Preimplantation diagnosis after assisted reproduction techniques for genetically-determined male infertility

The origin, mechanisms, incidence and clinical consequences of chromosomal mosaicism in humans

BACKGROUND

Chromosomal mosaicism, the presence of two or more distinct cell lines, is prevalent throughout human pre- and post-implantation development and can lead to genetic abnormalities, miscarriages, stillbirths or live births. Due to the prevalence and significance of mosaicism in the human species, it is important to understand the origins, mechanisms and incidence of mosaicism throughout development.

METHODS

Literature searches were conducted utilizing Pubmed, with emphasis on human pre- and post-implantation mosaicism.

RESULTS

Mosaicism persists in two separate forms: general and confined. General mosaicism is routine during human embryonic growth as detected by preimplantation genetic screening at either the cleavage or blastocyst stage, leading to mosaicism within both the placenta and fetus proper. Confined mosaicism has been reported in the brain, gonads and placenta, amongst other places. Mosaicism is derived from a variety of mechanisms including chromosome non-disjunction, anaphase lagging or endoreplication. Anaphase lagging has been implicated as the main process by which mosaicism arises in the preimplantation embryo. Furthermore, mosaicism can be caused by any one of numerous factors from paternal, maternal or exogenous factors such as culture media or possibly controlled ovarian hyperstimulation during in vitro fertilization (IVF). Mosaicism has been reported in as high as 70 and 90% of cleavage- and blastocyst-stage embryos derived from IVF, respectively.

CONCLUSIONS

The clinical consequences of mosaicism depend on which chromosome is involved, and when and where an error occurs. Mitotic rescue of a meiotic error or a very early mitotic error will typically lead to general mosaicism while a mitotic error at a specific cell lineage point typically leads to confined mosaicism. The clinical consequences of mosaicism are dependent on numerous aspects, with the consequences being unique for each event.

Chromosomal abnormalities in spontaneous abortion after assisted reproductive treatment

BACKGROUND

We evaluated cytogenetic results occurring with first trimester pregnancy loss, and assessed the type and frequency of chromosomal abnormalities after assisted reproductive treatment (ART) and compared them with a control group. We also compared the rate of chromosomal abnormalities according to infertility causes in ICSI group.

METHODS

A retrospective cohort analysis was made of all patients who were referred to the Genetics Laboratory of Fertility Center of CHA Gangnam Medical Center from 2005 to 2009 because of clinical abortion with a subsequent dilation and evacuation (D&E) performed, and patients were grouped by type of conception as follows: conventional IVF (in vitro fertilization) (n = 114), ICSI (intracytoplasmic sperm injection) (n = 140), and control (natural conception or intrauterine insemination [IUI]) (n = 128). Statistical analysis was performed using SPSS software.

RESULTS

A total 406 specimens were referred to laboratory, ten abortuses were excluded, and in 14 cases, we did not get any spontaneous metaphase, chromosomal constitutions of 382 specimens were successfully obtained with conventional cytogenetic methods. Overall, 52.62% of the miscarriages were found to be cytogenetically abnormal among all patients, the frequency was 48.4% in the control group, 54.3% of miscarriages after ICSI and 55.3% after conventional IVF (p = 0.503). The most prevalent abnormalities were autosomal trisomy, however, nine (11.69%) sex chromosome aneuploidy were noted in the ICSI group vs. four (6.45%) and two (3.23%) cases in the conventional IVF group and control group. We compared chromosomal abnormalities of miscarriages after ICSI according to infertility factor. 55.71% underwent ICSI due to male factors, 44.29% due to non-male factors. ICSI group having male factors showed significantly higher risk of chromosomal abnormalities than ICSI group having non-male factors (65.8% vs. 34.2%, p = 0.009, odds ratio = 1.529, 95% CI = 1.092-2.141).

CONCLUSIONS

There is no increased risk of chromosomal abnormalities due to ART was found with the exception of a greater number of sex chromosomal abnormalities in the ICSI group with male factor infertility. Therefore, these alterations could be correlated with the underlying parental risk of abnormalities and not with the ICSI procedure itself.

Prognostic factors for preimplantation genetic screening in repeated pregnancy loss

The objective of this study was to identify specific subgroups of recurrent pregnancy loss (RPL) patients of unknown aetiology in whom the selection of chromosomally normal embryos for transfer improves reproductive outcome in preimplantation genetic screening (PGS). A total of 428 PGS cycles were included and chromosomes 13, 15, 16, 18, 21, 22, X and Y were evaluated. In RPL patients < or =37 years, a lower incidence of chromosomal abnormalities (P = 0.0004) and miscarriages (P = 0.0283) was observed, and there were significantly higher pregnancy (P < 0.0384) and implantation (P < 0.0434) rates than in patients >37 years. In the former subset, results showed: (i) significantly higher implantation rates (P = 0.0411) in couples that had experienced a previous aneuploid miscarriage; (ii) similar aneuploidy, pregnancy and implantation rates in couples suffering previous miscarriages during fertility treatments and in those with previous spontaneous pregnancies; (iii) no miscarriages after PGS in couples in whom a fluorescence in-situ hybridization assay showed the male partner's sperm to be abnormal; and (iv) lower implantation rates in couples with > or =5 previous miscarriages, associated with a lower percentage of chromosomally abnormal embryos. It is concluded that PGS is to be strongly recommended when RPL is associated with miscarriages during infertility treatments, chromosomopathy in a previous miscarriage, up to five previous miscarriages and a high incidence of chromosomal abnormalities in spermatozoa.

No beneficial effect of preimplantation genetic screening in women of advanced maternal age with a high risk for embryonic aneuploidy

BACKGROUND

Human preimplantation embryos generated through in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) treatments show a variable rate of numerical chromosome abnormalities or aneuploidies. Preimplantation genetic screening (PGS) has been designed to screen for aneuploidies in high risk patients, with the aim of improving live birth rates in IVF/ICSI. We assessed whether the effect of PGS on live births rates differs in women of advanced maternal age with variable risks for embryonic aneuploidy, and weighed these effects against the results obtained after IVF/ICSI without PGS.

METHODS

The effect of PGS on live birth rates was compared between groups defined by maternal age, number of previous miscarriages, semen quality, total amount of recombinant FSH (rFSH) administered during ovarian stimulation and total number of top-quality embryos, using data from a randomized controlled trial among women of advanced maternal age (35-41 years).

RESULTS

There was no significant differential effect of PGS in groups based on maternal age (P-value of interaction 0.16), the number of previous miscarriages (P-value of interaction 0.93), semen quality (P-value of interaction 0.26), rFSH dose (P-value of interaction 0.15) or the number of top-quality embryos (P-value of interaction 0.59). Live birth rates after IVF/ICSI with PGS were lower in all groups when compared with live birth rates after IVF/ICSI without PGS.

CONCLUSIONS

The paradigm that the effect of PGS is determined by a woman's risk for embryonic aneuploidy seems incorrect. In fact, PGS has no clinical benefit over standard IVF/ICSI in women of advanced maternal age regardless of their risk for embryonic aneuploidy.

Chromosome topology in normal and aneuploid blastomeres from human embryos

OBJECTIVES

To find whether chromosomes 13, 16, 18, 21, 22, X and Y in blastomeres of human embryos are nonrandomly localized, whether their aneuploidy affects their localization and if eventual early inactivation of chromosome X with peripheral localization is present.

METHODS

Relative distances from the nucleus center and edge of 1,198 fluorescence in situ hybridization signals in 98 human blastomeres were measured in digital images for comparison with a mathematical model of random distribution in spherical nucleus.

RESULTS

Comparison with the mathematical model revealed that localization of chromosomes 13, 16, 21, 22, X and Y in normal and aneuploid blastomeres and that of chromosome 18 in normal blastomeres was not significantly different from random distribution. Similarly, chromosome X in blastomeres with more than one X did not appear to have a preferential localization. Only chromosome 18 in aneuploid blastomeres was differently distributed (p < 0.0001) with a shift to the nuclear periphery (p =or < 0.0001).

CONCLUSIONS

Peripheral localization of chromosome 18 in aneuploid blastomeres is related to embryo aneuploidy. Conversely, a peripheral localization of the inactive X chromosome was not found in blastomeres from 3-4 day old embryos. These results open the possibility to improve embryo selection after pre-implantation diagnosis.

Role of aneuploidy on embryo implantation

Approximately 30% of oocytes in the human species carry a chromosomal imbalance. This condition has severe clinical consequences as approximately one-third of spontaneous abortions are aneuploid. The most obvious link to the increase of aneuploidy in oocytes is maternal age. This has been directly confirmed by the analysis of polar bodies. Their analysis permits to give confirmation of the high predisposition of oocytes to meiotic errors. Also, the study of chromosomes on sperm has revealed a frequency of 6-7% aneuploidy in normal sperm samples, and is significantly increased in cases of severe oligoasthenoteratospermia or azoospermia due to testicular failure. During the preimplantation period there is a progressive loss of abnormal embryos at specific stages in early development, through growth arrest and degeneration of abnormal embryos. The frequency of chromosomal abnormalities is strictly related to the category of patients (advanced maternal age, repeated cycles, altered karyotype, repeated miscarriages, TESE). Based on these considerations, preimplantation genetic diagnosis for aneuploidy is proposed in reproductive medicine with the finality of improving the clinical outcome after IVF. Substantial evidence has been accumulated on the positive impact of the technique, reporting increased implantation rates and a concomitant decrease of spontaneous abortions and trisomic pregnancies.

Preliminary FISH studies on spermatozoa and embryos in patients with variable degrees of teratozoospermia and a history of poor prognosis

The aim of this study was to analyse to what extent sperm aneuploidy is associated with sperm morphology and subsequently with embryo aneuploidy. Fifty-nine men with variable degrees of teratozoospermia and previously poor assisted reproduction prognosis were included in the study. Samples from 10 normozoospermic men with proven fertility were used as controls. Individual spermatozoa were scored for chromosomes 13, 21 and for 18, X, Y separately. Compared with controls, 23 out of 59 cases (39.0%) were found to have increased sperm aneuploidy for at least one of the chromosomes analysed in a treatment cycle. Fifty-two patients underwent a treatment cycle and were documented according to the pregnancy and spermatozoa fluorescence in-situ hybridization results. A total of 121 previous unsuccessful assisted reproduction cycles of the cases were then retrospectively reviewed. In 23 of the latest cycles, preimplantation genetic diagnosis was applied to 106 cleavage stage embryos and 47 of 94 embryos analysed (50.0%) were found to be chromosomally abnormal. Furthermore, 16 of 47 (34.0%) embryos with chromosomal abnormality were carrying complex chromosomal defects. The results imply that increased aneuploidy is present in both spermatozoa and embryos in couples with severe male infertility with a history of repeated unsuccessful attempts. Therefore, proper genetic counselling should be considered in these cases.

Numerical chromosome anomalies detected in paternally derived pronuclei of tripronuclear zygotes after intracytoplasmic sperm injection

OBJECTIVE

To investigate after intracytoplasmic sperm injection (ICSI) the paternal-derived pronuclei of zygotes with three pronuclei (3PN) for numerical-chromosome anomalies by using fluorescence in situ hybridization.

DESIGN

A total of 211 ICSI 3PN zygotes have been analyzed for numerical-chromosome anomalies in paternally derived pronuclei and compared with the group of 82 zygotes originated during IVF. In the ICSI group, 163 zygotes were evaluated for numerical-chromosome anomalies by using DNA probes for chromosomes 18, X, and Y, and 48 zygotes, for chromosomes 21, X, and Y. In the IVF group, 68 zygotes were evaluated for numerical-chromosome anomalies by using probes for chromosomes 18, X, and Y, and 14 zygotes, by using chromosomes 21, X, and Y.

SETTING AND PATIENT(S)

Tripronuclear zygotes were obtained from 74 and 176 patients participating in IVF and ICSI treatment cycles at a university hospital in Switzerland.

INTERVENTION(S)

To evaluate the frequency of numerical-chromosome anomalies in different populations of infertile patients, a total of 211 ICSI zygotes were divided into three groups of zygotes from men with oligozoospermia (n = 124), severe oligozoospermia (n = 53), and azoospermia (n = 34).

MAIN OUTCOME MEASURE(S)

Incidence of sex-chromosome aneuploidy, diploidy, and aneuploidy for chromosomes 18 or 21.

RESULT(S)

Overall incidence of numerical-chromosome anomalies in paternal-derived pronuclei after ICSI (9.5%) was significantly higher than the rate found in paternal-derived pronuclei of IVF zygotes (1.2%). Among ICSI zygotes, sex-chromosome aneuploidy (5.2%) and diploidy (2.8%) were two dominant numerical anomalies in paternal-derived pronuclei. In contrast, aneuploidy for autosomes 18 or 21 was not significantly different when comparing ICSI with IVF zygotes. Regarding different groups of infertile patients, the highest incidence of numerical-chromosome anomalies was found in zygotes originating from men with severe oligozoospermia (13.2%), followed by those originating from men with azoospermia (8.8%) and oligozoospermia (8.1%).

CONCLUSION(S)

Sex-chromosome aneuploidy and diploidy were the most frequent numerical-chromosome anomalies found in paternal pronuclei of ICSI 3PN zygotes. Surprisingly, no statistically significant difference in the incidence of numerical-chromosome anomalies was observed in the three groups of pronuclei derived from men with oligozoospermia, severe oligozoospermia, and azoospermia.

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.

Preimplantation genetic diagnosis for aneuploidy screening in repeated implantation failure

Chromosomal abnormalities are thought to be responsible for implantation failure, and among chromosomal abnormalities in normally developing embryos, aneuploidy is the most frequent. Genetic testing of preimplantation embryos for chromosomal aneuploidy allows selection of chromosomally normal embryos, and early detection of chromosomal aberration will increase the chance of conceiving. Preimplantation genetic diagnosis for aneuploidy screening (PGD-AS), performed by polar body or blastomere analysis, is used in infertile patients treated with assisted reproduction technologies, especially in those with a poor prognosis, e.g. repeated IVF failure, advanced maternal age, or recurrent spontaneous abortion. The aim of this paper is to clarify the impact of PGD-AS in repeated implantation failure. In this review, the data collected so far regarding PGD-AS in this patient group will be discussed in depth.

Sperm and blastomere aneuploidy detection in reproductive genetics and medicine

The use of multiple probes in fluorescence in situ hybridization (FISH) permits the simultaneous analysis of several chromosomes in both blastomeres and spermatozoa. Preimplantation genetic diagnosis (PGD) for aneuploidy provides information on embryonic chromosomal status, enabling the selection of embryos carrying aneuploid condition. This strategy directly affects implantation, as documented for patients with a poor prognosis for pregnancy, who have the tendency to generate high proportions of chromosomally abnormal embryos. PGD for aneuploidy also has contributed information on early phases in human embryology by clarifying the molecular basis in some cases of irregular development. Multicolor FISH has also been used to study chromosomes on spermatozoa. Experimental strategies and modifications enabled the analysis of samples with a very low number of sperm cells, including samples retrieved from the genital tract or directly from the testicular tissue. The results confirmed that the incidence of aneuploidy increases proportionally with the severity of the male-factor condition. This observation suggests that, in selected cases, the paternal contribution to aneuploidy in the developing conceptus could be more relevant than expected from general data from aborted fetuses and live births.

Frequency of aneuploidy in sperm from patients with extremely severe male factor infertility

BACKGROUND

A protocol for the chromosomal analysis of sperm samples with a severely reduced number of sperm cells was designed.

METHODS

A severe male factor condition was the main cause of infertility for 38 couples: 27 were oligoasthenoteratospermic (OAT) and 11 with non-obstructive azoospermia underwent testicular sperm extraction (TESE). A two-round fluorescence in situ hybridization (FISH) protocol was performed with probes specific for the chromosomes X, Y, 13, 15, 16, 17, 18, 21 and 22. The recording of the position of each sperm cell at the microscope allowed diagnosis of each spermatozoon for the nine tested chromosomes.

RESULTS

A mean number of 122+/-78.5 sperm were diagnosed per patient with an incidence of total abnormalities corresponding to 13.4%. chi2-tests for the observed frequencies and goodness-of-fit test were highly significant in all cases. A significantly higher proportion of total aneuploidy was detected in 79% of the tested samples compared to the normal population. Testicular sperm were significantly more prone to aneuploidy than ejaculated sperm.

CONCLUSIONS

The designed FISH protocol for the analysis of severe OAT and TESE sperm samples is reliable, implying that the studied sample is representative of the original population. In view of the high incidence of aneuploidy in most severe OAT and TESE sperm, the FISH analysis of pathological sperm samples can be routinely performed in order to estimate the chances of the paternal contribution to aneuploidy in the resulting embryos.

FISH screening of aneuploidies in preimplantation embryos to improve IVF outcome

Preimplantation genetic diagnosis (PGD) has transformed the approach to the infertility patient in the IVF setting. Although the principal applications of PGD have been to prevent the transmission of sex-linked diseases, in time and with growing knowledge of the chromosomal abnormalities observed in preimplantation embryos, its applications have widened. Nowadays, apart from its implications in the prevention of transmission of chromosomal and genetic abnormalities, PGD is being used with increased frequency to improve the IVF outcome in patients with advanced maternal age (> or =38 years of age), recurrent miscarriage (> or =2 miscarriages), recurrent IVF failure (> or =3 failed IVF attempts) and severe male infertility. A high incidence of chromosomal abnormalities has been observed in these patient groups.

Negligible interchromosomal effect in embryos of Robertsonian translocation carriers

It has been suggested that translocations, and perhaps other chromosome rearrangements, disturb meiotic disjunction of chromosome pairs not involved in the translocation, resulting in non-disjunction in those chromosomes (interchromosomal effect) and predisposition to trisomy offspring. Other reports have suggested an increased risk of mosaicism and chaotic embryos in translocation carriers. This study was designed to determine if such interchromosomal effects are producing significantly more chromosome abnormalities than those expected from unbalanced gametes. For that purpose, two groups of PGD patients were compared, Robertsonian translocation carriers (RBT) and carriers of X-linked diseases (XLI), of similar age. Both groups were analysed by FISH with similar DNA probes. The results indicate that overall, the higher rate of chromosome abnormalities in the RBT group was solely due to unbalanced gametes and not to an interchromosomal effect or higher incidence of mosaicism. If unbalanced and normal were combined, this proportion was 53% in XLI and 59% in RBT. However, when specific RBT translocations were studied, only a slight increase in embryos with aneuploidy for chromosome 22 was found for the t(13;14) translocation carriers, while a higher rate of post-zygotic abnormalities was observed in the more rare RBT. In conclusion, the overall rate of non-translocation related abnormalities was not increased in the RBT group compared with the control group, but a slight interchromosomal effect may exist, as some Robertsonian translocations may be more prone to produce mosaic and chaotic embryos.

Preimplantation genetic diagnosis in patients with male meiotic abnormalities

Indications and candidates for preimplantation genetic diagnosis (PGD) have increased in recent years. This study evaluates whether IVF-intracytoplasmic sperm injection (ICSI) results could be improved by selecting embryos through PGD-AS (aneuploidy screening) in couples in whom the male partner presents meiotic abnormalities. Two hundred and fifty-six embryos were biopsied and 183 were suitable for analysis (73.2%). Ninety-two embryos showed normal chromosomal analysis (50.3% of the analysed embryos and 57.5% of the diagnosed embryos). Pregnancy, abortion and implantation rates were compared with 66 IVF-ICSI cycles performed in 44 patients with meiotic abnormalities without PGD (control group). No statistically significant differences in the pregnancy rate (52 versus 43.9%), implantation rate (32.1 versus 23.5%) and miscarriage rate (15.4 versus 10.3%) were observed between the groups. Although the embryos obtained from men with meiotic abnormalities showed a high frequency of chromosome abnormalities, no improvements in pregnancy and implantation rates were obtained after PGD-AS in the series analysed.

Effect of ICSI on subsequent blastocyst development and pregnancy rates

PURPOSE

To investigate whether ICSI (intracytoplasmic sperm injection) results in decreased blastocyst formation and pregnancy compared to IVF (in vitro fertilization).

METHODS

We performed a retrospective analysis of blastocyst transfer (BT) offered routinely to patients under age 40 with > or = three 8-cell embryos on day 3 and compared IVF to ICSI cycles. Sequential media were used with P1 until day 3, then Blastocyst Medium until day 5/6.

RESULTS

There were 131 IVF and 75 ICSI cycles. There was no difference in age, number of oocytes, zygotes, 8-cell embryos, blastocysts on days 5 and 6, or embryos transferred. Progression to blastocyst was similar (78% for IVF and 73% for ICSI) as was the viable pregnancy rate (51.4% for IVF and 55% for ICSI). No cycles failed to form blastocysts.

CONCLUSIONS

The progression to blastocyst and the likelihood of conceiving a viable pregnancy were unaltered by ICSI. Thus it seems appropriate for programs to offer BT to patients undergoing ICSI using the same inclusion criteria applied to their IVF patients.

The role of preimplantation diagnosis for aneuploidies

The clinical application of preimplantation genetic diagnosis (PGD) for aneuploidy has confirmed the hypothesis that implantation failure and spontaneous abortions are frequently due to aneuploidy. Following PGD, a higher implantation rate and a lower incidence of spontaneous abortions are obtained in patient categories where aneuploidy is the main cause of reproductive failure: women in advanced reproductive age, patients with an altered karyotype due to translocations or gonosomal mosaicism, and patients with recurrent spontaneous abortions. In these cases, the transfer of euploid embryos overcomes the poor prognosis condition in these couples. As expected, aneuploidy increases proportionally with female age; however, not all the chromosomes studied show this trend, suggesting that segregation errors could occur at different rates for each chromosome in relation to maternal age. Furthermore, the retrospective analysis of the results obtained in patients who repeated at least twice a PGD cycle permitted to estimate their chances of reproducing the same pattern of chromosomal abnormalities and consequently evaluating their possibility of a pregnancy: when no euploid embryos are detected at the first attempt, the chance of on-term pregnancy is below 10%; however, this chance is approximately 30% for couples with at least two euploid embryos in the first cycle.