Infertile couples with Robertsonian translocations: preimplantation genetic analysis of embryos reveals chaotic cleavage divisions

Morphokinetic Profiling Suggests That Rapid First Cleavage Division Accurately Predicts the Chances of Blastulation in Pig In Vitro Produced Embryos

The study of pig preimplantation embryo development has several potential uses: from agriculture to the production of medically relevant genetically modified organisms and from rare breed conservation to acting as a physiologically relevant model for progressing human and other (e.g., endangered) species' in vitro fertilisation technology. Despite this, barriers to the widespread adoption of pig embryo in vitro production include lipid-laden cells that are hard to visualise, slow adoption of contemporary technologies such as the use of time-lapse incubators or artificial intelligence, poor blastulation and high polyspermy rates. Here, we employ a commercially available time-lapse incubator to provide a comprehensive overview of the morphokinetics of pig preimplantation development for the first time. We tested the hypotheses that (a) there are differences in developmental timings between blastulating and non-blastulating embryos and (b) embryo developmental morphokinetic features can be used to predict the likelihood of blastulation. The abattoir-derived oocytes fertilised by commercial extended semen produced presumptive zygotes were split into two groups: cavitating/blastulating 144 h post gamete co-incubation and those that were not. The blastulating group reached the 2-cell and morula stages significantly earlier, and the time taken to reach the 2-cell stage was identified to be a predictive marker for blastocyst formation. Reverse cleavage was also associated with poor blastulation. These data demonstrate the potential of morphokinetic analysis in automating and upscaling pig in vitro production through effective embryo selection.

The Clinical Effectiveness of Preimplantation Genetic Diagnosis for Chromosomal Translocation Carriers: A Meta-analysis

Published data on the relationship between pregnancy outcomes of preimplantation genetic diagnosis (PGD) in translocation carriers have implicated inconclusive results. To identify potentially eligible reports, an electronic search was conducted in several databases, including PubMed, Scopus, Web of Knowledge, and Cochrane. Pooled odd ratios (ORs) and 95% confidence intervals (Cis) were estimated based on a random-effect model to evaluate the strength of association between PGD and successful pregnancy outcome in translocation carriers. A total of six cohort studies were included in the current study. The meta-analysis of these studies revealed that the PGD method was associated with an increased successful pregnancy outcome of translocation carriers (OR = 8.58; 95%CI: 1.40–52.76). In subgroup analysis, there was no significant association according to the chromosomal translocation carrier origin and the type of translocated chromosomes, as well as country. In developed countries, the pregnancy outcome of PGD was significantly improved in translocation carriers (OR = 21.79; 95%CI: 1.93–245.52). The current meta-analysis demonstrated that the PGD method is associated with successful pregnancy outcome in both types of reciprocal and Robertsonian translocation carriers, especially in developed countries.

Interchromosomal effect in carriers of translocations and inversions assessed by preimplantation genetic testing for structural rearrangements (PGT-SR)

PURPOSE

Balanced carriers of structural rearrangements have an increased risk of unbalanced embryos mainly due to the production of unbalanced gametes during meiosis. Aneuploidy for other chromosomes not involved in the rearrangements has also been described. The purpose of this work is to know if the incidence of unbalanced embryos, interchromosomal effect (ICE) and clinical outcomes differ in carriers of different structural rearrangements.

METHODS

Cohort retrospective study including 359 preimplantation genetic testing cycles for structural rearrangements from 304 couples was performed. Comparative genomic hybridisation arrays were used for chromosomal analysis. The results were stratified and compared according to female age and carrier sex. The impact of different cytogenetic features of chromosomal rearrangements was evaluated.

RESULTS

In carriers of translocations, we observed a higher percentage of abnormal embryos from day 3 biopsies compared with day 5/6 biopsies and for reciprocal translocations compared with other rearrangements. We observed a high percentage of embryos with aneuploidies for chromosomes not involved in the rearrangement that could be attributed to total ICE (aneuploid balanced and unbalanced embryos). No significant differences were observed in these percentages between types of rearrangements. Pure ICE (aneuploid balanced embyos) was independent of female age only for Robertsonian translocations, and significantly increased in day 3 biopsies for all types of abnormalities. Furthermore, total ICE for carriers of Robertsonian translocations and biopsy on day 3 was independent of female age too. High ongoing pregnancy rates were observed for all studied groups, with higher pregnancy rate for male carriers.

CONCLUSION

We observed a higher percentage of abnormal embryos for reciprocal translocations. No significant differences for total ICE was found among the different types of rearrangements, with higher pure ICE only for Robertsonian translocations. There was a sex effect for clinical outcome for carriers of translocations, with higher pregnancy rate for male carriers. The higher incidence of unbalanced and aneuploid embryos should be considered for reproductive counselling in carriers of structural rearrangements.

Effects of a carrier's sex and age on the segregation patterns of the trivalent of Robertsonian translocations

PURPOSE

To investigate the effects of a carrier's sex and age on the segregation patterns of the trivalent of Robertsonian translocations.

METHODS

This retrospective study was designed to analyze the segregation patterns of the trivalent and euploidy rates of blastocysts. Data were collected from 154 couples with Robertsonian translocation (77 with a female carrier and 77 with a male carrier). Embryos were diagnosed via array comparative genomic hybridization between January 2013 and July 2017. The segregation patterns of the trivalent of 604 blastocysts were analyzed according to the carrier's sex and age.

RESULTS

The proportion of alternate segregation was significantly higher (82.9% vs. 55.2%) in the male carriers than in the female carriers of Robertsonian translocation, and the proportion of adjacent segregation was significantly lower (16.8% vs. 42.6%), with no difference in 3:0 segregation. The segregation patterns were similar in same-sex carriers when analyzed according to the type of translocation. The carrier's age had no influence on the segregation patterns of the trivalent.

CONCLUSIONS

The proportions of the trivalent's meiotic segregation pattern differ significantly according to the carrier's sex in Robertsonian translocations and are independent of the carrier's age. A significantly higher proportion of alternate segregation for normal or balanced chromosome contents was observed in the blastocysts of the male carriers than in those of the female carriers.

Inheritance of imbalances in recurrent chromosomal translocation t(11;22): clarification by PGT-SR and sperm-FISH analysis

RESEARCH QUESTION

To analyse why unbalanced viable offspring are derived mainly from the 3:1 segregation mode in t(11;22)(q23;q11.2) reciprocal translocation.

DESIGN

Retrospective analysis of 24 pre-implantation genetic testing for chromosomal structural re-arrangements (PGT-SR) cycles was performed on seven male and five female carriers of t(11;22) translocation. Sperm analysis was performed on each male carrier. These patients were directed to the study centre after several years of miscarriages and/or abortions, primary infertility for male carriers or birth of an affected child.

RESULTS

Twenty-four PGT-SR cycles were performed to exclude imbalances in both male and female carriers. The unbalanced embryos derived from the adjacent-1 segregation mode were the most represented in both male and female carriers (68.4% and 50%, respectively). These results were positively related with meiotic segregation analysis of reciprocal translocation in spermatozoa. A thorough analysis of the unbalanced embryo karyotypes determined that the expected viable +der22 karyotype resulting from 3:1 malsegregation was less represented at 5.3%.

CONCLUSIONS

These findings highlight the divergence that may exist between meiotic segregation and post-zygotic selection. Post-zygotic selection would be responsible for the elimination of unbalanced embryos derived from the adjacent-1 segregation mode. The combined action of several factors occurs at the beginning of post-zygotic selection. Genetic counselling must consider the risk of a birth related to the adjacent-1 segregation mode, irrespective of the sex of the translocation carrier. These results will allow deeper understanding of the PGT results of t(11;22) carriers, which often include a high number of aneuploid embryos.

BasePhasing: a highly efficient approach for preimplantation genetic haplotyping in clinical application of balanced translocation carriers

BACKGROUND

Preimplantation genetic testing (PGT) has already been applied in chromosomally balanced translocation carriers to improve the clinical outcome of assisted reproduction. However, traditional methods could not further distinguish embryos carrying a translocation from those with a normal karyotype prior to implantation.

METHODS

To solve this problem, we developed a method named "Chromosomal Phasing on Base level" (BasePhasing), which based on Infinium Asian Screening Array-24 v1.0 (ASA) and a specially phasing pipeline. Firstly, by comparing the number of single nucleotide polymorphism (SNP) loci in different minor allele frequencies (MAFs) and in 2Mbp continuous windows of ASA chip and karyomap-12 chip, we verified whether ASA could be adopted for genome-wide haplotype linkage analysis. Besides, the whole gene amplification (WGA) of 3-10 cells of GM16457 cell line was used to verify whether ASA chip could be used for testing of WGA products. Finally, two balanced translocation families were utilized to carry out BasePhasing and to validate the feasibility of its clinical application.

RESULTS

The average number of SNP loci in each window of ASA (473.2) was twice of that of Karyomap-12 (201.2). The coincidence rate of SNP loci in genomic DNA and WGA products was about 97%. The 5.3Mbp deletion was detected positively in cell line GM16457 of both genomic DNA and WGA products, and haplotype linkage analysis was performed in genome wide successfully. In the two balanced translocation families, 18 blastocysts were analyzed, in which 8 were unbalanced and the other 10 were balanced or normal chromosomes. Two embryos were transferred back to the patients successfully, and prenatal cytogenetic analysis of amniotic fluid was performed in the second trimester. The results predicted by BasePhasing and prenatal diagnosis were totally consistent.

CONCLUSIONS

Infinium ASA bead chip based BasePhasing pipeline shows good performance in balanced translocation carrier testing. With the characteristics of simple operation procedure and accurate results, we demonstrate that BasePhasing is one of the most suitable methods to distinguish between balanced and structurally normal chromosome embryos from translocation carriers in PGT at present.

Is sperm FISH analysis still useful for Robertsonian translocations? Meiotic analysis for 23 patients and review of the literature

Background

Robertsonian translocations (RobT) are common structural chromosome rearrangements where carriers display a majority of chromosomally balanced spermatozoa from alternate segregation mode. According to some monotony observed in the rates of balanced segregation, is sperm FISH analysis obsolete for RobT carriers?

Methods

Retrospective cohort research study on 23 patients analyzed in our center from 2003 to 2017 and compared to the data of 187 patients in literature from 1983 to 2017.

Robertsonian translocation carriers were divided in six groups according to the chromosomes involved in the translocation: 9 patients from our center and 107 from literature carrying 45,XY,der(13;14) karyotype, 3 and 35 patients respectively with 45,XY,der(14;21), 5 and 11 patients respectively with 45,XY,der(13;15), 4 and 7 patients respectively with 45,XY,der(14;15), 1 and 4 patients respectively with 45,XY,der(13;22),and 1 and 10 patients respectively with 45,XY,der(14;22).

Results

Alternate segregation mode is predominant in our group of Robertsonian translocation carriers with 73.45% ±8.05 of balanced spermatozoa (min 50.92%; max 89.99%). These results are compliant with the data from literature for all translocations types (p > 0.05) and are consistent among the different types of Robertsonian translocations (p > 0.05) except for der(13;15) that exhibit lower balanced spermatozoa rates (p < 0.05 versus der(13;14), der(14;21), (13;21) and der(15;22)). Normozoospermic patients also display a significantly (p < 0.01) higher rate of balanced sperm cells than patients with abnormal seminograms whatever the defect implied.

Conclusions

According to the discrepancies observed between der(13;15) and all the other Rob T carriers, the differences observed among patients presenting normal and abnormal sperm parameters and the input in genetical counselling, sperm FISH does not seem obsolete for these patients. Moreover, it seems important to collect more data for rare RobT.

Translocations, inversions and other chromosome rearrangements

Chromosomal rearrangements have long been known to significantly impact fertility and miscarriage risk. Advancements in molecular diagnostics are challenging contemporary clinicians and patients in accurately characterizing the reproductive risk of a given abnormality. Initial attempts at preimplantation genetic diagnosis were limited by the inability to simultaneously evaluate aneuploidy and missed up to 70% of aneuploidy in chromosomes unrelated to the rearrangement. Contemporary platforms are more accurate and less susceptible to technical errors. These techniques also offer the ability to improve outcomes through diagnosis of uniparental disomy and may soon be able to consistently distinguish between normal and balanced translocation karyotypes. Although an accurate projection of the anticipated number of unbalanced embryos is not possible at present, confirmation of normal/balanced status results in high pregnancy rates (PRs) and diagnostic accuracy.

Recent advances in preimplantation genetic diagnosis and screening

Preimplantation genetic diagnosis/screening (PGD/PGS) aims to help couples lower the risks of transmitting genetic defects to their offspring, implantation failure, and/or miscarriage during in vitro fertilization (IVF) cycles. However, it is still being debated with regard to the practicality and diagnostic accuracy of PGD/PGS due to the concern of invasive biopsy and the potential mosaicism of embryos. Recently, several non-invasive and high-throughput assays have been developed to help overcome the challenges encountered in the conventional invasive biopsy and low-throughput analysis in PGD/PGS. In this mini-review, we will summarize the recent progresses of these new methods for PGD/PGS and discuss their potential applications in IVF clinics.

Chromosomal analysis of blastocysts from balanced chromosomal rearrangement carriers

Balanced chromosomal rearrangements (CRs) are among the most common genetic abnormalities in humans. In the present study, we have investigated the degree of consistency between the chromosomal composition of the blastocyst inner cell mass (ICM) and trophectoderm (TE) in carriers with balanced CR, which has not been previously addressed. As a secondary aim, we have also evaluated the validity of cleavage-stage preimplantation genetic diagnosis (PGD) based on fluorescence in situ hybridization (FISH) of blastocysts from CR carriers. Blastocyst ICM and TE were screened for chromosomal aneuploidy and imbalance of CR-associated chromosomes based on whole-genome copy number variation analysis by low-coverage next-generation sequencing (NGS) following single-cell whole-genome amplification by multiple annealing and looping-based amplification cycling. The NGS results were analyzed without knowledge of cleavage-stage FISH results. NGS results for blastocyst ICM and TE from CR carriers were 86.49% (32/37) consistent. Of the 1702 (37×46) chromosomes examined, 99.47% (1693/1702) showed consistency. However, only 40.0% (18/45) of all embryos had consistent results for chromosomes involved in CR, as determined by blastocyst NGS and cleavage-stage FISH. Of the 85 CR-affected chromosomes analyzed by FISH, 37.65% (32/85) were incongruous with NGS results, with 87.5% (28/32) showing imbalanced composition by FISH but balanced composition by NGS. These results indicate that chromosomal composition of blastocyst ICM and TE in balanced CR carriers is highly consistent, and that PGD based on cleavage-stage FISH is inaccurate; therefore, using blastocyst TE biopsies for NGS-based PGD is recommended for identifying chromosomal imbalance in embryos from balanced CR carriers.

The origin and significance of additional aneuploidy events in couples undergoing preimplantation genetic diagnosis for translocations by array comparative genomic hybridization

Diagnostic application of array comparative genomic hybridization (aCGH) in preimplantation genetic diagnosis for reciprocal and Robertsonian translocations has revealed 55-65% embryos with additional aneuploidies with or without translocation-related imbalances. The occurrence of these extra abnormalities with the balanced form of the translocation reduces the number of embryos suitable for transfer. Eighty-three embryos were followed up on days 5-7 of development from 23 infertile or sub-fertile carriers for whole chromosome and segmental aneuploidies present in addition to the balanced or unbalanced translocations detected on aCGH diagnosis. Embryos were analysed by fluorescence in-situ hybridization (n = 63) and aCGH (n = 20). Meiotic aneuploidy affected 35% of embryos and 47% had mitotic events; 15% had both types. Meiotic and mitotic events were almost equal (60 versus 64), 97 affected whole chromosomes (58 meiotic, 39 mitotic) and 27 were segmental (two meiotic, 25 mitotic). In 85.5% of embryos with whole chromosome additional aneuploidies, the aneuploidy was present throughout or in more than 50% of cells. All embryos diagnosed as abnormal (translocation balanced or unbalanced) after aCGH diagnosis at cleavage stage would have remained unsuitable for transfer if tested at later stages of development. Additional aneuploidies merit full consideration when considering the choice of embryos to transfer.

Validation of a semiconductor next-generation sequencing-based protocol for preimplantation genetic diagnosis of reciprocal translocations

OBJECTIVE

We aim to validate a semiconductor next-generation sequencing (NGS)-based method to detect unbalanced chromosome translocation in preimplantation embryos.

METHODS

The study consisted of a blinded retrospective evaluation with NGS of 145 whole-genome amplification products obtained from biopsy of cleavage-stage embryos or blastocysts, derived from 33 couples carrying different balanced translocations. Consistency of NGS-based copy number assignments was evaluated and compared with the results obtained by array-comparative genomic hybridization.

RESULTS

Reliably identified with the NGS-based protocol were 162 segmental imbalances derived from 33 different chromosomal translocations, with the smallest detectable chromosomal segment being 5 Mb in size. Of the 145 embryos analysed, 20 (13.8%) were balanced, 43 (29.6%) were unbalanced, 53 (36.5%) were unbalanced and aneuploid, and 29 (20%) were balanced but aneuploid. NGS sensitivity for unbalanced/aneuploid chromosomal call (consistency of chromosome copy number assignment) was 99.75% (402/403), with a specificity of 100% (3077/3077). NGS specificity and sensitivity for unbalanced/aneuploid embryo call were 100%.

CONCLUSIONS

Next-generation sequencing can detect chromosome imbalances in embryos with the added benefit of simultaneous comprehensive aneuploidy screening. Given the high level of consistency with array-comparative genomic hybridization, NGS has been demonstrated to be a robust high-throughput technique ready for clinical application in preimplantation genetic diagnosis for chromosomal translocations, with potential advantages of automation, increased throughput and reduced cost.

Morphometric analysis and developmental comparison of embryos from carriers with balanced chromosomal rearrangements in preimplantation genetic diagnosis cycles

The morphological parameters of embryos from 22 carriers with balanced chromosomal rearrangements (CRs) were quantified and evaluated to determine their possible link to chromosomal composition. The morphometric characteristics of 168 embryos diagnosed by fluorescence in situ hybridisation were measured using an imaging tool and then analysed retrospectively. The mean zygotic diameter of normal-balanced embryos was significantly smaller compared with that of abnormal embryos (P=0.015). In addition, the reduction in total cytoplasmic volume for Day-3 embryos was significantly lower in normal or balanced embryos than in abnormal embryos (P=0.027). Moreover, the pronuclear volumes of embryos that failed to reach the blastocyst stage were significantly smaller compared with those of blastocysts (P=0.016). These findings indicate that morphometric characteristics are correlated with developmental outcomes as well as with chromosomal composition in embryos from balanced CR carriers. However, an effective indicator of developmental outcomes may not accurately reflect chromosomal composition. Combining morphometric and traditional qualitative assessment may increase the precision and standardisation of embryo evaluation as well as contributing to improved efficiency of preimplantation genetic diagnosis by selecting embryos with high developmental potential and preferentially testing embryos predicted to have a low risk of chromosomal imbalance.

Embryos of robertsonian translocation carriers exhibit a mitotic interchromosomal effect that enhances genetic instability during early development

Balanced chromosomal rearrangements represent one of the most common forms of genetic abnormality affecting approximately 1 in every 500 (0.2%) individuals. Difficulties processing the abnormal chromosomes during meiosis lead to an elevated risk of chromosomally abnormal gametes, resulting in high rates of miscarriage and/or children with congenital abnormalities. It has also been suggested that the presence of chromosome rearrangements may also cause an increase in aneuploidy affecting structurally normal chromosomes, due to disruption of chromosome alignment on the spindle or disturbance of other factors related to meiotic chromosome segregation. The existence of such a phenomenon (an inter-chromosomal effect—ICE) remains controversial, with different studies presenting contradictory data. The current investigation aimed to demonstrate conclusively whether an ICE truly exists. For this purpose a comprehensive chromosome screening technique, optimized for analysis of minute amounts of tissue, was applied to a unique collection of samples consisting of 283 oocytes and early embryos derived from 44 patients carrying chromosome rearrangements. A further 5,078 oocytes and embryos, derived from chromosomally normal individuals of identical age, provided a robust control group for comparative analysis. A highly significant (P = 0.0002) increase in the rate of malsegregation affecting structurally normal chromosomes was observed in association with Robertsonian translocations. Surprisingly, the ICE was clearly detected in early embryos from female carriers, but not in oocytes, indicating the possibility of mitotic rather than the previously suggested meiotic origin. These findings have implications for our understanding of genetic stability during preimplantation development and are of clinical relevance for patients carrying a Robertsonian translocation. The results are also pertinent to other situations when cellular mechanisms for maintaining genetic fidelity are relaxed and chromosome rearrangements are present (e.g. in tumors displaying chromosomal instability).

Translocations involve exchange of material between two or more chromosomes and are a common form of genetic abnormality. The rearrangements are difficult to process during meiosis, frequently producing gametes with missing/extra pieces of the affected chromosomes. It has been suggested that translocations might also disrupt the segregation of structurally normal chromosomes, a so-called interchromosomal effect (ICE), but the published data is contradictory. Here we report results from a unique collection of samples, consisting of oocytes and embryos from translocation carriers. Examination of more than 210,000 chromosomes revealed no evidence of an ICE in oocytes, but a significant effect in embryos tested three days after fertilization (6–10 cell stage) in a subset of patients. Clinically, this means that some translocation carriers are at even higher risk of chromosomally abnormal pregnancies than previously suspected, a factor that should be considered during genetic counselling. Scientifically, the results illuminate a poorly understood stage of human development, characterized by chromosomal instability, reminiscent of that observed in some tumors. The restriction of the ICE to a narrow developmental window was unexpected, yet may explain why some earlier studies could not agree on the existence of an ICE.

Chromosome segregation analysis in human embryos obtained from couples involving male carriers of reciprocal or Robertsonian translocation

The objective of this study was to investigate the frequency and type of chromosome segregation patterns in cleavage stage embryos obtained from male carriers of Robertsonian (ROB) and reciprocal (REC) translocations undergoing preimplantation genetic diagnosis (PGD) at our reproductive center. We used FISH to analyze chromosome segregation in 308 day 3 cleavage stage embryos obtained from 26 patients. The percentage of embryos consistent with normal or balanced segregation (55.1% vs. 27.1%) and clinical pregnancy (62.5% vs. 19.2%) rates were higher in ROB than the REC translocation carriers. Involvement of non-acrocentric chromosome(s) or terminal breakpoint(s) in reciprocal translocations was associated with an increase in the percent of embryos consistent with adjacent 1 but with a decrease in 3∶1 segregation. Similar results were obtained in the analysis of nontransferred embryos donated for research. 3∶1 segregation was the most frequent segregation type in both day 3 (31%) and spare (35%) embryos obtained from carriers of t(11;22)(q23;q11), the only non-random REC with the same breakpoint reported in a large number of unrelated families mainly identified by the birth of a child with derivative chromosome 22. These results suggest that chromosome segregation patterns in day 3 and nontransferred embryos obtained from male translocation carriers vary with the type of translocation and involvement of acrocentric chromosome(s) or terminal breakpoint(s). These results should be helpful in estimating reproductive success in translocation carriers undergoing PGD.

Analysis using fish of sperm and embryos from two carriers of rare rob(13;21) and rob(15;22) robertsonian translocation undergoing PGD

The majority of fluorescence in situ hybridization (FISH) studies on the meiotic segregation of Robertsonian translocations focus on the most common types, rob(13; 14) and rob(14; 21). Here we report the first study for carriers of rare Robertsonian translocations rob(13; 21) and rob(15; 22) combining analysis of meiotic segregation in sperm and blastomeres following pre-implantation genetic diagnosis (PGD). Dual-colour FISH was applied to nuclei from spermatozoa and blastomeres from PGD embryos using two subterminal contig probes for each translocation, and a second round with probes for chromosomes 16 and 18. Patient 1 had a rob(13; 21) and patient 2 had a rob(15; 22), and 86.3% and 87.5% of gametes respectively were consistent with meiotic segregation resulting in a normal or balanced chromosome complement. Analysis of embryos showed that for patient 1 and 2 respectively, 25% and 46% were balanced, and of the unbalanced embryos, 50% and 31% were mosaic or chaotic. Our patients with a rob(13; 21) and rob(15; 22) were found to have a similar meiotic segregation pattern to that for male carriers of the common Robertsonian translocations. The observed rate in unbalanced embryos being mosaic or chaotic may result in an increased risk of chromosomal abnormalities. Our results may help to improve the genetic counseling for carriers of rare Robertsonian translocations.

Preimplantation genetic diagnosis for couples with a Robertsonian translocation: practical information for genetic counseling

PURPOSE

To evaluate the proportions of abnormal and normal embryos detected by preimplantation genetic diagnosis (PGD) of infertile couples of whom one was a Robertsonian translocation (RT) carrier, and to provide practical information, including details of reproductive outcomes, to aid in genetic counseling of such couples.

METHODS

We retrospectively analyzed all PGD cycles conducted to deal with RT at our center between January 2000 and December 2009. Subject demographic and clinical data were compared with the results of PGD.

RESULTS

Employing PGD, we conducted a total of 66 cycles on 34 couples of whom one was an RT carrier, including 24 female and 10 male carriers. Of the 514 blastomeres tested, 161 (31.3%) were normal or balanced. Of the 57 cycles that included embryo transfer, 17 (29.8%) attained positivity for human chorionic gonadotropin (hCG). A total of 17 embryos were implanted and 16 babies, including two sets of twins, were born. The takehome baby rate was 41.2% per couple and the loss rate 6.6%. Receiver operating characteristic curve analysis showed that the proportion of alternate embryos associated with a sensitivity of 70.6% for prediction of clinical pregnancy following PGD was 0.31. Sex of the carrier and type of translocation were not significantly associated with pregnancy outcomes.

CONCLUSION

Couples with RT may benefit from PGD; pregnancy success rate is improved and embryo loss reduced. We found that about 30% of embryos were of normal or balanced chromosomal constitution and that the percentage of normal or balanced embryos was predictive of PGD outcome.

Reproductive outcome after PGD in couples with recurrent miscarriage carrying a structural chromosome abnormality: a systematic review

BACKGROUND

Preimplantation genetic diagnosis (PGD) has been stated to improve live birth rates compared with natural conception in couples with recurrent miscarriage (RM) carrying a structural chromosome abnormality. It is unclear to what extent this claim can be substantiated by evidence. A systematic review of the literature was performed on the reproductive outcome of these couples after natural conception or after PGD.

METHODS

MEDLINE, EMBASE and the Cochrane database were searched until April 2009. Trials, patient series and case reports describing reproductive outcome in couples with RM carrying a structural chromosome abnormality after natural conception and/or after PGD were included. Since no randomized controlled trials or non-randomized comparative studies were found, separate searches for both groups were conducted. Primary outcome measure was live birth rate per couple. Secondary outcome measure was miscarriage rate per couple.

RESULTS

Four observational studies reporting on the reproductive outcome of 469 couples after natural conception and 21 studies reporting on the reproductive outcome of 126 couples after PGD were found. After natural conception, live birth rate per couple varied between 33 and 60% (median 55.5%) after parental chromosome analysis; miscarriage rate ranged from 21 to 40% (median 34%). After PGD, live birth rate per couple varied between 0 and 100% (median 31%) after parental chromosome analysis; miscarriage rate ranged from 0 to 50% (median 0%).

CONCLUSIONS

Currently, there are insufficient data indicating that PGD improves the live birth rate in couples with RM carrying a structural chromosome abnormality.

PGD for reciprocal and Robertsonian translocations using array comparative genomic hybridization

BACKGROUND

Fluorescence in situ hybridization (FISH) is the most widely used method for detecting unbalanced chromosome rearrangements in preimplantation embryos but it is known to have several technical limitations. We describe the clinical application of a molecular-based assay, array comparative genomic hybridization (array-CGH), to simultaneously screen for unbalanced translocation derivatives and aneuploidy of all 24 chromosomes.

METHODS

Cell biopsy was carried out on cleavage-stage embryos (Day 3). Single cells were first lysed and DNA amplified by whole-genome amplification (WGA). WGA products were then processed by array-CGH using 24sure + arrays, BlueGnome. Balanced/normal euploid embryos were then selected for transfer on Day 5 of the same cycle.

RESULTS

Twenty-eight consecutive cycles of preimplantation genetic diagnosis were carried out for 24 couples carrying 18 different balanced translocations. Overall, 187/200 (93.5%) embryos were successfully diagnosed. Embryos suitable for transfer were identified in 17 cycles (60.7%), with transfer of 22 embryos (mean 1.3 ± 0.5). Twelve couples achieved a clinical pregnancy (70.6% per embryo transfer), with a total of 14 embryos implanted (63.6% per transferred embryo). Three patients delivered three healthy babies, during writing, the other pregnancies (two twins and seven singletons) are ongoing beyond 20 weeks of gestation.

CONCLUSIONS

The data obtained demonstrate that array-CGH can detect chromosome imbalances in embryos, also providing the added benefit of simultaneous aneuploidy screening of all 24 chromosomes. Array-CGH has the potential to overcome several inherent limitations of FISH-based tests, providing improvements in terms of test performance, automation, sensitivity and reliability.

First births after preimplantation genetic diagnosis of structural chromosome abnormalities using comparative genomic hybridization and microarray analysis

BACKGROUND

Balanced chromosomal rearrangements represent one of the most frequent indications for preimplantation genetic diagnosis (PGD). Although fluorescence in situ hybridization (FISH) has been successfully employed for diagnosis in such cases, this approach usually restricts assessment of the chromosomes involved in the rearrangement. Furthermore, with FISH-based strategies, it is sometimes necessary to create patient-specific protocols, increasing the waiting time and costs. In the current study, we explored the use of two comprehensive chromosome screening methods, conventional metaphase comparative genomic hybridization (CGH) and microarray-CGH (aCGH), as alternatives for PGD of chromosome rearrangements.

METHODS

The study included 16 patients who underwent 20 cycles of PGD for a variety of chromosome rearrangements (reciprocal or Robertsonian translocations or inversions). Testing was performed at various embryonic stages using CGH (9 cases) or aCGH (11 cases).

RESULTS

Results were obtained for 121 out of 132 samples (91.7%). Of the diagnosed samples, 48.8% were found to carry abnormalities associated with the rearrangement, either alone or in combination with other chromosomal abnormalities. A further 28.9% of samples were normal/balanced for the rearranged chromosomes, but affected by aneuploidy for other chromosomes. Only 22.3% of samples were chromosomally normal. Of the 15 patients who completed their treatment cycles, 5 became pregnant after one or two cycles resulting in four healthy births. The delivery rate per cycle was 21% (27% per embryo transfer).

CONCLUSIONS

This is the first study to describe the clinical application of comprehensive chromosome screening applied to polar bodies, blastomeres or trophectoderm cells from patients carrying inversions and translocations. Using these techniques, most patients requesting PGD for a chromosome rearrangement can be treated using a single protocol. Additionally, the detection of abnormalities affecting chromosomes unrelated to the rearrangement may assist in the selection of viable embryos for transfer.

Meiotic segregation of Robertsonian translocations ascertained in cleavage-stage embryos--implications for preimplantation genetic diagnosis

BACKGROUND

The aim of this study was to ascertain the prevalence of meiotic segregation products in embryos from carriers of 13/14 and 14/21 Robertsonian translocations and to estimate the predictive value of testing single cells using the fluorescence in situ hybridization (FISH) technique, to provide more information for decision-making about PGD.

METHODS

In this prospective cohort study, the copy number of translocation chromosomes in nuclei from lysed blastomeres of cleavage-stage embryos was ascertained using locus-specific FISH probes. Logistic regression analysis, controlling for translocation type, female age and fertility status, was used to calculate the odds ratio (OR) of unbalanced segregation products for female and male heterozygotes. The primary diagnostic measure was the predictive value of the test result. The primary outcome measure was the live birth rate per couple.

RESULTS

Female carriers were four times more likely than male carriers to produce embryos with an unbalanced translocation product (OR 3.8, 95% confidence interval 2.0-7.2, P < 0.001). The prevalence of abnormality for the chromosomes tested in embryos from female or male heterozygotes was estimated to be 43 or 28%, respectively, while estimates of the predictive value were 93-100 or 96-100% for a normal test result and 79 or 57% for an abnormal test result. The live birth rate per couple was 58% for female carriers and 50% for male carriers.

CONCLUSIONS

For female carriers, PGD using FISH could reduce the risk of miscarriage from either translocation or the risk of Down syndrome from the 14/21 Robertsonian translocation. PGD using FISH for male carriers is unlikely to be indicated given the relatively low prevalence of chromosome imbalance and low predictive value.

Male and female meiotic behaviour of an intrachromosomal insertion determined by preimplantation genetic diagnosis

BACKGROUND

Two related family members, a female and a male balanced carrier of an intrachromosomal insertion on chromosome 7 were referred to our centre for preimplantation genetic diagnosis. This presented a rare opportunity to investigate the behaviour of the insertion chromosome during meiosis in two related carriers. The aim of this study was to carry out a detailed genetic analysis of the preimplantation embryos that were generated from the three treatment cycles for the male and two for the female carrier.Patients underwent in vitro fertilization and on day 3, 22 embryos from the female carrier and 19 embryos from the male carrier were biopsied and cells analysed by fluorescent in situ hybridization. Follow up analysis of 29 untransferred embryos was also performed for confirmation of the diagnosis and to obtain information on meiotic and mitotic outcome.

RESULTS

In this study, the female carrier produced more than twice as many chromosomally balanced embryos as the male (76.5% vs. 36%), and two pregnancies were achieved for her. Follow up analysis showed that the male carrier had produced more highly abnormal embryos than the female (25% and 15% respectively) and no pregnancies occurred for the male carrier and his partner.

CONCLUSION

This study compares how an intrachromosomal insertion has behaved in the meiotic and preimplantation stages of development in sibling male and female carriers. It confirms that PGD is an appropriate treatment in such cases. Reasons for the differing outcome for the two carriers are discussed.

Characteristics of embryo development in Robertsonian translocations' preimplantation genetic diagnosis cycles

OBJECTIVE

To explore the embryo development characteristics in Robertsonian translocations (RTs) in their preimplantation genetic diagnosis (PGD) cycles.

METHOD

A total of 37 RT carrier couples underwent 41 blastomere PGD cycles from August 2005 to September 2008. The development of 272 embryos was analyzed in their PGD cycles.

RESULT(S)

At D3, there were 161 high-grade embryos, including 59 normal/balanced embryos and 102 abnormal embryos. There was no difference between the normal/balanced embryo group and the abnormal embryo group in terms of the high-grade embryo percentage (64.84% vs 56.35%, p = 0.179). However, at D5-D6, the blastocyst percentage in the normal/balanced embryo group was significantly higher than that in the abnormal embryo group (43.96% vs 20.44%, p = 0.000).

CONCLUSION(S)

Normal/balanced embryos developed better and a self-selective mechanism may exist in the RTs' embryos at the blastocyst formation stage.

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.

Role of Preimplantation Genetic Diagnosis (PGD) in Current Infertility Practice

Chromosome imbalances are the leading cause of pregnancy loss in humans and play major roles in male and female infertility. Within the past two decades, the development and application of preimplantation genetic diagnosis (PGD) has played an important role in infertility practices worldwide. The purpose of this review is to discuss, how PGD may be applied in combating numerical chromosomal abnormalities and in Robertsonian and reciprocal chromosome translocations. We shall consider prevalence and risk of each aberration, interchromosomal effects and rationale behind use of PGD in each case. Numerical chromosome abnormalities (aneuploidy and polyploidy) in particular affect a very high proportion of preimplantation embryos (~ 50%). Given that a majority of preimplantation embryos are aneuploid, PGD can be used to screen embryos and transfer euploid embryos to improve pregnancy rates and reduce spontaneous abortions. The rationale of utilize PGD to transfer only euploid embryos would seem sound, but controversies exist surrounding application of PGD for aneuploidy detection. To this end, we will discuss the dichotomy between favorable descriptive reports and less favorable randomized clinical trial data. This review will discuss the trend towards differing sources of embryonic DNA (e.g. polar body vs blastomere vs blastocyst) as well as development of novel technologies for 24 chromosomes analysis.

Cytogenetic determinants of male fertility

BACKGROUND

Cytogenetic abnormalities have been known to be important causes of male infertility for decades.

METHODS

Research publications from 1978 to 2008, from PubMed, have been reviewed.

RESULTS

These studies have greatly improved our information on somatic chromosomal abnormalities such as translocations, inversions and sex chromosomal anomalies, and their consequences to the cytogenetic make-up of human sperm. Also, we have learned that infertile men with a normal somatic karyotype have an increased risk of chromosomally abnormal sperm and children. New techniques such as single sperm typing and synaptonemal complex analysis have provided valuable insight into the association between meiotic recombination and the production of aneuploid sperm. These meiotic studies have also unveiled errors of chromosome pairing and synapsis, which are more common in infertile men.

CONCLUSIONS

These studies allow us to provide more precise information to infertile patients, and further our basic knowledge in the causes of male infertility.

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.

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.

Preimplantation genetic diagnosis for Down syndrome pregnancy

OBJECTIVE

To evaluate the effect of preimplantation genetic diagnosis (PGD) conducted for women who had Down syndrome pregnancy previously.

METHODS

Trisomy 21 was diagnosed by using fluorescence in site hybridization (FISH) before embryo transfer in two women who had Down syndrome pregnancies. Each received one or two PGD cycles respectively.

RESULTS

Case 1: one PGD cycle was conducted, two oocytes were fertilized and biopsied. One embryo is of trisomy 21 and the other of monosomy 21. No embryo was transferred. Case 2: two PGD cycles were conducted, in total, sixteen oocytes were fertilized and biopsied. Four embryos were tested to be normal, six of trisomy 21, and one of monosomy 21. Five had no signal. Four normal embryos were transferred but no pregnancy resulted.

CONCLUSION

For couples who had pregnancies with Down syndrome previously, PGD can be considered, and has been shown to be an effective strategy.

Five years’ experience of preimplantation genetic diagnosis in the Parisian Center: outcome of the first 441 started cycles

OBJECTIVE

To investigate the evolution of techniques and strategies and to evaluate the results of preimplantation genetic diagnosis (PGD) from January 2000 to December 2004 in chromosomal, monogenic and mitochondrial DNA disorders treated at our institution.

DESIGN

Retrospective study.

SETTING

Single French Parisian PGD center.

PATIENT(S)

Patients at risk of transmitting a serious genetic disorder to their offspring.

INTERVENTION(S)

171 couples enrolled in the program undergoing stimulated and frozen embryo replacement cycles with PGD.

MAIN OUTCOME MEASURE(S)

Results of the 441 first PGD cycles performed for various genetic conditions.

RESULT(S)

During 5 years, 416 stimulation and 25 frozen embryo replacement cycles were started, among which 52 clinical and 47 ongoing pregnancies occurred. In stimulation cycles, the overall ongoing pregnancy rate was 24% per embryo transfer, 11% per started cycle, and 27% per couple. The implantation rate was 16%.

CONCLUSION(S)

These encouraging results demonstrate that PGD might be considered as a valid alternative to prenatal diagnosis. Nevertheless, couples referred for PGD must be selected and counseled appropriately, considering the complexity of the treatment and the relatively low take-home baby rate.

A retrospective study of preimplantation embryos diagnosed with monosomy by fluorescence in situ hybridization (FISH)

This report is a retrospective study of preimplantation embryos diagnosed with monosomy for chromosomes 13, 15, 16, 18, 21, 22, X and Y on day 3 to determine the rate of true positives, false positives and/or mosaicism and to assess if these embryos are suitable for in vitro fertilization (IVF) transfer. In a one year period, 80 patients went through preimplantation genetic diagnosis for aneuploidy screening (PGD-AS). Monosomy was diagnosed in 51 embryos. Fluorescence in situ hybridization (FISH) was then performed on the blastomeres at day 5-7 with commercially available probes using the same probe set that initially identified monosomy for chromosomes 13, 16, 21 and 22 or chromosomes 15, 18, X and Y. Based on FISH analysis, the monosomy diagnosed during routine PGD-AS analysis was confirmed in 17 of the 51 embryos. A euploid result for the specific chromosomes tested was observed in 16 of the 51 embryos while mosaicism was found in the remaining 18 embryos. This results in an estimated false positive rate of 3.8% for a diagnosis of monosomy. Reanalysis of these embryos demonstrates that the majority of monosomy diagnoses represents true monosomy or mosaicism and should be excluded for transfer in IVF. Furthermore, improved understanding from recent emerging data regarding the fate of oocytes in women with advanced maternal age undergoing IVF to the development of early embryos may provide a valuable insight into the mechanism of chromosome mosaicism.

Rare Robertsonian translocations and meiotic behaviour: sperm FISH analysis of t(13;15) and t(14;15) translocations: a case report

t(13;15) and t(14;15) are two rare Robertsonian translocations. Meiotic segregation was studied in four males heterozygous for the rare Robertsonian translocations t(13;15) and t(14;15). Both locus-specific probes (LSPs) and whole chromosome painting (WCP) probes, specific to chromosomes 13, 14 and 15, were used in this study. The number of spermatozoa scored for each carrier ranged from 891 to 5000. The frequencies of normal and balanced sperm resulting from the alternate mode of segregation ranged from 77.6 to 92.8%, confirming the prevalence of alternate segregation over other segregation modes in all Robertsonian translocations. The incidences of unbalanced complements ranged from 6.7 to 20.4%, with a significant excess of disomy rates over the complementary frequencies of nullisomy. This variability might reflect differences in the location of breakpoints in translocated chromosomes, leading to the variable production of unbalanced gametes and the variable alterations of semen parameters in Robertsonian translocation carriers.

Chromosomal segregation in spermatozoa of 14 Robertsonian translocation carriers

Male carriers of Robertsonian (Rob) translocations can have fertility problems associated with low sperm counts and abnormal sperm morphology. In this study, spermatozoa from 14 Rob translocation carriers, seven der(13;14), two der(13;15), two der(14;15), two der(14;21) and one der(21;22), were tested by fluorescence in-situ hybridization (FISH) for the chromosomes involved, to study meiotic segregation behaviour. It was shown that in each type of Rob translocation, meiotic segregation behaviour is similar, comparable and occurs non-randomly. Most of the spermatozoa results from alternate segregation (range: 76-89.47%). There is, however, still much unbalanced spermatozoa resulting from adjacent segregation mode (range: 10.24-23.41%). These data provide useful information for genetic counselling purposes. Moreover, aneuploidy for chromosomes 13,18, 21, X and Y was studied in five patients and suggested an inter-chromosomal effect.

Indications et résultats du diagnostic pré-implantatoire (DPI)

OBJECTIVE

To report the results of preimplantation genetic diagnosis (PGD) cycles performed in our unit from 2000 to 2004. Materials and methods. One hundred and seventy-one couples were enrolled in the PGD program over this period. The collected oocytes were inseminated by intracytoplasmic sperm injection (ICSI). The resulting embryos were biopsied on the third day of development and the genetic analysis was performed on the same day. Embryo transfers were carried out on the fourth day.

RESULTS

The 416 stimulation cycles started yielded 280 oocyte pick-ups, 3506 oocytes retrieved, of which 2966 were suitable for ICSI. Among the 1982 embryos obtained, 1337 embryos were biopsied and genetic diagnosis was performed for 1083 (81%) of them. 381 embryos were transferred during the course of 189 transfer procedures. There were 51 clinical and 46 ongoing (35 single, 11 twin) pregnancies. In addition, 25 frozen embryo replacement cycles were initiated, leading to 6 embryo transfers and 1 ongoing pregnancy. A total of 58 unaffected children were born.

CONCLUSION

PGD has gained a place among the choices offered to couples at risk of transmission of a serious and incurable genetic disease. It might be a realistic alternative to prenatal diagnosis for patients carrier of chromosomal rearrangements, single gene defects, X-linked disesases or mitochondrial DNA disorders.

The importance of aneuploidy screening in reciprocal translocation carriers

The purpose of this study is to investigate the aneuploidy rate and the mosaicism of chromosomes not involved in reciprocal translocations. Aneuploidy screening (AS) (13, 16, 18, 21 and 22) was performed as a re-analysis on fixed blastomeres from 126 embryos already analysed in preimplantation genetic diagnosis (PGD) cycles of eight female and five male reciprocal translocation carriers who had not achieved a pregnancy. A successful diagnosis for AS was achieved in 91.3% of embryos; 30.9% were euploid and 60.3% were aneuploid for the five chromosomes analysed. Of the embryos, 8.7% were euploid for AS and normal-balanced for the translocation and 22.2% were euploid for AS but unbalanced for the translocation; 8% of the embryos were aneuploid for AS but normal-balanced for the translocation and 52.4% were aneuploid for AS and also unbalanced for the translocation. At least 58.7% of the embryos were mosaic regarding mosaicism for the chromosomes involved and not involved in the translocations. Six of the 16 embryos transferred in the PGD cycles were aneuploid for the AS study; four of them were also mosaics. AS should be performed in reciprocal translocation carriers after segregation analysis in PGD.

Mechanisms of aneuploidy induction in human oogenesis and early embryogenesis

The mechanisms of aneuploidy induction in human oogenesis mainly involve nondisjunction arising during the first and second meiotic divisions. Nondisjunction equally affects both whole chromosomes and chromatids, in the latter case it is facilitated by "predivision" or precocious centromere division. Karyotyping and CGH studies show an excess of hypohaploidy, which is confirmed in studies of preimplantation embryos, providing evidence in favour of anaphase lag as a mechanism. Preferential involvement of the smaller autosomes has been clearly shown but the largest chromosomes are also abnormal in many cases. Overall, the rate of chromosomal imbalance in oocytes from women aged between 30 and 35 has been estimated at 11% from recent karyotyping data but accruing CGH results suggest that the true figure should be considerably higher. Clear evidence has been obtained in favour of germinal or gonadal mosaicism as a predisposing factor. Constitutional aneuploidy in embryos is most frequent for chromosomes 22, 16, 21 and 15; least frequently involved are chromosomes 14, X and Y, and 6. However, embryos of women under 37 are far more likely to be affected by mosaic aneuploidy, which is present in over 50% of 3-day-old embryos. There are two main types, diploid/aneuploid and chaotic mosaics. Chaotic mosaics arise independently of maternal age and may be related to centrosome anomalies and hence of male origin. Aneuploid mosaics most commonly arise by chromosome loss, followed by chromosome gain and least frequently by mitotic nondisjunction. All may be related to maternal age as well as to lack of specific gene products in the embryo. Partial aneuploidy as a result of chromosome breakage affects a minimum of 10% of embryos.

Preimplantation genetic diagnosis significantly improves the pregnancy outcome of translocation carriers with a history of recurrent miscarriage and unsuccessful pregnancies

Preimplantation genetic diagnosis (PGD) for translocations has been shown to significantly reduce the risk of recurrent miscarriage, but because the majority of embryos produced are unbalanced, pregnancy rate is relatively low since 20% or more cycles have no normal or balanced embryos to transfer. The purpose of this study was to evaluate whether PGD could improve pregnancy outcome in translocation carriers with a history of two or more consecutive miscarriages and no live births. PGD for translocations was offered to translocation carriers with two or more previous miscarriages (average 3.5) and no live births (0/117 pregnancies) using a combination of distal and proximal probes to the breakpoints. After PGD, only 18.3% of embryos were normal or balanced. Only 5.3% of pregnancies were lost after PGD compared with 100% before PGD (P < 0.001). The cumulative pregnancy rate was 57.6% and the cumulative ongoing pregnancy rate was 54.5% in the short period of time of 1.24 IVF cycles, or 46.3% and 43.9% respectively per cycle. In conclusion, PGD significantly reduced losses and increased the number of viable pregnancies (P < 0.001). IVF plus PGD are a faster method of conceiving a live child than natural conception, at least for translocation carriers with recurrent miscarriages and no previous live births.

Embryo aneuploidy screening for repeated implantation failure and unexplained recurrent miscarriage

Among other factors, chromosomal abnormalities that originate from gametogenesis and preimplantation embryonic development are thought to be one of the major contributing factors for early embryonic death and failure of pregnancy. However, so far, no non-invasive technique exists that allows the detection of the chromosomal complement of an oocyte or a developing embryo as a whole. Rather, by removing polar bodies/blastomeres, recent developments on preimplantation genetic diagnosis for aneuploidy screening (PGD-AS) have paved the way to detect and possibly eliminate the majority of chromosomally abnormal embryos, thereby increasing the chance of a healthy pregnancy. This article summarizes the origin and impact of chromosomal abnormalities on human reproduction in cases with repeated implantation failure (RIF) and unexplained recurrent miscarriage. It also discusses recent advances regarding the possible benefits of PGD-AS in such cases.

Validation of DNA probes for preimplantation genetic diagnosis (PGD) by fluorescencein situ hybridization (FISH) R1

BACKGROUND

Preimplantation genetic diagnosis (PGD) by fluorescence in situ hybridization (FISH) is being employed increasingly by medical centers and private companies. Validation of any clinical assay, particularly one with novel applications such as PGD by FISH, is of critical importance in the clinical setting. This importance is recognized by both the College of American Pathologists (CAP) and the American College of Medical Genetics (ACMG), who recommend validation of FISH assays in the clinical setting. Validation of FISH assays for PGD is especially significant, as only one or two cells (blastomeres) will be available for testing of a given embryo.

METHODS

We have developed validation protocols for a variety of FISH assays, including sex identification, structural chromosomal aneusomy, and aneuploidy screening with the Vysis, Inc., PGT probe panel.

RESULTS

Our validation results show good individual performance of commercially available probes, and decreasing overall efficiency as the number of probes included in an assay increases.

Analysis of chromosome segregation during preimplantation genetic diagnosis in both male and female translocation heterozygotes

Individuals carrying translocations suffer from reduced fertility or spontaneous abortions and seek help in form of assisted reproductive technology (ART) and preimplantation genetic diagnosis (PGD). While most translocations are relatively easy to detect in metaphase cells, the majority of embryonic cells biopsied in the course of in vitro fertilization (IVF) procedures are in interphase. These nuclei are thus unsuitable for analysis by chromosome banding or painting using fluorescence in situ hybridization (FISH). Thus several methods have been devised to detect translocation imbalance through FISH in single cells for purpose of PGD, among them polar body chromosome painting, interphase FISH with combination of subtelomeric and centromeric probes, breakpoint spanning probes, and cell conversion. Results with PGD indicate a significant decrease in spontaneous abortions, from 81% before PGD to 13% after PGD. They also indicate very high rates of chromosome abnormalities in embryos from translocation carriers, 72% for Robertsonian translocations and 82% for reciprocal translocations. Sperm analysis was found to be a good predictor of IVF and PGD outcome, with samples with more than 60% abnormal forms indicating poor prognosis. Similarly, the predictability from first PGD cycle results for future cycles was 90%. In summary, PGD can help translocation carriers to achieve viable pregnancies, but the success of the process is conversely related to the baseline of unbalanced gametes.

An update in recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA) is defined as three or more consecutive pregnancy losses prior to the 20th week of gestation. The etiology of recurrent spontaneous abortion is often unclear and may be multifactorial, with much controversy regarding diagnosis and treatment. Reasonably accepted etiologic causes include, genetics, anatomical, endocrine, placental anomalies, hormonal problems, infection, smoking and alcohol consumption, exposure to environmental factors, psychological trauma and stressful life event, certain coagulation and immunoregulatory protein defects. Detection of an abnormality in any of these areas may result into specific therapeutic measures, with varying degrees of success. However, the majority of cases of RSA remains unexplained and is found to be associated with certain autoimmune (APA, ANA, ACA, ATA, AECA) and alloimmune (APCA, Ab2, MLR-Bf) antibodies that may play major role in the immunologic failure of pregnancy and may lead to abortion. Alteration in the expression of HLA-G molecules, T-helper-1 (Th-1) pattern of cytokines and natural killer (NK) cells activity may also induce abortion. Various forms of treatment like antithrombotic therapies such as aspirin and heparin, intravenous immunoglobulin (IVIg) therapy, immunotherapy with paternal lymphocytes and vitamin D3 therapy are effective mode of treatment for unexplained cause of fetal loss in women with RSA.

Sperm segregation analysis of a (13;22) Robertsonian translocation carrier by FISH: a comparison of locus-specific probe and whole chromosome painting

BACKGROUND

The t(13;22) Robertsonian translocation constitutes a rare form of rearrangement between acrocentric human chromosomes. Most of the meiotic segregation studies of human Robertsonian translocations have been performed on common t(13;14) and t(14;21) translocations. Analysis of the chromosomal constitution in sperm of Robertsonian translocation carriers is of great interest for assessing the risk of unbalanced forms and adapting genetic counselling. In the present study, we present the first meiotic segregation study of a t(13;22) Robertsonian translocation in human sperm.

METHODS

A total of 11 787 sperm nuclei were scored using two distinct FISH labelling techniques, i.e. the locus-specific probes (LSI) method and the whole chromosome painting (WCP) technique.

RESULTS

The frequency of normal or balanced sperm resulting from alternate meiotic segregation was 86%. Incidences of unbalanced complements resulting from adjacent segregation modes were 12.79% and 14.36% in LSI and WCP assays, respectively. No significant excess of nullisomy or disomy for the affected chromosomes was observed.

CONCLUSIONS

Similar results in segregation were obtained with the two techniques, demonstrating the efficiency of the two strategies for the direct segregation analysis of Roberstsonian translocations. The results obtained indicated a moderate meiotic production of imbalance. This study shows that the rare Robertsonian translocation (13;22) displays a similar distribution of balanced and unbalanced sperm patterns as the common Robertsonian translocations previously studied. This suggests that the behaviour of acrocentric chromosomes was similar in all cases of centric fusion.

Genetics and assisted reproduction technology

In the past 20 years, a significant improvement has been shown in the treatment for infertility in both women and men through the development of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). Only donated sperm could be previously used for treatment; now oocytes can also be donated. Furthermore, the combination of IVF and ICSI with advanced genetic methods has made preimplantation genetic diagnosis possible for many genetic conditions. These methods enable genetic testing of the early human embryo by using only a single cell, one blastomere biopsied from the embryo, as the sample from which the diagnosis of many chromosome rearrangements and other inherited diseases can be made. It has also been established that a considerable proportion of infertility is caused by genetic defects, which have several implications for infertility treatment. The purpose of this review is to give a concise introduction on how genetics is involved in assisted reproduction technology to specialists who may not be working in this particular field of gynecology, but who would need some knowledge of this for proper care of their patients.