Paternal Age and Numerical Chromosome Abnormalities in Human Spermatozoa

Analysis of a preimplantation genetic test for aneuploidies in 893 screened blastocysts using KaryoLite BoBs: a single-centre experience

INTRODUCTION

Does euploidy of trophectoderm (TE) biopsies correlate with conventional blastocyst morphological, maternal age and implantation potential?

METHODS

This is a one-centre, retrospective, observational study.

RESULTS

Eight hundred and ninety-three blastocysts were biopsied; 57.73% were euploid. The euploidy rate was found to be significantly higher for the embryos with good morphology of inner cell mass (ICM) and TE. Between ICM and TE morphology variables, TE was more predictive of the euploidy rate. When broken down into different age groups, the percentage of good morphology embryos remained similar across all age groups, while the percentage of euploid embryos dropped with increasing age. These results suggest that the correlation between blastocyst morphology and ploidy status was present but poor. Faster growing day 5 blastocysts showed a significantly higher euploidy rate than slower growing day 6 or 7 blastocysts. The number of good-quality blastocysts per cycle, euploid blastocysts per cycle and the euploidy rate were strongly associated with maternal age. A trend towards an increased implantation rate was found with euploid embryo transfers compared to the control group without preimplantation genetic test for aneuploidies (PGT-A).

CONCLUSIONS

Blastocyst morphology, rate of development and maternal age were found to be significantly associated with euploidy rate. There is a trend that suggests PGT-A may help to improve the pregnancy rate, but it is not statistically different, and therefore, PGT-A remains an unproven hypothesis. Due to the limitation of a small size of the control group, further studies with more data are needed.

Sperm and Oocyte Chromosomal Abnormalities

Gametogenesis, the process of producing gametes, differs significantly between oocytes and sperm. Most oocytes have chromosomal aneuploidies, indicating that chromosomal aberrations in miscarried and newborn infants are of oocyte origin. Conversely, most structural anomalies are of sperm origin. A prolonged meiotic period caused by increasing female age is responsible for an increased number of chromosomal aberrations. Sperm chromosomes are difficult to analyze because they cannot be evaluated using somatic cell chromosome analysis methods. Nevertheless, researchers have developed methods for chromosome analysis of sperm using the fluorescence in situ hybridization method, hamster eggs, and mouse eggs, allowing for the cytogenetic evaluation of individual sperm. Reproductive medicine has allowed men with severe spermatogenic defects or chromosomal abnormalities to have children. However, using these techniques to achieve successful pregnancies results in higher rates of miscarriages and embryos with chromosomal abnormalities. This raises questions regarding which cases should undergo sperm chromosome analysis and how the results should be interpreted. Here, we reviewed clinical trials that have been reported on oocyte and sperm chromosome analyses. Examination of chromosomal abnormalities in gametes is critical in assisted reproductive technology. Therefore, it is necessary to continue to study the mechanism underlying gametic chromosomal abnormalities.

Monozygotic twins discordant for homologous Robertsonian translocation trisomy 21 of 46, XX, + 21, der (21;21) (q10; q10) in a twin-to-twin transfusion syndrome, case report

Background

Monozygotic twins are nearly identical in genotype and phenotype because monozygotic twins arise from one fertilized oocyte. In all cases of discordant karyotype in monozygotic twins, trisomy 21 accounts for about one in 385,000. Monozygotic twins discordant for Robertsonian translocation trisomy 21 of the der (21;21)(q10;q10), in which the additional chromosome originates from the father is rare.

Case presentation

A 28-year-old parous woman, G3P1A0, came to our institution for a dating scan at 8 weeks of gestation. The transvaginal ultrasound examination demonstrated a monochorionic diamniotic pregnancy. She and her husband were healthy, with no family history of trisomy 21 or other congenital diseases. The ultrasound examination of nuchal translucency thickness was discordant in twins at 13 weeks (twin A, NT 1.4 mm with CRL being 65 mm; twin B, NT 7.8 mm with CRL being 69 mm). At 17^+ 4 weeks, twin A was normal, but ventricular septal defect and the hypoplastic left heart was detected in twin B. The deepest vertical pocket was 18 mm in twin A (oligohydramnios) and 102 mm in Twin B (polyhydramnios). The bladder in twin A was absent. Ultrasound findings indicated TTTS Stage II. Amniocentesis was performed for the two fetuses. The karyotyping results revealed 46, XX in twin A but 46,XX,+ 21,der (21;21)(q10;q10) in twin B.

For twin B, the parents opted for selective fetal termination by radiofrequency ablation. The procedure was uneventful. At 40^+ 5 weeks, twin A was born with a birth weight of 4120 g by vaginal delivery.

Conclusions

The early detection of discordant karyotype and twin-to-twin transfusion syndrome is beneficial to the early intervention. In monozygotic twins with a discordant anomaly, the discordant karyotype should be considered.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-021-03587-x.

Next-generation sequencing analysis of each blastomere in good-quality embryos: insights into the origins and mechanisms of embryonic aneuploidy in cleavage-stage embryos

PURPOSE

To explore the whole-chromosome status, origins, and mechanisms of chromosomal abnormalities in good-quality cleavage embryos using multiple annealing and looping-based amplification cycle (MALBAC) sequencing.

METHODS

The embryos studied came from7 patients (maternal aged 26-35) who had healthy birth from the same IVF cycles. These 21 frozen day 3 good-quality embryos were thawed and disaggregated into individual blastomere. Each blastomere was collected and analyzed by MALBAC sequencing.

RESULTS

Conclusive results were obtained from a high percentage of blastomeres (95.3%). A total of 46.6% of blastomeres were diploid, 53.4% were abnormal, and 28.0% had complex aneuploidy. Out of 21 embryos, 3 (14.3%) were normal and 18 (85.7%) were mosaics, showing the occurrence of mitotic errors; aneuploidy was confirmed in all cells of 4 of the 18 embryos, which showed the coexistence of meiotic errors. Conclusive results were obtained from all blastomeres of 15 embryos (71.4%, 15/21), which enabled us to reconstruct the cell lineage on the basis of the chromosomal content of the blastomeres in each division. There were 9 mitotic errors (8.7%, 9/103): nondisjunction accounted for 88.9% (8/9), and endoreplication accounted for 11.1% (1/9).

CONCLUSIONS

In good-quality embryos, there was a high rate and diverse array of chromosomal abnormalities. Morphological evaluation does not appear to assist in the reduction in meiotic errors from parental origins. Mitotic errors were common, and nondisjunction was found to be the main mechanism causing malsegregation during the cleavage divisions.

Advanced paternal age and the risk of spontaneous abortion: an analysis of the combined 2011-2013 and 2013-2015 National Survey of Family Growth

BACKGROUND

Maternal and paternal age at first birth are increasing across the global population. Spontaneous abortion, one of the most common abnormal pregnancy outcomes, is known to occur more frequently with increasing maternal age. However, the relationship of advanced paternal age and spontaneous abortion is poorly understood, and previous results have yielded conflicting results.

OBJECTIVE

To examine the influence of paternal age on the risk of spontaneous abortion among singleton pregnancies conceived without assisted reproductive technologies.

MATERIALS AND METHODS

This was a retrospective, case-control study using combined pregnancy data from the Centers for Disease Control and Prevention's 2011-2013 and 2013-2015 National Survey of Family Growth. Spontaneous, singleton pregnancy data from women aged 15-45 years were analyzed. Ongoing pregnancies, induced abortions, ectopic pregnancies, preterm births, and intrauterine fetal deaths were excluded. Bivariate associations of pregnancy outcome (spontaneous abortion at <20 weeks and ≤12 weeks vs. live birth at ≥37 weeks) and paternal age were determined, along with those of maternal age and selected demographic and pregnancy characteristics. Significant associations were included in a multivariable logistic regression, which accounted for multiple pregnancies derived from the same respondent.

RESULTS

A total of 12,710 pregnancies from 6979 women were analyzed, consisting of 2300 (18.2%) spontaneous abortions and 10,410 (81.8%) term live births. Median maternal and paternal ages were 25 and 28 years, respectively. After adjusting for maternal age, race/ethnicity, socioeconomic status, marital status, and pregnancy intention, pregnancies resulting in spontaneous abortions had 2.05 (95% confidence interval, 1.06-2.20) times the odds of being from a father aged 50 years or older, vs. 25-29 years of age. These relationships remained significant when defining SABs at ≤12 weeks (adjusted odds ratio, 2.30; 95% confidence interval, 1.17-4.52).

CONCLUSION

Paternal age may increase the odds of spontaneous abortion, independent of selected factors, including demographics, pregnancy intention, and maternal age. This association was robust across several gestational age-based definitions of spontaneous abortion, even after adjustment.

Advanced paternal age does not affect embryo aneuploidy following blastocyst biopsy in egg donor cycles

PURPOSE

To study the impact of advanced paternal age on embryo aneuploidy.

METHODS

This is a multicenter international retrospective case series of couples undergoing assisted reproduction via in vitro fertilization using donor eggs to control for maternal factors and preimplantation genetic testing for aneuploidy via next-generation sequencing at Igenomix reproductive testing centers. The main outcome measure was the prevalence of embryo aneuploidy in egg donor cycles. Semen analysis data was retrieved for a small subset of the male patients.

RESULTS

Data from 1202 IVF/ICSI egg donor cycles using ejaculated sperm (total 6934 embryos) evaluated using PGT-A between January 2016 and April 2018 in a global population across all Igenomix centers were included. No significant association was identified between advancing paternal age and the prevalence of embryo aneuploidy overall and when analyzing for each chromosome. There was also no significant association between advancing paternal age and specific aneuploid conditions (monosomy, trisomy, partial deletion/duplication) for all chromosomes in the genome.

CONCLUSIONS

This is the largest study of its kind in an international patient population to evaluate the impact of advancing paternal age on embryo aneuploidy. We conclude there is no specific effect of paternal age on the prevalence of embryo aneuploidy in the context of embryo biopsies from egg donor cycles.

Tripolar chromosome segregation drives the association between maternal genotype at variants spanning PLK4 and aneuploidy in human preimplantation embryos

Aneuploidy is prevalent in human embryos and is the leading cause of pregnancy loss. Many aneuploidies arise during oogenesis, increasing with maternal age. Superimposed on these meiotic aneuploidies are frequent errors occurring during early mitotic divisions, contributing to widespread chromosomal mosaicism. Here we reanalyzed a published dataset comprising preimplantation genetic testing for aneuploidy in 24 653 blastomere biopsies from day-3 cleavage-stage embryos, as well as 17 051 trophectoderm biopsies from day-5 blastocysts. We focused on complex abnormalities that affected multiple chromosomes simultaneously, seeking insights into their formation. In addition to well-described patterns such as triploidy and haploidy, we identified 4.7% of blastomeres possessing characteristic hypodiploid karyotypes. We inferred this signature to have arisen from tripolar chromosome segregation in normally fertilized diploid zygotes or their descendant diploid cells. This could occur via segregation on a tripolar mitotic spindle or by rapid sequential bipolar mitoses without an intervening S-phase. Both models are consistent with time-lapse data from an intersecting set of 77 cleavage-stage embryos, which were enriched for the tripolar signature among embryos exhibiting abnormal cleavage. The tripolar signature was strongly associated with common maternal genetic variants spanning the centrosomal regulator PLK4, driving the association we previously reported with overall mitotic errors. Our findings are consistent with the known capacity of PLK4 to induce tripolar mitosis or precocious M-phase upon dysregulation. Together, our data support tripolar chromosome segregation as a key mechanism generating complex aneuploidy in cleavage-stage embryos and implicate maternal genotype at a quantitative trait locus spanning PLK4 as a factor influencing its occurrence.

The role of chromosome segregation and nuclear organisation in human subfertility

Spermatogenesis is central to successful sexual reproduction, producing large numbers of haploid motile male gametes. Throughout this process, a series of equational and reductional chromosome segregation precedes radical repackaging of the haploid genome. Faithful chromosome segregation is thus crucial, as is an ordered spatio-temporal ‘dance’ of packing a large amount of chromatin into a very small space. Ergo, when the process goes wrong, this is associated with an improper chromosome number, nuclear position and/or chromatin damage in the sperm head. Generally, screening for overall DNA damage is relatively commonplace in clinics, but aneuploidy assessment is less so and nuclear organisation studies form the basis of academic research. Several studies have focussed on the role of chromosome segregation, nuclear organisation and analysis of sperm morphometry in human subfertility observing significant alterations in some cases, especially of the sex chromosomes. Importantly, sperm DNA damage has been associated with infertility and both extrinsic (e.g. lifestyle) and intrinsic (e.g. reactive oxygen species levels) factors, and while some DNA-strand breaks are repaired, unexpected breaks can cause differential chromatin packaging and further breakage. A ‘healthy’ sperm nucleus (with the right number of chromosomes, nuclear organisation and minimal DNA damage) is thus an essential part of reproduction. The purpose of this review is to summarise state of the art in the fields of sperm aneuploidy assessment, nuclear organisation and DNA damage studies.

Evolutionary justifications for human reproductive limitations

Common human reproductive inefficiencies have multiple etiologies. Going against chance, many effects, such as polycystic ovaries, endometriosis, and folate metabolic issues, have genetic components, while aneuploid losses arise from diverse mitotic and meiotic errors at different stages, some transitory. This can be advantageous, since greater overall survival with fewer offspring can increase reproductive success. Benefits primarily accrue to mothers, who bear most child related costs, and for whom early losses are less costly than late. Different adaptations to different situations reflect human evolutionary history. For early speciation, periodic climate extremes repeatedly reduced resources, favoring limitations while contracted populations helped fix relevant genes. Later, under better conditions, evolving social cooperation could increase fecundity faster than it added resources, further supporting reproductive suppression through mitotic aneuploidy, with very early losses minimizing maternal costs. The grandmother hypothesis suggests benefits in limiting reproduction as maternal age increased pregnancy risks in order to support grandchildren as they arrived, selecting for maternal age-related meiotic aneuploidy. Finally, with variable short-term agricultural shortages, acute reproductive responses arose through chromatin "nutrient sensor"-regulated epigenetic effects that also shifted some lethal effects earlier, reducing both maternal and mutation load costs. Overall, despite suggestions to the contrary, it is likely that human selective pressures have not decreased with civilization, but that many of the costs have been shifted to early reproduction.

Paternal age and assisted reproductive technology: problem solver or trouble maker?

In our society, the number of couples with advanced reproductive age seeking fertility treatment is increasing steadily. While the negative effect of female age on assisted reproductive technology (ART) outcomes is well established, the impact of paternal age needs to be clarified. We reviewed the current literature to determine whether advanced paternal age affects the results of ART and the health of resulting offspring. We found that the published literature is overall supportive of a positive association between advanced paternal age (>40 years) and semen quality deterioration. However, the existing evidence does not corroborate nor discard the influence of advanced paternal age on ART outcomes. Similarly, the effect of paternal age on the health of ART offspring remains equivocal, although data from naturally-conceived children clearly indicates that advanced paternal age increases the frequency of genetic, neurodevelopmental, and psychiatric diseases in the progeny. Noteworthy, the current literature is limited and subjected to bias due to the impact of maternal age as a critical confounder. Health care providers should discuss with concerned couples the available options to counteract the possible negative influence of advanced paternal age on ART outcomes and health of resulting offspring. These include identification and treatment of underlying conditions with potential negative long-term effects on fertility, sperm freezing at a young age, and use of antioxidant supplements for men at risk of excessive oxidative stress. Aged male partner from couples undergoing ART, in particular men of 50 years and older, should consider use of preimplantation genetic testing as a means to detect embryo abnormalities and select euploid embryos for transfer to the uterine cavity.

Infertility in the Aging Male

PURPOSE OF REVIEW

In many countries, the average age of paternity is rising. The negative effect of older age on fertility in women is well documented; however, less is known about the impact of paternal age on fecundity. In this review, we summarize the current knowledge of how paternal age affects semen parameters, reproductive success, and offspring health.

RECENT FINDINGS

Contemporary evidence confirms that aged men have worse semen parameters, including overall negative changes in sperm genetics. Reproductive outcomes with unassisted pregnancy tend to be worse with older fathers. While most current studies of assisted pregnancy do show a negative effect of paternal age, there are some conflicting results. Studies continue to show an overall increased risk of health problems, particularly neuropsychiatric conditions, in the offspring of older men. While men can often maintain fertility potential throughout a lifetime, increasing evidence indicates worsening of semen parameters, including sperm genetics, and potentially worse reproductive success. Older men should also be counseled on their offspring's possible increased risk of certain medical conditions.

Evaluation of the impact of sperm morphology on embryo aneuploidy rates in a donor oocyte program

This study investigates the correlation between sperm morphology and the incidence of embryo aneuploidy in an oocyte donation program. A total of 1,165 embryos from 103 patients have been analyzed by fluorescent in situ hybridization (FISH) for numerical abnormalities in chromosome numbers 13, 18, 21, X, and Y. Data has been evaluated in five groups according to sperm morphology, which has been assessed according to the Kruger's strict criteria. The results did not show any difference in paternal (p = 0.878), maternal (p = 0.873), and donor ages (p = 0.871), sperm counts (p = 0.782) and motility (p = 0.124), and fertilization rate (p = 0.080) among the groups. However, total aneuploidy rate (p < 0.001) and its derivatives (trisomy p = 0,042, monosomy p = 0,004) differed significantly and they were reversibly correlated with sperm morphology (rho correlation test; total aneuploidy p < 0.001, trisomy p < 0.001, monosomy p = 0.004). Therefore, these results suggested that diminished sperm quality is correlated to the aneuploidy rate in preimplantation embryos.

ABBREVIATIONS

FISH: fluorescence in situ hybridization; ICSI: intracytoplasmic sperm injection; HCG: human chorionic gonadotropin.

Intracytoplasmic sperm injection: state of the art in humans

Among infertile couples, 25% involve both male and female factors, while male factor alone accounts for another 25% due to oligo-, astheno-, teratozoospermia, a combination of the three, or even a complete absence of sperm cells in the ejaculate and can lead to a poor prognosis even with the help of assisted reproductive technology (ART). Intracytoplasmic sperm injection (ICSI) has been with us now for a quarter of a century and in spite of the controversy generated since its inception, it remains in the forefront of the techniques utilized in ART. The development of ICSI in 1992 has drastically decreased the impact of male factor, resulting in millions of pregnancies worldwide for couples who, without ICSI, would have had little chance of having their own biological child. This review focuses on the state of the art of ICSI regarding utility of bioassays that evaluate male factor infertility beyond the standard semen analysis and describes the current application and advances in regard to ICSI, particularly the genetic and epigenetic characteristics of spermatozoa and their impact on reproductive outcome.