The occurrence of aneuploidy in human: lessons from the cytogenetic studies of human oocytes

Depletion of placental brain-derived neurotrophic factor (BDNF) is attributed to premature ovarian insufficiency (POI) in mice offspring

INTRODUCTION

Premature ovarian insufficiency (POI) is one of the causes of female infertility. Unexplained POI is increasingly affecting women in their reproductive years. However, the etiology of POI is diverse and remains elusive. We and others have shown that brain-derived neurotrophic factor (BDNF) plays an important role in adult ovarian function. Here, we report on a novel role of BDNF in the Developmental Origins of POI.

METHODS

Placental BDNF knockout mice were created using CRISPR/CAS9. Homozygous knockout (cKO(HO)) mice didn't survive, while heterozygous knockout (cKO(HE)) mice did. BDNF reduction in cKO(HE) mice was confirmed via immunohistochemistry and Western blots. Ovaries were collected from cKO(HE) mice at various ages, analyzing ovarian metrics, FSH expression, and litter sizes. In one-month-old mice, oocyte numbers were assessed using super-ovulation, and oocyte gene expression was analyzed with smart RNAseq. Ovaries of P7 mice were studied with SEM, and gene expression was confirmed with RT-qPCR. Alkaline phosphatase staining at E11.5 and immunofluorescence for cyclinD1 assessed germ cell number and cell proliferation.

RESULTS

cKO(HE) mice had decreased ovarian function and litter size in adulthood. They were insensitive to ovulation induction drugs manifested by lower oocyte release after superovulation in one-month-old cKO(HE) mice. The transcriptome and SEM results indicate that mitochondria-mediated cell death or aging might occur in cKO(HE) ovaries. Decreased placental BDNF led to diminished primordial germ cell proliferation at E11.5 and ovarian reserve which may underlie POI in adulthood.

CONCLUSION

The current results showed decreased placental BDNF diminished primordial germ cell proliferation in female fetuses during pregnancy and POI in adulthood. Our findings can provide insights into understanding the underlying mechanisms of POI.

Selfish centromeres and the wastefulness of human reproduction

Many human embryos die in utero owing to an excess or deficit of chromosomes, a phenomenon known as aneuploidy; this is largely a consequence of nondisjunction during maternal meiosis I. Asymmetries of this division render it vulnerable to selfish centromeres that promote their own transmission, these being thought to somehow underpin aneuploidy. In this essay, I suggest that these vulnerabilities provide only half the solution to the enigma. In mammals, as in utero and postnatal provisioning is continuous, the costs of early death are mitigated. With such reproductive compensation, selection can favour a centromere because it induces lethal aneuploidy: if, when taken towards the polar body, it instead kills the embryo via aneuploidy, it gains. The model is consistent with the observation that reduced dosage of a murine drive suppressor induces aneuploidy and with the fact that high aneuploidy rates in vertebrates are seen exclusively in mammals. I propose further tests of this idea. The wastefulness of human reproduction may be a price we pay for nurturing our offspring.

Why do so many human embryos have the wrong number of chromosomes? So-called ’selfish centromeres’ and the fact that new embryos can be produced may provide an answer.

Evaluation of Female Fertility-AMH and Ovarian Reserve Testing

CONTEXT

Evaluation of the infertile female requires an understanding of ovulation and biomarkers of ovarian reserve. Antimüllerian hormone (AMH) correlates with growing follicles in a menstrual cycle. Increasingly, AMH has been used as a "fertility test." This narrative review describes how to integrate the use of AMH into diagnosis and treatment.

METHODS

A PubMed search was conducted to find recent literature on measurements and use of serum AMH as a marker of ovarian reserve and in treatment of infertility.

RESULTS

Serum AMH estimates ovarian reserve, helps determine dosing in ovarian stimulation, and predicts stimulation response. As such, AMH is a good marker of oocyte quantity but does not reflect oocyte health or chances for pregnancy. Screening of AMH before fertility treatment should be used to estimate expected response and not to withhold treatment. Low AMH levels may suggest a shortened reproductive window. AMH levels must be interpreted in the context of the endogenous endocrine environment where low follicle-stimulating hormone, due to hypogonadotropic hypogonadism or hormonal contraceptive use, may lower AMH without being a true reflection of ovarian reserve. In addition, there is an inverse correlation between body mass index and AMH that does not reflect ovarian response.

CONCLUSION

AMH is a useful marker of ovarian reserve in reproductive-aged women. Increased screening of noninfertile women requires a thorough knowledge of situations that may affect AMH levels. In no situation does AMH reflect oocyte health or chances for conception. Age is still the strongest driver in determining success rates with fertility treatments.

Preimplantation genetic testing for aneuploidy (PGT-A)-a single-center experience

PURPOSE

The aim of this study was to determine the prevalence and nature of human embryonic aneuploidy based on the preimplantation genetic testing for aneuploidy (PGT-A), the distribution of aneuploidy across the individual chromosomes, and their relationship to maternal age.

METHODS

This is a retrospective cohort study conducted at a single center. The study includes subjects who opted for PGT-A in their in vitro fertilization (IVF) cycle from 2016 to 2020. PGT-A was performed on 1501 embryos from 488 patients in 535 cycles. PGT-A was performed using NGS-based technique on Ion Torrent PGM (Life Technologies). Analysis was performed to determine the (i) frequency of the aneuploidy, (ii) the chromosome most commonly affected, (iii) relationship between maternal age and the rate of aneuploidy, and (iv) incidence of segmental aneuploidy.

RESULTS

The overall frequency of aneuploidy was observed to be 46.8%. The incidence of aneuploidy rate was ~ 28% at maternal age < 30 years which steadily increased to ~ 67% in women above 40 years. High frequency of aneuploidy was observed in chromosomes 16, 22, 21, and 15. Segmental abnormalities, involving loss or gain of chromosomal fragments, were observed at a frequency of 5.3%, and highest incidence of segmental gain was observed on the q-arm of chromosome 9.

CONCLUSION

The study provides important information regarding the frequency of the aneuploidy in IVF cohort and the most frequent chromosomal abnormality. The study further emphasizes the relationship between maternal age and aneuploidy. This study has important implications which help clinicians and genetic counselors in providing information in patient counseling.

Tripronuclear Zygotes in IVF Laboratory Quality Control: Experimental Evaluation and Potential Applications

This study set out to evaluate quality control within a new in vitro fertilization (IVF) laboratory environment and of new incubators based on the culture results of tripronuclear zygotes. The representative environmental indicators within new and old IVF laboratories were monitored, and tripronuclear zygotes were cultured in the two laboratories; the results were analyzed and compared. Subsequently, tripronuclear (3PN) zygotes were cultured in both new and old incubators and the culture results were compared. No differences were found in embryo development between 3PN zygotes in the old and new laboratories. However, in the quality control test, the degeneration rate and developmental arrest rate in the new incubator early phase group were significantly increased when compared with the old incubators. Moreover, the grade I embryo rate also decreased significantly. Nevertheless, all the above comparisons in the new incubator later phase group showed no statistical significance as compared to those observed in old incubators. Tripronuclear zygotes are sensitive to the environment in IVF laboratories and can be considered useful during quality control trials of new IVF laboratories and new equipment including incubators.

Application of Two Blastocyst Biopsy Strategies in Preimplantation Genetic Testing Treatment and Assessment of Their Effects

BACKGROUND

Blastocyst biopsy has become the most mainstream biopsy method. Currently, there are two blastocyst biopsy strategies. Many studies have compared the advantages and disadvantages between blastomere and blastocyst biopsy, but fewer articles have compared the two blastocyst biopsy strategies. For the moment, no published studies have explored the entire set of information on embryo development, next-generation sequencing results, and clinical outcomes, including the baby's health status with the two blastocyst biopsy strategies.

METHODS

A total of 323 preimplantation genetic testing cycles from April 2018 to May 2020, including 178 cycles with Strategy A and 145 cycles with Strategy B. Strategy A was to create a laser-assisted zona pellucid opening for cleavage embryo on the third day after insemination, but Strategy B was not. Strategy A performed a biopsy for artificially assisted hatching blastocysts, while Strategy B performed a biopsy for expanded blastocysts on day 5 or 6. In this study, embryo development, next-generation sequencing results, pregnancy outcomes, and offspring health of the two strategies were compared and analyzed.

RESULTS

There were no statistical differences between the two groups in the rate of fertilization, blastocyst and abortion. The rate of cleavage from Strategy A was slightly higher than Strategy B, and the rate of high-quality cleavage embryo was lower than Strategy B, while the rate of high-quality blastocyst was higher than Strategy B. The rate of no-results blastocyst was significantly lower than Strategy B. In particular, the rate of biochemical pregnancy, clinical pregnancy, and live birth of Strategy A were significantly lower than those of Strategy B. The average Apgar scores of newborns were ≥8 in both groups, and there was no significant difference in average height and weight. In Strategy A, a baby was born with thumb syndactyly, and Strategy B had no congenital disabilities.

CONCLUSIONS

Blastocyst biopsy strategy without laser-assisted zona pellucid drilling on day 3 achieves better clinical treatment effects. Therefore, Strategy B is an optimal treatment regime for PGT.

The paternal toolbox for embryo development and health

The sperm is essential for reconstitution of embryonic diploidy and highly specialized developmental functions. Immediately after gamete fusion, the sperm-borne PLC-zeta triggers activation, generating intracellular free Ca2+ oscillations. Mutations in the PLC-zeta encoding gene are associated with the absence of this factor in mature sperm and inability to achieve fertilization. Sperm play also a role in the greater game of the choreography of fertilization. In the human, the sperm centrioles are introduced into the oocyte environment with gamete fusion. They interact with the oocyte cytoskeletal apparatus to form a functional pair of centrosomes and ultimately regulate pronuclear juxtaposition in preparation for the first cleavage. As a consequence, the fidelity of chromosome segregation during the first cell divisions depends on the function of sperm centrioles. Sperm DNA integrity is essential for embryo development and health. Damaged DNA does not impact on the sperm fertilization ability following ICSI. However, detrimental effects emerge at pre- and post-implantation stages. Sperm-specific epigenetic factors also play an active role in the regulation of embryonic development, as shown by correlations between reduced embryo morphological quality and incorrect chromatin packaging during spermiogenesis or abnormal methylation of sperm CpG islands. This functional landscape demonstrates that the contribution of the sperm to development goes far beyond its well-established role in fertilization. Clinical studies confirm this view and indicate sperm function as a crucial aspect of research to increase the efficacy of assisted reproduction treatments.

Recent advances in mammalian reproductive biology

Reproductive biology is a uniquely important topic since it is about germ cells, which are central for transmitting genetic information from generation to generation. In this review, we discuss recent advances in mammalian germ cell development, including preimplantation development, fetal germ cell development and postnatal development of oocytes and sperm. We also discuss the etiologies of female and male infertility and describe the emerging technologies for studying reproductive biology such as gene editing and single-cell technologies.

Preimplantation Genetic Testing of Aneuploidy by Next Generation Sequencing: Association of Maternal Age and Chromosomal Abnormalities of Blastocyst

BACKGROUND:

Aneuploidy is a major cause of miscarriages and implantation failure. Preimplantation genetic testing for aneuploidy (PGT-A) by Next Generation Sequencing (NGS) is able to detect of the numeral and structural chromosomal abnormalities of embryos in vitro fertilization (IVF).

AIM:

This study was aimed to assess the relationship between maternal age and chromosomal abnormalities NGS technology.

METHODS:

A group of 603 human trophectoderm (TE) biopsied samples were tested by Veriseq kit of Illumina. The relation of marternal age and chromosomal abnormality of blastocyst embryo was evaluated.

RESULTS:

Among the 603 TE samples, 247 samples (42.73%) presented as chromosomal abnormalities. The abnormalities occurred to almost chromosomes, and the most popular aneuploidy observed is 22. Aneuploidy rate from 0.87% in chromosome 11 to 6.06% in chromosome 22. The rate of abnormal chromosome increased dramatically in group of mother’s ages over 37 (54.17%) comparing to group of mother’s ages less than 37 (38.05%) (p < 0.000). The Abnormal chromosome and maternal age has a positive correlation with r = 0.4783 (p<0.0001).

CONCLUSION:

These results showed high rate abnormal chromosome and correlated with advanced maternal age of blastocyst embryos.

Ovarian stimulation for preimplantation genetic testing

A narrative review of the management of controlled ovarian stimulation in patients undergoing preimplantation genetic testing is presented. An electronic search was performed to identify research publications that addressed ovarian stimulation and preimplantation genetic testing published until December 2017. Studies were classified in decreasing categories: randomized controlled trials, prospective controlled trials, prospective non-controlled trials, retrospective studies and experimental studies. The aim of controlled ovarian stimulation has shifted from obtaining embryos available for transfer to yielding the maximum embryos available for biopsy to increase the odds of achieving one euploid embryo available for transfer, without the distress of inducing ovarian hyperstimulation syndrome or inadequate endometrium receptivity as vitrification and deferred embryo transfer usually will be planned. The present narrative review summarizes all treatment-related variables as well as stimulation strategies after controlled ovarian stimulation that could help patients undergoing an in vitro fertilization cycle coupled with preimplantation genetic testing, including the number of oocytes needed to achieve one healthy live birth, oral contraceptive pill usage, the role of mild ovarian stimulation or random-start stimulation, the stimulation protocol and type of gonadotropin of choice, the novel progesterone protocols, agonist or dual trigger as a final oocyte maturation trigger, the accumulation of oocytes/embryos and the optimal interval before proceeding with a subsequent controlled ovarian stimulation or the optimal medication to link stimulation cycles. The discussion is being presented according to how questions are posed in clinical practice. The aim of ovarian stimulation has shifted from obtaining embryos available for transfer to yielding the maximum embryos available for biopsy to increase the odds of achieving one euploid embryo available for transfer.

Childbirth close to natural menopause: does age at menopause matter?

RESEARCH QUESTION

Does a successful spontaneous pregnancy in the years close to natural menopause depend on age at menopause?

DESIGN

This was a retrospective population-based study of 4157 parous postmenopausal women in Norway, born during the years 1925-1940. Data were obtained by two self-administered questionnaires in the HUNT2 Survey (1995-1997). We calculated the proportions of women who gave birth within 5 years and within 10 years prior to menopause both among all women, and according to categories of age at menopause.

RESULTS

Overall, 2.7% (114/4157) of all women gave birth within 5 years, and 11.7% (487/4157) gave birth within 10 years, prior to menopause. Among women with menopause before the age of 45 years, 23.5% (81/344) gave birth within 5 years, and 55.5% (191/344) gave birth within 10 years, before menopause. Among the women with menopause at the age of 55 years or older, no women (0/474) gave birth within 5 years, and 0.2% (1/474) gave birth within 10 years, prior to menopause.

CONCLUSIONS

More than half of the women with menopause before the age of 45 years gave birth within the 10 years before natural menopause, whereas virtually no women with menopause at the age of 55 years or older did. Thus, the length of the sterile interval before natural menopause may vary by age at menopause.

Connecting links between genetic factors defining ovarian reserve and recurrent miscarriages

PURPOSE

Approximately 1-2% of the women faces three or more successive spontaneous miscarriages termed as recurrent miscarriage (RM). Many clinical factors have been attributed so far to be the potential risk factors in RM, including uterine anomalies, antiphospholipid syndrome, endocrinological abnormalities, chromosomal abnormalities, and infections. However, in spite of extensive studies, reviews, and array of causes known to be associated with RM, about 50% cases encountered by treating physicians remains unknown. The aims of this study were to evaluate recent publications and to explore oocyte-specific genetic factors that may have role in incidence of recurrent miscarriages.

METHOD

Recent studies have identified common molecular factors contributing both in establishment of ovarian reserve and in early embryonic development. Also, studies have pointed out the relationship between the age-associated depletion of OR and increase in the risk of miscarriages, thus suggestive of an interacting biology. Here, we have gathered literature evidences in establishing connecting links between genetic factors associated with age induced or pathological OR depletion and idiopathic RM, which are the two extreme ends of female reproductive pathology.

CONCLUSION

In light of connecting etiological link between infertility and RM as reviewed in this study, interrogating the oocyte-specific genes with suspected roles in reproductive biology, in cases of unexplained RM, may open new possibilities in widening our understanding of RM pathophysiology.

Ovarian stimulated cycle: not a better alternative for women without ovulation disorder in intrauterine insemination

To explore the related factors on the clinical pregnancy outcome in intrauterine insemination, a retrospective study was conducted on the clinical data of 580 cycles for 301 infertile couples who were treated with intrauterine insemination. The female age, male age, duration of infertility, treatment protocols, endometrial thickness and sperm parameters were compared between pregnant group and non-pregnant group. The results showed that there were statistical differences in female age, duration of infertility and endometrial thickness between the two groups. The pregnancy rate was 19.34% in Group A (female age ≤ 30 y) compared with 10.91% in Group B (female age > 30 y). The pregnancy rate was 18.44% when the duration of infertility ≤ 2 years, which was higher than another group 10.73% when the duration of infertility > 2 years. Group analysis according to endometrial thickness (Group1: < 8 mm; Group 2: ≥ 8 mm and ≤ 12 mm; Group 3: > 12 mm) demonstrated significant differences in clinical pregnancy rate (7.41%, 18.00% and 11.48% respectively). For those infertile female without ovulation failure, the higher clinical pregnancy rates were observed in patients undergoing intrauterine insemination in natural cycle 16.12% when compared with the patients in ovarian stimulated cycles 10.48%. Thus, we demonstrate that the pregnancy rate is related with female age, duration of infertility and endometrial thickness. The ovarian stimulated cycle couldn’t improve the pregnancy outcome for those women without ovulation disorder in intrauterine insemination.

Telomere length analysis in Down syndrome birth

Human reproductive fitness depends upon telomere chemistry. Maternal age, meiotic nondisjunction error and telomere length of mother of trisomic child are someway associated. Reports exhibiting maternal inheritance of telomere length in Down syndrome child are very scanty. To investigate this, we collected peripheral blood from 170 mothers of Down syndrome child and 186 age matched mothers of euploid child with their newly born babies. Telomere length was measured by restriction digestion - southern blotting technique. Meiotic nondisjunction error was detected by STR genotyping. Subjects are classified by age (old >35 years and young ˂35 years) and by meiotic error (MI and MII). Linear regression was run to explore the age - telomere length relationship in each maternal groups. The study reveals that with age, telomere erodes in length. Old MII mothers carry the shortest (p˂0.001), control mothers have the longest telomere and MI lies in between. Babies from older mother have longer telomere (p˂0.001) moreover; telomeres are longer in Down syndrome babies than control babies (p˂0.001). To conclude, this study represents not only the relation between maternal aging and telomere length but also explore the maternal heritability of telomere length in families with Down syndrome child.

Maternal antimullerian hormone as a predictor of fetal aneuploidy occurring in an early pregnancy loss

Objective

The purpose of the study was to examine the relationship between the parameter representing ovarian reserve and the fetal aneuploidy in early spontaneous miscarriage.

Methods

A multicenter retrospective cohort study was performed in patients who were diagnosed with early pregnancy loss (≤13 gestational weeks) and examined for fetal karyotype at the CHA Gangnam Medical Center, CHA Bundang Medical Center, and CHA Gumi Medical Center between January 2011 and December 2012. Karyotyping was performed by the Genetic Laboratory of the Fertility Center of CHA Gangnam Medical Center. Medical records were reviewed for demographics, karyotype analysis and hormonal assay of ovarian reserve including antimullerian hormone (AMH) and follicle stimulating hormone. Statistical analysis was performed using SPSS software.

Results

A total 462 patients were included in this study. The mean age of the patients was 35.31±4.12 years and the mean AMH level was 3.88±3.50 ng/mL (n=195). Two hundred eleven conceptuses (45.7%) of patients showed the euploid and 251 (54.3%) showed the aneuploid. There are significant differences in maternal age, AMH and gestational age between fetal euploid and aneuploid groups (34.46±4.35 vs. 36.04±3.78 years, P<0.001; 4.60±3.86 vs. 3.43±3.18 ng/mL, P=0.022; 7.67±1.54 vs. 8.27±1.46 weeks, P<0.001, respectively). Multivariate analysis revealed that low AMH level and early gestational age were maternal age-independent markers for fetal aneuploid (P<0.001 and P=0.045, respectively).

Conclusion

Low maternal AMH level might be a predicting marker for fetal aneuploid in early pregnancy loss.

Short- and long-term effects of chromosome mis-segregation and aneuploidy

Dividing cells that experience chromosome mis-segregation generate aneuploid daughter cells, which contain an incorrect number of chromosomes. Although aneuploidy interferes with the proliferation of untransformed cells, it is also, paradoxically, a hallmark of cancer, a disease defined by increased proliferative potential. These contradictory effects are also observed in mouse models of chromosome instability (CIN). CIN can inhibit and promote tumorigenesis. Recent work has provided insights into the cellular consequences of CIN and aneuploidy. Chromosome mis-segregation per se can alter the genome in many more ways than just causing the gain or loss of chromosomes. The short- and long-term effects of aneuploidy are caused by gene-specific effects and a stereotypic aneuploidy stress response. Importantly, these recent findings provide insights into the role of aneuploidy in tumorigenesis.

Kagami-Ogata syndrome: a clinically recognizable upd(14)pat and related disorder affecting the chromosome 14q32.2 imprinted region

Human chromosome 14q32.2 carries paternally expressed genes including DLK1 and RTL1, and maternally expressed genes including MEG3 and RTL1as, along with the germline-derived DLK1-MEG3 intergenic differentially methylated region (IG-DMR) and the postfertilization-derived MEG3-DMR. Consistent with this, paternal uniparental disomy 14 (upd(14)pat), and epimutations (hypermethylations) and microdeletions affecting the IG-DMR and/or the MEG3-DMR of maternal origin, result in a unique phenotype associated with characteristic face, a small bell-shaped thorax with coat-hanger appearance of the ribs, abdominal wall defects, placentomegaly and polyhydramnios. Recently, the name ‘Kagami–Ogata syndrome' (KOS) has been approved for this clinically recognizable disorder. Here, we review the current knowledge about KOS. Important findings include the following: (1) the facial ‘gestalt' and the increased coat-hanger angle constitute pathognomonic features from infancy through childhood/puberty; (2) the unmethylated IG-DMR and MEG3-DMR of maternal origin function as the imprinting control centers in the placenta and body respectively, with a hierarchical interaction regulated by the IG-DMR for the methylation pattern of the MEG3-DMR in the body; (3) RTL1 expression level becomes ~2.5 times increased in the absence of functional RTL1as-encoded microRNAs that act as a trans-acting repressor for RTL1; (4) excessive RTL1 expression and absent MEG expression constitute the primary underlying factor for the phenotypic development; and (5) upd(14)pat accounts for approximately two-thirds of KOS patients, and epimutations and microdeletions are identified with a similar frequency. Furthermore, we refer to diagnostic and therapeutic implications.

Targeting oocyte maturation to improve fertility in older women

Reproductive aging is an increasingly pressing problem facing women in modern society, due to delay in child bearing. According to Statistics Canada, 52% of all Canadian births in 2011 were by women aged 30 years and older, up from 24% in 1981 ( http://www.statcan.gc.ca/pub/91-209-x/2013001/article/11784-eng.htm ). Women older than 35 years of age experience significantly increased risks of infertility, miscarriage and congenital birth defects, mostly due to poor quality of the eggs. Increasingly sophisticated, and often invasive, assisted reproductive technologies (ARTs) have helped millions of women to achieve reproductive success. However, by and large, ARTs do not address the fundamental issue of reproductive aging in women: age-related decline in egg quality. More importantly, ARTs are not, and will never be, the main solution for the general population. Here, I attempt to review the scientific literature on age-related egg quality decline, based mostly on studies in mice and in humans. Emphasis is given to the brief period of time called oocyte maturation, which occurs just prior to ovulation. The rationale for this emphasis is that oocyte maturation represents a critical window where unfavorable ovarian conditions in older females contribute significantly to the decline of egg quality, and that science-based intervention during oocyte maturation represents the best chance of improving egg quality in older women. Finally, I summarize our own work in recent years on peri-ovulatory putrescine supplementation as a possible remedy for reproductive aging.

Increased chromosome 16 disomy rates in human spermatozoa and recurrent spontaneous abortions

OBJECTIVE

To investigate if unexplained recurrent spontaneous abortions (RSA) are associated with increased rates of aneuploidy in spermatozoa of RSA partners ("RSA-men").

DESIGN

Case-control study.

SETTING

Academic research center.

PATIENT(S)

Patients enrolled at the Hormone and Fertility Center and controls at the Department of Urology (LMU-Munich).

INTERVENTION(S)

Sperm samples of 11 partners of unexplained RSA cases evaluated for elevated diploidy and disomy levels of chromosomes 1-22, X, and Y by multicolor sperm fluorescence in situ hybridization (FISH).

MAIN OUTCOME MEASURE(S)

Aneuploidy rates obtained in RSA-men compared with controls from the literature and internally; an increase of the aneuploidy rate was considered statistically significant, when it differed ≥ 2 standard deviations from the mean baseline level in controls.

RESULT(S)

Our sperm FISH data on RSA men showed increased disomy rates for at least three chromosomes in more than 60% of patients but no statistically significant increase of the overall mean sperm disomy or diploidy rate. In particular, meiotic errors involving chromosome 16 contributed to increased sperm disomy in more than 60% of our patients.

CONCLUSION(S)

These data suggest that among paternal meiotic errors nondisjunction of chromosome 16 might have similar relative influence on fetal aneuploidy compared with maternal chromosome 16 disomy.

Molecular turnover, the H3.3 dilemma and organismal aging (hypothesis)

The H3.3 histone variant has been a subject of increasing interest in the field of chromatin studies due to its two distinguishing features. First, its incorporation into chromatin is replication independent unlike the replication-coupled deposition of its canonical counterparts H3.1/2. Second, H3.3 has been consistently associated with an active state of chromatin. In accordance, this histone variant should be expected to be causally involved in the regulation of gene expression, or more generally, its incorporation should have downstream consequences for the structure and function of chromatin. This, however, leads to an apparent paradox: In cells that slowly replicate in the organism, H3.3 will accumulate with time, opening the way to aberrant effects on heterochromatin. Here, we review the indications that H3.3 is expected both to be incorporated in the heterochromatin of slowly replicating cells and to retain its functional downstream effects. Implications for organismal aging are discussed.

Meiosis and maternal aging: insights from aneuploid oocytes and trisomy births

In most organisms, genome haploidization requires reciprocal DNA exchanges (crossovers) between replicated parental homologs to form bivalent chromosomes. These are resolved to their four constituent chromatids during two meiotic divisions. In female mammals, bivalents are formed during fetal life and remain intact until shortly before ovulation. Extending this period beyond ∼35 years greatly increases the risk of aneuploidy in human oocytes, resulting in a dramatic increase in infertility, miscarriage, and birth defects, most notably trisomy 21. Bivalent chromosomes are stabilized by cohesion between sister chromatids, which is mediated by the cohesin complex. In mouse oocytes, cohesin becomes depleted from chromosomes during female aging. Consistent with this, premature loss of centromeric cohesion is a major source of aneuploidy in oocytes from older women. Here, we propose a mechanistic framework to reconcile data from genetic studies on human trisomy and oocytes with recent advances in our understanding of the molecular mechanisms of chromosome segregation during meiosis in model organisms.

Consumption of low-moderate level arsenic contaminated water does not increase spontaneous pregnancy loss: a case control study

BACKGROUND

Previous work suggests an increased risk for spontaneous pregnancy loss linked to high levels of inorganic arsenic (iAs) in drinking water sources (>10 μg/L). However, there has been little focus to date on the impact of low-moderate levels of iAs in drinking water (<10 μg/L). To address this data gap we conducted a hospital-based case-control study in Timis County, Romania.

METHODS

We recruited women with incident spontaneous pregnancy loss of 5-20 weeks completed gestation as cases (n = 150), and women with ongoing pregnancies matched by gestational age (±1 week) as controls (n = 150). Participants completed a physician-administered questionnaire and we collected water samples from residential drinking sources. We reconstructed residential drinking water exposure histories using questionnaire data weighted by iAs determined using hydride generation-atomic absorption spectrometry (HG-AAS). Logistic regression models were used to generate odds ratios (OR) and 95% confidence intervals (CI) for associations between iAs exposure and loss, conditioned on gestational age and adjusted for maternal age, cigarette smoking, education and prenatal vitamin use. We explored potential interactions in a second set of models.

RESULTS

Drinking water arsenic concentrations ranged from 0.0 to 175.1 μg/L, with median 0.4 μg/L and 90th%tile 9.4 μg/L. There were no statistically significant associations between loss and average or peak drinking water iAs concentrations (OR 0.98, 95% CI 0.96-1.01), or for daily iAs intake (OR 1.00, 95% CI 0.98-1.02). We detected modest evidence for an interaction between average iAs concentration and cigarette smoking during pregnancy (P = 0.057) and for daily iAs exposure and prenatal vitamin use (P = 0.085).

CONCLUSIONS

These results suggest no increased risk for spontaneous pregnancy loss in association with low to moderate level drinking water iAs exposure. Though imprecise, our data also raise the possibility for increased risk among cigarette smokers. Given the low exposures overall, these data should reassure pregnant women and policy makers with regard to the potential effect of drinking water iAs on early pregnancy, though a larger more definitive study to investigate the potential risk increase in conjunction with cigarette smoking is merited.

The association of low socioeconomic status and the risk of having a child with Down syndrome: a report from the National Down Syndrome Project

PURPOSE

Advanced maternal age and altered recombination are known risk factors for Down syndrome cases due to maternal nondisjunction of chromosome 21, whereas the impact of other environmental and genetic factors is unclear. The aim of this study was to investigate an association between low maternal socioeconomic status and chromosome 21 nondisjunction.

METHODS

Data from 714 case and 977 control families were used to assess chromosome 21 meiosis I and meiosis II nondisjunction errors in the presence of three low socioeconomic status factors: (i) both parents had not completed high school, (ii) both maternal grandparents had not completed high school, and (iii) an annual household income of <$25,000. We applied logistic regression models and adjusted for covariates, including maternal age and race/ethnicity.

RESULTS

As compared with mothers of controls (n = 977), mothers with meiosis II chromosome 21 nondisjunction (n = 182) were more likely to have a history of one low socioeconomic status factor (odds ratio = 1.81; 95% confidence interval = 1.07-3.05) and ≥2 low socioeconomic status factors (odds ratio = 2.17; 95% confidence interval = 1.02-4.63). This association was driven primarily by having a low household income (odds ratio = 1.79; 95% confidence interval = 1.14-2.73). The same statistically significant association was not detected among maternal meiosis I errors (odds ratio = 1.31; 95% confidence interval = 0.81-2.10), in spite of having a larger sample size (n = 532).

CONCLUSION

We detected a significant association between low maternal socioeconomic status and meiosis II chromosome 21 nondisjunction. Further studies are warranted to explore which aspects of low maternal socioeconomic status, such as environmental exposures or poor nutrition, may account for these results.

Current understanding of ovarian aging

The reproductive system of human female exhibits a much faster rate of aging than other body systems. Ovarian aging is thought to be dominated by a gradual decreasing numbers of follicles, coinciding with diminished quality of oocytes. Menopause is the final step in the process of ovarian aging. This review focuses on the mechanisms underlying the ovarian aging involving a poor complement of follicles at birth and a high rate of attrition each month, as well as the alternated endocrine factors. We also discuss the possible causative factors that contribute to ovarian aging, e.g., genetic factors, accumulation of irreparable damage of microenvironment, pathological effect and other factors. The appropriate and reliable methods to assess ovarian aging, such as quantification of follicles, endocrine measurement and genetic testing have also been discussed. Increased knowledge of the ovarian aging mechanisms may improve the prevention of premature ovarian failure.

Human aneuploidy: mechanisms and new insights into an age-old problem

Trisomic and monosomic (aneuploid) embryos account for at least 10% of human pregnancies and, for women nearing the end of their reproductive lifespan, the incidence may exceed 50%. The errors that lead to aneuploidy almost always occur in the oocyte but, despite intensive investigation, the underlying molecular basis has remained elusive. Recent studies of humans and model organisms have shed new light on the complexity of meiotic defects, providing evidence that the age-related increase in errors in the human female is not attributable to a single factor but to an interplay between unique features of oogenesis and a host of endogenous and exogenous factors.

Relative frequency of underlying genetic causes for the development of UPD(14)pat-like phenotype

Paternal uniparental disomy 14 (UPD(14)pat) results in a unique constellation of clinical features, and a similar phenotypic constellation is also caused by microdeletions involving the DLK1-MEG3 intergenic differentially methylated region (IG-DMR) and/or the MEG3-DMR and by epimutations (hypermethylations) affecting the DMRs. However, relative frequency of such underlying genetic causes remains to be clarified, as well as that of underlying mechanisms of UPD(14)pat, that is, trisomy rescue (TR), gamete complementation (GC), monosomy rescue (MR), and post-fertilization mitotic error (PE). To examine this matter, we sequentially performed methylation analysis, microsatellite analysis, fluorescence in situ hybridization, and array-based comparative genomic hybridization in 26 patients with UPD(14)pat-like phenotype. Consequently, we identified UPD(14)pat in 17 patients (65.4%), microdeletions of different patterns in 5 patients (19.2%), and epimutations in 4 patients (15.4%). Furthermore, UPD(14)pat was found to be generated through TR or GC in 5 patients (29.4%), MR or PE in 11 patients (64.7%), and PE in 1 patient (5.9%). Advanced maternal age at childbirth (≥35 years) was predominantly observed in the MR/PE subtype. The results imply that the relative frequency of underlying genetic causes for the development of UPD(14)pat-like phenotype is different from that of other imprinting disorders, and that advanced maternal age at childbirth as a predisposing factor for the generation of nullisomic oocytes through non-disjunction at meiosis 1 may be involved in the development of MR-mediated UPD(14)pat.

Constitutional and acquired autosomal aneuploidy

Chromosomal imbalances can result from numerical or structural anomalies. Numerical chromosomal abnormalities are often referred to as aneuploid conditions. This article focuses on the occurrence of constitutional and acquired autosomal aneuploidy in humans. Topics covered include frequency, mosaicism, phenotypic findings, and etiology. The article concludes with a consideration of anticipated advances that might allow for the development of screening tests and/or lead to improvements in our understanding and management of the role that aneuploidy plays in the aging process and acquisition of age-related and constitutional conditions.

Cellular and molecular mechanisms of various types of oocyte aging

It is well established that age-related decline of a woman's fertility is related to the poor developmental potential of her gametes. The age-associated decline in female fertility is largely attributable to the oocyte aging caused by ovarian aging. Age-associated oocyte aging results in a decrease in oocyte quality. In contrast to ovarian aging, there is a concept of postovulatory oocyte aging. Postovulatory aging of oocytes, not being fertilized for a prolonged time after ovulation, is known to significantly affect the development of oocytes. Both categories of oocyte aging have similar phenotypes of reproductive failure. However, the mechanisms of the decline in oocyte quality are not necessarily equivalent. An age-dependent increase in aneuploidy is a key determinant of oocyte quality. The reduced expression of molecules regulating cell cycle control during meiosis might be involved in the age-dependent increase in aneuploidy. The mechanism of age-associated oocyte aging might be involved in mitochondrial dysfunction, whose etiologies are still unknown. Alternatively, the mechanism of postovulatory oocyte aging might be involved in reactive oxygen species-induced mitochondrial injury pathways followed by abnormal intracellular Ca²⁺ regulation of the endoplasmic reticulum. We suggest that future research into the mechanism of oocyte aging will be necessary to develop a method to rescue the poor developmental potential of aged oocytes.

Maternal age effect on the development of Prader-Willi syndrome resulting from upd(15)mat through meiosis 1 errors

Prader-Willi syndrome (PWS) is primarily caused by deletions involving the paternally derived imprinted region at chromosome 15q11.2-q13 and maternal uniparental disomy 15 (upd(15)mat). The underlying mechanisms for upd(15)mat include trisomy rescue (TR), gamete complementation (GC), monosomy rescue and post-fertilization mitotic error, and TR/GC is mediated by non-disjunction at maternal meiosis 1 (M1) or meiosis 2 (M2). Of these factors involved in the development of upd(15)mat, M1 non-disjunction is a maternal age-dependent phenomenon. We studied 117 Japanese patients with PWS and identified deletions in 84 patients (Deletion group) and TR/GC type upd(15)mat through M1 non-disjunction in 15 patients (TR/GC (M1) group), together with other types of abnormalities. Maternal age was significantly higher in TR/GC (M1) group than in Deletion group (median (range), 37 (35-45) versus 30 (19-42); P=1.0 × 10(-7)). Furthermore, delayed childbearing age became obvious since the year 2003 in Japan, and relative frequency of TR/GC (M1) group was significantly larger in patients born since the year 2003 than in those born until the year 2002. The results imply that the advanced maternal age at childbirth is a predisposing factor for the development of upd(15)mat because of increased M1 errors.

Aneuploidy in human spermatozoa

We reviewed the frequency and distribution of disomy in spermatozoa obtained by multicolor-FISH analysis on decondensed sperm nuclei in (a) healthy men, (b) fathers of aneuploid offspring of paternal origin and (c) individuals with Klinefelter syndrome and XYY males. In series of healthy men, disomy per autosome is approximately 0.1% but may range from 0.03 (chromosome 8) to 0.47 (chromosome 22). The great majority of authors find that chromosome 21 (0.18%) and the sex chromosomes (0.27%) have significantly elevated frequencies of disomy although these findings are not universal. The total disomy in FISH studies is 2.26% and the estimated aneuploidy (2× disomy) is 4.5%, more than double that seen in sperm karyotypes (1.8%). Increased disomy levels of low orders of magnitude have been reported in spermatozoa of some normal men (stable variants) and in men who have fathered children with Down, Turner and Klinefelter syndromes. These findings suggest that men with a moderately elevated aneuploidy rate may be at a higher risk of fathering paternally derived aneuploid pregnancies. Among lifestyle factors, smoking, alcohol and caffeine have been studied extensively but the compounding effects of the 3 are difficult to separate because they are common lifestyle behaviors. Increases in sex chromosome abnormalities, some autosomal disomies, and in the number of diploid spermatozoa are general features in 47,XXY and 47,XYY males. Aneuploidy of the sex chromosomes is more frequent than aneuploidy of any of the autosomes not only in normal control individuals, but also in patients with sex chromosome abnormalities and fathers of paternally derived Klinefelter, Turner and Down syndromes.

Age-related meiotic segregation errors in mammalian oocytes are preceded by depletion of cohesin and Sgo2

BACKGROUND

The growing trend for women to postpone childbearing has resulted in a dramatic increase in the incidence of trisomic pregnancies. Maternal age-related miscarriage and birth defects are predominantly a consequence of chromosome segregation errors during the first meiotic division (MI), which involves the segregation of replicated recombined homologous chromosomes. Despite the importance to human reproductive health, the events precipitating female age-related meiotic errors are poorly understood.

RESULTS

Here we use a long-lived wild-type mouse strain to show that the ability to segregate chromosomes synchronously during anaphase of MI declines dramatically during female aging. This is preceded by depletion of chromosome-associated cohesin in association with destabilization of chiasmata, the physical linkages between homologous chromosomes, and loss of the tight association between sister centromeres. Loss of cohesin is not due to an age-related decline in the ability of the spindle checkpoint to delay separase-mediated cleavage of cohesin until entry into anaphase I. However, we find that reduced cohesin is accompanied by depletion of Sgo2, which protects centromeric cohesin during MI.

CONCLUSIONS

The data indicate that cohesin declines gradually during the long prophase arrest that precedes MI in female mammals. In aged oocytes, cohesin levels fall below the level required to stabilize chiasmata and to hold sister centromeres tightly together, leading to chromosome missegregation during MI. Cohesin loss may be amplified by a concomitant decline in the levels of the centromeric cohesin protector Sgo2. These findings indicate that cohesin is a key molecular link between female aging and chromosome missegregation during MI.

Analysis of pronuclear zygote configurations in 459 clinical pregnancies obtained with assisted reproductive technique procedures

BACKGROUND

Embryos selection is crucial to maintain high performance in terms of pregnancy rate, reducing the risk of multiple pregnancy during IVF. Pronuclear and nucleolar characteristics have been proposed as an indicator of embryo development and chromosomal complement in humans, providing information about embryo viability.

METHODS

To correlate the zygote-score with the maternal age and the outcome of pregnancy, we analyzed the pronuclear and nucleolar morphology, the polar body alignment and the zygote configuration in 459 clinical pregnancies obtained by IVF and ICSI in our public clinic in Reggio Emilia, Italy. We derived odds ratios (OR) and Corenfield's 95% confidence intervals (CI). Continuous variables were compared with Student's t-test; P lower than .05 was considered statistically significant.

RESULTS

We observed a significant increase of "A" pronuclear morphology configuration in 38-41 years old patients in comparison to that lower than or equal to 32 years old and a significant decrease of "B" configuration in 38-41 years old patients in comparison to that lower than or equal to 32 and in comparison to that of 33-37 years old. Related to maternal age we found no significant differences in P1 and in P2 configuration. We found no correlation between zygote-score, embryo cleavage and embryo quality.

CONCLUSIONS

Our results confirm the limited clinical significance of zygote-score suggesting that it can not be associated with maternal age, embryo cleavage and embryo quality. The evaluation of embryo quality based on morphological parameters is probably more predictive than zygote-score.

High-density lipoprotein metabolism and the human embryo

BACKGROUND

High-density lipoprotein (HDL) appears to be the dominant lipoprotein particle in human follicular fluid (FF). The reported anti-atherogenic properties of HDL have been attributed in part to reverse cholesterol transport. The discoveries of the scavenger receptor class B type I (SR-BI) and the ATP-binding cassette A1 lipid (ABCA1) transporter have generated studies aimed at unraveling the pathways of HDL biogenesis, remodeling and catabolism. The production of SR-BI and ABCA1 knockout mice as well as other lipoprotein metabolism-associated mutants has resulted in reduced or absent fertility, leading us to postulate the existence of a human hepatic-ovarian HDL-associated axis of fertility. Here, we review an evolving literature on the role of HDL metabolism on mammalian fertility and oocyte development.

METHODS

An extensive online search was conducted of published articles relevant to the section topics discussed. All relevant English language articles contained in Pubmed/Medline, with no specific time frame for publication, were considered for this narrative review. Cardiovascular literature was highly cited due to the wealth of relevant knowledge on HDL metabolism, and the dearth thereof in the reproductive field.

RESULTS

Various vertebrate models demonstrate a role for HDL in embryo development and fertility. In our clinical studies, FF levels of HDL cholesterol and apolipoprotein AI levels were negatively associated with embryo fragmentation, but not with embryo cell cleavage rate. However, the HDL component, paraoxonase 1 arylesterase activity, was positively associated with embryo cell cleavage rate.

CONCLUSIONS

HDL contributes to intra-follicular cholesterol homeostasis which appears to be important for successful oocyte and embryo development.

[Half a century of human and medical cytogenetics]

In 1956, the number of chromosomes in humans is set at 46; in 1959, the link between a disability (mongolism) and a chromosomal anomaly (the Down syndrome) is established: human and medical cytogenetics were born. Since then, progress has been remarkable: the techniques of chromosomal and molecular cytogenetics can reach a resolution of the size of a single gene with a pangenomic scope. Practical applications are constantly expanded. The clinical impact is significant, from the genetic counselling in constitutional to the targeted therapies. Fifty years later, cytogenetics can be defined as the science which aims to detect chromosomal abnormalities, whether constitutional or acquired, using chromosomal or molecular techniques aiming to study the arrangement of genes in chromosomes, to quantify the number of gene copy and to look for the presence of gene fusion.

Ovarian aging: mechanisms and clinical consequences

Menopause is the final step in the process referred to as ovarian ageing. The age related decrease in follicle numbers dictates the onset of cycle irregularity and the final cessation of menses. The parallel decay in oocyte quality contributes to the gradual decline in fertility and the final occurrence of natural sterility. Endocrine changes mainly relate to the decline in the negative feedback from ovarian factors at the hypothalamo-pituitary unit. The declining cohort of antral follicles with age first results in gradually elevated FSH levels, followed by subsequent stages of overt cycle irregularity. The gradual decline in the size of the antral follicle cohort is best represented by decreasing levels of anti-Mullerian hormone. The variability of ovarian ageing among women is evident from the large variation in age at menopause. The identification of women who have severely decreased ovarian reserve for their age is clinically relevant. Ovarian reserve tests have appeared to be fairly accurate in predicting response to ovarian stimulation in the assisted reproductive technology (ART) setting. The capacity to predict the chances for spontaneous pregnancy or pregnancy after ART appears very limited. As menopause and the preceding decline in oocyte quality seem to have a fixed time interval, tests that predict the age at menopause may be useful to assess individual reproductive lifespan. Especially genetic studies, both addressing candidate gene and genome wide association, have identified several interesting loci of small genetic variation that may determine fetal follicle pool development and subsequent wastage of his pool over time. Improved knowledge of the ovarian ageing mechanisms may ultimately provide tools for prediction of menopause and manipulation of the early steps of folliculogenesis for the purpose of contraception and fertility lifespan extension.

Effects of in vitro maturation and age on oocyte quality in the rhesus macaque Macaca mulatta

OBJECTIVE

To evaluate oocyte quality in a primate model.

DESIGN

Analysis of oocyte karyotype by chromosome spreading and oocyte spindles by confocal microscopy.

SETTING

Research laboratory, Caribbean Primate Research Center.

ANIMAL(S)

Rhesus macaques aged 6-22 years.

INTERVENTION(S)

Fourteen females underwent both Regimen A (FSH + hCG) and Regimen B (FSH only) stimulation cycles to facilitate collection of mature and immature oocytes. Immature oocytes from Regimens A and B underwent in vitro maturation (IVM) to produce metaphase II oocytes. All metaphase II oocytes underwent gradual fixation to spread chromosomes or were fixed and stained with probes specific to alpha-tubulin, actin, and DNA for visualization of the meiotic spindle using confocal microscopy.

MAIN OUTCOME MEASURE(S)

Karyotype and meiotic spindle architecture differences among in vivo matured (IVO) and IVM oocytes from young and old rhesus macaques.

RESULT(S)

In all, 4.7% of IVO oocytes (Regimen A) from young females were hyperhaploid versus 25.0% of IVM oocytes (Regimen B) from old females; 4.5% of IVO oocytes (Regimen A) from young females versus 51.5% of IVM oocytes (Regimen B) from old females displayed abnormal chromosome alignment on the metaphase spindle.

CONCLUSION(S)

IVM can induce meiotic anomalies in macaque oocytes, especially those obtained from older females. Results from this study provide possible explanations for the reported reduction in developmental competence of IVM primate oocytes.

[Anti-Müllerian hormone--its role in management of involuntary infertility]

BACKGROUND

Although fertility in women decreases significantly after the age of 35 years, women in Norway - as in many other developed countries- postpone having children. It has long been recognised that there is a need for a better marker of ovarian function. This article provides an overview of physiological development of follicles in the ovaries and the special place Anti-Müllerian- hormone has in this process.

MATERIAL AND METHODS

Literature was retrieved from the databases PubMed, Athens and Embase by using the keywords Anti-Müllerian hormone, follicle, ovarian reserve, ovarian response and fertility. The reference lists of relevant articles were searched for additional information.

RESULTS AND INTERPRETATION

32 articles with relevant information were retrieved. The level of Anti-Müllerian hormone is relatively stable throughout the menstruation cycle. The hormone appears to be a reliable marker for ovarian reserve and ovarian response after controlled ovarian hyperstimulation during in vitro fertilisation. Determination of the hormone level will enable identification of women with high risk of deviating response upon ovarian hyperstimulation.

The clinical content of preconception care: genetics and genomics

The prevalence of paternal and maternal genetic conditions that affect pregnancy varies according to many factors that include parental age, medical history, and family history. Although some genetic conditions that affect pregnancy are identified easily early in life, other conditions are not and may require additional diagnostic testing. A complete 3-generation family medical history that includes ethnicity information about both sides of the family is arguably the single best genetic "test" that is applicable to preconception care. Assessment of genetic risk by an experienced professional has been shown to improve the detection rate of identifiable risk factors. Learning about possible genetic issues in the preconception period is ideal, because knowledge permits patients to make informed reproductive decisions. Options that are available to couples before conception include adoption, surrogacy, use of donor sperm, in vitro fertilization after preimplantation genetic diagnosis, and avoidance of pregnancy. Future technologic advances will increase the choices that are available to couples.