Genetic Causes Of Male Infertility Research Articles

Genetic causes of male infertility

Male infertility, affecting around half of the couples with a problem to get pregnant, is a very heterogeneous condition. Part of patients are having a defect in spermatogenesis of which the underlying causes (including genetic ones) remain largely unknown. The only genetic tests routinely used in the diagnosis of male infertility are the analyses for the presence of Yq microdeletions and/or chromosomal abnormalities. Various other single gene or polygenic defects have been proposed to be involved in male fertility. Yet, their causative effect often remains to be proven. The recent evolution in the development of whole genome-based techniques may help in clarifying the role of genes and other genetic factors involved in spermatogenesis and spermatogenesis defects.

Genetic susceptibility to male infertility: news from genome‐wide association studies

A thorough understanding of the genetic basis of male infertility has eluded researchers in spite of significant efforts to identify novel genetic causes of the disease, particularly over the past decade. Approximately half of male factor infertility cases have no known cause; however, it is likely that the majority of idiopathic male factor infertility cases have some unidentified genetic basis. Well-established genetic causes of male infertility are limited to Y chromosome microdeletions and Klinefelter's syndrome, together accounting for 10-20% of cases of severe spermatogenic failure. In addition to these, several genetic polymorphisms have been demonstrated to be significantly associated with male infertility. The discovery of new genetic associations with male infertility has been hampered by two primary factors. First, most studies are underpowered because of insufficient sample size and ethnic and phenotypic heterogeneity. Second, most studies evaluate a single gene, an approach that is very inefficient in the context of male infertility, considering that many hundreds of genes are involved in the process of testicular development and spermatogenesis. Significant recent advances in microarray and next-generation sequencing technologies have enabled the application of whole-genome approaches to the study of male infertility. We recently performed a pilot genome-wide association study (GWAS) for severe spermatogenic failure, and several additional male infertility GWAS have since been published. More recently, genomic microarray tools have been applied to the association of copy number variants with male infertility. These studies are beginning to shed additional light on the genetic architecture of male infertility, and whole-genome studies have proven effective in identifying novel genetic causes of the disease. This review will discuss some of the recent findings of these whole-genome studies as well as future directions for this research that will likely be the most productive moving forward.

Relevance of genetic investigation in male infertility

Genetic causes can be directly responsible for various clinical conditions of male infertility and spermatogenic impairment. With the increased use of assisted reproduction technologies our understanding of genetic basis of male infertility has large implications not only for understanding the causes of infertility but also in determining the prognosis and management of such couples. For these reasons, the genetic investigations represent today an essential and useful tool in the treatment of male infertility. Several evidences are available for the clinical practice regarding the diagnosis; however, there are less information relative to the treatment of the genetic causes of male infertility. Focus of this review is to discuss the main and more common genetic causes of male infertility to better direct the genetics investigation in the treatment of spermatogenic impairment.

Genetic and molecular diagnostics of male infertility in the clinical practice

Male infertility represents one of the clearest examples of complex phenotype with substantial genetic basis. It is indeed well established that genetic causes account for 10-15% of infertility cases, including chromosomal abnormalities and single-gene mutations. However, a large proportion of infertile males does not receive a clear diagnosis and thus they are reported as idiopathic or unexplained. Male (in)fertility is commonly based on standard semen analysis, which, however, cannot clearly distinguish fertile from infertile populations and therefore fails to detect any abnormality in many cases. Abnormal sperm function or specific molecular defects can be hypothesized in these cases. This review considers practical genetic and molecular diagnostic tests for male infertility, reporting on the most frequent genetic causes of male infertility and on the pros and cons of most commonly used techniques for genetic, molecular and functional sperm evaluation. Finally, this review will discuss recent advances in pharmacogenetics and new developments on sperm analysis that will form the basis for future research.

The sperm’s tale

The sperm’s tale

Azoospermia factor microdeletions: occurrence in infertile men with azoospermia and severe oligozoospermia from China

Azoospermia factor (AZF) microdeletions are the most frequent genetic cause of male infertility after Klinefelter's syndrome. Although some assisted reproductive techniques such as intracytoplasmic sperm injection (ICSI) have been successfully introduced to clinical treatment for infertile males, the AZF microdeletions might be transmitted from infertile fathers to their male offspring during these procedures. Thus, it is important to carefully evaluate AZF microdeletions in infertile males before assisted reproductive techniques are performed. In this article, we aimed to investigate the frequencies of AZF microdeletions in 137 infertile males with azoospermia and severe oligozoospermia from Jilin province of China and analyse the relationship between the levels of reproductive hormones and AZF microdeletions. Result analysis showed that AZF microdeletions were present in 8 (8.70%) azoospermic males and 3 (6.67%) severely oligozoospermic males. The most frequent microdeletions were detected in the AZFc region, followed by AZFb+c, AZFb and AZFa. And there was no significant correlation between the AZF microdeletion and the levels of reproductive hormones. These findings reinforce the necessity of AZF microdeletion testing among infertile males prior to employment of assisted reproduction techniques in Jilin province of China.

Y chromosome microdeletions in infertile men: prevalence, phenotypes and screening markers for the Indian population

Yq microdeletions are the leading genetic cause of male infertility and its detection is clinically relevant for appropriate genetic counseling. We aimed to determine the prevalence and type of Yq microdeletions, the associated seminal phenotypes and the STS markers that are relevant for its testing in Indian population. Yq microdeletion analysis was carried out in 1,636 infertile cases in our centers. Additional data was collected from published studies in Indian population leading to a total of 3,647 cases. In our cohort, 3.4% (56/1,636) of infertile men had Yq microdeletions. Combining the data from other published studies identified 215/3,647 (5.8%) infertile individuals to harbor Yq microdeletions; with 6.4% in azoopsermia, 5.8% in oligozoospermia and 3.2% in oligoasthenozoospermia and teratozoospermia cases. No significant differences in the deletion frequencies were observed between idiopathic vs non idiopathic cases (5.8 vs 8.6% respectively). Deletions of AZFc were at highest frequency (46.6%) with double deletions most commonly observed in azoospermic subjects. With respect to the STS markers, screening with the six European Academy of Andrology (EAA) markers would miss 3.1% of cases; additional non EAA markers that would contribute significantly to screening are sY746, sY82, sY121, sY128, sY130, sY143, sY145 & sY160. The frequency of Yq microdeletions is lower in Indian population as compared to Western counterparts. There is no major association of Yq microdeletions with seminal parameters or cause of infertility. Clinically it will be necessary to offer Yq microdeletion testing to all the classes of infertile men. The EAA markers may not be adequate to detect microdeletions in Indian infertile men.

Cytogenetic abnormalities in 200 male infertile cases in the southern region of India

Chromosomal abnormalities are one of the major causes of male infertility. But the exact mechanism by which chromosomal anomalies induces infertility is still not clear. Many studies have documented the chromosomal abnormalities ranging from 2.2% to 15.7% in infertile men. The present study has been carried out to document and find out the genetic cause of male infertility in the Southern region of India. The cytogenetic analysis of 200 male infertile cases, referred due to primary infertility from 2009 to 2012, were analyzed by GTG banding and evaluated retrospectively. The semen analysis was also performed. A total of 15 cases (7.5%) showed chromosomal aberrations. Four (2%) were 47, XXY and mosaic 47,XXY; Two (1%) were structural autosomal abnormalities; Two (1%) were inversion Y; Seven (3.5%) cases were Y heterochromatin variants and 185 cases (92.5%) showed normal 46,XY karyotype. The chromosomal abnormalities in our study is also in agreement with the data from the literature. Also abnormal spermatogenesis is observed in these cases. Apart from chromosomal analysis further in depth molecular analysis and genetic counseling is suggestive in such cases, especially those interested in IVF technologies.

Assessment of the infertile male

Key content Male factors alone account for up to 30% of subfertile couples undergoing in vitro fertilisation. Male infertility may be due to problems with sperm production or transport and also sexual dysfunction. The underlying cause in most cases is idiopathic. Modifiable lifestyle factors can have an impact on male fertility, but medical treatments have a limited value in enhancing semen quality. Most treatments are based on assisted fertilisation techniques, rather than treatment of the underlying cause. The number and quality of sperm that can be recovered, either from the ejaculate or surgically, determines the available options for assisted conception. Intracytoplasmic sperm injection (ICSI) is considered relatively safe; however, because of the ability to bypass natural barriers to conception, there are concerns regarding its potential to transmit genetic defects. Learning objectives To review appropriate practice in the assessment and investigation of the infertile male. To critically appraise the currently available investigations for male fertility. To summarise the treatment options for subfertile men. Ethical issues Does ICSI propagate genetic causes of male infertility? Could there ever be a role for the use of artificial sperm in assisted reproduction?

Cytogenetic abnormalities and Y-chromosome microdeletions in infertile Syrian males

Infertility is an important health issue affecting numerous couples. Approximately 30-50% of the cases of male infertility is due to unknown reasons. The main genetic factors involved in male infertility are chromosomal abnormalities and Y chromosome microdeletions within the Yq11 region. The genes controlling spermatogenesis located in the Yq11 region are termed azoospermia factor genes (AZF). Klinefelter syndrome (KS) is the most common of the chromosomal anomalies in the infertile male. AZF microdeletions on the Y chromosome are the most frequent genetic cause of male infertility. Screening for microdeletions in the AZFa, b and c regions of the Y chromosome showed a marked variation among different studies. The present study aimed to investigate the prevalence of such deletions in Syrian men. A total of 162 infertile males (97 azoospermic, 49 oligospermic and 16 severely oligospermic) were screened for chromosomal abnormalities and Y chromosome microdeletions using 28 markers in the AZF region. Twenty (12.34%) patients had chromosomal rearrangements, 17 of them showed sex chromosome abnormalities (11 of 17 patients within the azoospermic group had a KS of 64.7%), 2 patients had apparently balanced autosomal rearrangements, while 1 patient had an inversion. Of the 162 infertile men, 46 patients (28.4%) had Y chromosome microdeletions within the AZF-regions. Most frequently hit were the AZFc (34.8%), followed by the AZFbc, AZFa, AZFac, AZFbc, AZFb, AZFd, AZFab, AZFad, AZFbd, AZFabc and the AZFbcd. Combined AZF deletions involving three regions with chromosomal abnormalities were observed in one case. The higher frequency of AZF deletions in our study was comparable with frequencies in other countries and regions of the world, possibly due to the elevated number of the sequence-tagged site (STS) markers used for this screening.

Global human tissue profiling and protein network analysis reveals distinct levels of transcriptional germline-specificity and identifies target genes for male infertility

Mammalian spermatogenesis is a process that involves a complex expression program in both somatic and germ cells present in the male gonad. A number of studies have attempted to define the transcriptome of male meiosis and gametogenesis in rodents and primates. Few human transcripts, however, have been associated with testicular somatic cells and germ cells at different post-natal developmental stages and little is known about their level of germline-specificity compared with non-testicular tissues. We quantified human transcripts using GeneChips and a total of 47 biopsies from prepubertal children diagnosed with undescended testis, infertile adult patients whose spermatogenesis is arrested at consecutive stages and fertile control individuals. These results were integrated with data from enriched normal germ cells, non-testicular expression data, phenotype information, predicted regulatory DNA-binding motifs and interactome data. Among 3580 genes for which we found differential transcript concentrations in somatic and germ cells present in human testis, 933 were undetectable in 45 embryonic and adult non-testicular tissues, including many that were corroborated at protein level by published gene annotation data and histological high-throughput protein immunodetection assays. Using motif enrichment analyses, we identified regulatory promoter elements likely involved in germline development. Finally, we constructed a regulatory disease network for human fertility by integrating expression signals, interactome information, phenotypes and functional annotation data. Our results provide broad insight into the post-natal human testicular transcriptome at the level of cell populations and in a global somatic tissular context. Furthermore, they yield clues for genetic causes of male infertility and will facilitate the identification of novel cancer/testis genes as targets for cancer immunotherapies.

Impaired spermatogenesis and GR/GR deletions related to Y chromosome haplogroups in Korean men

Microdeletion of the Azoospermia Factor (AZF) regions in Y chromosome is a well-known genetic cause of male infertility resulting from spermatogenetic impairment. However, the partial deletions of AZFc region related to spermatogenetic impairment are controversial. Therefore, this study was designed to characterize the partial AZFc deletion patterns and their clinical consequences in Korean population.

Impaired Spermatogenesis and gr/gr Deletions Related to Y Chromosome Haplogroups in Korean Men

Microdeletion of the Azoospermia Factor (AZF) regions in Y chromosome is a well-known genetic cause of male infertility resulting from spermatogenetic impairment. However, the partial deletions of AZFc region related to spermatogenetic impairment are controversial. In this study, we characterized partial deletion of AZFc region in Korean patients with spermatogenetic impairment and assessed whether the DAZ and CDY1 contributes to the phenotype in patients with gr/gr deletions. Total of 377 patients with azoo-/oligozoospermia and 217controls were analyzed using multiplex polymerase chain reaction (PCR), analysis of DAZ-CDY1 sequence family variants (SFVs), and quantitative fluorescent (QF)-PCR. Of the 377 men with impaired spermatogenesis, 59 cases (15.6%) had partial AZFc deletions, including 32 gr/gr (8.5%), 22 b2/b3 (5.8%), four b1/b3 (1.1%) and one b3/b4 (0.3%) deletion. In comparison, 14 of 217 normozoospermic controls (6.5%) had partial AZFc deletions, including five gr/gr (2.3%) and nine b2/b3 (4.1%) deletions. The frequency of gr/gr deletions was significantly higher in the azoo-/oligozoospermic group than in the normozoospermic control group (p = 0.003; OR = 3.933; 95% CI = 1.509–10.250). Concerning Y haplogroup, we observed no significant differences in the frequency of gr/gr deletions between the case and the control groups in the YAP+ lineages, while gr/gr deletion were significantly higher in azoo-/oligozoospermia than normozoospermia in the YAP− lineage (p = 0.004; OR = 6.341; 95% CI = 1.472–27.312). Our data suggested that gr/gr deletion is associated with impaired spermatogenesis in Koreans with YAP− lineage, regardless of the gr/gr subtypes.

TEX11 Modulates Germ Cell Proliferation by Competing with Estrogen Receptor β for the Binding to HPIP

Klinefelter syndrome (KS), characterized by the presence of more than one X-chromosome in men, is a major genetic cause of male infertility. Germ cell degeneration in KS patients is thought to be the consequences of overexpression of some genes on the X-chromosome. However, the identity of these genes and the underlying mechanisms remain unclear. Testis-expressed 11 (TEX11) is an X-chromosome-encoded germ-cell-specific protein that is expressed most abundantly in spermatogonia and early spermatocytes in the testes. In our search for TEX11-interacting partners using the yeast two-hybrid system, we identified hematopoietic pre-B cell leukemia transcription factor-interacting protein (HPIP), which anchors estrogen receptors (ER) to the cytoskeleton and modulates their functions. We found that mouse spermatogonial stem cells expressed Tex11, Hpip, and Esr2 but not Esr1. In cultured cells, TEX11 competed with ERβ for binding to HPIP. Upon treatment with 17β-estradiol or an ERβ agonist diarylpropionitrile, TEX11 promoted the nuclear translocation of ERβ and enhanced its transcriptional activities. On the other hand, TEX11 suppressed the nongenomic activities of ERβ in the cytoplasm, as indicated by reduced phosphorylation of AKT and ERK signaling molecules. Overexpression of TEX11 in mouse germ-cell-derived GC-1 and GC-2 cells suppressed the cell proliferation and the expression of cFos, Ccnd1, and Ccnb1 that were stimulated by 17β-estradiol or diarylpropionitrile and elevated the expression level of the proapoptotic Bax gene. The negative effect of TEX11 on cell proliferation suggests that increased expression of TEX11 in the germ cells may partially contribute to the spermatogenic defect observed in KS patients.

Study of GT-repeat expansion in Heme oxygenase-1 gene promoter as genetic cause of male infertility

The length of GT-repeats polymorphic region in the promoter of human Heme oxygenase-1 gene (HO-1) alters the level of its transcriptional activity in response to oxidative stresses. Decreased level of HO-1 protein in the seminal plasma has been reported to be associated with oligospermia and azoospermia in male infertility. This is the first study to investigate the association between GT-repeats expansion in the promoter of the HO-1 gene and male infertility. The frequencies of different GT-repeats alleles in the promoter of HO-1 gene were determined in 100 cases and 100 normal controls using PCR-PAGE, ABI fragment analysis genotyping and sequencing analysis. All alleles were classified into S and L alleles. S alleles were specified as number 0 to 3 with <27 GT-repeats and L alleles were specified as number 4 to 6 with >27 repeats. The L allele frequency was significantly higher among case group (54.5%) than that was obtained in the normal control group (37.5%). Statistical analysis provided a significant relationship between L allele and male infertility (P < 0.001). This study shows for the first time that GT-repeats expansion in promoter of the HO-1 gene is associated with oligospermia and azoospermia among Iranian infertile cases.

Meiotic recombination and male infertility: from basic science to clinical reality?

Infertility is a common problem that affects approximately 15% of the population. Although many advances have been made in the treatment of infertility, the molecular and genetic causes of male infertility remain largely elusive. This review will present a summary of our current knowledge on the genetic origin of male infertility and the key events of male meiosis. It focuses on chromosome synapsis and meiotic recombination and the problems that arise when errors in these processes occur, specifically meiotic arrest and chromosome aneuploidy, the leading cause of pregnancy loss in humans. In addition, meiosis-specific candidate genes will be discussed, including a discussion on why we have been largely unsuccessful at identifying disease-causing mutations in infertile men. Finally clinical applications of sperm aneuploidy screening will be touched upon along with future prospective clinical tests to better characterize male infertility in a move towards personalized medicine.

Mouse models in male fertility research

Limited knowledge of the genetic causes of male infertility has resulted in few treatment and targeted therapeutic options. Although the ideal approach to identify infertility causing mutations is to conduct studies in the human population, this approach has progressed slowly due to the limitations described herein. Given the complexity of male fertility, the entire process cannot be modeled in vitro. As such, animal models, in particular mouse models, provide a valuable alternative for gene identification and experimentation. Since the introduction of molecular biology and recent advances in animal model production, there has been a substantial acceleration in the identification and characterization of genes associated with many diseases, including infertility. Three major types of mouse models are commonly used in biomedical research, including knockout/knockin/gene-trapped, transgenic and chemical-induced point mutant mice. Using these mouse models, over 400 genes essential for male fertility have been revealed. It has, however, been estimated that thousands of genes are involved in the regulation of the complex process of male fertility, as many such genes remain to be characterized. The current review is by no means a comprehensive list of these mouse models, rather it contains examples of how mouse models have advanced our knowledge of post-natal germ cell development and male fertility regulation.

73 MUTATIONS IN AZF, SRY, CFTR GENES AS GENETIC CAUSES OF MALE INFERTILITY

73 MUTATIONS IN AZF, SRY, CFTR GENES AS GENETIC CAUSES OF MALE INFERTILITY

Evaluation of a Multiplex PCR Kit Used for Detecting Y Chromosome Microdeletions

In addition to Klinefelter's syndrome, microdeletion of Yq is the most common genetic cause of male infertility; 15% of azoospermic or 5-10% of oligozoospermic males have Yq deletions. We evaluated a Yq microdeletion kit (LG Life Sciences, Korea) for identifying microdeletions in the azoospermic factor (AZF) regions of the Yq. The kit was designed to amplify 3 regions of the AZF gene (AZFa, AZFb, and AZFc) using 15 sequence-tagged sites. We evaluated the preclinical performance of the kit. For clinical validation, 58 patients including 25 idiopathic azoospermic or oligozoospermic patients were examined. We observed clear bands on electrophoresis of DNA, up to a DNA concentration of 3.12 ng/microL; the known microdeletion regions of all 6 reference cell-lines (Coriell, USA) were accurately detected and no false positive/negative results showed with normal female (n=11) and fertile male (n=15) specimens. This kit could identify the same microdeletions in the common regions, similar to another commercial kit. Among the 58 male infertile patients, 7 (12.1%) had microdeletions of the Yq. Among the idiopathic azoospermic (n=22) and oligozoospermic (n=3) patients, 3 (12.0%) had microdeletions. Further, 2 of 21 varicocele patients (9.5%), 1 of 4 patients with testicular failure, and 1 patient with a 45,X/46,XY mosaic had microdeletions. The kit was effective for detecting microdeletions of the Yq. We identified microdeletions in 12% of the infertile patients. This Y chromosome microdeletion detection kit is useful for screening Yq microdeletions in infertile patients.

A biopsy sample reduction approach to identify significant alterations of the testicular transcriptome in the presence of Y-chromosomal microdeletions that are independent of germ cell composition

Y-chromosomal microdeletions (YCMD) are the major genetic cause of male infertility. To date, it is not known which global changes are induced by the presence of AZFc or AZFb + c deletions in the human testicular transcriptome. We investigated this question by microarray analysis in which we had to eliminate the ‘germ cell effect’, i.e., the dominating effect of germ cell transcripts due to the quantitative difference in germ cell composition in samples with/without YCMD. This problem was tackled by selecting 26 samples from an initial cohort of 34 samples by their homogeneity in respect to cellular composition as obtained from gene expression clustering. This way, the ‘germ cell effect’ was minimized, and a distinct ‘deletion effect’ became more apparent. Several hundred genes are influenced by YCMD as shown on the three different phenotypes hypospermatogenesis, meiotic arrest, and Sertoli-cell only syndrome. We validated on an independent cohort of samples five genes by quantitative real-time PCR that are expressed in germ cells or the somatic compartment and which are exclusively altered by the presence of YCMD. We conclude that the deletion of Y-chromosomal genes has a significant effect on spermatogenesis by modulating the transcriptional network of the germ cell and somatic compartment.Electronic supplementary materialThe online version of this article (doi:10.1007/s00439-010-0865-9) contains supplementary material, which is available to authorized users.