for hemophilia A.

RESULTS

Two blastomeres were aspirated from each of the four- to eight-cell embryos, and only the embryos with both fluorescent in situ hybridization and PCR results indicating female sex chromosomal complement were transferred, resulting in a singleton pregnancy and delivery of a healthy female infant, after prenatal confirmation of the diagnosis as female. The male embryos or embryos diagnosed as females only by PCR were followed up by confirmatory fluorescent in situ hybridization analysis demonstrating a discrepancy of PCR and fluorescent in situ hybridization results in four embryos, presumably because of a possible sperm contamination of the PCR reaction or chromosomal mosaicism.

CONCLUSION

The analysis of two blastomeres from the same embryo by a combination of PCR sexing and fluorescent in situ hybridization increases the reliability of preimplantation gender identification at the cleavage stage.

Detection of aneuploidy in human oocytes and corresponding first polar bodies by fluorescent in situ hybridization

PURPOSE

The purpose of the study was to investigate the reliability of the fluorescent in situ hybridization (FISH) analysis of the first polar body (IPB) for cytogenetic evaluation of human oocytes as a method of choice in preimplantation diagnosis of chromosomal aneuploidies.

DESIGN

Human unfertilized oocytes and their extruded IPB were analyzed using the directly labeled fluorescence alpha-satellite DNA probes to chromosomes X and 18.

RESULTS

Paired signals for chromosomes X and 18 were observed in the second meiotic prophase (MII) of unfertilized oocytes and their extruded IPB. In the series of 156 unfertilized oocytes in which the number of X chromosome- and chromosome 18-specific signals were analyzed in both MII and IPB, five nondisjunction events have been detected, with corresponding signals in MII and their IPB: missing signals in MII corresponded to extra signals in their IPB and extra signals in MII corresponded to missing signals in IPB. In one oocyte chromosome 18 nondisjunction was detected, with both chromosome 18 signals in MII and no chromosome 18 signal in IPB. In four oocytes chromatid malsegregations for chromosome X or chromosome 18 were detected: in two oocytes, three of four chromosome 18 signals were present in MII, with only one in IPB, and in the other two oocytes, three of four chromosome signals were present in MII, with only one left in IPB.

CONCLUSIONS

The data suggest the possibility of detecting chromosomal aneuploidy in oocytes through cytogenetic analysis of their corresponding IPB by FISH as a possible approach for preimplantation diagnosis of major chromosomal trisomies.

Review: preimplantation diagnosis of inherited disease

Preimplantation diagnosis of inherited diseases has become possible with the techniques of in vitro fertilization, blastomere biopsy of the 6- to 10-cell embryo and DNA analysis of the single blastomeres. Disease-free embryos are selected for transfer to the uterus, thereby avoiding the need for termination of a fetus diagnosed as affected in prenatal diagnosis in the first or early-second trimester of pregnancy. The genetic indications for preimplantation diagnosis are theoretically the same as for prenatal diagnosis, but the defects must be detectable by the polymerase chain reaction. For X-linked recessive diseases, fluorescence in situ hybridization can be used as an alternative for the selection of female embryos. So far almost 40 healthy children have been born worldwide after preimplantation diagnosis for genetic disease. The possibilities and limitations of preimplantation diagnosis, especially in prevention of inherited disease, are discussed in this review.

Marfan syndrome as a paradigm for transcript-targeted preimplantation diagnosis of heterozygous mutations

Among the many clinical applications of the polymerase chain reaction (PCR) is its potential use in preimplantation diagnosis of genetic disorders. Performing PCR on single blastomeres from early cleavage stage (six- to eight-cell) human embryos should, in principle, enable reliable determination of disease status for certain inherited conditions. However, reports of misdiagnoses using this technique have diminished enthusiasm for its widespread clinical use. One principal source of error is the propensity for genome-targeted PCR to exclusively amplify one allele in reactions assaying a single heterozygous diploid cell. Complete reaction failure is also common. Employing the Marfan syndrome (MFS) as a paradigm, we have developed a reliable, reverse transcription-PCR-based method of genotyping single cells that overcomes these obstacles. The technique should facilitate accurate preimplantation diagnosis of MFS and other selected genetic diseases caused by heterozygous or compound-heterozygous mutations.

Assessment of numeric abnormalities of X, Y, 18, and 16 chromosomes in preimplantation human embryos before transfer

OBJECTIVE

Our purpose was to determine the feasibility of ascertaining aneuploidy for chromosomes X, Y, 18, and 16 by use of multiple-probe fluorescence in situ hybridization in blastomeres from preimplantation human embryos.

STUDY DESIGN

A short fluorescence in situ hybridization procedure involving the simultaneous use of four deoxyribonucleic acid probes detected with red, green, blue, or a mixture of red and green fluorochromes was developed to determine numeric abnormalities of chromosomes X, Y, 18, and 16. Embryos underwent biopsy, and all or most cells were analyzed to distinguish true aneuploidy from mosaicism and to assess technique variations within the same embryo (n = 64).

RESULTS

The analysis of all the blastomeres of an embryo was achieved in 91% of the embryos. Successful analyses including biopsy, fixation, and fluorescence in situ hybridization were achieved in 87.8% of the blastomeres. Of the four chromosomes tested, numeric aberrations were found in 23% and 42% of normally and abnormally developing embryos, respectively, including aneuploidy, polyploidy, haploidy, and mosaicism. When diploid embryos containing one or several tetraploid cells are counted as chromosomally abnormal, then 49% and 61% of normally and abnormally developing embryos, respectively, were chromosomally abnormal. Aneuploid embryos consisted of two monosomies for chromosome 16, one for chromosome 18, and a trisomy for chromosome 16. There was a tendency for aneuploidy to increase with maternal age.

CONCLUSIONS

Fluorescence in situ hybridization is a more efficient method than cytogenetic analysis to study specific aneuploidies at preimplantation stages of development in human embryos. In addition, the preimplantation genetic diagnosis of two blastomeres per eight-cell embryo may be sufficient to ensure successful analysis of polyploidy, haploidy, and specific aneuploidies without endangering the survival of the embryo. The technique can be easily modified to consider other chromosomes, including 13 and 21. Because most chromosomally abnormal embryos do not develop to term, the use of this technique may increase the delivery rate per embryo by allowing only transfer of embryos normal for the tested chromosomes. This technique would be most useful for older women undergoing in vitro fertilization, because aneuploidy appears to increase with advancing maternal age.