Preimplantation genetic diagnosis--an overview

Assessment of quadrivalent characteristics influencing chromosome segregation by analyzing human preimplantation embryos from reciprocal translocation carriers

Patterns of meiotic chromosome segregation were analyzed in cleavage stage and blastocyst stage human embryos from couples with autosomal reciprocal translocations (ART). The influence of quadrivalent asymmetry degree, the presence of terminal breakpoints, and the involvement of acrocentric chromosomes in the rearrangement were analyzed to evaluate their contribution to the formation of non-viable embryos with significant chromosomal imbalance due to pathological segregation patterns and to assess the selection of human embryos by the blastocyst stage. A selection of viable embryos resulting from alternate and adjacent-1 segregation and a significant reduction in the detection frequency of the 3 : 1 segregation pattern were observed in human embryos at the blastocyst stage. The presence of terminal breakpoints increased the frequency of 3 : 1 segregation and was also associated with better survival of human embryos resulting from adjacent-1 mode, reflecting the process of natural selection of viable embryos to the blastocyst stage. The demonstrated patterns of chromosome segregation and inheritance of a balanced karyotype in humans will contribute to optimizing the prediction of the outcomes of in vitro fertilization programs and assessing the risks of the formation of unbalanced embryos for ART carriers.

Haplotyping by linked-read sequencing (HLRS) of the genetic disease carriers for preimplantation genetic testing without a proband or relatives

BACKGROUND

In order to mitigate the risk of allele dropout (ADO) and ensure the accuracy of preimplantation genetic testing for monogenic disease (PGT-M), it is necessary to construct parental haplotypes. Typically, haplotype resolution is obtained by genotyping multiple polymorphic markers in both parents and a proband or a relative. Sometimes, single sperm typing, or tests on the polar bodies may also be useful. Nevertheless, this process is time-consuming. At present, there was no simple linkage analysis strategy for patients without affected relatives.

METHOD

To solve this problem, we established a haplotyping by linked-read sequencing (HLRS) method without the requirement for additional relatives. First, the haplotype of the genetic disease carriers in the family was constructed by linked-read sequencing, and then the informative single nucleotide polymorphisms (SNPs) in upstream and downstream mutation region were selected to construct the embryo haplotype and to determine whether the embryo was carrying the mutation. Two families were selected to validate this method; one with alpha thalassemia and the other with NDP gene disorder.

RESULTS

The haplotyping by linked-read sequencing (HLRS) method was successfully applied to construct parental haplotypes without recruiting additional family members; the method was also validated for PGT-M. The mutation carriers in these families were sequenced by linked-read sequencing, and their haplotypes were successfully phased. Adjacent SNPs of the mutation gene were identified. The informative SNPs were chosen for linkage analyses to identify the carrier embryos. For the alpha thalassemia family, a normal blastocyst was transferred to the uterus and the accuracy of PGT-M was confirmed by amniocentesis at 16 weeks of gestation.

CONCLUSIONS

Our results suggest that HLRS can be applied for PGT-M of monogenic disorders or de novo mutations where the mutations haplotype cannot be determined due to absence of affected relatives.

Analysis of segregation patterns of quadrivalent structures and the effect on genome stability during meiosis in reciprocal translocation carriers

STUDY QUESTION

Do specific factors affect the segregation patterns of a quadrivalent structure and can the quadrivalent affect genome stability during meiosis?

SUMMARY ANSWER

Meiotic segregation patterns can be affected by the carrier's gender and age, location of breakpoints and chromosome type, and the quadrivalent structure can increase genome instability during meiosis.

WHAT IS KNOWN ALREADY

Carriers of reciprocal translocations have an increased genetic reproductive risk owing to the complex segregation patterns of a quadrivalent structure. However, the results of previous studies on the factors that affect segregation patterns seem to be contradictory, and the effect of a quadrivalent on genome stability during meiosis is unknown.

STUDY DESIGN, SIZE, DURATION

We designed a retrospective study to analyze the segregation patterns of 24 chromosomes from reciprocal translocation and non-translocation patients. Data for 356 reciprocal translocation carriers and 53 patients with the risk to transmit monogenic inherited disorders (RTMIDs) undergoing PGD-single nucleotide polymorphism array analysis were collected. The study was performed between March 2014 and July 2017.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Segregation patterns of a quadrivalent in 1842 blastocysts from 466 assisted reproduction cycles of reciprocal translocation carriers were analyzed according to the location of chromosome breakpoints, the carrier's gender and age, and chromosome type. In addition, to analyze the effect of quadrivalent structure on genome stability, segregation products of chromosomes which are not involved in the translocation from translocation carriers were compared with those of 23 pairs of chromosomes in 318 blastocysts from 72 assisted reproduction cycles of patients with RTMIDs.

MAIN RESULTS AND THE ROLE OF CHANCE

The percentage of adjacent-2 products with severe asymmetric quadrivalent was significantly higher than those with mild asymmetric quadrivalent (P = 0.020) while, in contrast, the incidence of 4:0/others was lower (P = 0.030). The frequencies of adjacent-1, adjacent-2 and 3:1 products differed between male and female carriers (P < 0.001, P = 0.015 and P = 0.001, respectively), and also for adjacent-1 and 4:0/others products in young versus older carriers (P = 0.04 and P = 0.002, respectively). In addition, adjacent-1 products of a quadrivalent with an acrocentric chromosome were significantly higher than those of a quadrivalent without an acrocentric chromosome (P = 0.001). Moreover, a quadrivalent could significantly increase the frequencies of abnormal chromosomes compared to patients with RTMIDs (P = 0.048, odds ratio (OR) = 1.43, 95% CI = 1.01-2.43), especially for the male carriers (P = 0.018, OR = 1.58, 95% CI = 1.08-2.25). In contrast, for older carriers, no difference was found in both aneuploidy and segmental anomalies compared to patients with RTMIDs.

LIMITATIONS, REASONS FOR CAUTION

The study contained appropriate controls, yet the analysis was limited by a small number of control patients and embryos.

WIDER IMPLICATIONS OF THE FINDINGS

Until now, there had been no definite report about the effect of quadrivalents on genome stability in reciprocal translocation carriers compared with control samples, and in the present study the large sample size ensured a detailed analysis of factors with a possible impact on segregation patterns. These data provide a better insight into the meiotic mechanisms involved in non-disjunction events in gametes from reciprocal translocation carriers. In addition, our results will help to provide each reciprocal translocation carrier couple undergoing PGD with more appropriate genetic counseling and a better understanding of the large numbers of abnormal embryos with chromosome aneuploidy.

STUDY FUNDING/COMPETING INTEREST(S)

The research was supported by the Research Funding of Shanghai Ji Ai Genetics & IVF Institute and the authors declare a lack of competing interests in this study.

Pre-implantation genetic screening among women experiencing recurrent failure of in vitro fertilization

OBJECTIVE

To determine the efficiency of pre-implantation genetic screening (PGS) among women scheduled to undergo intracytoplasmic sperm injection who had experienced recurrent in vitro fertilization (IVF) failure.

METHODS

The present retrospective cohort study reviewed the medical records of consecutive women who had experienced recurrent IVF failure and had presented at a private IVF facility in Trabzon Province, Turkey, to undergo intracytoplasmic sperm injection between May 1, 2012, and December 31, 2014. Patient data and perinatal outcomes were compared between patients who underwent PGS and those who did not.

RESULTS

There were 88 patients included in the study; 43 patients had undergone PGS and 45 had declined to do so. No differences were detected in the clinical pregnancy rate (P=0.846), spontaneous abortion rate (P=0.416), number of perinatal deaths (P=0.162), or the number of live deliveries (P=0.188) between the groups of patients. The pregnancies included in the study resulted in 25 neonates being delivered; 24 had normal karyotypes, and one neonate from the control group had a karyotype of 46, XX, 9ph. Among the 19 embryos that were not transferred, the most frequently encountered chromosomal anomalies were diploidy, monosomy X, and 2N/N/4N mosaicism, detected in 7 (37%), 2 (11%), and 2 (11%) embryos, respectively.

CONCLUSION

PGS had no effect on perinatal outcomes among women experiencing recurrent IVF failure.

Pre-pregnancy cytogenetic analysis of general couples in eastern China

The aim of this study was to investigate the contribution of chromosomal anomalies and the frequency of particular types of aberrations in general couples preparing for pregnancy and make recommendations for pregnancy on the basis of the medical literature. A total of 6,198 general couples were included in the present study. The karyotypes were generated from the peripheral blood lymphocyte cultures and the cytogenetic analysis was performed using G-banding. In 12,396 cases, chromosomal anomalies were detected in 59 cases (0.48%, 59/12,396). Among of them, the frequency of translocation was 0.35% (n = 43). Sex chromosomal anomalies accounted for 0.07% (n = 9), including Klinefelter syndrome (KS) (n = 4), Turner syndrome (TS) (n = 4), and XYY syndrome (n = 1). The others, including inversions (n = 6) and deletion (n = 1), accounted for 0.06%. Our study indicates that clinically important chromosomal defects are present at a remarkable frequency in the general couples in eastern China, suggesting pre-pregnancy cytogenetic analysis should be routinely performed among general couples in this area so that informed decision can be made, which will help to improve the quality of the pregnancy.

Is preimplantation genetic diagnosis the ideal embryo selection method in aneuploidy screening?

To select cytogenetically normal embryos, preimplantation genetic diagnosis (PGD) aneuploidy screening (AS) is used in numerous centers around the world. Chromosomal abnormalities lead to developmental problems, implantation failure, and early abortion of embryos. The usefulness of PGD in identifying single-gene diseases, human leukocyte antigen typing, X-linked diseases, and specific genetic diseases is well-known. In this review, preimplantation embryo genetics, PGD research studies, and the European Society of Human Reproduction and Embryology PGD Consortium studies and reports are examined. In addition, criteria for embryo selection, technical aspects of PGD-AS, and potential noninvasive embryo selection methods are described. Indications for PGD and possible causes of discordant PGD results between the centers are discussed. The limitations of fluorescence in situ hybridization, and the advantages of the array comparative genomic hybridization are included in this review. Although PGD-AS for patients of advanced maternal age has been shown to improve in vitro fertilization outcomes in some studies, to our knowledge, there is not sufficient evidence to use advanced maternal age as the sole indication for PGD-AS. PGD-AS might be harmful and may not increase the success rates of in vitro fertilization. At the same time PGD, is not recommended for recurrent implantation failure and unexplained recurrent pregnancy loss.

Molecular cytogenetics: making it safe for human embryonic stem cells to enter the clinic

Regenerative therapies based on transplantation of cells derived from human embryonic stem cells (hESC) are currently being prepared for clinical trials. Unfortunately, recent evidence indicates that many kinds of changes can occur to hESC during expansion in culture, and alterations to the growth control mechanisms may be required to establish hESC lines at all. Changes in the genome and epigenome can affect the validity of in vitro and animal studies, and put transplant recipients at increased risk of cancer. New molecular cytogenetic technologies enable us to examine the whole human genome with ever-finer resolution. This review describes several techniques for whole-genome analysis and the information they can provide about hESC lines. Adoption of high-resolution genotyping into routine characterization may prevent highly discouraging clinical outcomes.

Preimplantation genetic diagnosis for monogenic diseases: overview and emerging issues

Preimplantation genetic diagnosis (PGD) is an established reproductive option for couples at risk of conceiving a pregnancy affected with a known genetic disease, who wish to avoid an (additional) affected child, termination of pregnancy or recurrent miscarriages. Early technologies concentrated on different approaches to direct mutation testing for monogenic diseases using single cell PCR protocols, or sex selection by fluorescent in situ hybridization for X-linked monogenic disease. Development of multiplex fluorescent PCR allowed simultaneously testing of linked markers alongside the mutation test, increasing the accuracy by controlling for contamination and identifying allele drop-out. The advent of highly effective whole genome amplification methods has opened the way for new technologies such as preimplantation genetic haplotyping and microarrays, thus increasing the number of genetic defects that can be detected in preimplantation embryos; the number of cases carried out and the new indications tested increases each year. Different countries have taken very different approaches to legislating and regulating PGD, giving rise to the phenomenon of reproductive tourism. PGD is now being performed for scenarios previously not undertaken using prenatal diagnosis, some of which raise significant ethical concerns. While PGD has benefited many couples aiming to have healthy children, ethical concerns remain over inappropriate use of this technology.

Genetic risk assessments in individuals at high risk for inherited breast cancer in the breast oncology care setting

BACKGROUND

It has become increasingly common to consider BRCA mutation status when determining optimal cancer risk management and treatment options in order to improve patient outcomes. Knowledge about the risk for hereditary cancer at or as close as possible to the time of diagnosis allows patients access to the most risk reduction options available.

METHODS

This paper illustrates the role of genetic risk assessment for hereditary breast cancer, using hereditary breast and ovarian cancer (HBOC) syndrome as a model due to germline mutations in the BRCA1 and BRCA2. Specifically, the value of genetic counseling and testing for HBOC across the cancer prevention and control continuum is outlined as it pertains to breast cancer.

RESULTS

In recognition of the importance of risk assessment for hereditary breast cancer, leading health professional organizations have developed specific guidelines and recommendations to providers for identification of women at increased risk for carrying a BRCA mutation.

CONCLUSIONS

Institutional efforts specific to genetic counseling and testing have resulted in the implementation of a model driven by physician recommendation as a referral system for high-risk breast cancer patients. Establishing an infrastructure to support research, education, and outreach initiatives focused on BRCA genetic counseling and testing will provide information that can improve the delivery of cancer genetics services.

Is human enhancement also a personal matter?

Emerging technologies are increasingly used in an attempt to "enhance the human body and/or mind" beyond the contemporary standards that characterize human beings. Yet, such standards are deeply controversial and it is not an easy task to determine whether the application of a given technology to an individual and its outcome can be defined as a human enhancement or not. Despite much debate on its potential or actual ethical and social impacts, human enhancement is not subject to any consensual definition. This paper proposes a timely and much needed examination of the various definitions found in the literature. We classify these definitions into four main categories: the implicit approach, the therapy-enhancement distinction, the improvement of general human capacities and the increase of well-being. After commenting on these different approaches and their limitations, we propose a definition of human enhancement that focuses on individual perceptions. While acknowledging that a definition that mainly depends on personal and subjective individual perceptions raises many challenges, we suggest that a comprehensive approach to define human enhancement could constitute a useful premise to appropriately address the complexity of the ethical and social issues it generates.

Benefits and drawbacks of preimplantation genetic diagnosis (PGD) for reciprocal translocations: lessons from a prospective cohort study

Preimplantation genetic diagnosis (PGD) using fluorescence in situ hybridisation probes was carried out for 59 couples carrying reciprocal translocations. Before treatment, 85% of pregnancies had resulted in spontaneous miscarriage and five couples had achieved a healthy live-birth delivery. Following treatment, 33% of pregnancies failed and 21 of 59 couples had a healthy live-born child. The accuracy of diagnosis was 92% (8% false abnormal and 0% false normal results). The overall incidence of 2:2 alternate segregation products was 44%; however, products consistent with 2:2 adjacent segregation were ~twice as likely from male heterozygotes, and those with 3:1 disjunction were three times more likely from female heterozygotes. Our results indicate that up to three stimulation cycles per couple would give an ~50% chance of a successful live birth, with the risk of miscarriage reduced to the level found in the general population. In our study, 87% of all normal/balanced embryos available were identified as being suitable for transfer. We conclude that PGD provides benefit for couples with high-risk translocations by reducing the risk of miscarriage and avoiding a pregnancy with an unbalanced form of the translocation; however, for fertile carriers of translocations with a low risk of conceiving a chromosomally unbalanced offspring, natural conception may be a more viable option.

Views of internists towards uses of PGD

Preimplantation genetic diagnosis (PGD) is increasingly available, but how physicians view it is unclear. Internists are gatekeepers and sources of information, often treating disorders for which PGD is possible. This quantitative study surveyed 220 US internists, who were found to be divided. Many would recommend PGD for cystic fibrosis (CF; 33.7%), breast cancer (BRCA; 23.4%), familial adenomatous polyposis (FAP; 20.6%) and familial hypertrophic cardiomyopathy (19.9%), but few for social sex selection (5.2%); however, in each case, >50% were unsure. Of those surveyed, 4.9% have suggested PGD to patients. Only 7.1% felt qualified to answer patient questions about it. Internists who would refer for PGD had completed medical training less recently and, for CF, were more likely to have privately insured patients (P<0.033) and patients who reported genetic discrimination (P<0.013). Physicians more likely to refer for BRCA and FAP were less likely to have patients ask about genetic testing. This study suggests that internists often feel they have insufficient knowledge about it and may refer for PGD based on limited understanding. They view possible uses of PGD differently, partly reflecting varying ages of onset and disease treatability. These data have critical implications for training, research and practice. Preimplantation genetic diagnosis (PGD) allows embryos to be screened prior to transfer to a woman's womb for various genetic markers. This procedure raises complex medical, social, psychological and ethical issues, but how physicians view it is unclear. Internists are gatekeepers and sources of information, often treating disorders for which PGD use is possible. We surveyed 220 US internists, who were found to be divided: many would recommend PGD for cystic fibrosis (CF; 33.7%), breast cancer (BRCA; 23.4%), familial adenomatous polyposis (FAP; 20.6%), and familial hypertrophic cardiomyopathy (FHC; 19.9%) and a few for sex selection (5.2%); but in each case, >50% were unsure. Of those surveyed, 4.9% have suggested PGD to patients. Only 7.1% felt qualified to answer patient questions. Internists who would refer for PGD completed medical training less recently and, for CF, were more likely to have privately insured patients and patients who reported genetic discrimination. Physicians more likely to refer for BRCA and FAP were less likely to have patients ask about genetic testing. This quantitative study suggests that internists often feel they have insufficient knowledge and may refer for PGD based on limited understanding. They view possible uses of PGD differently, partly reflecting varying ages of onset and disease treatability. Internists should be made aware of the potential benefit of PGD, but also be taught to refer patients, when appropriate, to clinical geneticists who could then refer the patient to an IVF/PGD team. These data thus have critical implications for training, research and practice.

High-risk consumers' perceptions of preimplantation genetic diagnosis for hereditary cancers: a systematic review and meta-analysis

Individuals carrying deleterious germline mutations placing them at increased risk for hereditary cancer syndromes (high-risk consumers) often have a great deal of fear and concern over transmitting mutations to their offspring, particularly conditions which are autosomal dominant. Preimplantation genetic diagnosis (PGD) is a procedure that can detect certain germline cancer predisposing mutations present in embryos. The objective of this review was to assess high-risk consumers' knowledge and perceptions of PGD for hereditary cancers. A systematic literature review was conducted through PubMed, Wiley Interscience, PsychInfo, and Cochrane Library databases to identify all articles assessing consumer knowledge and attitudes of PGD for hereditary cancer syndromes. We assessed heterogeneity and the robustness of findings through additional analyses according to study location, hereditary cancer type, and sample size. Thirteen articles remained eligible after the application of specific criteria. Results show a general low level of knowledge about PGD for hereditary cancers, moderate rates of acceptability among high-risk groups, and high levels of need for information about PGD. Individuals in specific risk groups such as those with a personal or family history of hereditary breast and ovarian cancer (HBOC) syndrome or familial adenomatous polyposis (FAP) may benefit from educational information from healthcare professionals about the use of PGD.

Outcomes of ovarian stimulation in a two-day oocyte collection week with PGD cycles compared to a five-day oocyte collection week with conventional IVF/ICSI cycles

We assessed the outcomes of ovarian stimulation in a two-day egg collection (EC) week with preimplantation genetic diagnosis (PGD) cycles (N = 307) compared to a five-day EC week with conventional in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles (N = 2,417). The mean (SD) age of women undergoing PGD was 34 (3.97) and 35 (3.85) for IVF/ICSI (P < 0.001), the number of oocytes collected was 13 (7.37) and 11 (7.02), (P < 0.001), while the mean (SD) number of fertilized oocytes was 8 (5.09) and 6 (4.58), respectively (P < 0.001). The clinical pregnancy rate per embryo transfer (ET) was 37% with PGD and 38% with IVF/ICSI (P = 0.49), while the implantation rate was 0.35 and 0.30, respectively (P = 0.05). After adjusting for age and confounding variables including the number of oocytes collected and fertilized normally, the mode of treatment (PGD or IVF/ICSI) had no effect on clinical pregnancy (P = 0.48). In conclusion, scheduling of PGD cycles to a two-day EC week did not compromise the outcomes of ovarian stimulation when compared to a five-day EC week with conventional IVF/ICSI cycles. This can allow the provision of a more patient friendly service, increase the flexibility of satellite PGD services, and facilitate cycle programming with the genetics team providing PGD.

Viability of equine embryos after puncture of the capsule and biopsy for preimplantation genetic diagnosis

The equine embryo possesses a capsule that is considered essential for its survival. We assessed viability after breaching the capsule of early (Day 6) and expanded (Day 7 and 8) equine blastocysts by micromanipulation. The capsule was penetrated using a Piezo drill, and trophoblast biopsy samples were obtained for genetic analysis. Pregnancy rates for Day-6 embryos, which had intact zonae pellucidae at the time of recovery, were 3/3 for those biopsied immediately after recovery and 2/3 for those biopsied after being shipped overnight under warm (∼28 °C) conditions. The pregnancy rates for encapsulated Day-7 expanded blastocysts were 5/6 for those biopsied immediately and 5/6 for those biopsied after being shipped overnight warm. Two of four encapsulated Day-8 blastocysts, 790 and 1350 μm in diameter, established normal pregnancies after biopsy. Nine mares were allowed to maintain pregnancy, and they gave birth to nine normal foals. Biopsied cells from eight embryos that produced foals were subjected to whole-genome amplification. Sex was successfully determined from amplified DNA in 8/8 embryos. Identification of disease-causing mutations matched in the analyses of 6/6 samples for the sodium channel, voltage-gated, type IV, alpha subunit (SCN4A) gene and in 6/7 samples for the peptidylprolyl isomerase B (PPIB) gene, in embryo-foal pairs. Thus, the capsule of the equine embryo can be breached without impairing viability. Further work is needed to determine whether this breach is transient or permanent. These findings are relevant to the understanding of equine embryo development and to the establishment of methods for micromanipulation and embryo cryopreservation in this species.

Human embryonic stem cells as models for aneuploid chromosomal syndromes

Syndromes caused by chromosomal aneuploidies are widely recognized genetic disorders in humans and often lead to spontaneous miscarriage. Preimplantation genetic screening is used to detect chromosomal aneuploidies in early embryos. Our aim was to derive aneuploid human embryonic stem cell (hESC) lines that may serve as models for human syndromes caused by aneuploidies. We have established 25 hESC lines from blastocysts diagnosed as aneuploid on day 3 of their in vitro development. The hESC lines exhibited morphology and expressed markers typical of hESCs. They demonstrated long-term proliferation capacity and pluripotent differentiation. Karyotype analysis revealed that two-third of the cell lines carry a normal euploid karyotype, while one-third remained aneuploid throughout the derivation, resulting in eight hESC lines carrying either trisomy 13 (Patau syndrome), 16, 17, 21 (Down syndrome), X (Triple X syndrome), or monosomy X (Turner syndrome). On the basis of the level of single nucleotide polymorphism heterozygosity in the aneuploid chromosomes, we determined whether the aneuploidy originated from meiotic or mitotic chromosomal nondisjunction. Gene expression profiles of the trisomic cell lines suggested that all three chromosomes are actively transcribed. Our analysis allowed us to determine which tissues are most affected by the presence of a third copy of either chromosome 13, 16, 17 or 21 and highlighted the effects of trisomies on embryonic development. The results presented here suggest that aneuploid embryos can serve as an alternative source for either normal euploid or aneuploid hESC lines, which represent an invaluable tool to study developmental aspects of chromosomal abnormalities in humans.

PGD for X-linked and gender-dependent disorders using a robust, flexible single-tube PCR protocol

X-linked genetic diseases include a wide range of disorders such as the dystrophinopathies. Additionally in some rare genetic diseases, severity of expression is gender dependent. Prevention of such disorders usually involves prenatal diagnosis and termination of affected pregnancies, while preimplantation genetic diagnosis (PGD) represents a specialized alternative that avoids pregnancy termination. To preclude the rejection of unaffected male embryos that cannot be differentiated from those affected when using fluorescence in-situ hybridization, a flexible protocol based on multiplex fluorescence polymerase chain reaction (PCR) was standardized and validated for gender determination in single cells, which can potentially incorporate any disease-specific locus. The final panel of nine loci included four loci on the Y chromosome, two on the X chromosome plus up to three microsatellite markers to either support the gender diagnosis or to further monitor extraneous contamination. The protocol, standardized on single lymphocytes, established a PCR efficiency of >93% for all loci with maximum allele dropout rates of 4%. Microsatellite analysis excluded external contamination and confirmed biallelic inheritance. Proof of principle for the simplicity and flexibility of the assay was demonstrated through its application to clinical PGD cycles for lipoid congenital adrenal hyperplasia, which presents a more severe clinical course in males, and Duchenne muscular dystrophy.

Slow and ultrarapid cryopreservation of biopsied mouse blastocysts and its effect on DNA integrity index

PURPOSE

To evaluate the effect of slow and ultra-rapid freezing on biopsied blastocysts' DNA integrity.

METHODS

Forty eight mouse blastocysts were biopsied of which 16 were cryopreserved by slowly freezing and 17 by vitrification. Fourteen intact blastocysts were slowly cryopreserved and 24 were vitrified. Eighteen fresh intact blastocysts and fifteen biopsied blastocysts served as controls. The DNA integrity index of all blastocysts was evaluated using (TUNEL) staining and confocal imaging

RESULTS

Both slow freezing and vitrification of biopsied blastocysts induced apoptosis to a similar extent. Biopsying blastocysts before vitrification resulted in less apoptosis than vitrification of intact blastocysts.

CONCLUSION

Slow freezing and vitrification are equal options for preservation of biopsied blastocysts as regards the DNA integrity index (DII). Biopsied blastocysts better tolerate vitrification than intact expanded blastocysts.

Factors associated with preimplantation genetic diagnosis acceptance among women concerned about hereditary breast and ovarian cancer

PURPOSE

To assess sociodemographic, clinical, awareness, and attitudinal factors associated with acceptance of preimplantation genetic diagnosis among women concerned about hereditary breast and ovarian cancer.

METHODS

Participants (n = 962) were members of a national advocacy organization dedicated to empowering women at high risk for developing breast or ovarian cancer. Participants completed a web-based survey assessing factors associated with preimplantation genetic diagnosis acceptance. Factors significantly associated with acceptance in the bivariate analyses were used to build a logistic regression model.

RESULTS

Among the 962 respondents, 318 (33.1%) selected the option that they would consider preimplantation genetic diagnosis, 367 (38.2%) would not consider preimplantation genetic diagnosis, and 277 (28.8%) selected "don't know." Significant predictors of preimplantation genetic diagnosis acceptance were the desire to have more children, having had a prenatal genetic test, preimplantation genetic diagnosis awareness, belief that preimplantation genetic diagnosis is acceptable for individuals at risk for hereditary breast and ovarian cancer, belief that preimplantation genetic diagnosis information should be given to individuals at risk for hereditary breast and ovarian cancer, concerns about preimplantation genetic diagnosis, perceived benefits of preimplantation genetic diagnosis, and how preimplantation genetic diagnosis is considered.

CONCLUSION

Women at increased risk for hereditary cancer may consider preimplantation genetic diagnosis as part of their reproductive decision making. Therefore, it is important to understand existing levels of awareness and attitudes toward this technology to provide optimal counseling and support.

Conflict between values and technology: perceptions of preimplantation genetic diagnosis among women at increased risk for hereditary breast and ovarian cancer

Members of families affected by hereditary cancer are often concerned about passing on risk to offspring. Preimplantation genetic diagnosis is a procedure performed to identify embryos that inherit mutations placing them at risk for hereditary conditions. Little is known about attitudes toward the use of this technology among individuals at risk for hereditary breast and ovarian cancer. We sought to determine high risk women's attitudes. This study is a qualitative examination of comments from women who participated in an online survey regarding knowledge and attitudes of preimplantation genetic diagnosis among individuals affected by hereditary breast and ovarian cancer. More than half the respondents held less favorable attitudes about the use of preimplantation genetic diagnosis for hereditary breast and ovarian cancer for both themselves and others. However, among the women who felt favorable about its usage, the majority said it became a new option for them to pursue parenthood whereas previously they had opted to not have a biological child. The high percentage of respondents who have never heard of preimplantation genetic diagnosis and who were in favor of this technology for hereditary breast and ovarian cancer indicates the need for educational campaigns to increase awareness and provide information about the procedure, access and affordability. Further research is needed to determine how this population would like this information presented to them and how best to instruct health care professionals to present this topic to women who do not know to ask about it.

Derivation of euploid human embryonic stem cells from aneuploid embryos

Human embryonic stem cells (HESCs) are pluripotent cells derived from the inner cell mass of preimplantation embryos. In this study, to isolate new lines of HESCs, we used blastocyst-stage embryos diagnosed as aneuploid in preimplantation genetic screening (PGS). During in vitro fertilization treatments, PGS is widely applied to identify chromosomal aneuploidies, especially in cases of advanced maternal age. Embryos that are detected as carrying aneuploidies are destined to be discarded unless donated for research. From 74 fresh PGS-defined aneuploid embryos, we derived seven HESC lines. Most of the embryos were left to hatch spontaneously through the hole created for blastomere biopsy and further treated by immunosurgery. The seven HESC lines exhibited morphology and markers typical of HESCs and the capacity for long-term proliferation. The derived HESC lines manifested pluripotent differentiation potential both in vivo and in vitro. Surprisingly, karyotype analysis of the HESC lines that were derived from these aneuploid embryos showed that the cell lines carry a normal euploid karyotype. We show that the euploidy was not achieved through chromosome duplication. Alternatively, we suggest that the euploid HESC lines originated from mosaic embryos consisting of aneuploid and euploid cells, and in vitro selection occurred to favor euploid cells. We assume that aneuploid HESC lines could be isolated mostly from embryos that are uniform for the aneuploidy. These results led us to conclude that the aneuploid mosaic embryos that are destined to be discarded can serve as an alternative source for normal euploid HESC lines.

Elucidating the origin of chromosomal aberrations in IVF embryos by preimplantation genetic analysis

Preimplantation genetic screening (PGS) has been proposed as a method for improving success rates in patients with repeated IVF failures. This approach is based on the hypothesis that such failures are the result of aneuploid embryos. It has been suggested that FISH analysis of blastomeres removed from preimplantation embryos represent the chromosomal constitution of the entire embryo. However, it is not yet clear whether it also represents the chromosomal constitution of the implanted embryo. PGS reanalysis on day 5 of embryos designated as "aneuploid" on day 3 may demonstrate a high rate of mosaicism for chromosomal aberration. Some of these mosaic embryos are capable of developing into normal embryos by "self-correction". Others, however, may accumulate additional chromosomal anomalies. It is therefore concluded that the chromosomal constitution of a preimplantation embryo may evolve during early cleavages. Meiotic and post zygotic mitotic errors may account for these chromosomal aberrations. This review will focus on elucidating the origin of chromosomal changes during preimplantation embryo development by studying their chromosomal constitution at different stages.

Determination of the genetic status of cleavage-stage human embryos by microsatellite marker analysis following multiple displacement amplification

OBJECTIVES

To analyse genotype information from cleavage-stage human embryos and assess the chromosomal status and feasibility of performing aneuploidy screening by microsatellite analysis.

METHODS

DNA from 49 blastomeres from eight cleavage-stage human embryos was amplified using multiple displacement amplification, then tested for panels of 64 polymorphic microsatellite markers on seven different chromosomes, and for two non-polymorphic sequences on the X and Y chromosomes.

RESULTS

There was an overall allele drop out (ADO) rate of 28%. Novel alleles in single cells were seen in 0.3% of amplifications, interpreted as either somatic microsatellite mutation events or 'slippage' of the MDA phi 29 polymerase. Three-allele results for a single marker in a single cell were found in 0.07% of amplifications, interpreted as 'slippage' of the MDA phi 29 polymerase. One apparent segmental duplication was found. Only one embryo with no normal cells was found, probably arising from the chaotic cleavage division following a triploid conception. Six embryos were mosaic, of which four had only one abnormal cell.

CONCLUSIONS

Abnormalities in human embryos may be present in only a single cell, leading to potentially false abnormal results at pre-implantation genetic diagnosis. ADO associated with MDA reduces the efficacy of this approach for detection of aneuploidy. Statistical analysis showed that, for ADO of 28%, seven informative markers would be required to give 95% confidence of detecting trisomic embryos.

Modelling the developmental origins of health and disease in the early embryo

The concept that certain adult diseases, such as hypertension, type 2 diabetes and dyslipidaemia can originate from events occurring in utero arose from epidemiological studies in humans but has since been supported by numerous animal-based studies. Referred to as the "developmental origins of health and disease" or "DOHaD" hypothesis, nutritional studies to date have largely focused on two experimental paradigms involving either calorie or protein restriction for varying intervals during pregnancy, where the favoured animal models have been the sheep and rat. In recent times, attention has been directed towards the earliest stages of gestation, where there is emerging evidence to indicate that the pre-implantation embryo may be particularly sensitive to environmentally induced perturbations leading to impaired health in adulthood. In this article, we make the case for hESCs as a model of the human pre-implantation embryo. Working with comparatively large populations of embryonic cells from the species of clinical interest, the scope exists to investigate the effects of specific genetic manipulations or combinations of metabolites against contrasting genetic backgrounds, where the consequences can be evaluated in downstream tissue specific progenitor and/or terminally differentiated cells. In order to fully realize these potentials, however, both derivation and culture conditions need to be harmonized and refined so as to preclude the requirement for feeder cells and serum.

Merging fields: stem cells in neurogenesis, transplantation, and disease modeling

Traditionally, applied stem cell research has been segregating into strategies aiming at endogenous repair and cell transplantation. Recent advances in both fields have unraveled unexpected potential for synergy between these disparate fields. The increasing dissection of the step-wise integration of adult-born neurons into an established brain circuitry provides a highly informative blueprint for the functional incorporation of grafted neurons into a host brain. On the other hand, in vitro recapitulation of developmental differentiation cascades permits the de novo generation of various neural cell types from pluripotent embryonic stem (ES) cells. Advanced tools in stem cell engineering enable not only genetic selection and instruction of disease-specific donor cells for neural replacement but also the exploitation of stem cells as transgenic cellular model systems for human diseases. In a comparative approach we here illuminate the functional integration of neurons derived from endogenous and transplanted stem cells, the evolving technologies for advanced stem cell engineering and the impact of cloned and mutated stem cells on disease modeling.

Proof of principle and first cases using preimplantation genetic haplotyping--a paradigm shift for embryo diagnosis

Preimplantation genetic haplotyping (PGH) proof-of-principle was demonstrated by multiple displacement amplification (MDA) of single buccal cells from a female donor and genotyping using 12 polymorphic markers within the dystrophin gene; the known paternal genotype enabled identification of the paternal haplotype in the MDA products despite 27% allele dropout. MDA amplified DNA from 49 single human blastomeres with 100% success. The MDA products were genotyped using a total of 57 polymorphic markers for chromosomes 1, 7, 13, 18, 21, X and Y; 72% of alleles amplified providing results at 90% of the loci tested. A PGH cycle was carried out for Duchenne muscular dystrophy. One embryo was biopsied: PGH showed a non-carrier female, which was transferred with no resulting pregnancy. A PGH cycle was carried out for cystic fibrosis. Seven embryos were biopsied and PGH allowed the exclusion of 2 affected embryos; a carrier and a non-carrier embryo were transferred resulting in an on-going twin pregnancy. PGH represents a paradigm shift in embryo diagnosis, as one panel of markers can be used for all carriers of the same monogenic disease, bypassing the need for development of mutation-specific tests, and widening the scope and availability of preimplantation genetic testing.

Cancer genetic testing and assisted reproduction

PURPOSE

Because of increasing uptake of cancer genetic testing and the improving survival of young patients with cancer, health care practitioners including oncologists will increasingly be asked about options for assisted reproduction by members of families affected by hereditary cancer syndromes. Among these reproductive options, preimplantation genetic diagnosis (PGD) offers the opportunity to select embryos without familial cancer-predisposing mutations.

METHODS

A review of the published literature supplemented by a survey of PGD centers in the United States.

RESULTS

Prenatal diagnosis and/or embryo selection after genetic testing has already been performed in the context of more than a dozen familial cancer syndromes, including the common syndromes of genetic predisposition to colon and breast cancer.

CONCLUSION

While constituting new reproductive options for families affected by cancer, the medical indications and ethical acceptance of assisted reproductive technologies for adult-onset cancer predisposition syndromes remain to be defined. Continued discussion of the role of PGD in the reproductive setting is needed to inform the responsible use of these technologies to decrease the burden of heritable cancers.

Single cell PCR amplification of microsatellites flanking the COL7A1 gene and suitability for preimplantation genetic diagnosis of Hallopeau–Siemens recessive dystrophic epidermolysis bullosa

BACKGROUND

Hallopeau-Siemens recessive dystrophic epidermolysis bullosa (HS-RDEB) is a severe inherited blistering skin disorder caused by mutations in the anchoring fibril type VII collagen gene, COL7A1. There is currently no effective treatment but DNA-based prenatal testing in families at risk of recurrence is possible, mostly involving chorionic villus sampling at 10-11 weeks' gestation.

OBJECTIVES

An alternative method, for avoiding recurrence of HS-RDEB, is preimplantation genetic diagnosis (PGD). This involves DNA analysis of single blastomeres extracted from late cleavage stage embryos following in vitro fertilisation.

METHODS

To establish PGD for HS-RDEB, we designed and optimised a sensitive single cell semi-duplex polymerase chain reaction (PCR) assay for two highly polymorphic dinucleotide repeat microsatellite markers, D3S1581 (telomeric) and D3S1289 (centromeric), close to the COL7A1 gene.

RESULTS

We demonstrated high PCR efficiency, low allele drop out rates and no contamination in testing this assay on 50 single buccal cells of known heterozygous genotype and 13 research blastomeres from donated embryos.

CONCLUSIONS

This semi-duplex PCR method provides robust, reproducible and informative amplification results for single cells. Moreover, this test has now been approved for clinical application by the UK Human Fertilisation and Embryology Authority (HFEA). As such, the development of PGD for HS-RDEB broadens the range of prenatal testing options and personal choice for couples at reproductive risk of this severe genetic skin disease.

Towards the analysis of the genomes of single cells: Further characterisation of the multiple displacement amplification

The development of methods for the analysis and comparison of the nucleic acids contained in single cells is an ambitious and challenging goal that may provide useful insights in many physiopathological processes. We review here some of the published protocols for the amplification of whole genomes (WGA). We focus on the reaction known as Multiple Displacement Amplification (MDA), which probably represents the most reliable and efficient WGA protocol developed to date. We discuss some recent advances and applications, as well as some modifications to the reaction, which should improve its use and enlarge its range of applicability possibly to degraded genomes, and also to RNA via complementary DNA.

Therapeutic strategies for the inherited neuropathies

More than 30 genetic causes have been identified for the inherited neuropathies collectively referred to as Charcot-Marie-Tooth (CMT) disease. Previous therapies for CMT were limited to traditional approaches such as rehabilitation medicine, ambulation aids, and pain management. Identification of the genes causing CMT has led to improved genetic counseling and assistance in family planning. Identification of these genes is beginning to delineate common molecular pathways in multiple forms of CMT that can be exploited in future molecular therapies. Scientifically based clinical trials for CMT are currently being implemented. Techniques of gene therapy are advancing to the point that they may become feasible options for patients with CMT and other neurodegenerative diseases.

PGD patients' and providers' attitudes to the use and regulation of preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) providers and patients have a vested interest in policy related to the use and regulation of PGD. To understand their experiences and attitudes, 32 in-depth interviews were conducted. Participants included 13 people at risk of transmitting a single-gene alteration to their children (10/13 had actually used PGD to try to have an unaffected child) and 19 PGD service providers (four nurses, five genetic counsellors, two reproductive endocrinologists, two geneticists, two physician-geneticists, two embryologists, and two laboratory directors). Virtually all participants supported the use of PGD to avoid severe, life-threatening genetic illness or to select embryos that are a tissue match for a sick sibling, but their attitudes varied significantly over the appropriateness of using PGD to avoid adult-onset genetic disease, to select for sex, or to select for other non-medical characteristics. There was disagreement within the PGD provider community about whether or not PGD is experimental. Participants were more concerned about overzealous government regulation of PGD creating barriers to access than potential abuses of the technology, and expected the PGD provider community to take the lead in ensuring that PGD is used for ethically appropriate purposes.

Practical and ethical issues with genetic screening

Clinical hematologists are faced with a growing list of new genetic-based tools for identifying a patient's risk of disease. While many of the disease-specific tests are readily available, validation studies are required. Furthermore, genetic-based tests are being pushed to their technical limits, such as testing a single cell prior to embryo selection and transfer for couples at risk of genetic disease. As a result, misdiagnosis or misinterpretation of the data may result. As new genetic testing opportunities proliferate, the hematologist needs to be aware of the medical and legal issues surrounding their use. Furthermore, the hematologist needs to consider the psychological, ethical and social implications of this new field of genomic-based medicine.