Next-generation sequencing for patients with non-obstructive azoospermia: implications for significant roles of monogenic/oligogenic mutations

Systematic molecular analyses for 115 karyotypically normal men with isolated non-obstructive azoospermia

STUDY QUESTION

Do copy-number variations (CNVs) in the azoospermia factor (AZF) regions and monogenic mutations play a major role in the development of isolated (non-syndromic) non-obstructive azoospermia (NOA) in Japanese men with a normal 46, XY karyotype?

SUMMARY ANSWER

Deleterious CNVs in the AZF regions and damaging sequence variants in eight genes likely constitute at least 8% and approximately 8% of the genetic causes, respectively, while variants in other genes play only a minor role.

WHAT IS KNOWN ALREADY

Sex chromosomal abnormalities, AZF-linked microdeletions, and monogenic mutations have been implicated in isolated NOA. More than 160 genes have been reported as causative/susceptibility/candidate genes for NOA.

STUDY DESIGN, SIZE, DURATION

Systematic molecular analyses were conducted for 115 patients with isolated NOA and a normal 46, XY karyotype, who visited our hospital between 2017 and 2021.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We studied 115 unrelated Japanese patients. AZF-linked CNVs were examined using sequence-tagged PCR and multiplex ligation-dependent probe amplification, and nucleotide variants were screened using whole exome sequencing (WES). An optimized sequence kernel association test (SKAT-O), a gene-based association study using WES data, was performed to identify novel disease-associated genes in the genome. The results were compared to those of previous studies and our in-house control data.

MAIN RESULTS AND THE ROLE OF CHANCE

Thirteen types of AZF-linked CNVs, including the hitherto unreported gr/gr triplication and partial AZFb deletion, were identified in 63 (54.8%) cases. When the gr/gr deletion, a common polymorphism in Japan, was excluded from data analyses, the total frequency of CNVs was 23/75 (30.7%). This frequency is higher than that of the reference data in Japan and China (11.1% and 14.7%, respectively). Known NOA-causative AZF-linked CNVs were found in nine (7.8%) cases. Rare damaging variants in known causative genes (DMRT1, PLK4, SYCP2, TEX11, and USP26) and hemizygous/multiple-heterozygous damaging variants in known spermatogenesis-associated genes (TAF7L, DNAH2, and DNAH17) were identified in nine cases (7.8% in total). Some patients carried rare damaging variants in multiple genes. SKAT-O detected no genes whose rare damaging variants were significantly accumulated in the patient group.

LIMITATIONS, REASONS FOR CAUTION

The number of participants was relatively small, and the clinical information of each patient was fragmentary. Moreover, the pathogenicity of identified variants was assessed only by in silico analyses.

WIDER IMPLICATIONS OF THE FINDINGS

This study showed that various AZF-linked CNVs are present in more than half of Japanese NOA patients. These results broadened the structural variations of AZF-linked CNVs, which should be considered for the molecular diagnosis of spermatogenic failure. Furthermore, the results of this study highlight the etiological heterogeneity and possible oligogenicity of isolated NOA.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by Grants from the Japan Society for the Promotion of Science (21K19283 and 21H0246), the Japan Agency for Medical Research and Development (22ek0109464h0003), the National Center for Child Health and Development, the Canon Foundation, the Japan Endocrine Society, and the Takeda Science Foundation. The results of this study were based on samples and patient data obtained from the International Center for Reproductive Medicine, Dokkyo Medical University Saitama Medical Center, Koshigaya, Japan. The authors have no conflicts of interest to disclose.

TRIAL REGISTRATION NUMBER

N/A.

Genetic variants underlying spermatogenic arrests in men with non-obstructive azoospermia

Spermatogenic arrest is a severe form of non-obstructive azoospermia (NOA), which occurs in 10-15% of infertile men. Interruption in spermatogenic progression at premeiotic, meiotic, or postmeiotic stage can lead to arrest in men with NOA. Recent studies have intensively focused on defining genetic variants underlying these spermatogenic arrests by making genome/exome sequencing. A number of variants were discovered in the genes involving in mitosis, meiosis, germline differentiation and other basic cellular events. Herein, defined variants in NOA cases with spermatogenic arrests and created knockout mouse models for the related genes are comprehensively reviewed. Also, importance of gene panel-based screening for NOA cases was discussed. Screening common variants in these infertile men with spermatogenic arrests may contribute to elucidating the molecular background and designing novel treatment strategies.

Sohlh1 loss of function male and female infertility model impacts overall health beyond gonadal dysfunction in mice†

Reproductive longevity is associated with health outcomes. Early menopause, loss of ovarian function, and male infertility are linked to shorter lifespan and increased adverse health outcomes. Here we examined the extragonadal effects of whole animal loss of spermatogenesis and oogenesis specific basic helix-loop-helix 1 (Sohlh1) gene in mice, a well-described mouse model of female and male infertility. Sohlh1 encodes a transcription factor that is primarily expressed in the male and female germline and regulates germline differentiation. The Sohlh1 knockout mouse model, just like human individuals with SOHLH1 loss of function, presents with hypergonadotropic hypogonadism and loss of ovarian function in females and impaired spermatogenesis in males, with a seemingly gonad restricted phenotype in both sexes. However, extragonadal phenotyping revealed that Sohlh1 deficiency leads to abnormal immune profiles in the blood and ovarian tissues of female animals, sex-specific alterations of metabolites, and behavior and cognition changes. Altogether, these results show that Sohlh1 deficiency impacts overall health in both male and female mice.

Single-cell transcriptome profiling reveals several LncRNAs differentially expressed in idiopathic germ cell aplasia

Mechanisms underlying severe male infertility are still largely elusive. However, recently, a single-cell transcription study by our group identified several differentially expressed coding genes in all the somatic cell types in testes of patients with idiopathic germ cell aplasia (iGCA). Here, we leverage this work by extending the analysis also to the non-coding portion of the genome. As a result, we found that 43 LncRNAs were differentially expressed in the somatic cells of these patients. Interestingly, a significant portion of the overexpressed LncRNAs was found to be a target of TAF9B, a transcription factor known to be involved in germ cell survival. Moreover, several overexpressed LncRNAs were also found to be activated in a mouse model of Sertoli cells treated with bisphenol A, a widespread environmental contaminant, long suspected to impair male fertility. Finally, a literature search for MEG3, a maternally imprinted LncRNA overexpressed as well in our patients, found it to be involved, among other things, in obesity and inflammation, known comorbidities of iGCA, ultimately suggesting that our findings deepen the understanding of the molecular insights coupled not only to the pathogenesis, but also to the clinical course of this class of patients.

Identification of pathogenic mutations from nonobstructive azoospermia patients

It is estimated that approximately 25% of nonobstructive azoospermia (NOA) cases are caused by single genetic anomalies, including chromosome aberrations and gene mutations. The identification of these mutations in NOA patients has always been a research hot spot in the area of human infertility. However, compared with more than 600 genes reported to be essential for fertility in mice, mutations in approximately 75 genes have been confirmed to be pathogenic in patients with male infertility, in which only 14 were identified from NOA patients. The small proportion suggested that there is much room to improve the methodology of mutation screening and functional verification. Fortunately, recent advances in whole exome sequencing and CRISPR-Cas9 have greatly promoted research on the etiology of human infertility and made improvements possible. In this review, we summarized the pathogenic mutations found in NOA patients and the efforts we have made to improve the efficiency of mutation screening from NOA patients and functional verification with the application of new technologies.

Identification of deleterious variants in patients with male infertility due to idiopathic non-obstructive azoospermia

BACKGROUND

Non-obstructive azoospermia (NOA) is the most severe type of male infertility, affecting 1% of men worldwide. Most of its etiologies remain idiopathic. Although genetic studies have identified dozens of NOA genes, monogenic mutations can also account for a small proportion of idiopathic NOA cases. Hence, this genetic study was conducted to explore the causes of monogenic variants of NOA in a cohort of Chinese patients.

METHODS

Following the screening using chromosomal karyotyping, Y chromosome microdeletion analyses, and sex hormone assessments, subsequent whole-exome sequencing analysis was performed in 55 unrelated idiopathic NOA patients with male infertility to explore potential deleterious variants associated with spermatogenesis. We also performed Sanger sequencing to demonstrate the variants. Testicular biopsy or microsurgical testicular sperm extraction was also performed to confirm the diagnosis of NOA and identify spermatozoa. Hematoxylin and eosin staining was performed to assess the histopathology of spermatogenesis.

RESULTS

Abnormal testicular pathological phenotypes included Sertoli cell-only syndrome, maturation arrest, and hypospermatogenesis. Using bioinformatics analysis, we detected novel variants in two recessive genes, FANCA (NM_000135, c.3263C > T, c.1729C > G) and SYCE1 (NM_001143763, c.689_690del); one X-linked gene, TEX11 (NM_031276, c.466A > G, c.559_560del); and two dominant genes, DMRT1 (NM_021951, c.425C > T, c.340G > A) and PLK4 (NM_001190799, c.2785A > G), in eight patients, which corresponded to 14.55% (8/55) of the patients.

CONCLUSION

This study presented some novel variants of known pathogenic genes for NOA. Further, it expanded the variant spectrum of NOA patients, which might advance clinical genetic counseling in the future.

OUP accepted manuscript

The pathways of gametogenesis encompass elaborate cellular specialization accompanied by precise partitioning of the genome content in order to produce fully matured spermatozoa and oocytes. Transcription factors are an important class of molecules that function in gametogenesis to regulate intrinsic gene expression programs, play essential roles in specifying (or determining) germ cell fate and assist in guiding full maturation of germ cells and maintenance of their populations. Moreover, in order to reinforce or redirect cell fate in vitro, it is transcription factors that are most frequently induced, over-expressed or activated. Many reviews have focused on the molecular development and genetics of gametogenesis, in vivo and in vitro, in model organisms and in humans, including several recent comprehensive reviews: here, we focus specifically on the role of transcription factors. Recent advances in stem cell biology and multi-omic studies have enabled deeper investigation into the unique transcriptional mechanisms of human reproductive development. Moreover, as methods continually improve, in vitro differentiation of germ cells can provide the platform for robust gain- and loss-of-function genetic analyses. These analyses are delineating unique and shared human germ cell transcriptional network components that, together with somatic lineage specifiers and pluripotency transcription factors, function in transitions from pluripotent stem cells to gametes. This grand theme review offers additional insight into human infertility and reproductive disorders that are linked predominantly to defects in the transcription factor networks and thus may potentially contribute to the development of novel treatments for infertility.

The expression of Beclin-1 in testicular tissues of non-obstructive azoospermia patients and its predictive value in sperm retrieval rate

Background

Beclin-1 is an autophagy gene and higher levels suggest mammalian testicular damage. Our study aims at exploring the role of Beclin-1 in non-obstructive azoospermia (NOA) patients and clarifying the predictive value of Beclin-1for sperm retrieval in microdissection testicular sperm extraction (micro-TESE).

Methods

In the present study, 62 NOA patients were finally recruited. Serum hormone including luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol II (E2), testosterone (T) and prolactin (PRL), as well as testicular volume were measured. Testicular histopathology was diagnosed by two independent pathologists. The expression of Beclin-1 was detected by real-time PCR in testicular tissue.

Results

Our study illustrated that Beclin-1 was differently expressed in three pathological types of NOA. Compared with hypospermatogenesis (HS, P=0.002) or maturation arrest (MA, P=0.049), Beclin-1 showed significantly up-regulated in Sertoli cell-only syndrome (SCOS) group. Moreover, Beclin-1 expression was obviously positive related with serum LH (rho =0.269, P=0.036), meanwhile significantly negative correlation with testicular volume (rho =-0.370, P=0.003), serum T (rho =-0.326, P=0.010), Johnsen score (rho =-0.318, P=0.012), and pathologic type (rho =-0.452, P<0.001). Furthermore, a logistic regression model demonstrated that Beclin-1 is an important predictor of failed sperm retrieval (OR =0.001, P=0.007), which exhibited a pretty AUC =78.6 (P=0.001).

Conclusions

Beclin-1 may play a critical role in spermatogenesis. Elevated Beclin-1 may be obviously associated with lower chances of positive sperm retrieval.

Aging, inflammation and DNA damage in the somatic testicular niche with idiopathic germ cell aplasia

Molecular mechanisms associated with human germ cell aplasia in infertile men remain undefined. Here we perform single-cell transcriptome profiling to highlight differentially expressed genes and pathways in each somatic cell type in testes of men with idiopathic germ cell aplasia. We identify immaturity of Leydig cells, chronic tissue inflammation, fibrosis, and senescence phenotype of the somatic cells, as well markers of chronic inflammation in the blood. We find that deregulated expression of parentally imprinted genes in myoid and immature Leydig cells, with relevant changes in the ratio of Lamin A/C transcripts and an active DNA damage response in Leydig and peritubular myoid cells are also indicative of senescence of the testicular niche. This study offers molecular insights into the pathogenesis of idiopathic germ cell aplasia.

Molecular mechanisms associated with human germ cell aplasia in infertile men remain undefined. Here the authors perform single-cell transcriptome profiling to highlight differentially expressed genes and pathways in each somatic cell type in testes of men with idiopathic germ cell aplasia.

The mutation c.346-1G > a in SOHLH1 impairs sperm production in the homozygous but not in the heterozygous condition

Non-obstructive azoospermia (NOA) is an important cause of male infertility, and the genetic pathogenesis is still incompletely understood. The previous study reported that heterozygous mutation of c.346-1G > A in spermatogenesis and oogenesis specific basic helix–loop–helix 1 (SOHLH1) was identified in two NOA patients and suggested it is the pathogenic factor for NOA. However, in our research, this heterozygous mutation was confirmed in three Chinese infertile patients who suffered from teratozoospermia, but they had normal sperm number. Intriguingly, a homozygous mutation of c.346-1G > A in SOHLH1 was detected in a severe oligozoospermia (SOZ) patient, characterized with severely decreased sperm count. Notably, we unprecedently revealed that this homozygous mutation of c.346-1G > A in SOHLH1 leads to the sharp decrease in various germ cells and spermatogenesis dysfunction, which is similar to the phenotype of SOHLH1 knockout male mice. Moreover, western blotting confirmed that the homozygous mutation declined SOHLH1 protein expression. Additionally, we correlated the good prognosis of intracytoplasmic sperm injection (ICSI) in the patients carrying the mutation of c.346-1G > A in SOHLH1. Thus, we suggested that the heterozygous mutation of c.346-1G > A in SOHLH1 is responsible for teratozoospermia, and this homozygous mutation in SOHLH1 impairs spermatogenesis and further leads to the reduced sperm count, eventually causing male infertility, which unveils a new recessive-inheritance pattern of SOHLH1-associated male infertility initially.

OTOGL, a gelforming mucin protein, is nonessential for male germ cell development and spermatogenesis in mice

Otogelin-like protein (encoded by Otogl) was highly structural similar to the gelforming mucin proteins. Although human OTOG mutations have been linked to deafness, the biological function of OTOGL in male germ cell development remains enigmatic. In screening 336 patients with non-obstructive azoospermia (NOA), OTOGL displays the high mutant ratio (13.99 %). Then, we examined the expression of OTOGL in developing mouse testes. Otogl mRNA and protein are continually expressed in postnatal developing testes from postnatal day 0 (P0) testes to P21 testes exhibiting a decreased trend with the age growth. We thus generated a global Otogl knockout mouse (KO) model using the CRISPR/Cas9 technology; however, Otogl KO mice displayed normal development and fertility. Further histological analysis of Otogl knockout mouse testes revealed that all types of spermatogenic cells are present in Otogl KO seminiferous tubules. Together, our study suggested that OTOGL is nonessential for male germ cell development and spermatogenesis.

Pathogenic variants of ATG4D in infertile men with non-obstructive azoospermia identified using whole-exome sequencing

Non-obstructive azoospermia (NOA) is the most severe form of male infertility, and it is primarily associated with genetic defects. We performed whole-exome sequencing of 236 patients with NOA and identified a homozygous pathogenic variant of autophagy-related 4D cysteine peptidase (ATG4D) in two siblings from a consanguineous family and compound heterozygous pathogenic variants of ATG4D in two sporadic cases. The expression of LC3B, a regulator of autophagic activity, was significantly decreased, and the apoptosis rate of spermatogenic cells in testicular tissues was increased. Transfection of GC-2spd cells with a ATG4D mutant plasmid (Flag-Atg4d^mut ) significantly decreased the expression level of Lc3b and increased the rate of apoptosis. Moreover, a pathogenic variant in X-linked ATG4A and compound heterozygous pathogenic variants of ATG4B were identified in one patient each. All novel variants were segregated by disease phenotype and were predicted to be pathogenic. Our findings revealed that autophagy-related cysteine peptidase family genes may play crucial roles in human spermatogenesis and identified ATG4D as a novel candidate gene for male infertility due to NOA.

Whole-Exome Sequencing Analysis of Human Semen Quality in Russian Multiethnic Population

The global trend toward the reduction of human spermatogenic function observed in many countries, including Russia, raised the problem of extensive screening and monitoring of male fertility and elucidation of its genetic and ethnic mechanisms. Recently, whole-exome sequencing (WES) was developed as a powerful tool for genetic analysis of complex traits. We present here the first Russian WES study for identification of new genes associated with semen quality. The experimental 3 × 2 design of the WES study was based on the analysis of 157 samples including three ethnic groups—Slavs (59), Buryats (n = 49), and Yakuts (n = 49), and two different semen quality groups—pathozoospermia (n = 95) and normospermia (n = 62). Additionally, our WES study group was negative for complete AZF microdeletions of the Y-chromosome. The normospermia group included men with normal sperm parameters in accordance with the WHO-recommended reference limit. The pathozoospermia group included men with impaired semen quality, namely, with any combined parameters of sperm concentration <15 × 10⁶/ml, and/or progressive motility <32%, and/or normal morphology <4%. The WES was performed for all 157 samples. Subsequent calling and filtering of variants were carried out according to the GATK Best Practices recommendations. On the genotyping stage, the samples were combined into four cohorts: three sets corresponded to three ethnic groups, and the fourth set contained all the 157 whole-exome samples. Association of the obtained polymorphisms with semen quality parameters was investigated using the χ2 test. To prioritize the obtained variants associated with pathozoospermia, their effects were determined using Ensembl Variant Effect Predictor. Moreover, polymorphisms located in genes expressed in the testis were revealed based on the genomic annotation. As a result, the nine potential SNP markers rs6971091, rs557806, rs610308, rs556052, rs1289658, rs278981, rs1129172, rs12268007, and rs17228441 were selected for subsequent verification on our previously collected population sample (about 1,500 males). The selected variants located in seven genes FAM71F1, PPP1R15A, TRIM45, PRAME, RBM47, WDFY4, and FSIP2 that are expressed in the testis and play an important role in cell proliferation, meiosis, and apoptosis.

Human testis-expressed (TEX) genes: a review focused on spermatogenesis and male fertility

Spermatogenesis is a complex process regulated by a multitude of genes. The identification and characterization of male-germ-cell-specific genes is crucial to understanding the mechanisms through which the cells develop. The term “TEX gene” was coined by Wang et al. (Nat Genet. 2001; 27: 422–6) after they used cDNA suppression subtractive hybridization (SSH) to identify new transcripts that were present only in purified mouse spermatogonia. TEX (Testis expressed) orthologues have been found in other vertebrates (mammals, birds, and reptiles), invertebrates, and yeasts. To date, 69 TEX genes have been described in different species and different tissues. To evaluate the expression of each TEX/tex gene, we compiled data from 7 different RNA-Seq mRNA databases in humans, and 4 in the mouse according to the expression atlas database.

Various studies have highlighted a role for many of these genes in spermatogenesis. Here, we review current knowledge on the TEX genes and their roles in spermatogenesis and fertilization in humans and, comparatively, in other species (notably the mouse). As expected, TEX genes appear to have a major role in reproduction in general and in spermatogenesis in humans but also in all mammals such as the mouse. Most of them are expressed specifically or predominantly in the testis. As most of the TEX genes are highly conserved in mammals, defects in the male (gene mutations in humans and gene-null mice) lead to infertility. In the future, cumulative data on the human TEX genes’ physiological functions and pathophysiological dysfunctions should become available and is likely to confirm the essential role of this family in the reproductive process. Thirteen TEX genes are now referenced in the OMIM database, and 3 have been linked to a specific phenotype. TEX11 (on Xq13.1) is currently the gene most frequently reported as being associated with azoospermia.

Genetics of Azoospermia

Azoospermia affects 1% of men, and it can be due to: (i) hypothalamic-pituitary dysfunction, (ii) primary quantitative spermatogenic disturbances, (iii) urogenital duct obstruction. Known genetic factors contribute to all these categories, and genetic testing is part of the routine diagnostic workup of azoospermic men. The diagnostic yield of genetic tests in azoospermia is different in the different etiological categories, with the highest in Congenital Bilateral Absence of Vas Deferens (90%) and the lowest in Non-Obstructive Azoospermia (NOA) due to primary testicular failure (~30%). Whole-Exome Sequencing allowed the discovery of an increasing number of monogenic defects of NOA with a current list of 38 candidate genes. These genes are of potential clinical relevance for future gene panel-based screening. We classified these genes according to the associated-testicular histology underlying the NOA phenotype. The validation and the discovery of novel NOA genes will radically improve patient management. Interestingly, approximately 37% of candidate genes are shared in human male and female gonadal failure, implying that genetic counselling should be extended also to female family members of NOA patients.

Splicing regulation in brain and testis: common themes for highly specialized organs

Expansion of the coding and regulatory capabilities of eukaryotic transcriptomes by alternative splicing represents one of the evolutionary forces underlying the increased structural complexity of metazoans. Brain and testes stand out as the organs that mostly exploit the potential of alternative splicing, thereby expressing the largest repertoire of splice variants. Herein, we will review organ-specific as well as common mechanisms underlying the high transcriptome complexity of these organs and discuss the impact exerted by this widespread alternative splicing regulation on the functionality and differentiation of brain and testicular cells.

Male Infertility in Humans: An Update on Non-obstructive Azoospermia (NOA) and Obstructive Azoospermia (OA)

Non-obstructive azoospermia (NOA) and obstructive azoospermia (OA) are two common causes of infertility that affect a considerable number of men. However, few studies were performed to understand the molecular etiology of these disorders. Studies based on bioinformatics and genetic analyses in recent years, however, have yielded insightful information and have identified a number of genes that are involved in these disorders. In this review, we briefly summarize and evaluate these findings. We also discuss findings based on epigenetic modifications of sperm DNAs that affect a number of genes pertinent to NOA and OA. The information summarized in this Chapter should be helpful to investigators in future functional studies of NOA and OA.

Next-generation sequencing: toward an increase in the diagnostic yield in patients with apparently idiopathic spermatogenic failure

A large proportion of patients with idiopathic spermatogenic failure (SPGF; oligozoospermia or nonobstructive azoospermia [NOA]) do not receive a diagnosis despite an extensive diagnostic workup. Recent evidence has shown that the etiology remains undefined in up to 75% of these patients. A number of genes involved in germ-cell proliferation, spermatocyte meiotic divisions, and spermatid development have been called into play in the pathogenesis of idiopathic oligozoospermia or NOA. However, this evidence mainly comes from case reports. Therefore, this study was undertaken to identify the molecular causes of SPGF. To accomplish this, 15 genes (USP9Y, NR5A1, KLHL10, ZMYND15, PLK4, TEX15, TEX11, MEIOB, SOHLH1, HSF2, SYCP3, TAF4B, NANOS1, SYCE1, and RHOXF2) involved in idiopathic SPGF were simultaneously analyzed in a cohort of 25 patients with idiopathic oligozoospermia or NOA, accurately selected after a thorough diagnostic workup. After next-generation sequencing (NGS) analysis, we identified the presence of rare variants in the NR5A1 and TEX11 genes with a pathogenic role in 3/25 (12.0%) patients. Seventeen other different variants were identified, and among them, 13 have never been reported before. Eleven out of 17 variants were likely pathogenic and deserve functional or segregation studies. The genes most frequently mutated were MEIOB, followed by USP9Y, KLHL10, NR5A1, and SOHLH1. No alterations were found in the SYCP3, TAF4B, NANOS1, SYCE1, or RHOXF2 genes. In conclusion, NGS technology, by screening a specific custom-made panel of genes, could help increase the diagnostic rate in patients with idiopathic oligozoospermia or NOA.

Molecular genetics of infertility: loss-of-function mutations in humans and corresponding knockout/mutated mice

BACKGROUND

Infertility is a major issue in human reproductive health, affecting an estimated 15% of couples worldwide. Infertility can result from disorders of sex development (DSD) or from reproductive endocrine disorders (REDs) with onset in infancy, early childhood or adolescence. Male infertility, accounting for roughly half of all infertility cases, generally manifests as decreased sperm count (azoospermia or oligozoospermia), attenuated sperm motility (asthenozoospermia) or a higher proportion of morphologically abnormal sperm (teratozoospermia). Female infertility can be divided into several classical types, including, but not limited to, oocyte maturation arrest, premature ovarian insufficiency (POI), fertilization failure and early embryonic arrest. An estimated one half of infertility cases have a genetic component; however, most genetic causes of human infertility are currently uncharacterized. The advent of high-throughput sequencing technologies has greatly facilitated the identification of infertility-associated gene mutations in patients over the past 20 years.

OBJECTIVE AND RATIONALE

This review aims to conduct a narrative review of the genetic causes of human infertility. Loss-of-function mutation discoveries related to human infertility are summarized and further illustrated in tables. Corresponding knockout/mutated animal models of causative genes for infertility are also introduced.

SEARCH METHODS

A search of the PubMed database was performed to identify relevant studies published in English. The term 'mutation' was combined with a range of search terms related to the core focus of the review: infertility, DSD, REDs, azoospermia or oligozoospermia, asthenozoospermia, multiple morphological abnormalities of the sperm flagella (MMAF), primary ciliary dyskinesia (PCD), acephalic spermatozoa syndrome (ASS), globozoospermia, teratozoospermia, acrosome, oocyte maturation arrest, POI, zona pellucida, fertilization defects and early embryonic arrest.

OUTCOMES

Our search generated ∼2000 records. Overall, 350 articles were included in the final review. For genetic investigation of human infertility, the traditional candidate gene approach is proceeding slowly, whereas high-throughput sequencing technologies in larger cohorts of individuals is identifying an increasing number of causative genes linked to human infertility. This review provides a wide panel of gene mutations in several typical forms of human infertility, including DSD, REDs, male infertility (oligozoospermia, MMAF, PCD, ASS and globozoospermia) and female infertility (oocyte maturation arrest, POI, fertilization failure and early embryonic arrest). The causative genes, their identified mutations, mutation rate, studied population and their corresponding knockout/mutated mice of non-obstructive azoospermia, MMAF, ASS, globozoospermia, oocyte maturation arrest, POI, fertilization failure and early embryonic arrest are further illustrated by tables. In this review, we suggest that (i) our current knowledge of infertility is largely obtained from knockout mouse models; (ii) larger cohorts of clinical cases with distinct clinical characteristics need to be recruited in future studies; (iii) the whole picture of genetic causes of human infertility relies on both the identification of more mutations for distinct types of infertility and the integration of known mutation information; (iv) knockout/mutated animal models are needed to show whether the phenotypes of genetically altered animals are consistent with findings in human infertile patients carrying a deleterious mutation of the homologous gene; and (v) the molecular mechanisms underlying human infertility caused by pathogenic mutations are largely unclear in most current studies.

WILDER IMPLICATIONS

It is important to use our current understanding to identify avenues and priorities for future research in the field of genetic causes of infertility as well as to apply mutation knowledge to risk prediction, genetic diagnosis and potential treatment for human infertility.

The study investigating the determination of protamine in seminal plasma from azoospermic donors: Suggestion of new methods to diagnose obstructive azoospermia, and to capture childbearing sperm for testicular sperm extraction (TESE) and insemination sperm injection (ICSI)

We analyzed seminal plasma of 88 normozoospermic, 40 oligozoospermic and 32 azoospermic donors. During this study, we focus to record the protamine concentration in the seminal plasma of azoospermic donors. The seminal protamine concentrations were found to be 19.6-62.8 IU/ml in normozoospermic donors; 25.4-100.8 IU/ml in oligozoospermic donors; and, most notably, 23.7-219.4 IU/ml in azoospermic donors. These results indicate that, based on seminal plasma protamine concentrations, even azoospermic donors were able to produce as much sperm as normo- and/or oligozoospermic donors. Using statistical analyses, significant differences were found between azoospermic and normozoospermic donors (p = 0.0018). Protamine content was found to be a direct marker for the presence of sperm. The data from this study provided evidence for a new therapeutic approach for testicular varicose veins, which are found in obstructive or non-obstructive azoospermia. High seminal protamine concentrations indicated the future possibility of acquiring childbearing sperm for insemination sperm injection (ICSI) and testicular sperm extraction (TESE), even with azoospermic donors. Given these results, we also suggest a new cut-off value for acquisition of childbearing sperm in selection for ICSI.

Over-expression of hsa_circ_0000116 in patients with non-obstructive azoospermia and its predictive value in testicular sperm retrieval

BACKGROUND

Non-obstructive azoospermia (NOA), identified in approximately 10% of infertile males, is a multifactorial disease whose molecular mechanisms remain unknown.

OBJECTIVES

The aim of this study was to identify the role of hsa_circ_0000116 in NOA and illustrate its predictive value in testicular sperm retrieval.

MATERIALS AND METHODS

The study included 78 individuals, 58 with NOA and 20 with obstructive azoospermia (OA). Serum hormones including testosterone (T), follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), and estradiol II (E2) were measured. Testicular histopathology was analyzed by at least two pathologists. The expression of hsa_circ_0000116 in testicular tissue samples was detected using real-time PCR, and the circRNA-miRNA-mRNA networks were predicted using bioinformatics analysis.

RESULTS

Our study illustrated that the expression of hsa_circ_0000116 was significantly higher in testicular tissue samples of NOA patients than in that of OA patients. Moreover, hsa_circ_0000116 was aberrantly expressed in three different pathological types of NOA: It was significantly up-regulated in patients with Sertoli cell-only syndrome (SCOS) when compared to patients with hypospermatogenesis (HS). In addition, the expression of hsa_circ_0000116 was negatively correlated with Johnsen score, while it was positively correlated with serum FSH level. A multivariate logistic regression model demonstrated that a high level of hsa_circ_0000116 was associated with a low rate of successful testicular sperm retrieval. Bioinformatics analysis and verification experiments showed that one of the most probable potential target miRNA for hsa_circ_0000116 was hsa-miR-449a. Further analysis indicated that hsa_circ_0000116 may be affecting the fertility function through a hsa_circ_0000116-miR-449-autophagy-related competing endogenous RNA (ceRNA) network.

DISCUSSION AND CONCLUSION

We report for the first time that hsa_circ_0000116 may play pivotal roles in regulating spermatogenesis and may also be a potential biomarker for the diagnosis and treatment of NOA, while acting as a predictive tool for the rate of successful testicular sperm retrieval in NOA patients.

Conversion from spermatogonia to spermatocytes: Extracellular cues and downstream transcription network

Spermatocyte (spc) formation from spermatogonia (spg) differentiation is the first step of spermatogenesis which produces prodigious spermatozoa for a lifetime. After decades of studies, several factors involved in the functioning of a mouse were discovered both inside and outside spg. Considering the peculiar expression and working pattern of each factor, this review divides the whole conversion of spg to spc into four consecutive development processes with a focus on extracellular cues and downstream transcription network in each one. Potential coordination among Dmrt1, Sohlh1/2 and BMP families mediates Ngn3 upregulation, which marks progenitor spg, with other changes. After that, retinoic acid (RA), as a master regulator, promotes A1 spg formation with its helpers and Sall4. A1-to-B spg transition is under the control of Kitl and impulsive RA signaling together with early and late transcription factors Stra8 and Dmrt6. Finally, RA and its responsive effectors conduct the entry into meiosis. The systematic transcription network from outside to inside still needs research to supplement or settle the controversials in each process. As a step further ahead, this review provides possible drug targets for infertility therapy by cross-linking humans and mouse model.

Development of a novel next-generation sequencing panel for diagnosis of quantitative spermatogenic impairment

PURPOSE

To develop and assess a novel custom next-generation sequencing (NGS) panel for male infertility genetic diagnosis.

METHODS

A total of 241 subjects with diagnosis of idiopathic infertility ranging from azoospermia to normozoospermia were sequenced by a custom NGS panel including AR, FSHB, FSHR, KLHL10, NR5A1, NANOS1, SEPT12, SYCP3, TEX11 genes. Variants with minor allele frequency < 1% were confirmed by Sanger sequencing.

RESULTS

Nineteen missense variants were detected in 23 subjects with abnormal sperm count, whilst no variants were identified in normozoospermic men. Of identified variants, we prioritized variants classified as pathogenic and of uncertain significance (VUS) (63.1%, 12/19). No missense variants were found in males with normal seminal parameters (0/67). Therefore, the prevalence of variants was significantly higher in patients with spermatogenic impairment (16/174 vs 0/67, p = 0.007).

CONCLUSION

This study confirms the utility to apply NGS panel for infertility diagnosis in order to find new genetic variants potentially linked to male infertility with much higher accuracy than standard tests suggested by guidelines. Indeed, based on biological significance, prevalence in the general population and clinical data of patients, it is plausible that identified variants in this study might be linked to quantitative spermatogenic impairment, although further studies are needed.

Loss of Cx43 in Murine Sertoli Cells Leads to Altered Prepubertal Sertoli Cell Maturation and Impairment of the Mitosis-Meiosis Switch

Male factor infertility is a problem in today’s society but many underlying causes are still unknown. The generation of a conditional Sertoli cell (SC)-specific connexin 43 (Cx43) knockout mouse line (SCCx43KO) has provided a translational model. Expression of the gap junction protein Cx43 between adjacent SCs as well as between SCs and germ cells (GCs) is known to be essential for the initiation and maintenance of spermatogenesis in different species and men. Adult SCCx43KO males show altered spermatogenesis and are infertile. Thus, the present study aims to identify molecular mechanisms leading to testicular alterations in prepubertal SCCx43KO mice. Transcriptome analysis of 8-, 10- and 12-day-old mice was performed by next-generation sequencing (NGS). Additionally, candidate genes were examined by qRT-PCR and immunohistochemistry. NGS revealed many significantly differentially expressed genes in the SCCx43KO mice. For example, GC-specific genes were mostly downregulated and found to be involved in meiosis and spermatogonial differentiation (e.g., Dmrtb1, Sohlh1). In contrast, SC-specific genes implicated in SC maturation and proliferation were mostly upregulated (e.g., Amh, Fshr). In conclusion, Cx43 in SCs appears to be required for normal progression of the first wave of spermatogenesis, especially for the mitosis-meiosis switch, and also for the regulation of prepubertal SC maturation.

A different look at genetic factors in individuals with non-obstructive azoospermia or oligospermia in our research study: To whom, which threshold, when, in what way?

INTRODUCTION

In our study, we sought answers to many questions about male infertility from a different perspective. The first step in male infertility is anamnesis, physical examination and sperm count. The European Academy of Andrology recommends examination of genetic causes in individuals with fewer than 5million/ml semen counts. The American Urological Association and American Society for Reproductive Medicine have guidelines recommending performing karyotype and AZF subgroup deletion testing in azoospermia and fewer than 5 million sperm total count. Klinefelter syndrome and Y chromosome microdeletions are still very important in male infertility. Based on patients with Klinefelter syndrome or Y microdeletion, we sought answers to many questions in male infertility.

MATERIALS AND METHODS

In the presented study 327 male patients with having fewer than 15millionsperm/ml detected in at least two consecutive sperm analysis were examined. Patients were divided into sub-groups according to the presence of semen count, chromosomal anomaly and Y microdeletion. In addition, FSH, LH and testosterone levels were analyzed.

RESULTS

Numerical chromosomal anomalies were observed in 34 (10.4%) of 327 patients, and all of these anomalies were found as 47, XXY. Individuals with no AZF microdeletion constituted 95.1% (n=311) of the study group. The overall frequency of AZF microdeletions was 4.9% (16/327). No AZF microdeletions were detected for the patients who have sperm counts above 2million/ml. FSH, LH and testosterone levels were found significantly different between the groups.

DISCUSSION

The results of our study provide another layer of evidence to demonstrate the controversial threshold value of the EAA. In light of our data and current literature, we recommend to set the threshold value at 2million/ml for semen analysis. Further studies conducted in different ethnic groups and larger patient groups would contribute to clarify what exact value should be used to apply genetic tests.

Role of carotenoids and retinoids during heart development

The nutritional requirements of the developing embryo are complex. In the case of dietary vitamin A (retinol, retinyl esters and provitamin A carotenoids), maternal derived nutrients serve as precursors to signaling molecules such as retinoic acid, which is required for embryonic patterning and organogenesis. Despite variations in the composition and levels of maternal vitamin A, embryonic tissues need to generate a precise amount of retinoic acid to avoid congenital malformations. Here, we summarize recent findings regarding the role and metabolism of vitamin A during heart development and we survey the association of genes known to affect retinoid metabolism or signaling with various inherited disorders. A better understanding of the roles of vitamin A in the heart and of the factors that affect retinoid metabolism and signaling can help design strategies to meet nutritional needs and to prevent birth defects and disorders associated with altered retinoid metabolism. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

Genetic Landscape of Nonobstructive Azoospermia and New Perspectives for the Clinic

Nonobstructive azoospermia (NOA) represents the most severe expression of male infertility, involving around 1% of the male population and 10% of infertile men. This condition is characterised by the inability of the testis to produce sperm cells, and it is considered to have an important genetic component. During the last two decades, different genetic anomalies, including microdeletions of the Y chromosome, karyotype defects, and missense mutations in genes involved in the reproductive function, have been described as the primary cause of NOA in many infertile men. However, these alterations only explain around 25% of azoospermic cases, with the remaining patients showing an idiopathic origin. Recent studies clearly suggest that the so-called idiopathic NOA has a complex aetiology with a polygenic inheritance, which may alter the spermatogenic process. Although we are far from a complete understanding of the molecular mechanisms underlying NOA, the use of the new technologies for genetic analysis has enabled a considerable increase in knowledge during the last years. In this review, we will provide a comprehensive and updated overview of the genetic basis of NOA, with a special focus on the possible application of the recent insights in clinical practice.

IGF2 Mutations

OBJECTIVE

IGF2 is a paternally expressed growth-promoting gene. Here, we report five cases with IGF2 mutations and review IGF2 mutation-positive patients described in the literature. We also compare clinical features between patients with IGF2 mutations and those with H19/IGF2:IG-DMR epimutations.

RESULTS

We recruited five cases with IGF2 mutations: case 1 with a splice site mutation (c.-6-1G>C) leading to skipping of exon 2 and cases 2-5 with different missense mutations (p.(Cys70Tyr), p.(Cys71Arg), p.(Cys33Ser), and p.(Cys45Ser)) affecting cysteine residues involved in the S-S bindings. All the mutations resided on the paternally inherited allele, and the mutation of case 5 was present in a mosaic condition. Clinical assessment revealed Silver-Russell syndrome (SRS) phenotype with Netchine-Harbison scores of ≥5/6 in all the apparently nonmosaic 14 patients with IGF2 mutations (cases 1-4 described in this study and 10 patients reported in the literature). Furthermore, compared with H19/IGF2:IG-DMR epimutations, IGF2 mutations were associated with low frequency of hemihypoplasia, high frequency of feeding difficulty and/or reduced body mass index, and mild degree of relative macrocephaly, together with occasional development of severe limb malformations, high frequency of cardiovascular anomalies and developmental delay, and low serum IGF-II values.

CONCLUSIONS

This study indicates that IGF2 mutations constitute a rare but important cause of SRS. Furthermore, while both IGF2 mutations and H19/IGF2:IG-DMR epimutations lead to SRS, a certain degree of phenotypic difference is observed between the two groups, probably due to the different IGF2 expression pattern in target tissues.

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.

The Role of Number of Copies, Structure, Behavior and Copy Number Variations (CNV) of the Y Chromosome in Male Infertility

The World Health Organization (WHO) defines infertility as the inability of a sexually active, non-contracepting couple to achieve spontaneous pregnancy within one year. Statistics show that the two sexes are equally at risk. Several causes may be responsible for male infertility; however, in 30–40% of cases a diagnosis of idiopathic male infertility is made in men with normal urogenital anatomy, no history of familial fertility-related diseases and a normal panel of values as for endocrine, genetic and biochemical markers. Idiopathic male infertility may be the result of gene/environment interactions, genetic and epigenetic abnormalities. Numerical and structural anomalies of the Y chromosome represent a minor yet significant proportion and are the topic discussed in this review. We searched the PubMed database and major search engines for reports about Y-linked male infertility. We present cases of Y-linked male infertility in terms of (i) anomalies of the Y chromosome structure/number; (ii) Y chromosome misbehavior in a normal genetic background; (iii) Y chromosome copy number variations (CNVs). We discuss possible explanations of male infertility caused by mutations, lower or higher number of copies of otherwise wild type, Y-linked sequences. Despite Y chromosome structural anomalies are not a major cause of male infertility, in case of negative results and of normal DNA sequencing of the ascertained genes causing infertility and mapping on this chromosome, we recommend an analysis of the karyotype integrity in all cases of idiopathic fertility impairment, with an emphasis on the structure and number of this chromosome.

Identification of KISS1R gene mutations in disorders of non-obstructive azoospermia in the northeast population of China

Background

Non‐obstructive azoospermia (NOA), a serious phenotype of male spermatogenesis failure, is a multifactorial disease which is regulated by genetic, epigenetic, and environmental factors. Some gene structural variants have been demonstrated to be related to NOA. Loss‐of‐function mutations of KISS1R cause normosmic idiopathic hypogonadotropic hypogonadism (IHH) which result in azoospermia at the pre‐testicular level. The objective of this research was to investigate genetic variants of KISS1R in NOA patients.

Methods

The entire coding region of 52 spermatogenesis‐associated genes (KISS1R included) was sequenced from 200 NOA patients. Mutation screening was performed to identify genetic variations of these genes by targeted exome sequencing. Sequencing data analysis was carried out by a series of bioinformatics tools. Candidate variants confirmation was performed by Sanger sequencing. Functional analysis of candidate variants was evaluated using SIFT and PolyPhen‐2.

Results

Three heterozygous missense variants in KISS1R were identified in three patients, respectively. No deleterious variations in other candidate genes were found in the three patients. Two of these three variants, p.A211T and p.G186E, had been reported in the ExAC and dbSNP database, respectively, while the other variant p.A301D was novel. These variants were all predicted to be likely pathogenic by in silico analysis.

Conclusion

Our study revealed three heterozygous missense variants in KISS1R which expanded the mutation spectrum of KISS1R in infertile men with NOA in the northeast of China.

Recent advances and future opportunities to diagnose male infertility

PURPOSE OF REVIEW

Infertility affects 10-15% of couples, making it one of the most frequent health disorders for individuals of reproductive age. The state of childlessness and efforts to restore fertility cause substantial emotional, social, and financial stress on couples. Male factors contribute to about half of all infertility cases, and yet are understudied relative to female factors. The result is that the majority of men with infertility lack specific causal diagnoses, which serves as a missed opportunity to inform therapies for these couples.

RECENT FINDINGS

In this review, we describe current standards for diagnosing male infertility and the various interventions offered to men in response to differential diagnoses. We then discuss recent advances in the field of genetics to identify novel etiologies for formerly unexplained infertility.

SUMMARY

With a specific genetic diagnosis, male factors can be addressed with appropriate reproductive counseling and with potential access to assisted reproductive technologies to improve chances of a healthy pregnancy.

CircRNA expression profile and functional analysis in testicular tissue of patients with non-obstructive azoospermia

BACKGROUND

Non-obstructive azoospermia (NOA) is a multifactorial disorder whose molecular basis remains largely unknown. Circular RNAs (CircRNAs), a novel class of endogenous RNAs, have been recognized to play important roles in many biological processes. However, little is known about the expression patterns and functions of circRNAs in human testes involved in NOA.

METHODS

In this study, the testicular circRNA expression profile were explored in NOA patients and the controls by high-throughput circRNA microarray. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) was performed to confirm the microarray data. Bioinformatics analyses including the circRNA/miRNA/mRNA interaction network, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were used to predict the functions of differentially expressed circRNAs.

RESULTS

A total of 368 differentially down-regulated and 526 up-regulated circRNAs were detected in NOA patients. These findings have been verified by qRT-PCR on 6 selected circRNAs. Among these differentially expressed circRNAs, the hsa_circRNA_0023313 was obviously up-regulated in testicular tissue of NOA patients. The most likely potential target miRNA for hsa_circRNA_0023313 include hsa-miR-520d-3p, hsa-miR-373-3p, hsa-miR-372-3p, hsa-miR-302c-3p and hsa-miR-130b-5p. Function analysis indicated that hsa_circRNA_0023313 was ubiquitin-protein transferase activity and chromatin binding. KEGG analysis revealed that the top five pathways related to hsa_circRNA_0023313 were endocytosis, meiosis, FoxO signaling pathway, ubiquitin mediated proteolysis and AMPK signaling pathway.

CONCLUSIONS

This is the first report that the testicular circRNA expression profile is altered in NOA patients indicating circRNAs might play important roles in regulating spermatogenesis and be potential biomarkers for the diagnosis and treatment of NOA.

Sequence analysis of 37 candidate genes for male infertility: challenges in variant assessment and validating genes

BACKGROUND

The routine genetic analysis for diagnosing male infertility has not changed over the last twenty years, and currently available tests can only determine the etiology of 4% of unselected infertile patients. Thus, to create new diagnostic assays, we must better understand the molecular and genetic mechanisms of male infertility. Although next-generation sequencing allows for simultaneous analysis of hundreds of genes and the discovery of novel candidates related to male infertility, so far only a few gene candidates have enough sound evidence to support the gene-disease relationship.

OBJECTIVE

Since complementary studies are required to validate genes, we aimed to analyze the presence of potentially pathogenic rare variants in a set of candidate genes related to azoospermia in a hitherto understudied South American population.

SUBJECTS AND METHODS

We performed whole exome sequencing in a group of 16 patients with non-obstructive azoospermia from Ribeirão Preto, Brazil. Based on a recent systematic review of monogenic causes of male infertility, we selected a set of 37 genes related to azoospermia, Sertoli-Cell-Only histology, and spermatogenic arrest to analyze. The identified variants were confirmed by Sanger sequencing, and their functional consequence was predicted by in silico programs.

RESULTS

We identified potential pathogenic variants in seven genes in six patients. Two variants, c.671A>G (p.(Asn224Ser)) in DMRT1 and c.91C>T (p.(Arg31Cys)) in REC8, have already been described in association with azoospermia. We also found new variants in genes that already have moderate evidence of being linked to spermatogenic failure (TEX15, KLHL10), in genes with limited evidence (DNMT3B, TEX14) and in one novel promising candidate gene that has no evidence so far (SYCE1L).

DISCUSSION

Although this study included a small number of patients, the process of rationally selecting genes allowed us to detect rare potentially pathogenic variants, providing supporting evidence for validating candidate genes associated with azoospermia.

Non-syndromic monogenic male infertility

Infertility is a widespread clinical problem affecting 8-12% of couples worldwide. Of these, about 30% are diagnosed with idiopathic infertility since no causative factor is found. Overall 40-50% of cases are due to male reproductive defects. Numerical or structural chromosome abnormalities have long been associated with male infertility. Monogenic mutations have only recently been addressed in the pathogenesis of this condition. Mutations of specific genes involved in meiosis, mitosis or spermiohistogenesis result in spermatogenic failure, leading to the following anomalies: insufficient (oligozoospermia) or no (azoospermia) sperm production, limited progressive and/or total sperm motility (asthenozoospermia), altered sperm morphology (teratozoospermia), or combinations thereof. Androgen insensitivity, causing hormonal and sexual impairment in males with normal karyotype, also affects male fertility. The genetic causes of non-syndromic monogenic of male infertility are summarized in this article and a gene panel is proposed. (www.actabiomedica.it)

Chloride Channel Accessory 4 (CLCA4) Gene Polymorphisms and Non-Obstructive Azoospermia: A Case-Control Study

Background

Genetic mechanisms are associated with male infertility, but the association with non-obstructive azoospermia (NOA) remains unclear. Mutations in the chloride channel accessory 4 (CLCA4) gene have been shown to have a role in male infertility. The aim of this study was to investigate the associations between single nucleotide polymorphisms (SNPs) of the CLCA4 gene and NOA in a Chinese Han population of Northeast China using combined targeted gene capture next-generation sequencing and bioinformatics analysis.

Material/Methods

The study group included 100 men with NOA, and there were 100 normal controls. Targeted gene capture next-generation sequencing was performed combined with bioinformatics analysis. Ten CLCA4 SNPs were screened in the cases of NOA and control subjects. The associations between SNPs and NOA were analyzed.

Results

Six SNPs, c.390C>T (rs190628533), c.1474A>G (rs2231599), c.2105C>G (rs757773924), c.2371A>T) (rs759981524), c.956G>A (rs763334876), and c.895T>C (rs79822589) were identified in the study group of cases in NOA but not in control subjects. All CLCA4 SNPs were in Hardy-Weinberg equilibrium. The allele and genotype frequencies of the six SNPs were not significantly different between the study group and the controls. Haplotype analysis showed the existence of two haplotypes, CTAGACTACG and CTCGACTACG, which showed statistical significance of 0.074, and 0.088 between cases of NOA and the controls, respectively.

Conclusions

There were no significant associations between CLCA4 SNPs and NOA in men in a Chinese Han population of Northeast China.

New insights into the genetics of spermatogenic failure: a review of the literature

Genetic anomalies are known to affect about 15% of infertile patients with azoospermia or severe oligozoospermia. Despite a throughout diagnostic work-up, in up to the 72% of the male partners of infertile couples, no etiological factor can be found; hence, the cause of infertility remains unclear. Recently, several novel genetic causes of spermatogenic failure (SPGF) have been described. The aim of this review was to collect all the available evidence of SPGF genetics, matching data from in-vitro and animal models with those in human beings to provide a comprehensive and updated overview of the genes capable of affecting spermatogenesis. By reviewing the literature, we provided a list of 60 candidate genes for SPGF. Their investigation by Next Generation Sequencing in large cohorts of patients with apparently idiopathic infertility would provide new interesting data about their racial- and ethnic-related prevalence in infertile patients, likely raising the diagnostic yields. We propose a phenotype-based approach to identify the genes to look for.

Associations between DNAH1 gene polymorphisms and male infertility: A retrospective study

Genetic abnormalities could account for 10% to 15% of male infertility cases, so increasing attention is being paid to gene mutations in this context. DNAH1 gene polymorphisms are highly correlated with astheno-teratozoospermia, but limited information has been reported on pathogenic variations in DNAH1 in the Chinese population. We explored 4 novel variations of the DNAH1 gene in Chinese infertile patients. Mutation screening of the DNAH1 gene was performed on 87 cases of asthenozoospermia with targeted high-throughput sequencing technology; another 200 nonobstructive azoospermia cases were further analyzed to investigate the prevalence of DNAH1 variations. The effects of the variations on protein function were further assessed by bioinformatic prediction. For carriers of DNAH1 variations, genetic counseling should be considered. Assisted reproductive technologies should be performed for these individuals and microsurgery should be considered for patients with azoospermia. DNAH1 variations were identified in 6 of 287 patients. These included 8 heterozygous variations in exons and a splicing site. Among these, 4 variations (g.52400764G>C, g.52409336C>T, g.52430999_52431000del, g.52412624C>A) had already been registered in the 1000 Genomes and Exome Aggregation Consortium databases. The other 4 novel variations (g.52418050del, g.52404762T>G, g.52430536del, g.52412620del) were all predicted to be pathogenic by in silico analysis. The variations g.52418050del and g.52430999_52431000del were detected in 1 patient who was more severe than another patient with the variation g.52430999_52431000del. Physicians should be aware of genetic variants in male infertility patients and DNAH1 mutations should be considered in patients with asthenospermia or azoospermia.

STX2 is a causative gene for nonobstructive azoospermia

STX2 encodes a sulfoglycolipid transporter. Although Stx2 nullizygosity is known to cause spermatogenic failure in mice, STX2 mutations have not been identified in humans. Here, we performed STX2 mutation analysis for 131 Japanese men clinically diagnosed with nonobstructive azoospermia. As a result, we identified a homozygous frameshift mutation [c.8_12delACCGG, p.(Asp3Alafs*8)] in one patient. The mutation-positive patient exhibited loss-of-heterozygosity for 58.4 Mb genomic regions involving STX2, suggesting possible parental consanguinity. The patient showed azoospermia, relatively small testes, and a mildly elevated follicle stimulating hormone level, but no additional clinical features. Testicular histology of the patient showed universal maturation arrest and multinucleated spermatocytes, which have also been observed in mice lacking Stx2. PCR-based cDNA screening revealed wildtype STX2 expression in various tissues including the testis. Our results indicate that STX2 nullizygosity results in nonsyndromic maturation arrest with multinucleated spermatocytes, and accounts for a small fraction of cases with nonobstructive azoospermia.

Effects of the insulin-like growth factor system on testicular differentiation and function: a review of the literature

We recently described the occurrence of cryptorchidism, oligoasthenoteratozoospermia, and genital abnormalities in patients with distal 15q chromosome structural abnormalities. This observation brought us to hypothesize that insulin-like growth factor (IGF) receptor (IGF1R), mapping on the 15q 26.3 chromosomal band, may be involved in testicular function. To further evaluate this topic, we reviewed in vitro and in vivo studies exploring the role of the IGF system [IGF1, IGF2, IGF1R, insulin receptor substrates (IRS)] at the testicular level both in animals and in humans. In animals, IGF1/IGF1R has been found to be involved in testicular development during embryogenesis, in Sertoli cell (SC) proliferation, and in germ cell (GS) proliferation and differentiation. Interestingly, IGF1R seems to mediate follicle-stimulating hormone (FSH) effects through the PI3K/AKT pathway. In humans, IGF1 directly increases testicular volume. The molecular pathways responsible for testicular differentiation and IGF1/IGF1R signaling are highly conserved among species; therefore, the IGF system may be involved in FSH signaling also in humans. We suggest a possible molecular pathway occurring in human SCs, which involves both IGF1 and FSH through the PI3K/AKT pathway. The acknowledgment of an IGF1 mediation of the FSH-induced effects may open new ways for a targeted therapy in idiopathic non-FSH-responder oligoasthenoteratozoospermia.