Genetic testing and counselling for male infertility

Methylation Status of cAMP-responsive Element Modulator (CREM) Gene in Infertile Men and Its Association with Sperm Parameters

The methylation pattern of non-imprinting genes was little studied, although it is widely known that the abnormal methylation levels of imprinting genes are associated with different forms of male infertility. The purpose of this research was to assess the CREM gene's methylation status and seminal characteristics in infertile individuals who were potential intracytoplasmic sperm injection (ICSI) candidates. A total of 45 semen samples (15 normospermia, 15 asthenospermia, and 15 oligoasthenoteratospermia) were examined. Using aniline blue (AB) staining, we carried out conventional semen analysis, chromatin quality, and sperm maturity testing. DNA was taken from semen samples, and all isolated DNA was assessed using Nanodrop and gel electrophoresis. A quantitative methylation-specific polymerase chain reaction (Q-MSP) approach was used to quantify the methylation at the DMRs of the CREM gene. According to our findings, sperm count (P=0.012), concentration (P= 0.019), motility (P=0.006), progression (P=0.006), and normal morphology (P=0.004) were all inversely correlated with abnormal sperm chromatin condensation. Additionally, we noted that the methylation level of the CREM gene was considerably more significant in the oligoasthenoteratospermia group compared to the asthenospermia and normospermia groups (P<0.05). Additionally, sperm count (P=0.043), progression (P=0.026), and normal morphology (P=0.024) were all inversely linked with CREM methylation. Overall, the abnormal CREM methylation patterns have a negative impact on sperm parameters. Additionally, the CREM gene's DNA methylation status may serve as an epigenetic indicator of male infertility.

Nuclear sperm integrity and ICSI prognosis in Tunisian patients with MMAF syndrome (multiple morphological abnormalities of the sperm flagella)

Multiple Morphological Abnormalities of the Sperm Flagella (MMAF) is a severe form of teratozoospermia associated with several sperm flagellar abnormalities. The study included 52 patients with MMAF syndrome and a control group of 25 fertile men. The impact of nuclear sperm quality on intracytoplasmic sperm injection (ICSI) results was studied in 20 couples. TUNEL assay was used to assess sperm DNA fragmentation and aniline-blue staining was used to assess chromatin condensation. To investigate chromosomal meiotic segregation, we used fluorescence in situ hybridization (FISH). Semen morphology analysis revealed a mosaic of multiple flagella morphological abnormalities, including 46.73% short flagella, 16.22% bent flagella, 22.07% coiled flagella, and 10.90% absent flagella, all of which were associated with a high percentage of sperm head abnormalities. The mean DNA fragmentation index was substantially higher in patients compared to controls (p = 0.001), whereas the rate of aniline blue-reacted spermatozoa was not significantly different. There was a significant difference in aneuploidy frequencies between the two groups (p < 0.05). Infertile males with MMAF syndrome had lower sperm nuclear quality, which affected ICSI results. As a result, better sperm selection procedures are being employed to increase the success rate of assisted reproductive technologies (ART).

Genetics of Male Infertility - Present and Future: A Narrative Review

Infertility affects 8%–12% of couples worldwide with a male factor contributing to nearly 50% of couples either as a primary or contributing cause. Several genetic factors that include single-gene and multiple-gene defects associated with male infertility were reported in the past two decades. However, the etiology remains ambiguous in a majority of infertile men (~40%). The objective of this narrative review is to provide an update on the genetic factors associated with idiopathic male infertility and male reproductive system abnormalities identified in the last two decades. We performed a thorough literature search in online databases from January 2000 to July 2021. We observed a total of 13 genes associated with nonobstructive azoospermia due to maturation/meiotic arrest. Several studies that reported novel genes associated with multiple morphological abnormalities of the sperm flagella are also discussed in this review. ADGRG2, PANK2, SCNN1B, and CA12 genes are observed in non-CFTR-related vas aplasia. The genomic analysis should be quickly implemented in clinical practice as the detection of gene abnormalities in different male infertility phenotypes will facilitate genetic counseling.

Influence of tobacco cigarette heavy smoking on DNA methylation patterns and transcription levels of MAPK8IP3, GAA, ANXA2, PRRC2A, and PDE11A genes in human spermatozoa

Background

Tobacco smoking is considered as one of the lifestyles factors that influence the sperm DNA methylation and global sperm DNA methylation and that may affect the sperm phenotype. This study was performed to investigate whether tobacco cigarette heavy smoking influences sperm DNA methylation patterns and semen parameters and to determine whether there is an alteration in the transcription level of MAPK8IP3, GAA, ANXA2, PRRC2A, and PDE11A genes in heavy smokers compared to non-smokers. Thirty samples were subjected to 450K arrays as a screening study to assess the variation in sperm DNA methylation levels between heavy smokers and non-smokers. Five CpG sites have the highest difference in methylation levels (cg07869343, cg05813498, cg09785377, cg06833981, and cg02745784), which are located in the MAPK8IP3, GAA, ANXA2, PRRC2A, and PDE11A genes, respectively, and were selected for further analysis using deep bisulfite sequencing in 280 independent samples (120 proven non-smokers and 160 heavy smokers) with a mean age of 33.8 ± 8.4 years. The global sperm DNA methylation, sperm DNA fragmentation, and chromatin non-condensation were evaluated also.

Results

A significant increase was found in the methylation level at seven, three, and seventeen CpGs within the GAA, ANXA2, and MAPK8IP3 genes amplicon, respectively (P< 0.01) in heavy smokers compared to non-smokers. Additionally, a significant increase was found in the methylation levels at all CpGs within PRRC2A and PDE11A gene amplicon (P< 0.01). A significant increase was found in the level of sperm chromatin non-condensation, DNA fragmentation, and global DNA methylation (P < 0.001) in heavy smokers compared to non-smokers.

Conclusion

These results indicate that tobacco cigarette smoking can alter the DNA methylation level at several CpGs, the status of global DNA methylation, and transcription level of the following genes “MAPK8IP3, GAA, ANXA2, PRRC2A, and PDE11A” in human spermatozoa. These findings may affect negatively semen parameters and men’s fertility.

Sperm DNA integrity status is associated with DNA methylation signatures of imprinted genes and non-imprinted genes

PURPOSE

To evaluate the association between the DNA methylation of specific genes and sperm DNA integrity status in human sperm samples.

METHODS

A total of 166 semen samples were evaluated (86 controls and 80 cases with impaired sperm DNA integrity). We detected the methylation status of 257 CpG sites among two imprinted genes (H19 and SNRPN) and four non-imprinted genes related to male infertility (MTHFR, GSTM1, DAZL, and CREM) by using a targeted next-generation sequencing method.

RESULTS

Differential methylation was found in 43 CpG sites of the promoters of the six candidate genes. H19, SNRPN, MTHFR, DAZL, GSTM1, and CREM contained 22, 12, 1, 4, 0, and 4 differentially methylated CpG sites (P<0.05), respectively. The imprinting genes were associated with relatively higher rates of differentially methylated CpG sites (28.21% in H19 and 41.38% in SNRPN) than the non-imprinting genes. One CpG site in H19 remained significant after performing strict Bonferroni correction.

CONCLUSION

In this study, we found that different site-specific DNA methylation signatures were correlated with sperm DNA integrity status. Further studies are needed to investigate the specific mechanisms leading to the epigenetic modifications.

Y-microdeletions: a review of the genetic basis for this common cause of male infertility

The human Y-chromosome contains genetic material responsible for normal testis development and spermatogenesis. The long arm (Yq) of the Y-chromosome has been found to be susceptible to self-recombination during spermatogenesis predisposing this area to deletions. The incidence of these deletions is estimated to be 1/4,000 in the general population but has been found to be much higher in infertile men. Currently, Y-microdeletions are the second most commonly identified genetic cause of male infertility after Klinefelter syndrome. This has led to testing for these deletions becoming standard practice in men with azoospermia and severe oligospermia. There are three commonly identified Y-microdeletions in infertile males, termed azoospermia factor (AZF) microdeletions AZFa, AZFb and AZFc. With increased understanding and investigation of this genetic basis for infertility a more comprehensive understanding of these deletions has evolved, with several other deletion subtypes being identified. Understanding the genetic basis and pathology behind these Y-microdeletions is essential for any clinician involved in reproductive medicine. In this review we discuss the genetic basis of Y-microdeletions, the various subtypes of deletions, and current technologies available for testing. Our understanding of this issue is evolving in many areas, and in this review we highlight future testing opportunities that may allow us to stratify men with Y-microdeletion associated infertility more accurately

Nonsurgical Management of Oligozoospermia

Male infertility secondary to oligozoospermia is surprisingly common. Although a majority of cases are idiopathic, oligozoospermia can be caused by endocrine dysfunction, anatomic abnormalities, medications, or environmental exposures. The work-up includes excluding reversible factors such as hormonal deficiency, medication effects, and retrograde ejaculation and identifying any underlying genetic syndrome and treating reversible medical causes. If no reversible cause is found, appropriate referrals to urology and assisted reproductive technology should be initiated. Lastly, clinicians should be aware of and respond to the psychological and general health ramifications of a diagnosis of oligozoospermia as part of the comprehensive care of men and couples struggling with a diagnosis of infertility.

Novel homozygous truncating variants in ZMYND15 causing severe oligozoospermia and their implications for male infertility

Sequence variants of ZMYND15 cause azoospermia in humans, but they have not yet been reported in infertile men with severe oligozoospermia (SO). We performed whole-exome and Sanger sequencing to identify suspected causative variants in 414 idiopathic participating infertile men with SO or azoospermia. Three novel homozygous truncating variants in ZMYND15 were identified in three of the 219 (1.37%) unrelated patients with SO, including c.1209T>A(p.Tyr403*), c.1650delC (p.Glu551Lysfs*75), and c.1622_1636delinsCCAC (p.Leu541Profs*39). In silico bioinformatic analyses as well as in vivo and in vitro experiments showed that the ZMYND15 variants carried by the affected subjects might be the underlying cause for their infertility. One patient accepted intracytoplasmic sperm injection therapy, using his ejaculated sperm, and his wife successfully became pregnant. Our findings expand the disease phenotype spectrum by indicating that ZMYND15 variants cause SO and male infertility and suggest a possible correlation between the severity of male infertility caused by ZMYND15 variants and male age.

Genetics in human reproduction

Approximately 50% of the causes of infertility are of genetic origin. The objective of this study was to analyze the role of genetics in human reproduction by reviewing the main genetic causes of infertility and the use of preimplantation genetic testing in Brazil. This literature review comprised articles in English and Portuguese published on databases PubMed, Scielo, and Bireme from 1990 to 2019. Randomized clinical trials and specialized guidelines were given preference whenever possible. Genetic cause can be traced back to up to 20% of the cases of severe azoospermia or oligozoospermia. Subjects with these conditions are good candidates for genetic screening. In women, genetic causes of infertility (fragile X syndrome, X-trisomy, and Turner's syndrome, some of which diagnosed with karyotyping) culminate with premature ovarian failure. Genetic screening helps advise couples of the risk of experiencing early reproductive capacity loss and of the chances of their offspring carrying genetic disorders. In addition to enhancing the prevention of serious diseases in the offspring of couples at increased risk of genetic diseases, preimplantation genetic screening improves the success rates of assisted reproduction procedures by allowing the selection of euploid embryos for transfer. The interface between genetics and human reproduction has gained significant relevance, but discussions are still needed on which procedures are clinically and ethically acceptable and how they should be regulated.

MRI findings of nonobstructive azoospermia: lesions in and out of pelvic cavity

Nonobstructive azoospermia (NOA) can be caused by various diseases, including congenital disorders, endocrine disorders, infections, tumor or tumor-like diseases, vascular diseases, etc. Diagnosis of the underlying cause of NOA is complicated and challenging. In this study, we introduce an MR examination protocol for the etiological diagnosis of NOA, and demonstrate a series of NOA patients with different causes and imaging findings. Except for lesions of testes, the patients may also combine abnormalities of adrenal glands and central nervous system. In such cases, the patients could benefit from additional abdominal and intracranial scans.

Aryl hydrocarbon receptor rs2066853 gene polymorphisms and male infertility risk: a meta-analysis

To evaluate the relationship between the aryl hydrocarbon receptor (AHR) rs2066853 gene polymorphism and the risk of male infertility. PubMed, Embase, Web of Science, and Chinese National Knowledge Infrastructure (CNKI) were searched for relevant case–control studies up to 31 July 2019. Odds ratio (OR) and 95% confidence interval (95% CI) were used to assess the strength of associations. Finally, seven case–control studies involving 1247 cases and 1762 controls were included in this meta-analysis. The pooled results showed that there was no significant association between AHR rs2066853 gene polymorphism and male infertility risk (A vs. G: OR = 1.08, 95% CI = 0.83–1.39; AA vs. GG: OR = 1.16, 95% CI = 0.65–2.04; AA vs. GA + GG: OR = 1.17, 95% CI = 0.66–2.07; AA + GA vs. GG: OR = 0.99, 95% CI = 0.85–1.15). Subgroup analysis by ethnicity showed the same result. However, significant association was found between AHR rs2066853 gene polymorphism and male infertility risk in oligoasthenotspermia (A vs. G: OR = 2.52, 95% CI = 1.72–3.70). In conclusion, our meta-analysis indicated that AHR rs2066853 gene polymorphism might be associated with an increased susceptibility to oligoasthenotspermia.

Reproductive endocrinologists are the gatekeepers for male infertility care in North America: results of a North American survey on the referral patterns and characteristics of men presenting to male infertility specialists for infertility investigations

OBJECTIVE

To characterize the referral patterns and characteristics of men presenting for infertility evaluation using data obtained from the Andrology Research Consortium.

DESIGN

Standardized male infertility questionnaire.

SETTING

Male infertility centers.

PATIENT(S)

Men presenting for fertility evaluation.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Demographic, infertility history, and referral data.

RESULT(S)

The questionnaires were completed by 4,287 men, with a mean male age of 40 years ± 7.4 years and female partners age of 37 years ± 4.9 years. Most were Caucasian (54%) with other races being less commonly represented (Asian 18.6%, and African American 5.5%). The majority (59.7%) were referred by a reproductive gynecologist, 19.4% were referred by their primary care physician, 4.2% were self-referred, and 621 (14.5%) were referred by "other." Before the male infertility investigation, 12.1% of couples had undergone intrauterine insemination, and 4.9% of couples had undergone in vitro fertilization (up to six cycles). Among the male participants, 0.9% reported using finasteride (5α-reductase inhibitor) at a dose used for androgenic alopecia, and 1.6% reported exogenous testosterone use.

CONCLUSION(S)

This broad North American patient survey shows that reproductive gynecologists are the de facto gateway for most male infertility referrals, with most men being assessed in the male infertility service being referred by reproductive endocrinologists. Some of the couples with apparent male factor infertility are treated with assisted reproductive technologies before a male factor investigation. The survey also identified potentially reversible causes for the male infertility including lifestyle factors such as testosterone and 5α-reductase inhibitor use.

Monogenic Forms of Male Infertility

Male infertility is a multifactorial and heterogeneous pathological condition affecting 7% of the general male population. The genetic landscape of male infertility is highly complex as semen and testis histological phenotypes are extremely heterogeneous, and at least 2000 genes are predicted to be involved in spermatogenesis. Genetic factors have been described in each etiological category of male reproductive impairment: (1) hypothalamic-pituitary axis dysfunction; (2) quantitative and qualitative alterations of spermatogenesis; (3) ductal obstruction/dysfunction. In 25% of azoospermic and in 10% of oligozoospermic men, a genetic anomaly can be diagnosed with the current genetic testing. However, up to now, only a relatively low number of monogenic factors have a clear-cut cause-effect relationship with impaired reproductive function. Thanks to the widespread diffusion of Next-Generation Sequencing, a continuously increasing number of monogenic causes of male infertility are being discovered and their validation is currently ongoing. The identification of genetic factors is of outmost clinical importance since there is a risk of transmission of genetic defects through natural or assisted reproductive techniques. The benefit of the genetic diagnosis of infertility has an obvious clinical significance for the patient itself with implications not only for his reproductive health but in many instances also for his general health.

TP53 gene Arg72Pro polymorphism and male infertility risk: A meta-analysis

To evaluate the association between TP53 codon72 polymorphism and male infertility risk. We conducted a search on Medline, Embase, Web of Science and CNKI up to April 30, 2017. Odds ratio (OR) and 95% confidence interval (95% CI) were used to assess the strength of the association. Seven studies including 1,818 cases and 2,278 controls met the inclusion criteria. The pooled results indicated that no significant association was observed between TP53 codon72 polymorphism and male infertility risk (G versus C: OR = 1.11, 95%CI = 0.94-1.32; GG versus CC: OR = 1.26, 95%CI = 0.90-1.78; GG versus GC+CC: OR = 1.16, 95%CI = 0.90-1.49; GG+GC versus CC: OR = 1.15, 95%CI = 0.88-1.49). In the subgroup analysis by ethnicity, significant association was observed between TP53 codon72 polymorphism and male infertility risk in non-Chinese (G versus C: OR = 1.47, 95%CI = 1.14-1.89), but not in Chinese population (G versus C: OR = 1.03, 95%CI = 0.87-1.22). In conclusion, this study suggested that TP53 codon72 polymorphism might be associated with an increased susceptibility to male infertility in non-Chinese population, but not in Chinese population. Studies with larger sample sizes and representative population-based cases and well-matched controls are needed to validate our results.

Relationship of genetic causes and inhibin B in non obstructive azoospermia spermatogenic failure

Background

Chromosomal disorders in non obstructive azoospermia (NOA) may have an important influence on spermatogenesis, which may be reflected by the serum inhibin B levels. Till now, few studies have concerned the relationship of genetic causes and inhibin B in NOA.

Methods

In this retrospective study, 322 men with NOA in Center for Reproductive Medicine, Nanfang Hospital, Southern Medical University were collected. The level of follicle stimulating hormone (FSH), inhibin B, Y chromosome microdeletion test (YCMD) and karyotype were measured.

Results

Abnormal karyotypes were present in 38.5% of NOA, and YCMD were present in 18.0%, there was a high correlation between karyotypes and YCMD (χ² = 11.892, P < 0.001). The level of inhibin B in chromosomal abnormality from lowest to highest was 46,XX (or 45,X), 47, XXY, mosaics, polymorphisms, inversion and translocation. And the level of inhibin B within Non-AZF a&b region deletion was higher than AZF a&b microdeletion.

Conclusion

According to the level of inhibin B, spermatogenesis in chromosomal abnormality from lowest to highest was 46,XX (or 45,X), 47, XXY, mosaics, polymorphisms, inversion and translocation. And spermatogenesis within Non-AZF a&b region deletion was better than AZF a&b microdeletion.

The susceptibility of FSHB -211G > T and FSHR G-29A, 919A > G, 2039A > G polymorphisms to men infertility: an association study and meta-analysis

BACKGROUND

Male infertility is a complex disorder caused by genetic, developmental, endocrine, or environmental factors as well as unknown etiology. Polymorphisms in the follicle stimulating hormone beta subunit (FSHB) (rs10835638, c.-211G > T) and follicle stimulating hormone receptor (FSHR) (rs1394205, c.-29G > A; rs6165, c.919A > G; rs6166, c.2039 A > G) genes might disturb normal spermatogenesis and affect male reproductive ability.

METHODS

To further ascertain the aforementioned effects, we conducted a case-control study of 255 infertile men and 340 fertile controls from South China using the Mass ARRAY method, which was analyzed by the t-tests and logistic regression analysis using SPSS for Windows 14.0. In addition, a meta-analysis was performed by combining our results with previous reports using STATA 12.0.

RESULTS

In the FSHB or FSHR gene single nucleotide polymorphism (SNP) evaluation, no statistically-significant difference was found in the frequency of allelic variants or in genotype distribution between cases and controls. However, a significant association for the comparison of GAA (P: 0.022, OR: 0.63, 95%CI: 0.43-0.94) was seen between the oligozoospermia and controls in haplotype analysis of rs1394205/rs6165/rs6166. In the meta-analysis, rs6165G allele and rs6166 GG genotype were associated with increased risk of the male infertility.

CONCLUSIONS

This study suggested that FSHR GAA haplotype would exert protective effects against male sterility, which indicated that the combination of three SNP genotypes of FSHR was predicted to have a much stronger impact than either one alone. Then in the meta-analysis, a significant association was seen between FSHR rs6165, rs6166 polymorphisms and male infertility. In terms of male infertility with multifactorial etiology, further studies with larger sample sizes and different ethnic backgrounds or other risk factors are warranted to clarify the potential role of FSHB and FSHR polymorphisms in the pathogenesis of male infertility.

Splicing mutation in Sbf1 causes nonsyndromic male infertility in the rat

In the inbred SHR/OlaIpcv rat colony, we identified males with small testicles and inability to reproduce. By selectively breeding their parents, we revealed the infertility to segregate as an autosomal recessive Mendelian character. No other phenotype was observed in males, and females were completely normal. By linkage using a backcross with Brown Norway strain, we mapped the locus to a 1.2Mbp segment on chromosome 7, harboring 35 genes. Sequencing of candidate genes revealed a G to A substitution in a canonical 'AG' splice site of intron 37 in Sbf1 (SET binding factor 1, alias myotubularin-related protein 5). This leads to either skipping exon 38 or shifting splicing one base downstream, invariantly resulting in frameshift, premature stop codon and truncation of the protein. Western blotting using two anti-Sbf1 antibodies revealed absence of the full-length protein in the mutant testis. Testicles of the mutant males were significantly smaller compared with SHR from 4weeks, peaked at 84% wild-type weight at 6weeks and declined afterward to 28%, reflecting massive germ cell loss. Histological examination revealed lower germ cell number; latest observed germ cell stage were round spermatids, resulting in the absence of sperm in the epididymis (azoospermia). SBF1 is a member of a phosphatase family lacking the catalytical activity. It probably modulates the activity of a phosphoinositol phosphatase MTMR2. Human homozygotes or compound heterozygotes for missense SBF1 mutations exhibit Charcot-Marie-Tooth disease (manifested mainly as progressive neuropathy), while a single mouse knockout reported in the literature identified male infertility as the only phenotype manifestation.

Recurrent Microdeletions at Xq27.3-Xq28 and Male Infertility: A Study in the Czech Population

Background

Genetic causes of male infertility are hypothesized to involve multiple types of mutations, from single gene defects to complex chromosome rearrangements. Recently, several recurrent X-chromosome microdeletions (located in subtelomeric region of the long arm) were reported to be associated with male infertility in Spanish and Italian males. The aim of our study was to test their prevalence and infertility association in population of men from the Czech Republic.

Methods

107 males with pathological sperm evaluation resulting in nonobstructive infertility were compared to 131 males with normal fecundity. X-chromosome microdeletions were assessed by +/- PCR with three primer pairs for each region Xcnv64 (Xq27.3), Xcnv67 (Xq28) and Xcnv69 (Xq28). The latter microdeletion was further characterized by amplification across the deleted region, dividing the deletion into three types; A, B and C.

Results

We detected presence of isolated Xcnv64 deletion in 3 patients and 14 controls, and Xcnv69 in 3 patients and 6 controls (1 and 1 patient vs.4 and 1 control for types A and B respectively). There was one control with combined Xcnv64 and Xcnv69 type B deletions, and one patient with combination of Xcnv64 and Xcnv69 type C deletions. The frequency of the deletions was thus not higher in patient compared to control group, Xcnv64 was marginally associated with controls (adjusted Fisher´s exact test P = 0.043), Xcnv69 was not associated (P = 0.452). We excluded presence of more extensive rearrangements in two subjects with combined Xcnv64 and Xcnv69 deletions. There was no Xcnv67 deletion in our cohort.

Conclusion

In conclusion, the two previously reported X-linked microdeletions (Xcnv64 and Xcnv69) do not seem to confer a significant risk to impaired spermatogenesis in the Czech population. The potential clinical role of the previously reported patient-specific Xcnv67 remains to be determined in a larger study population.

Spermatogonial stem cell autotransplantation and germline genomic editing: a future cure for spermatogenic failure and prevention of transmission of genomic diseases

BACKGROUND

Subfertility affects approximately 15% of all couples, and a severe male factor is identified in 17% of these couples. While the etiology of a severe male factor remains largely unknown, prior gonadotoxic treatment and genomic aberrations have been associated with this type of subfertility. Couples with a severe male factor can resort to ICSI, with either ejaculated spermatozoa (in case of oligozoospermia) or surgically retrieved testicular spermatozoa (in case of azoospermia) to generate their own biological children. Currently there is no direct treatment for azoospermia or oligozoospermia. Spermatogonial stem cell (SSC) autotransplantation (SSCT) is a promising novel clinical application currently under development to restore fertility in sterile childhood cancer survivors. Meanwhile, recent advances in genomic editing, especially the clustered regulatory interspaced short palindromic repeats-associated protein 9 (CRISPR-Cas9) system, are likely to enable genomic rectification of human SSCs in the near future.

OBJECTIVE AND RATIONALE

The objective of this review is to provide insights into the prospects of the potential clinical application of SSCT with or without genomic editing to cure spermatogenic failure and to prevent transmission of genetic diseases.

SEARCH METHODS

We performed a narrative review using the literature available on PubMed not restricted to any publishing year on topics of subfertility, fertility treatments, (molecular regulation of) spermatogenesis and SSCT, inherited (genetic) disorders, prenatal screening methods, genomic editing and germline editing. For germline editing, we focussed on the novel CRISPR-Cas9 system. We included papers written in English only.

OUTCOMES

Current techniques allow propagation of human SSCs in vitro, which is indispensable to successful transplantation. This technique is currently being developed in a preclinical setting for childhood cancer survivors who have stored a testis biopsy prior to cancer treatment. Similarly, SSCT could be used to restore fertility in sterile adult cancer survivors. In vitro propagation of SSCs might also be employed to enhance spermatogenesis in oligozoospermic men and in azoospermic men who still have functional SSCs albeit in insufficient numbers. The combination of SSCT with genomic editing techniques could potentially rectify defects in spermatogenesis caused by genomic mutations or, more broadly, prevent transmission of genomic diseases to the offspring. In spite of the promising prospects, SSCT and germline genomic editing are not yet clinically applicable and both techniques require optimization at various levels.

WIDER IMPLICATIONS

SSCT with or without genomic editing could potentially be used to restore fertility in cancer survivors to treat couples with a severe male factor and to prevent the paternal transmission of diseases. This will potentially allow these couples to have their own biological children. Technical development is progressing rapidly, and ethical reflection and societal debate on the use of SSCT with or without genomic editing is pressing.

A network-based method for the identification of putative genes related to infertility

BACKGROUND

Infertility has become one of the major health problems worldwide, with its incidence having risen markedly in recent decades. There is an urgent need to investigate the pathological mechanisms behind infertility and to design effective treatments. However, this is made difficult by the fact that various biological factors have been identified to be related to infertility, including genetic factors.

METHODS

A network-based method was established to identify new genes potentially related to infertility. A network constructed using human protein-protein interactions based on previously validated infertility-related genes enabled the identification of some novel candidate genes. These genes were then filtered by a permutation test and their functional and structural associations with infertility-related genes.

RESULTS

Our method identified 23 novel genes, which have strong functional and structural associations with previously validated infertility-related genes.

CONCLUSIONS

Substantial evidence indicates that the identified genes are strongly related to dysfunction of the four main biological processes of fertility: reproductive development and physiology, gametogenesis, meiosis and recombination, and hormone regulation.

GENERAL SIGNIFICANCE

The newly discovered genes may provide new directions for investigating infertility. This article is part of a Special Issue entitled "System Genetics" Guest Editor: Dr. Yudong Cai and Dr. Tao Huang.

Male Reproductive Disorders and Fertility Trends: Influences of Environment and Genetic Susceptibility

It is predicted that Japan and European Union will soon experience appreciable decreases in their populations due to persistently low total fertility rates (TFR) below replacement level (2.1 child per woman). In the United States, where TFR has also declined, there are ethnic differences. Caucasians have rates below replacement, while TFRs among African-Americans and Hispanics are higher. We review possible links between TFR and trends in a range of male reproductive problems, including testicular cancer, disorders of sex development, cryptorchidism, hypospadias, low testosterone levels, poor semen quality, childlessness, changed sex ratio, and increasing demand for assisted reproductive techniques. We present evidence that several adult male reproductive problems arise in utero and are signs of testicular dysgenesis syndrome (TDS). Although TDS might result from genetic mutations, recent evidence suggests that it most often is related to environmental exposures of the fetal testis. However, environmental factors can also affect the adult endocrine system. Based on our review of genetic and environmental factors, we conclude that environmental exposures arising from modern lifestyle, rather than genetics, are the most important factors in the observed trends. These environmental factors might act either directly or via epigenetic mechanisms. In the latter case, the effects of exposures might have an impact for several generations post-exposure. In conclusion, there is an urgent need to prioritize research in reproductive physiology and pathophysiology, particularly in highly industrialized countries facing decreasing populations. We highlight a number of topics that need attention by researchers in human physiology, pathophysiology, environmental health sciences, and demography.

Decreased fecundity and sperm DNA methylation patterns

OBJECTIVE

To evaluate the relationship between epigenetic patterns in sperm and fecundity.

DESIGN

Prospective study.

SETTING

Academic andrology and in vitro fertilization laboratory.

PATIENT(S)

Twenty-seven semen samples from couples who conceived within 2 months of attempting a pregnancy and 29 semen samples from couples unable to achieve a pregnancy within 12 months.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Genomewide assessment of differential sperm DNA methylation and standard semen analysis.

RESULT(S)

We analyzed DNA methylation alterations associated with fecundity in 124 semen samples, and identified regions of interest in 27 semen samples from couples who conceived within 2 months of attempting a pregnancy and a total of 29 semen samples from couples who were unable to achieve a pregnancy within 12 months. No differences in sperm count, sperm morphology, or semen volume were observed between the patients achieving a pregnancy within 2 months of study time and those not obtaining a pregnancy within 12 months. However, using data from the human methylation 450k array analysis we did identify two genomic regions with statistically significantly decreased (false discovery rate <0.01) methylation and three genomic regions with statistically significantly increased methylation in the failure-to-conceive group. The only two sites where decreased methylation was associated with reduced fecundity are at closely related genes known to be expressed in sperm, HSPA1L and HSPA1B.

CONCLUSION(S)

Our data suggest that there are genomic loci where DNA methylation alterations are associated with decreased fecundity. We have thus identified candidate loci for future study to verify these results and investigate the causative or contributory relationship between altered sperm methylation and decreased fecundity.