Complete cytogenetic investigation of oocytes from a young cancer patient with the use of comparative genomic hybridisation reveals meiotic errors

Does ICSI for in vitro fertilization cause more aneuploid embryos?

Background

High proportion of human embryos produced by in vitro fertilization (IVF) is aneuploidy. Many factors are related to the prevalence of embryonic aneuploidies, such as maternal age, sperm quality, and in vitro manipulation of oocytes. Oocytes are usually inseminated by intracytoplasmic sperm injection (ICSI) procedures for preimplantation genetic testing. There is still no available information whether insemination procedures, regular IVF or ICSI, affect embryonic aneuploidies.

Methods

In this case report, a patient at her age of 47 years old received donated oocytes from a young donor for infertility treatment. Half of oocytes were inseminated by regular IVF and other half of oocytes were inseminated by ICSI. Fertilized oocytes were cultured to blastocyst stage and then biopsied for preimplantation genetic testing for aneuploidies (PGT-A). The proportions of aneuploidies were compared between two insemination procedures.

Results

Forty-seven oocytes were retrieved, 23 were inseminated by regular IVF and 24 were removed from enclosed cumulus cells for ICSI. Out of 24 oocytes, 21 oocytes at metaphase II were inseminated by ICSI. After fertilization assessment, it was found that 12 oocytes from regular IVF fertilized normally. Nine blastocysts (75%) were biopsied and 1 (11.1%) was aneuploidy. By contrast, 19 out of 21 oocytes inseminated by ICSI fertilized normally, 14 blastocysts (73.7%) were obtained and 7 (50.0%) were aneuploidy. Transfer of a euploid blastocyst from regular IVF resulted in a healthy baby delivery.

Conclusion

These results indicate that more embryos produced by ICSI are aneuploidy as compared with embryos produced by regular IVF. The results indicate that in vitro manipulation of oocytes for ICSI procedure may have adverse effect on human oocytes, and it may be one of the reasons causing aneuploid embryos in human IVF.

Earlier day of blastocyst development is predictive of embryonic euploidy across all ages: essential data for physician decision-making and counseling patients

PURPOSE

The purpose of this study is to evaluate whether day of blastocyst development is associated with embryo chromosomal status as determined by high-density oligonucleotide microarray comparative genomic hybridization (aCGH).

METHODS

This is a retrospective cohort analysis, including women who underwent in vitro fertilization (IVF) with trophectoderm biopsy at a single private fertility center from January 2014 to December 2014. Repeat cycles were excluded. Cycles were assessed for percentage of blastocysts biopsied on days 5, 6, or 7 and rate of euploid embryos per cycle. Cycles were stratified by Society for Assisted Reproductive Technology (SART) age groups (< 35, 35-37, 38-40, 41-42, > 42) and by donor status.

RESULTS

A total of 388 IVF cycles and 2132 biopsied blastocysts were evaluated. The percentages of blastocysts biopsied on days 5, 6, and 7 were 62.5, 35.8, and 1.7%, respectively. Blastocyst euploid rates on days 5, 6, and 7 were 49.5, 36.5, and 32.9%, respectively. Earlier blastocyst development was associated with a significantly increased euploid rate (p < 0.0001). Younger maternal age (p < 0.0001) and higher number of blastocysts biopsied per patient (p = 0.0063) were both independently associated with greater percentage of euploidy.

CONCLUSIONS

Earlier blastocyst development is independently associated with a higher likelihood of embryonic euploidy in both autologous and donor embryos. In non-biopsied embryos, these data support selection of day 5 blastocysts for transfer over later-developing embryos. These results can assist with patient counseling regarding expectations and outcomes. To our knowledge, this is the first study to examine embryonic euploidy as stratified by both day of blastocyst development and SART age group.

Microarray analysis reveals abnormal chromosomal complements in over 70% of 14 normally developing human embryos

STUDY QUESTION

What are the aneuploidy rates and incidence of mosaicism in good-quality human preimplantation embryos.

SUMMARY ANSWER

High-level mosaicism and structural aberrations are not restricted to arrested or poorly developing embryos but are also common in good-quality IVF embryos.

WHAT IS KNOWN ALREADY

Humans, compared with other mammals, have a poor fertility rate, and even IVF treatments have a relatively low success rate. It is known that human gametes and early preimplantation embryos carry chromosomal abnormalities that are thought to lower their developmental potential.

STUDY DESIGN, SIZE AND DURATION

The embryos studied came from nine young (age <35 years old) IVF patients and were part of a cohort of embryos that all resulted in healthy births. These 14 embryos inseminated by ICSI and cryopreserved on Day 2 of development were thawed, cultured overnight and allowed to succumb by being left at room temperature for 24 h. Following removal of the zona pellucida, blastomeres were disaggregated and collected.

PARTICIPANTS/MATERIALS, SETTING AND METHODS

There were 91 single blastomeres collected and amplified by multiple displacement amplification. Array-comparative genomic hybridization was performed on the amplified DNA. Array-data were normalized and aneuploidy was detected by the circular binary segmentation method.

MAIN RESULTS AND THE ROLE OF CHANCE

The good-quality embryos exhibited high rates of aneuploidy, 10 of 14 (71.4%) of the embryos being mosaic. While none of the embryos had the same aneuploidy pattern in all cells, 4 of 14 (28.6%) were uniformly diploid. Of the 70 analysed blastomeres, 55.7% were diploid and 44.3% had chromosomal abnormalities, while 29% of the abnormal cells carried structural aberrations.

WIDER IMPLICATIONS OF THE FINDINGS

Finding such a high rate of aneuploidy and mosaicism in excellent quality embryos from cycles with a high implantation rate warrants further research on the origin and significance of chromosomal abnormalities in human preimplantation embryos.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by the Instituut voor de aanmoediging van innovatie door Wetenschap en Technologie in Vlaanderen (IWT-Vlaanderen). A.M. is a PhD student at the IWT-Vlaanderen. C.S. is a postdoctoral fellow at the FWO Vlaanderen. There are no competing interests.

Mutations in the sarcosine dehydrogenase gene in patients with sarcosinemia

Sarcosinemia is an autosomal recessive metabolic trait manifested by relatively high concentrations of sarcosine in blood and urine. Sarcosine is a key intermediate in 1-carbon metabolism and under normal circumstances is converted to glycine by the enzyme sarcosine dehydrogenase. We encountered six families from two different descents (French and Arab), each with at least one individual with elevated levels of sarcosine in blood and urine. Using the "candidate gene approach" we sequenced the gene encoding sarcosine dehydrogenase (SARDH), which plays an important role in the conversion of sarcosine to glycine, and found four different mutations (P287L, V71F, R723X, R514X) in three patients. In an additional patient, we found a uniparental disomy in the region of SARDH gene. In two other patients, we did not find any mutations in this gene. We have shown for the first time that mutations in the SARDH gene are associated with sarcosinemia. In addition, our results indicate that other genes are most probably involved in the pathogenesis of this condition.

Screening of human pluripotent stem cells using CGH and FISH reveals low-grade mosaic aneuploidy and a recurrent amplification of chromosome 1q

Pluripotency and proliferative capacity of human embryonic stem cells (hESCs) make them a promising source for basic and applied research as well as in therapeutic medicine. The introduction of human induced pluripotent cells (hiPSCs) holds great promise for patient-tailored regenerative medicine therapies. However, for hESCs and hiPSCs to be applied for therapeutic purposes, long-term genomic stability in culture must be maintained. Until recently, G-banding analysis was considered as the default approach for detecting chromosomal abnormalities in stem cells. Our goal in this study was to apply fluorescence in-situ hybridization (FISH) and comparative genomic hybridization (CGH) for the screening of pluripotent stem cells, which will enable us identifying chromosomal abnormalities in stem cells genome with a better resolution. We studied three hESC lines and two hiPSC lines over long-term culture. Aneuploidy rates were evaluated at different passages, using FISH probes (12,13,16,17,18,21,X,Y). Genomic integrity was shown to be maintained at early passages of hESCs and hiPSCs but, at late passages, we observed low rates mosaiciam in hESCs, which implies a direct correlation between number of passages and increased aneuploidy rate. In addition, CGH analysis revealed a recurrent genomic instability, involving the gain of chromosome 1q. This finding was detected in two unrelated cell lines of different origin and implies that gains of chromosome 1q may endow a clonal advantage in culture. These findings, which could only partially be detected by conventional cytogenetic methods, emphasize the importance of using molecular cytogenetic methods for tracking genomic instability in stem cells.

Whole-chromosome aneuploidy analysis in human oocytes: focus on comparative genomic hybridization

The study of aneuploidy in human oocytes, discarded from IVF cycles, has provided a better understanding of the incidence of aneuploidy of female origin and the responsible mechanisms. Comparative genomic hybridization (CGH) is an established technique that allows for the detection of aneuploidy in all chromosomes avoiding artifactual chromosome losses. In this review, results obtained using CGH in single cells (1PB and/or MII oocytes) are included. The results of oocyte aneuploidy rates obtained by CGH from discarded oocytes of IVF patients and of oocyte donors are summarized. Moreover, the mechanisms involved in the aneuploid events, e.g. whether alterations occurred due to first meiotic errors or germ-line mitotic errors are also discussed. Finally, the incidence of aneuploid oocyte production due to first meiotic errors and germ-line mitotic errors observed in oocytes coming from IVF patients and IVF oocyte donors was assessed.

PGD for monogenic disorders: aspects of molecular biology

Preimplantation genetic diagnosis (PGD) for monogenic diseases has known a considerable evolution since its first application in the early 1990s. Especially the technical aspects of the genetic diagnosis itself, the single-cell genetic analysis, has constantly evolved to reach levels of accuracy and efficiency nearing those of genetic diagnosis on regular DNA samples. In this review, we will focus on the molecular biological techniques that are currently in use in the most advanced centers for PGD for monogenic disorders, including multiplex polymerase chain reaction (PCR) and post-PCR diagnostic methods, whole genome amplification (WGA) and multiple displacement amplification (MDA). As it becomes more and more clear that when it comes to ethically difficult indications, PGD goes further than prenatal diagnosis (PND), we will also briefly discuss ethical issues.

Whole genome amplification from a single cell: a new era for preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) is a technique used for determining the genetic status of a single cell biopsied from embryos or oocytes. Genetic analysis from a single cell is both rewarding and challenging, especially in PGD. The starting material is very limited and not replaceable, and the diagnosis has to be made in a very short time. Different whole genome amplification (WGA) techniques have been developed to specifically increase the DNA quantities originating from clinical samples with limited DNA contents. In this review, currently available WGA techniques are introduced and, among them, multiple displacement amplification (MDA) is discussed in detail. MDA generates abundant assay-ready DNA to perform broad panels of genetic assays through its ability to rapidly amplify genomes from single cells. The utilization of MDA for single-cell molecular analysis is expanding at a high rate, and MDA is expected to soon become an integral part of PGD.

Increased susceptibility to maternal aneuploidy demonstrated by comparative genomic hybridization analysis of human MII oocytes and first polar bodies

Single cell comparative genomic hybridization (CGH) was employed to extensively investigate 24 unfertilized or in vitromatured meiosis II oocytes and their corresponding first polar bodies (PBs), to determine how and whether all 23 chromosomes participate in female meiosis I errors and to accurately estimate the aneuploidy rate in the examined cells. Results were obtained for 15 oocytes and 16 PBs, representing 23 eggs (MII oocyte-PB complexes) donated from 15 patients (average age 32.2 years). Abnormalities were detected in ten eggs, giving an overall aneuploidy rate of 43.5%. In all, fourteen anomalies were scored, with the fertilized oocyte being at risk of monosomy in eight cases and at risk of trisomy in six; chromosomes of various sizes participated. CGH was able to give a comprehensive aneuploidy rate, as both absence of chromosomal material and the presence of extra copies were accurately scored. The aneuploidy mechanisms determined were: classical whole univalent non-disjunction; chromatid predivision prior to anaphase I, leading to metaphase II imbalance. There was also evidence of germinal mosaicism for a trisomic cell line. Three patients appeared to be predisposed to meiosis I errors, based on the presence of either multiple abnormalities in one or more of their examined cells, or of the same type of abnormality in all of their cells. Exclusion of these susceptible patients reduces the aneuploidy rate to 20%. Various hypotheses are put forward to explain these observations in order to stimulate research into the complex nature of female meiotic regulation.