A systematic review and evidence assessment of monogenic gene-disease relationships in human female infertility and differences in sex development

BACKGROUND

As in other domains of medicine, high-throughput sequencing methods have led to the identification of an ever-increasing number of gene variants in the fields of both male and female infertility. The increasing number of recently identified genes allows an accurate diagnosis for previously idiopathic cases of female infertility and more appropriate patient care. However, robust evidence of the gene-disease relationships (GDR) allowing the proper translation to clinical application is still missing in many cases.

OBJECTIVE AND RATIONALE

An evidence-based curation of currently identified genes involved in female infertility and differences in sex development (DSD) would significantly improve both diagnostic performance and genetic research. We therefore performed a systematic review to summarize current knowledge and assess the available GDR.

SEARCH METHODS

PRISMA guidelines were applied to curate all available information from PubMed and Web of Science on genetics of human female infertility and DSD leading to infertility, from 1 January 1988 to 1 November 2021. The reviewed pathologies include non-syndromic as well as syndromic female infertility, and endocrine and reproductive system disorders. The evidence that an identified phenotype is caused by pathogenic variants in a specific gene was assessed according to a standardized scoring system. A final score (no evidence, limited, moderate, strong, or definitive) was assigned to every GDR.

OUTCOMES

A total of 45 271 publications were identified and screened for inclusion of which 1078 were selected for gene and variant extraction. We have identified 395 genes and validated 466 GDRs covering all reported monogenic causes of female infertility and DSD. Furthermore, we present a genetic diagnostic flowchart including 105 genes with at least moderate evidence for female infertility and suggest recommendations for future research. The study did not take into account associated genetic risk factor(s) or oligogenic/polygenic causes of female infertility.

WIDER IMPLICATIONS

We have comprehensively reviewed the existing research on the genetics of female infertility and DSD, which will enable the development of diagnostic panels using validated genes. Whole genome analysis is shifting from predominantly research to clinical application, increasing its diagnostic potential. These new diagnostic possibilities will not only decrease the number of idiopathic cases but will also render genetic counselling more effective for infertile patients and their families.

Improved clinical utility of preimplantation genetic testing through the integration of ploidy and common pathogenic microdeletions analyses

STUDY QUESTION

Can chromosomal abnormalities beyond copy-number aneuploidies (i.e. ploidy level and microdeletions (MDs)) be detected using a preimplantation genetic testing (PGT) platform?

SUMMARY ANSWER

The proposed integrated approach accurately assesses ploidy level and the most common pathogenic microdeletions causative of genomic disorders, expanding the clinical utility of PGT.

WHAT IS KNOWN ALREADY

Standard methodologies employed in preimplantation genetic testing for aneuploidy (PGT-A) identify chromosomal aneuploidies but cannot determine ploidy level nor the presence of recurrent pathogenic MDs responsible for genomic disorders. Transferring embryos carrying these abnormalities can result in miscarriage, molar pregnancy, and intellectual disabilities and developmental delay in offspring. The development of a testing strategy that integrates their assessment can resolve current limitations and add valuable information regarding the genetic constitution of embryos, which is not evaluated in PGT providing new level of clinical utility and valuable knowledge for further understanding of the genomic causes of implantation failure and early pregnancy loss. To the best of our knowledge, MDs have never been studied in preimplantation human embryos up to date.

STUDY DESIGN, SIZE, DURATION

This is a retrospective cohort analysis including blastocyst biopsies collected between February 2018 and November 2021 at multiple collaborating IVF clinics from prospective parents of European ancestry below the age of 45, using autologous gametes and undergoing ICSI for all oocytes. Ploidy level determination was validated using 164 embryonic samples of known ploidy status (147 diploids, 9 triploids, and 8 haploids). Detection of nine common MD syndromes (-4p=Wolf-Hirschhorn, -8q=Langer-Giedion, -1p=1p36 deletion, -22q=DiGeorge, -5p=Cri-du-Chat, -15q=Prader-Willi/Angelman, -11q=Jacobsen, -17p=Smith-Magenis) was developed and tested using 28 positive controls and 97 negative controls. Later, the methodology was blindly applied in the analysis of: (i) 100 two pronuclei (2PN)-derived blastocysts that were previously defined as uniformly euploid by standard PGT-A; (ii) 99 euploid embryos whose transfer resulted in pregnancy loss.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The methodology is based on targeted next-generation sequencing of selected polymorphisms across the genome and enriched within critical regions of included MD syndromes. Sequencing data (i.e. allelic frequencies) were analyzed by a probabilistic model which estimated the likelihood of ploidy level and MD presence, accounting for both sequencing noise and population genetics patterns (i.e. linkage disequilibrium, LD, correlations) observed in 2504 whole-genome sequencing data from the 1000 Genome Project database. Analysis of phased parental haplotypes obtained by single-nucleotide polymorphism (SNP)-array genotyping was performed to confirm the presence of MD.

MAIN RESULTS AND THE ROLE OF CHANCE

In the analytical validation phase, this strategy showed extremely high accuracy both in ploidy classification (100%, CI: 98.1-100%) and in the identification of six out of eight MDs (99.2%, CI: 98.5-99.8%). To improve MD detection based on loss of heterozygosity (LOH), common haploblocks were analyzed based on haplotype frequency and LOH occurrence in a reference population, thus developing two further mathematical models. As a result, chr1p36 and chr4p16.3 regions were excluded from MD identification due to their poor reliability, whilst a clinical workflow which incorporated parental DNA information was developed to enhance the identification of MDs. During the clinical application phase, one case of triploidy was detected among 2PN-derived blastocysts (i) and one pathogenic MD (-22q11.21) was retrospectively identified among the biopsy specimens of transferred embryos that resulted in miscarriage (ii). For the latter case, family-based analysis revealed the same MD in different sibling embryos (n = 2/5) from non-carrier parents, suggesting the presence of germline mosaicism in the female partner. When embryos are selected for transfer based on their genetic constitution, this strategy can identify embryos with ploidy abnormalities and/or MDs beyond aneuploidies, with an estimated incidence of 1.5% (n = 3/202, 95% CI: 0.5-4.5%) among euploid embryos.

LIMITATIONS, REASONS FOR CAUTION

Epidemiological studies will be required to accurately assess the incidence of ploidy alterations and MDs in preimplantation embryos and particularly in euploid miscarriages. Despite the high accuracy of the assay developed, the use of parental DNA to support diagnostic calling can further increase the precision of the assay.

WIDER IMPLICATIONS OF THE FINDINGS

This novel assay significantly expands the clinical utility of PGT-A by integrating the most common pathogenic MDs (both de novo and inherited ones) responsible for genomic disorders, which are usually evaluated at a later stage through invasive prenatal testing. From a basic research standpoint, this approach will help to elucidate fundamental biological and clinical questions related to the genetics of implantation failure and pregnancy loss of otherwise euploid embryos.

STUDY FUNDING/COMPETING INTEREST(S)

No external funding was used for this study. S.C., M.F., F.C., P.Z., I.P., L.G., C.P., M.P., D.B., J.J.-A., D.B.-J., J.M.-V., and C.R. are employees of Igenomix and C.S. is the head of the scientific board of Igenomix. A.C. and L.P. are employees of JUNO GENETICS. Igenomix and JUNO GENETICS are companies providing reproductive genetic services.

TRIAL REGISTRATION NUMBER

N/A.

P-063 Multivariate analysis identifies oxidative stress levels and acrosome status of motile spermatozoa as independent predictors of motile sperm hyaluronan binding ability

Study question

Is it possible to predict motile sperm hyaluronan binding ability (HBA) from motile sperm functional parameters?

Summary answer

Using multivariate analysis, oxidative stress levels and acrosome status of motile spermatozoa, derived from semen swim-up, were identified as predictors of sperm HBA.

What is known already

Semen analysis is a gold standard practice for fertility evaluation. However, motility and morphology of spermatozoa are not always indicative of the molecular makeup of sperm cells. In this context, several sperm functional tests were developed to enhance our understanding of spermatozoa biology. Interestingly, several studies have shown that the plasma membrane of mature sperm cells contain hyaluronan binding sites. HBA was associated with intact acrosome, decreased DNA damage, and high viability. Nevertheless, it has not been demonstrated yet if hyaluronan binding ability can be predicted solely by swim-up derived- motile spermatozoa functional parameters.

Study design, size, duration

A prospective study was performed at Al-Hadi Medical Center, beirut, Lebanon, between January and July 2020. Freshly ejaculated semen samples obtained from infertile men with concentration of ≥ 20 x 106/ml and with total sperm motility of ≥ 30% were included. The primary outcome was to assess if the motile sperm functional parameters may influence HBA. A sample size of 54 was calculated using power = 85% and alpha = 5% for multiple linear regression.

Participants/materials, setting, methods

54 semen samples were assessed according to WHO guidelines (2010). Thereafter, samples were processed using the semen swim-up technique. Supernatants containing motile spermatozoa were collected for further analysis. In motile spermatozoa-enriched fractions, chromatin integrity was assessed using toluidine blue (TB) staining. Oxidative stress levels were detected using a nitroblue tetrazolium (NBT) test. Acrosome status was determined using triple staining technique. HBA was evaluated via a commercially available hyaluronan binding assay (HBA® Assay).

Main results and the role of chance

In the motile spermatozoa-enriched fractions, mean ± standard deviations for concentration, progressive motility, non-progressive motility and normal morphology were 26.17±11.48, 76±18.97, 20.94±12.61 and 0.75 ± 1.4, respectively. In addition, mean ± standard deviations for TB + cells, NBT + cells, living spermatozoa with intact acrosome, and HBA were 16.42 ± 13.4, 57.4 ± 9.4, 93.9 ±3.2, and 48.98±11.95, respectively. The values of the HBA had a non-normal distribution; therefore, these values were first linearized by taking the logarithm of the outcome. Afterwards, multiple linear regression (MLR) was used to predict the outcome. The overall regression of the final model was statistically significant (R2 = 0.346), F(4.43) =5.962, p = 0.001. The results of the final MLR model indicated that a unit increase in non-progressive motility (%) (p = 0.002) and NBT + cells (%) (p = 0.009) increased the HBA by 1.505 units and 1.409 units, respectively. However, a unit increase in dead spermatozoa with unreacted acrosome (%) (p = 0.032) and living spermatozoa with reacted acrosome (%) (p = 0.026) decreased the HBA by 1.317 units and 1.342 units, respectively.

Limitations, reasons for caution

This is an interim study and these results should be taken as preliminary. In order to confirm these findings, further studies including larger sample size and motile spermatozoa derived from semen samples with abnormal parameters (such as severe asthenozoospermia, leukocytospermia, severe oligozoospermia) are required.

Wider implications of the findings

Several studies indicated that using damaged spermatozoa may affect the intracytoplasmic sperm injection (ICSI) outcomes. In addition, using damaged spermatozoa during fertilization may predispose the offspring to various diseases later in life. These results may be considered as an impetus to reconsider sperm selection during ICSI.

Trial registration number

Not applicable

P-126 Investigation of the deterministic value of presence of visible spindle on fertilization and blastocytes utilization potential in frozen/thawed oocyte cycle

Study question

Does presence or absence of birefringent spindle after warming of the oocytes has deterministic value on fertilization and early embryonic development potentiaL?

Summary answer

The warmed oocytes with birefringent spindle seem to have a higher potential to fertilize and become good quality blastocytes.

What is known already

To date, characteristics of the meiotic spindles in human oocytes were studied by several authors by using a non-invasive method (PolScope) and shown that they are associated with fertilization, embryo quality, pregnancy, and live birth rates. Also, it has been known that meiotic spindle structures are very susceptible to cryodamage and can be disassembled and re-assembled depending on the change in temperature. Thus, studying spindle characteristics of the vitrified-warmed oocytes is important and can provide information about the full recovery of the oocytes, fertilization, embryo development, and pregnancy, which the data is limited in the literature.

Study design, size, duration

A retrospective study consisting 40 egg donation cycles by using vitrified-warmed oocytes between December 2017 and December 2019 at British Cyprus IVF Hospital.

Participants/materials, setting, methods

Spindle morphologies of vitrified-warmed oocytes were analyzed by PolScope (RI) combined with an image analysis system after approximately 1.5 hours post-warming. The data is divided into two according to the presence or absence of visible nucleus and correlation with embryonic development analyzed accordingly. To make a comparison in groups a new numerical scoring system for embryo quality on days 5 and 6 was created where embryos scored depending on the stage of expansion,

Main results and the role of chance

In total, 587 out of 648 vitrified/warmed oocytes survived (90.6%) and 447 of them were fertilized (75.0%). Among the survived oocytes, 503 (85.5%) oocytes were containing detectable spindle (Group I) while spindles were missing in 84 oocytes (Group II). The results showed that the fertilization rate (78.1% vs. 64.3%, p < 0.01), the proportion of good PN morphology (Z Score: Z1 and Z2 over other parameters: 50.4% vs 35.2%, p = 0.036), and viable embryo count (40.6% vs 15.1%, p < 0.01) which is defined as embryos that good enough to transfer or freezing, were higher in group I. Similarly, the degree of expansion on day 5/6 (p = 0.013, p = 0.015 respectively) and the quality of the cells in ICM and TE (p < 0.01) were found higher in group I. We further investigated the differences in embryo quality between groups by converting the embryo grades to numerical value starting from arrested (Score=0) to 6AA (Score=22) and found that embryo scores on day 5 (p = 0.01) and day 6 (p = 0.013) were higher in group I.

Limitations, reasons for caution

The main limitation of this study is the lack of data regarding the spindle status of the frozen oocytes before vitrification where some of the oocytes might not have visible spindle due to incomplete maturation rather than cryodamage.

Wider implications of the findings

The present data showed that the presence of birefringent meiotic spindles in warmed oocytes is a very important sign for a full recovery and early embryonic development potential, which can be useful for egg banks and IVF clinics.

Trial registration number

not applicable

Investigating the level of DNA double-strand break in human spermatozoa and its relation to semen characteristics and IVF outcome using phospho-histone H2AX antibody as a biomarker

BACKGROUND

Sperm DNA fragmentation and its relation to conventional semen parameters are well studied. However, there is limited information regarding the rate of DNA double-strand breaks (DSBs) and its correlation to basic semen parameters and IVF outcome.

OBJECTIVES

The present study aimed to investigate the rate of DNA DSBs in human spermatozoa and its correlation to basic semen parameters and IVF outcome.

MATERIALS AND METHODS

The prospective study includes 60 assisted reproductive treatment cycles (52 autologous and eight donors) in which the semen profiles and sperm DNA DSBs have been assessed. The level of sperm DNA DSBs in each sample has been evaluated by using a method to detect histone H2AX phosphorylation. The results were compared with basic semen values and IVF outcomes.

RESULTS

No significant correlation was observed between phospho-histone H2AX (γH2AX) levels and basic semen parameters such as semen volume (p = 0.129), sperm count (p = 0.454), total motility (p = 0.934), progressive motility (p = 0.314) and normal sperm morphology (p = 0.720). Similarly, the mean values of γH2AX did not differ with regard to the age of male participants (p = 0.300). However, cycles that resulted in live birth exhibited lower levels of γH2AX (p = 0.007). Accordingly, the level of γH2AX (p < 0.004) and rate of normal sperm morphology (p = 0.015) were found to be variables that affect the live birth outcomes.

DISCUSSION AND CONCLUSION

The low levels of γH2AX in sperm cells may be an indicator to IVF outcome independently from the conventional semen parameters and male age.