Biallelic variants in α-tubulin isotypes cause female infertility characterised as recurrent preimplantation embryo arrest.

BACKGROUND: Recurrent preimplantation embryo developmental arrest (RPEA) is the most common phenotype in assisted reproductive technology treatment failure associated with identified genetic abnormalities. Currently known maternal genetic variants explain only a limited number of cases. Variants of the ß-tubulin subunit gene, TUBB8, cause oocyte meiotic arrest and RPEA through a broad spectrum of spindle defects. In contrast, α-tubulin subunit genes are poorly studied in the context of preimplantation embryonic development. METHODS: Whole exome sequencing was performed on the PREA cohort. Functional characterisations of the identified candidate disease-causing variants were validated using Sanger sequencing, bioinformatics, in vitro functional analyses and single-cell RNA-sequencing of arrested embryos. RESULTS: Four homozygous variants were identified in the PREA cohort: two of TUBA1C (p.Gln358Ter and p.Asp444Metfs*42) and two of TUBA4A (p.Arg339Cys and p.Tyr440Ter). These variants cause varying degrees of spindle assembly defects. Additionally, we characterised changes in the human arrested embryo transcriptome carrying TUBA4A variants, with a particular focus on spindle organisation, chromosome segregation and mRNA decay. CONCLUSION: Our findings identified TUBA1C as a novel genetic marker and expanded the genetic and phenotypic spectrum of TUBA4A in female infertility and RPEA, which altogether highlighted the importance of α-tubulin isotypes in preimplantation embryonic development.

Homozygous pathogenic variants in ACTL9 cause fertilization failure and male infertility in humans and mice.

Total fertilization failure (TFF) can occur during in vitro fertilization (IVF) treatments, even following intracytoplasmic sperm injection (ICSI). Various male or female factors could contribute to TFF. Increasing evidence suggested that genetic variations in PLCZ1, which encodes 1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase zeta-1 (PLCζ), is involved in oocyte activation and is a key male factor in TFF. In the present study, we explored the genetic variants in male individuals that led to TFF. A total of 54 couples with TFF or poor fertilization (fertilization rate < 20%) were screened, and 21 couples were determined to have a male infertility factor by the mouse oocyte activation test. Whole-exome sequencing of these 21 male individuals identified three homozygous pathogenic variants in ACTL9 (actin like 9) in three individuals. ACTL9 variations led to abnormal ultrastructure of the perinuclear theca (PT), and PLCζ was absent in the head and present in the neck of the mutant sperm, which contributed to failed normal calcium oscillations in oocytes and subsequent TFF. The key roles of ACTL9 in the PT structure and TFF after ICSI were further confirmed in an Actl9-mutated mouse model. Furthermore, assisted oocyte activation by calcium ionophore exposure successfully overcame TFF and achieved live births in a couple with an ACTL9 variant. These findings identified the role of ACTL9 in the PT structure and the correct localization of PLCζ. The results also provide a genetic marker and a therapeutic option for individuals who have undergone ICSI without successful fertilization.

Extended application of PGT-M strategies for small pathogenic CNVs.

PURPOSE: The preimplantation genetic testing for aneuploidy (PGT-A) platform is not currently available for small copy-number variants (CNVs), especially those < 1 Mb. Through strategies used in PGT for monogenic disease (PGT-M), this study intended to perform PGT for families with small pathogenic CNVs. METHODS: Couples who carried small pathogenic CNVs and underwent PGT at the Reproductive and Genetic Hospital of CITIC-Xiangya (Hunan, China) between November 2019 and April 2023 were included in this study. Haplotype analysis was performed through two platforms (targeted sequencing and whole-genome arrays) to identify the unaffected embryos, which were subjected to transplantation. Prenatal diagnosis using amniotic fluid was performed during 18-20 weeks of pregnancy. RESULTS: PGT was successfully performed for 20 small CNVs (15 microdeletions and 5 microduplications) in 20 families. These CNVs distributed on chromosomes 1, 2, 6, 7, 13, 15, 16, and X with sizes ranging from 57 to 2120 kb. Three haplotyping-based PGT-M strategies were applied. A total of 89 embryos were identified in 25 PGT cycles for the 20 families. The diagnostic yield was 98.9% (88/89). Nineteen transfers were performed for 17 women, resulting in a 78.9% (15/19) clinical pregnancy rate after each transplantation. Of the nine women who had healthy babies, eight accepted prenatal diagnosis and the results showed no related pathogenic CNVs. CONCLUSION: Our results show that the extended haplotyping-based PGT-M strategy application for small pathogenic CNVs compensated for the insufficient resolution of PGT-A. These three PGT-M strategies could be applied to couples with small pathogenic CNVs.

Very severe oligozoospermia with AZFc microdeletion patients may affect intracytoplasmic sperm injection clinical outcomes: A propensity score matching analysis.

Purpose: To explore whether spermatozoa from AZFc microdeletion patients affect their outcomes of intracytoplasmic sperm injection (ICSI). Methods: Eighty-five patients with AZFc microdeletion were recruited. A control group of one hundred and forty patients with severe oligozoospermia but without AZF microdeletion was selected using propensity score matching analysis with a 1:2 nearest neighbor algorithm ratio. The ICSI outcomes of the two groups were compared. Results: AZFc microdeletion had lower rates of normal fertilization (73% vs. 80%, p = 0.17) and high-quality embryos (44% vs. 58%, p = 0.07) than the control group. There was no significant difference in the clinical pregnancy rate, miscarriage rate, and live birth rate between the two groups. When the sperm concentration was <1 million/mL, the AZFc microdeletion group exhibited lower rates of fertilization (71% vs. 80%, p = 0.03), high-quality embryo (44% vs. 58%, p = 0.02), clinical pregnancy (57% vs. 76%, p = 0.02), and live birth (49% vs. 72%, p = 0.01) than the control group. However, if sperm concentration was ≥1 million/mL, no significant differences were found. Conclusion: If the sperm concentration is <1 million/mL, AZFc microdeletion do have a detrimental effect on most outcomes of ICSI.

Homozygous Mutations in BTG4 Cause Zygotic Cleavage Failure and Female Infertility.

Zygotic cleavage failure (ZCF) is a unique early embryonic phenotype resulting in female infertility and recurrent failure of in vitro fertilization (IVF) and/or intracytoplasmic sperm injection (ICSI). With this phenotype, morphologically normal oocytes can be retrieved and successfully fertilized, but they fail to undergo cleavage. Until now, whether this phenotype has a Mendelian inheritance pattern and which underlying genetic factors play a role in its development remained to be elucidated. B cell translocation gene 4 (BTG4) is a key adaptor of the CCR4-NOT deadenylase complex, which is involved in maternal mRNA decay in mice, but no human diseases caused by mutations in BTG4 have previously been reported. Here, we identified four homozygous mutations in BTG4 (GenBank: NM_017589.4) that are responsible for the phenotype of ZCF, and we found they followed a recessive inheritance pattern. Three of them-c.73C>T (p.Gln25Ter), c.1A>G (p.?), and c.475_478del (p.Ile159LeufsTer15)-resulted in complete loss of full-length BTG4 protein. For c.166G>A (p.Ala56Thr), although the protein level and distribution of mutant BTG4 was not altered in zygotes from affected individuals or in HeLa cells, the interaction between BTG4 and CNOT7 was abolished. In vivo studies further demonstrated that the process of maternal mRNA decay was disrupted in the zygotes of the affected individuals, which provides a mechanistic explanation for the phenotype of ZCF. Thus, we provide evidence that ZCF is a Mendelian phenotype resulting from mutations in BTG4. These findings contribute to our understanding of the role of BTG4 in human early embryonic development and provide a genetic marker for female infertility.

Exploring the efficacy and beneficial population of preimplantation genetic testing for aneuploidy start from the oocyte retrieval cycle: a real-world study.

BACKGROUND: Preimplantation genetic testing for aneuploidy (PGT-A) is widely used as an embryo selection technique in in vitro fertilization (IVF), but its effectiveness and potential beneficiary populations are unclear. METHODS: This retrospective cohort study included patients who underwent their first oocyte retrieval cycles at CITIC-Xiangya between January 2016 and November 2019, and the associated fresh and thawed embryo transfer cycles up to November 30, 2020. PGT-A (PGT-A group) and intracytoplasmic sperm injection (ICSI)/IVF (non-PGT-A group) cycles were included. The numbers of oocytes and embryos obtained were unrestricted. In total, 60,580 patients were enrolled, and baseline data were matched between groups using 1:3 propensity score matching. Sensitivity analyses, including propensity score stratification and traditional multivariate logistic regression, were performed on the original unmatched cohort to check the robustness of the overall results. Analyses were stratified by age, body mass index, ovarian reserve/responsiveness, and potential indications to explore benefits in subgroups. The primary outcome was cumulative live birth rate (CLBR). The other outcomes included live birth rate (LBR), pregnancy loss rate, clinical pregnancy rate, pregnancy complications, low birth weight rate, and neonatal malformation rate. RESULTS: In total, 4195 PGT-A users were matched with 10,140 non-PGT-A users. A significant reduction in CLBR was observed in women using PGT-A (27.5% vs. 31.1%; odds ratio (OR) = 0.84, 95% confidence interval (CI) 0.78-0.91; P < 0.001). However, women using PGT-A had higher first-transfer pregnancy (63.9% vs. 46.9%; OR = 2.01, 95% CI 1.81-2.23; P < 0.001) and LBR (52.6% vs. 34.2%, OR = 2.13, 95% CI 1.92-2.36; P < 0.001) rates and lower rates of early miscarriage (12.8% vs. 20.2%; OR = 0.58, 95% CI 0.48-0.70; P < 0.001), preterm birth (8.6% vs 17.3%; P < 0.001), and low birth weight (4.9% vs. 19.3%; P < 0.001). Moreover, subgroup analyses revealed that women aged ≥ 38 years, diagnosed with recurrent pregnancy loss or intrauterine adhesions benefited from PGT-A, with a significant increase in first-transfer LBR without a decrease in CLBR. CONCLUSION: PGT-A does not increase and decrease CLBR per oocyte retrieval cycle; nonetheless, it is effective in infertile populations with specific indications. PGT-A reduces complications associated with multiple gestations.

Biallelic variants in ZFP36L2 cause female infertility characterised by recurrent preimplantation embryo arrest.

BACKGROUND: Recurrent preimplantation embryo developmental arrest (RPEA) is the most common cause of assisted reproductive technology treatment failure associated with identified genetic abnormalities. Variants in known maternal genes can only account for 20%-30% of these cases. The underlying genetic causes for the other affected individuals remain unknown. METHODS: Whole exome sequencing was performed for 100 independent infertile females that experienced RPEA. Functional characterisations of the identified candidate disease-causative variants were validated by Sanger sequencing, bioinformatics and in vitro functional analyses, and single-cell RNA sequencing of zygotes. RESULTS: Biallelic variants in ZFP36L2 were associated with RPEA and the recurrent variant (p.Ser308_Ser310del) prevented maternal mRNA decay in zygotes and HeLa cells. CONCLUSION: These findings emphasise the relevance of the relationship between maternal mRNA decay and human preimplantation embryo development and highlight a novel gene potentially responsible for RPEA, which may facilitate genetic diagnoses.

Oxygen concentration from days 1 to 3 after insemination affects the embryo culture quality, cumulative live birth rate, and perinatal outcomes.

PURPOSE: We aimed to compare embryo development, cumulative live birth rate (CLBR), and perinatal outcomes of embryos cultured in 20% and 5% oxygen from days 1 to 3 after insemination. METHODS: This retrospective study included patients who received in vitro fertilization (IVF) treatment between January 2015 and November 2019. Embryos of each patient were cultured at 20% or 5% oxygen from days 1-3 after insemination. The primary outcome was CLBR. Propensity score matching (PSM) was used to balance patients' baseline data in both oxygen groups. RESULTS: In total, 31,566 patients were enrolled. After PSM, the rate of high-quality day 3 embryos was significantly lower in the 20% than in the 5% oxygen group (0.49 ± 0.33 vs 0.51 ± 0.33; adjusted ß = -0.03; 95% confidence interval [CI], -0.03 to -0.02). The CLBR was significantly lower in the 20% than in the 5% oxygen group (58.6% vs. 62.4%; adjusted odds ratio = 0.85; 95% CI, 0.81-0.90). The birthweight and Z score of singletons were significantly higher in the 20% than in the 5% oxygen group (birthweight: 3.30 ± 0.50 vs. 3.28 ± 0.48; adjusted ß = 0.022; 95% CI, 0.004-0.040; Z score: 0.26 ± 1.04 vs. 0.22 ± 1.01; adjusted ß = 0.037; 95% CI, 0.001-0.074). CONCLUSION: Culturing embryos at atmospheric oxygen concentrations from days 1 to 3 compromises embryo quality, reduces CLBR, and affects birthweight. The 5% oxygen concentration is more suitable for embryo culture in IVF laboratories to achieve successful outcomes.

Embryo development, pregnancy and live birth outcomes following IVF treatment were not compromised during the COVID-19 pandemic.

PURPOSE: To evaluate whether outcomes of in vitro fertilization (IVF) are affected during the coronavirus disease-19 (COVID-19) pandemic. METHODS: This was a single-center, retrospective study. Embryo development, pregnancy, and live birth outcomes were compared between COVID-19 and pre-COVID-19 groups. Blood samples from patients during the COVID-19 pandemic were tested for COVID-19. RESULTS: After 1:1 random matching, 403 cycles for each group were included in the study. The rates of fertilization, normal fertilization, and blastocyst formation were higher in the COVID-19 group than in the pre-COVID-19 group. No difference was observed in the rates of day 3 good-quality embryos and good-quality blastocysts between the groups. A multivariate analysis showed that the live birth rate in the COVID-19 group was higher than that in the pre-COVID-19 group (51.4% vs. 41.4%, P = 0.010). In fresh cleavage-stage embryo and blastocyst transfer cycles, there were no differences between the groups in terms of pregnancy, obstetric, and perinatal outcomes. In the freeze-all cycles, the live birth rate was higher during the COVID-19 pandemic (58.0% vs. 34.5%, P = 0.006) than during the pre-COVID-19 period following frozen cleavage stage embryo transfer. The rate of gestational diabetes during the COVID-19 pandemic was higher than that during the pre-COVID-19 period (20.3% vs. 2.4%, P = 0.008) following frozen blastocyst transfer. All the serological results of the patients during the COVID-19 pandemic were negative. CONCLUSION: Our results indicate that embryo development, pregnancy, and live birth outcomes in uninfected patients were not compromised during the COVID-19 pandemic at our center.

Conventional IVF is feasible in preimplantation genetic testing for aneuploidy.

PURPOSE: To investigate the feasibility of the application of conventional in vitro fertilization (cIVF) for couples undergoing preimplantation genetic testing for aneuploidies (PGT-A) with non-male factor infertility. METHODS: To evaluate the efficiency of sperm whole-genome amplification (WGA), spermatozoa were subjected to three WGA protocols: Picoplex, ChromInst, and multiple displacement amplification (MDA). In the clinical studies, 641 couples who underwent PGT-A treatment for frozen embryos between January 2016 and December 2021 were included to retrospectively compare the chromosomal and clinical outcomes of cIVF and intracytoplasmic sperm injection (ICSI). Twenty-six couples were prospectively recruited for cIVF and PGT-A treatment between April 2021 and April 2022; parental contamination was analyzed in biopsied samples; and 12 aneuploid embryos were donated to validate the PGT-A results. RESULTS: Sperm DNA failed to amplify under Picoplex and ChromInst conditions but could be amplified using MDA. In frozen PGT-A cycles, no significant differences in the average rates of euploid, mosaic, and aneuploid embryos per cycle between the cIVF-PGT-A and ICSI-PGT-A groups were observed. The results of the prospective study that recruited couples for cIVF-PGT-A treatment showed no paternal contamination and one case of maternal contamination in 150 biopsied trophectoderm samples. Among the 12 donated embryos with whole-chromosome aneuploidy, 11 (91.7%) presented uniform chromosomal aberrations, which were in agreement with the original biopsy results. CONCLUSIONS: Under the Picoplex and ChromInst WGA protocols, the risk of parental contamination in the cIVF-PGT-A cycles was low. Therefore, applying cIVF to couples with non-male factor infertility who are undergoing PGT-A is feasible.

Non-invasive preimplantation genetic testing for conventional IVF blastocysts.

BACKGROUND: Previous studies suggested that non-invasive preimplantation genetic testing (niPGT) for intracytoplasmic sperm injection (ICSI) blastocysts can be used to identify chromosomal ploidy and chromosomal abnormalities. Here, we report the feasibility and performance of niPGT for conventional in vitro fertilization (IVF) blastocysts. METHODS: This was a prospective observational study. In the preclinical stage, whole genome amplification and NGS were performed using the sperm spent culture medium (SCM). Then, trophectoderm (TE) biopsies and corresponding SCM derived from 27 conventional IVF monopronuclear embryos were collected. In the clinical stage, samples from 25 conventional IVF cycles and 37 ICSI cycles from April 2020-August 2021 were collected for performance evaluation. RESULTS: Preclinically, we confirmed failed sperm DNA amplification under the current amplification system. Subsequent niPGT from the 27 monopronuclear blastocysts showed 69.2% concordance with PGT results of corresponding TE biopsies. In the clinical stage, no paternal contamination was observed in any of the 161 SCM samples from conventional IVF. While maternal contamination was observed in 29.8% (48/161) SCM samples, only 2.5% (4/161) samples had a contamination ratio ≥ 50%. Compared with that of TE biopsy, the performances of NiPGT from 161 conventional IVF embryos and 122 ICSI embryos were not significantly different (P > 0.05), with ploidy concordance rates of 75% and 74.6% for IVF and ICSI methods, respectively. Finally, evaluation of the euploid probability of embryos with different types of niPGT results showed prediction probabilities of 82.8%, 77.8%, 62.5%, 50.0%, 40.9% and 18.4% for euploidy, sex-chromosome mosaics only, low-level mosaics, multiple abnormal chromosomes, high-level mosaics and aneuploidy, respectively. CONCLUSIONS: Our research results preliminarily confirm that the niPGT approach using SCM from conventional IVF has comparable performance with ICSI and might broadening the application scope of niPGT.

Segmental aneuploidies with 1 Mb resolution in human preimplantation blastocysts.

PURPOSE: This study aimed to investigate the spectrum and characteristics of segmental aneuploidies (SAs) of <10 megabase (Mb) length in human preimplantation blastocysts. METHODS: Preimplantation genetic testing for aneuploidy was performed in 15,411 blastocysts from 5171 patients using a validated 1 Mb resolution platform. The characteristics and spectrum of SAs, including the incidence, sizes, type, inheritance pattern, clinical significance, and embryo distribution, were studied. RESULTS: In total, 6.4% of the 15,411 blastocysts carried SAs of >10 Mb, 4.9% of embryos had SAs ranging between 1 to 10 Mb, and 84.3% of 1 to 10 Mb SAs were <5 Mb in size. Inheritance pattern analysis indicated that approximately 63.8% of 1 to 10 Mb SAs were inherited and were predominantly 1 to 3 Mb in size. Furthermore, 18.4% of inherited SAs and 51.9% de novo 1 to 10 Mb SAs were pathogenic or likely pathogenic (P/LP). Different from whole-chromosome aneuploidies, reanalysis indicated that 50% of the de novo 1 to 10 Mb SAs and 70% of the >10 Mb SAs arose from mitotic errors. CONCLUSION: Based on the established platform, 1 to 10 Mb SAs are common in blastocysts and include a subset of P/LP SAs. Inheritance pattern analysis and clinical interpretation based on the American College of Medical Genetics and Genomics/Association for Molecular Pathology guidelines contributed to determine the P/LP SAs.

An increase of phosphatidylcholines in follicular fluid implies attenuation of embryo quality on day 3 post-fertilization.

BACKGROUND: Although oocyte quality is the dominant factor determining embryo quality, few studies have been conducted to evaluate embryo quality based on the metabolites related to the oocyte. With quantification of the follicular fluid (FF) metabolites, in assisted reproductive technology (ART), this study sought to evaluate the embryo or oocyte quality through an informative approach. RESULTS: An evaluation model consisting of 17 features was generated to distinguish the embryo quality on day 3 post-fertilization, and phosphatidylcholines (PCs) were the key contributors to the evaluation. The model was extended to the patients under different ages and hyperstimulations, and the features were further enriched to facilitate the evaluation of the embryo quality. The metabolites were clustered through pathway analysis, leading to a hypothesis that accumulation of arachidonic acid induced by PCs might weaken embryo quality on day 3 post-fertilization. CONCLUSIONS: A discriminating model with metabolic features elicited from follicular fluid was established, which enabled the evaluation of the embryo or oocyte quality even under certain clinical conditions, and the increase of PCs in follicular fluid implies the attenuation of embryo quality on day 3 post-fertilization.

Expanding the genetic and phenotypic spectrum of the subcortical maternal complex genes in recurrent preimplantation embryonic arrest.

The subcortical maternal complex (SCMC) is an oocyte-to-embryo-specific maternal functional module. Some variants of SCMC genes that contribute to preimplantation embryonic arrest have been identified. However, more novel variants should be identified to broaden the genetic and phenotypic spectrum of SCMC genes and establish their roles in embryonic development. We identified 13 novel variants in the SCMC genes, TLE6, NLRP5, NLRP2, and PADI6, from 10 of a total of 50 infertile females with recurrent preimplantation embryonic arrest. Six variants in TLE6 were found in five patients with embryonic arrest, accompanied by direct cleavage and severe fragmentation at the cleavage stage. Three patients carried NLRP5 variants, and one patient each who carried NLRP2 and PADI6 variants had subsequent poor or failed fertilization and cleavage arrest with a relatively lower ratio of severely fragmented embryos. Our findings expand the genetic and phenotypic spectrum of SCMC genes associated with human embryogenesis and might help lay the foundation for the genetic diagnosis of female infertility.

Complex mosaic blastocysts after preimplantation genetic testing: prevalence and outcomes after re-biopsy and re-vitrification.

RESEARCH QUESTION: What is the incidence of complex mosaic in preimplantation genetic testing (PGT) blastocysts and can it be managed in clinical practice? DESIGN: A retrospective study of PGT cycles conducted between January 2018 and October 2019 at a single centre. Biopsies of blastocysts were collected and analysed by next-generation sequencing (NGS). Complex mosaic blastocysts were defined as those with three or more mosaic chromosomes. The cryopreserved complex mosaic blastocysts underwent a second round of biopsy, NGS analysis and vitrification. The euploid blastocysts identified by the re-biopsy were warmed again for embryo transfer. The main outcomes included the prevalence of the complex mosaic and the ongoing pregnancy rate. RESULTS: The prevalence of the complex mosaic was 2.4% (437/17,979). The prevalence of the complex mosaic was not associated with maternal age and morphological quality. A total of 89 complex mosaic blastocysts underwent re-biopsy and 96.6% (86/89) survived the first warming. For the re-biopsy samples, 61.6% (53/86) were euploid. The poor-quality blastocysts had higher rates of aneuploidy compared with good-quality blastocysts. The survival rate for blastocysts undergoing the second warming was 100% (18/18) and resulted in an ongoing pregnancy rate of 38.9% (7/18) as well as the birth of six healthy infants. CONCLUSION: Re-biopsy may rescue blastocysts with development potential for transfer and improve the cumulative pregnancy rate per stimulation cycle in patients containing complex mosaic blastocysts.

The comprehensive variant and phenotypic spectrum of TUBB8 in female infertility.

PURPOSE: TUBB8 is a gene that is frequently analysed in the genetic diagnosis of female infertility; 102 variants of this gene have been identified. However, the evaluation of its pathogenicity and the resulting phenotypes vary. Here, we aimed to identify novel TUBB8 variants as well as to summarize the reported variants and phenotypes in order for them to be included in genetic counselling analyses. METHODS: We performed whole exome sequencing to screen for candidate variants in 100 infertile female subjects and 100 controls who were able to conceive naturally. All variants were confirmed by Sanger sequencing. The effects of the variants in oocytes/arrested embryos were assessed by morphological observations, polar body biopsies, and chromosome analysis. A molecular modelling analysis was used to evaluate the possible effects of variants on protein secondary structure. RESULTS: We identified 29 TUBB8 variants, of which 20 were novel and five were maternally inherited. We identified three of a total of six recurrent variants that were specific for complete cleavage failure. Moreover, we obtained evidence that TUBB8 variants with large polar bodies had chromosome segregation errors. CONCLUSIONS: Our study expands the spectrum of TUBB8 variants, particularly for embryonic arrest. Together with the extant knowledge of TUBB8 variants, this study provides a foundation for the genetic counselling of female infertility.

The mitochondrial DNA copy number of cumulus granulosa cells may be related to the maturity of oocyte cytoplasm.

STUDY QUESTION: Is the mitochondrial DNA (mtDNA) copy number of cumulus granulosa cells (CGCs) related to the maturation of oocyte cytoplasm? SUMMARY ANSWER: Compared with the mtDNA copy number of CGCs from germinal vesicles (GV), CGCs from Metaphase I (MI) oocytes appear to have a lower mtDNA copy number. WHAT IS KNOWN ALREADY: The growth and development of CGCs and oocyte are synchronised. The interaction between CGCs and the oocyte provides the appropriate balance of energy, which is necessary for mammalian oocyte development. Moreover, in the oocyte-cumulus complex (OCC), mature oocytes with higher mtDNA copy numbers tend to have corresponding CGCs with higher mtDNA copy numbers. STUDY DESIGN, SIZE, DURATION: This is a prospective study of 302 OCCs obtained from 70 women undergoing in vitro fertilisation with intracytoplasmic sperm injection (ICSI) at the Reproductive and Genetic Hospital of CITIC-Xiangya, between 24 February 2018 and 21 December 2019. The CGCs were divided into three groups (GV, MI and MII stages) based on the maturation status of their corresponding oocyte. The sample sizes (n = 302) of CGCs in the three stages were 63 (CGCGV), 70 (CGCMI) and 169 (CGCMII), respectively. Some of the samples (n = 257) was used to quantify the mtDNA copy number, while the rest (n = 45) were used to analyse the expression level of mitochondrial genes. Furthermore, we retrieved 82 immature oocytes from among the 257 OCCs used for mtDNA copy numbers, including 36 GV oocytes and 46 MI oocytes, for analysis of oocyte mtDNA. PARTICIPANTS/MATERIALS, SETTING, METHODS: We selected genes with high consistency of real-time PCR results to accurately measure the mtDNA copy number by testing the efficacy and the reproducibility in whole genome amplification (WGA) samples from a human embryonic stem cell line. The CGCs of each oocyte were individually isolated. The mtDNA copy number and gene expression of the CGCs were assessed using real-time PCR techniques. Mitochondrial DNA copy number of the corresponding immature oocytes was also evaluated. MAIN RESULTS AND THE ROLE OF CHANCE: MT-ND1, MT-CO1 and ß-globin genes were chosen for the assessment of mtDNA content, and mRNA expressions of MT-ND1, MT-CO1, PGC-1α and TFAM were also measured. The genome of 257 CGCs and 82 immature oocytes were amplified according to the multiple displacement amplification (MDA) protocol, and RNA was extracted from 45 CGCs. Compared with CGCGV, CGCMI had a significantly lower mtDNA copy number. In the MT-ND1 assay, the CGCGV: CGCMI was [270 ± 302]: [134 ± 201], P = 0.015. In the MT-CO1 assay, CGCGV: CGCMI was [205 ± 228]: [92 ± 112], P = 0.026. There was no statistical difference in mtDNA between CGCGV and CGCMII. In the MT-ND1 assay, CGCGV: CGCMII was [270 ± 302]: [175 ± 223], P = 0.074. In the MT-CO1 assay, CGCGV: CGCMII was [205 ± 228]: [119 ± 192], P = 0.077. No statistical difference of mtDNA copy number was observed between CGCMI and CGCMII. In the MT-ND1 assay, CGCMI: CGCMII was [134 ± 201]: [175 ± 223], P = 0.422. In the MT-CO1 assay, CGCMI: CGCMII was [92 ± 112]: [119 ± 192], P = 0.478. To verify the reliability of the above results, we further analysed the mtDNA copy number of CGCs of 14 patients with GV, MI and MII oocytes, and the results showed that the mtDNA copy number of CGCMI may be lower. The mtDNA copy number of CGCGV and CGCMI was statistically different in the MT-ND1 assay where CGCGV: CGCMI was [249 ± 173]: [118 ± 113], P = 0.016, but in the MT-CO1 assay, CGCGV: CGCMI was [208 ± 199]: [83 ± 98], P = 0.109. There was no significant difference in mtDNA between CGCGV and CGCMII. In the MT-ND1 assay, CGCGV: CGCMII was [249 ± 173]: [185 ± 200], P = 0.096. In the MT-CO1 assay, CGCGV: CGCMII was [208 ± 199]: [114 ± 139], P = 0.096. There was also no significant difference in mtDNA between CGCMI and CGCMII. In the MT-ND1 assay, CGCMI: CGCMII was [118 ± 113]: [185 ± 200], P = 0.198. In the MT-CO1 assay, CGCMI: CGCMII was [83 ± 98]: [114 ± 139], P = 0.470. Moreover, there were no statistical differences in the expression levels of MT-ND1, MT-CO1, PGC-1α and TFAM between CGCGV, CGCMI and CGCMII (P > 0.05). LARGE SCALE DATA: N/A. LIMITATIONS, REASONS FOR CAUTION: Due to the ethical issues, the study did not quantify the mtDNA content of MII oocytes. Thus, whether the change in mtDNA copy number in CGCs is related to the different developmental stages of oocytes has not been further confirmed. Moreover, the sample size was relatively small. WIDER IMPLICATIONS OF THE FINDINGS: The mtDNA copy number of CGCs decreases from the GV phase to the MI phase and stays steady from the MI to MII stage. At different stages of oocyte maturation, the mtDNA of CGCs may undergo self-degradation and replication to meet the energy requirements of the corresponding oocyte and the maturation of the oocyte cytoplasm. STUDY FUNDING/COMPETING INTEREST(S): Funding was provided by the National Key R&D Program of China (Grant 2018YFC1003100, to L.H.), the science and technology major project of the Ministry of Science and Technology of Hunan Province, China (grant 2017SK1030, to G.L.), the National Natural Science Foundation of China (grant 81873478, to L.H.), and Merck Serono China Research Fund for Fertility Experts (to L.H.). There is no conflict of interest.

ZP2 pathogenic variants cause in vitro fertilization failure and female infertility.

PURPOSE: The oocyte-borne genetic causes leading to fertilization failure are largely unknown. We aimed to identify novel human pathogenic variants (PV) and genes causing fertilization failure. METHODS: We performed exome sequencing for a consanguineous family with a recessive inheritance pattern of female infertility characterized by oocytes with a thin zona pellucida (ZP) and fertilization failure in routine in vitro fertilization. Subsequent PV screening of ZP2 was performed in additional eight unrelated infertile women whose oocytes exhibited abnormal ZP and similar fertilization failure. Expression of ZP proteins was assessed in mutant oocytes by immunostaining, and functional studies of the wild-type and mutant proteins were carried out in CHO-K1 cells. RESULTS: Two homozygous s PV (c.1695-2A>G, and c.1691_1694dup (p.C566Wfs*5), respectively) of ZP2 were identified in the affected women from two unrelated consanguineous families. All oocytes carrying PV were surrounded by a thin ZP that was defective for sperm-binding. Immunostaining indicated a lack of ZP2 protein in the thin ZP. Studies in CHO cells showed that both PV resulted in a truncated ZP2 protein, which might be intracellularly sequestered and prematurely interacted with other ZP proteins. CONCLUSION: We identified loss-of-function PV of ZP2 causing a structurally abnormal and dysfunctional ZP, resulting in fertilization failure and female infertility.

ZP1 mutations are associated with empty follicle syndrome: evidence for the existence of an intact oocyte and a zona pellucida in follicles up to the early antral stage. A case report.

Empty follicle syndrome (EFS) is the complete failure to retrieve oocytes after ovarian stimulation. Although LHCGR and ZP3 were identified as causative genes, it is still unclear what happens to these patients' oocytes, and the pathogenesis of EFS remains obscure. Here, we identified six novel ZP1 mutations associated with EFS and female infertility that was inherited recessively in five unrelated families. Studies in CHO-K1 cells showed that these mutations resulted in either degradation or truncation of ZP1 protein. Immunohistochemistry using ovarian serial sections demonstrated that all preantral follicles had normal architecture, but with a thin ZP, lacking ZP1, surrounding the growing oocytes. The antral follicles were also defective in normal cumulus-oocyte complex organisation, leading us to speculate that the lack of ZP1 might lead to oocyte degeneration or increased fragility of the oocyte during follicular puncture, ultimately resulting in EFS. To our knowledge, this is the first study that presents morphological evidence showing normal preantral folliculogenesis with abnormal ZP assembly in EFS patients. Our data provides a better understanding of the biological functions of ZP1 in human ZP assembly and folliculogenesis and gives new insights into the pathogenesis of EFS and possible therapeutic developments.

Increased pregnancy complications following frozen-thawed embryo transfer during an artificial cycle.

PURPOSE: This study aimed to clarify the risks of adverse pregnancy outcomes in patients and their offspring after frozen embryo transfer (FET) during an artificial cycle (AC). METHODS: We conducted a retrospective cohort study that included all FET cycles and subsequent deliveries in a single centre between August 2013 and March 2016. Pregnancy, obstetric and neonatal outcomes were compared among patients treated during an AC or a natural cycle with luteal phase support (NC-LPS). Multivariate logistic regression was performed to evaluate the relationship between endometrial preparation schemes and pregnancy, obstetric and neonatal outcomes. RESULTS: AC-FET was not a significant risk factor for clinical pregnancy rate, multiple birth rate or miscarriage rate after adjusting for potential confounders. However, AC-FET was a significant risk factor for ectopic pregnancy rate (adjusted odds ratio (AOR), 1.738; 95% confidence interval (CI), 1.086-2.781) and live birth rate (AOR, 0.709; 95% CI, 0.626-0.802). Regarding obstetric outcomes, AC-FET was found to be associated with an increased risk for hypertension disorder (AOR, 1.780; 95% CI, 1.262-2.510) and caesarean section (AOR, 1.507; 95% CI, 1.195-1.900). In multiples, birth weight (2550 g (2150-2900 g) in AC-FET vs. 2600 g (2350-2900 g) in NC-LPS; P = 0.023), gestational age (36.6 weeks (35.3-37.6 weeks) vs. 37.1 weeks (36.1-37.9 weeks); P < 0.001), and z-score (- 0.5 (- 1.1, - 0.0) vs. - 0.4 (- 1.0, 0.2); P = 0.009) were higher in the NC-LPS group than in the AC-FET group, although there were no differences in these variables among singletons. CONCLUSION: Compared with NC-LPS, AC-FET seemed to have a negative effect on obstetric outcomes.