A frequent Y chromosome b2/b3 subdeletion shows strong association with male infertility in Han-Chinese population

Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries

BACKGROUND

Numerous studies have reported declines in semen quality and other markers of male reproductive health. Our previous meta-analysis reported a significant decrease in sperm concentration (SC) and total sperm count (TSC) among men from North America-Europe-Australia (NEA) based on studies published during 1981-2013. At that time, there were too few studies with data from South/Central America-Asia-Africa (SAA) to reliably estimate trends among men from these continents.

OBJECTIVE AND RATIONALE

The aim of this study was to examine trends in sperm count among men from all continents. The broader implications of a global decline in sperm count, the knowledge gaps left unfilled by our prior analysis and the controversies surrounding this issue warranted an up-to-date meta-analysis.

SEARCH METHODS

We searched PubMed/MEDLINE and EMBASE to identify studies of human SC and TSC published during 2014-2019. After review of 2936 abstracts and 868 full articles, 44 estimates of SC and TSC from 38 studies met the protocol criteria. Data were extracted on semen parameters (SC, TSC, semen volume), collection year and covariates. Combining these new data with data from our previous meta-analysis, the current meta-analysis includes results from 223 studies, yielding 288 estimates based on semen samples collected 1973-2018. Slopes of SC and TSC were estimated as functions of sample collection year using simple linear regression as well as weighted meta-regression. The latter models were adjusted for predetermined covariates and examined for modification by fertility status (unselected by fertility versus fertile), and by two groups of continents: NEA and SAA. These analyses were repeated for data collected post-2000. Multiple sensitivity analyses were conducted to examine assumptions, including linearity.

OUTCOMES

Overall, SC declined appreciably between 1973 and 2018 (slope in the simple linear model: -0.87 million/ml/year, 95% CI: -0.89 to -0.86; P < 0.001). In an adjusted meta-regression model, which included two interaction terms [time × fertility group (P = 0.012) and time × continents (P = 0.058)], declines were seen among unselected men from NEA (-1.27; -1.78 to -0.77; P < 0.001) and unselected men from SAA (-0.65; -1.29 to -0.01; P = 0.045) and fertile men from NEA (-0.50; -1.00 to -0.01; P = 0.046). Among unselected men from all continents, the mean SC declined by 51.6% between 1973 and 2018 (-1.17: -1.66 to -0.68; P < 0.001). The slope for SC among unselected men was steeper in a model restricted to post-2000 data (-1.73: -3.23 to -0.24; P = 0.024) and the percent decline per year doubled, increasing from 1.16% post-1972 to 2.64% post-2000. Results were similar for TSC, with a 62.3% overall decline among unselected men (-4.70 million/year; -6.56 to -2.83; P < 0.001) in the adjusted meta-regression model. All results changed only minimally in multiple sensitivity analyses.

WIDER IMPLICATIONS

This analysis is the first to report a decline in sperm count among unselected men from South/Central America-Asia-Africa, in contrast to our previous meta-analysis that was underpowered to examine those continents. Furthermore, data suggest that this world-wide decline is continuing in the 21st century at an accelerated pace. Research on the causes of this continuing decline and actions to prevent further disruption of male reproductive health are urgently needed.

Proliferation of human spermatogonial stem cells on optimized PCL/Gelatin nanofibrous scaffolds

Improvement of culture system and increasing the proliferation of spermatogonia stem cells under in vitro condition are the essential treatment options for infertility before autologous transplantation. Therefore, the present study aimed to evaluate the proliferation of human spermatogonia stem cells on the electrospun polycaprolactone/gelatin nanocomposite. Therefore, for this purpose, nanofiber porous scaffolds were prepared using the electrospinning method and their structures were then confirmed by SEM. After performing swelling, biodegradability and cell adhesion tests, human spermatogonia stem cells were cultured on scaffolds. In addition, both cell viability and proliferation were assessed using immunocytochemistry, flow cytometry and real-time PCR techniques in culturing during a 3-week period. SEM images indicated the presence of fibres with suitable diameters and arrangement as well as a sufficient porosity in nanocomposite scaffolds, showing good biocompatibility and biodegradability. The results show a significant increase in the number of spermatogonia stem cells in the cultured group on scaffold compared with the control group (p ≤ 0.05). As well, the results show that the expressions of integrin ɑ6 and β1 and Plzf genes estimated using real-time PCR in nanofiber scaffolds were significantly higher than those of the control group (p ≤ 0.05). However, the expression of c-Kit gene in the 3D group showed a significant decrease compared with the 2D group. Flow cytometry analysis also showed that the number of Plzf-positive cells was significantly higher in nanofiber porous scaffolds compared with the control group (p ≤ 0.05). Additionally, immunocytochemistry findings confirmed the presence of human spermatogonia stem cell colonies. In general, it seems that the designed nanocomposite scaffold could provide a suitable capacity for self-renewal of human spermatogonia stem cells, which can have a good application potential in research and reconstructive medicine related to the field of male infertility.

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

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

Direct reprogramming of human Sertoli cells into male germline stem cells with the self-renewal and differentiation potentials via overexpressing DAZL/DAZ2/BOULE genes

We propose a new concept that human somatic cells can be converted to become male germline stem cells by the defined factors. Here, we demonstrated that the overexpression of DAZL, DAZ2, and BOULE could directly reprogram human Sertoli cells into cells with the characteristics of human spermatogonial stem cells (SSCs), as shown by their similar transcriptomes and proteomics with human SSCs. Significantly, human SSCs derived from human Sertoli cells colonized and proliferated in vivo, and they could differentiate into spermatocytes and haploid spermatids in vitro. Human Sertoli cell-derived SSCs excluded Y chromosome microdeletions and assumed normal chromosomes. Collectively, human somatic cells could be converted directly to human SSCs with the self-renewal and differentiation potentials and high safety. This study is of unusual significance, because it provides an effective approach for reprogramming human somatic cells into male germ cells and offers invaluable male gametes for treating male infertility.

Copy number variants within AZF region of Y chromosome and their association with idiopathic male infertility in Serbian population

Results of numerous studies gave contradictory conclusions when analysing associations between copy number variants (CNVs) within the azoospermia factor (AZF) locus of the Y chromosome and idiopathic male infertility. The aim of this study was to identify the presence and possible association of CNVs in the AZF region of Y chromosome with idiopathic male infertility in the Serbian population. Using the multiplex ligation-dependent probe amplification technique, we were able to detect CNVs in 24 of 105 (22.86%) infertile men and in 11 of 112 (9.82%) fertile controls. The results of Fisher's exact test showed a statistically significant difference between cases and controls after merging g(reen)-r(ed)/g(reen)-r(ed) and b(lue)2/b(lue)3 partial deletions identified in the AZFc region (p = 0.024). At the same time, we observed a trend towards statistical significance for a deletion among gr/gr amplicons (p = 0.053). In addition to these, we identified a novel complex CNV involving inversion of r2/r3 amplicons, followed by b2/b3 duplication and b3/b4 deletion, respectively. Additional analyses on a larger study group would be necessary to draw meaningful conclusions about associations among CNVs that presented with higher frequency in the infertile men than the fertile controls.

Do partial AZFc deletions affect the sperm retrieval rate in non-mosaic Klinefelter patients undergoing microdissection testicular sperm extraction?

BACKGROUND

The purpose of this study is to evaluate the prognostic factors for sperm retrieval and determine if Y chromosome deletion is associated with deleterious effects on spermatogenesis in non-mosaic Klinefelter patients. Whether Y chromosome deletion determines the sperm retrieval rate in non-mosaic Klinefelter patients has not yet been addressed.

METHODS

We retrospectively collected medical records of azoospermic patients from Sep 2009 to Dec 2018, and enrolled 66 non-mosaic 47, XXY patients who were receiving mTESE. The predictive values of patients age, serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone, prolactin, estradiol and Y chromosome deletion were assessed for successful sperm recovery.

RESULTS

Testicular sperm recovery was successful in 24 (36.4%) of 66 men. The mean age (36.0 vs. 36.6 years), and levels of FSH (30.0 vs 36.9 IU/L), LH (17.7 vs 21.9 IU/L), testosterone (2.4 vs. 2.1 ng/ml), prolactin (9.1 vs. 8.8 ng/ml), and estradiol (19.4 vs. 22.3 pg/ml) did not show any significant difference when comparing patients with and without successful sperm retrieval. Partial deletion of azoospermic factor c (AZFc) was noted in 5 (20.8%) of 24 patients with successful sperm retrieval, including three b2/b3 and two gr/gr deletion cases, whereas 4 (9.5%) of 42 patients with unsuccessful sperm retrieval were noted to have AZFc partial deletion (one b2/b3, one sY1206 and two gr/gr deletion), though the difference was not statistically significant (p = 0.27).

CONCLUSION

According to present results, age and AZFc partial deletion status should not be a deterrent for azoospermic males with non-mosaic Klinefelter syndrome to undergo mTESE.

The Association of Partial Azoospermia Factor C Deletions and Male Infertility in Northwestern China

BACKGROUND

Male infertility is a major health issue worldwide. Y chromosome microdeletions are well-characterized genetic causes of male infertility. The association of partial AZFc deletions (gr/gr, b2/b3, and b1/b3) with male infertility is not well confirmed in diverse populations. The purpose of the present study was to investigate the frequency of partial AZFc deletions and their association with male infertility in a population from Northwestern China.

METHODS

Multiplex polymerase chain reaction was used to detect partial AZFc deletions in 228 infertile patients. We analyzed 141 cases of azoospermia (AS), 87 cases of oligozoospermia (OS), and 200 fertile controls.

RESULTS

Our data showed that the frequency of a b2/b3 deletion in infertile men, men with AS, men with OS, and controls was 3.51, 2.13, 5.75, and 0.00%, respectively. The frequency of this deletion was significantly different between the infertile group and the control group (3.51 vs. 0.00%, respectively, p = 0.021) and between the OS group and the control group (5.75 vs. 0.00%, respectively, p = 0.003). The frequency of a gr/gr deletion in each group was 11.84, 9.22, 16.09, and 7.50%, respectively. The frequency of a gr/gr deletion was significantly different between the OS group and the control group (16.09 vs. 7.50%, respectively, p = 0.026) but not between the infertile group and the control group (11.84 vs. 7.50%, p = 0.132) or the AS group and the control group (9.22 vs. 7.50%, p = 0.569). The frequency of a b1/b3 deletion was 0.44, 0.71, 0.00, and 3.00%, respectively. For this deletion, there was no significant difference between the infertile (0.44 vs. 3.00%, p = 0.089), AS (0.71 vs. 3.00%, p = 0.276), and OS groups (0.00 vs. 3.00%, p = 0.236) and the control group.

CONCLUSIONS

Our results suggest that the b2/b3 deletion might be associated with male infertility and that the gr/gr deletion might be associated with spermatogenic failure in men with OS in Northwestern China (Ningxia).

Y-chromosome haplogroup architecture confers susceptibility to azoospermia factor c microrearrangements: a retrospective study

Aim

To assess the association between azoospermia factor c microrearrangements and semen quality, and between Y-chromosome background with distinct azoospermia factor c microrearrangements and semen quality impairment.

Methods

This retrospective study, carried out in the Research Center for Genetic Engineering and Biotechnology “Georgi D. Efremov,” involved 486 men from different ethnic backgrounds referred for couple infertility from 2002-2017: 338 were azoospermic/oligozoospermic and 148 were normozoospermic. The azoospermia factor c microrearrangements were analyzed with sequence tagged site and sequence family variant markers, quantitative fluorescent polymerase chain reaction, and multiplex ligation probe amplification analysis. The Y-haplogroups of all participants were determined with direct single nucleotide polymorphism typing and indirect prediction with short tandem repeat markers.

Results

Our participants had two types of microdeletions: gr/gr and b2/b3; three microduplications: b2/b4, gr/gr, and b2/b3; and one complex rearrangement gr/gr deletion + b2/b4 duplication. Impaired semen quality was not associated with microrearrangements, but b2/b4 and gr/gr duplications were significantly associated with haplogroup R1a (P < 0.001 and P = 0.003, respectively) and b2/b3 deletions with haplogroup E (P = 0.005). There were significantly more b2/b4 duplication carriers in Albanians than in Macedonians with haplogroup R1a (P = 0.031).

Conclusion

Even though azoospermia factor c partial deletions/duplications and Y-haplogroups were not associated with impaired semen quality, specific deletions/duplications were significantly associated with distinct haplogroups, implying that the Y chromosome background may confer susceptibility to azoospermia factor c microrearrangements.

High frequencies of Non Allelic Homologous Recombination (NAHR) events at the AZF loci and male infertility risk in Indian men

Deletions in the AZoospermia Factor (AZF) regions (spermatogenesis loci) on the human Y chromosome are reported as one of the most common causes of severe testiculopathy and spermatogenic defects leading to male infertility, yet not much data is available for Indian infertile men. Therefore, we screened for AZF region deletions in 973 infertile men consisting of 771 azoospermia, 105 oligozoospermia and 97 oligoteratozoospermia cases, along with 587 fertile normozoospermic men. The deletion screening was carried out using AZF-specific markers: STSs (Sequence Tagged Sites), SNVs (Single Nucleotide Variations), PCR-RFLP (Polymerase Chain Reaction - Restriction Fragment Length Polymorphism) analysis of STS amplicons, DNA sequencing and Southern hybridization techniques. Our study revealed deletion events in a total of 29.4% of infertile Indian men. Of these, non-allelic homologous recombination (NAHR) events accounted for 25.8%, which included 3.5% AZFb deletions, 2.3% AZFbc deletions, 6.9% complete AZFc deletions, and 13.1% partial AZFc deletions. We observed 3.2% AZFa deletions and a rare long AZFabc region deletion in 0.5% azoospermic men. This study illustrates how the ethnicity, endogamy and long-time geographical isolation of Indian populations might have played a major role in the high frequencies of deletion events.

Human mitochondrial DNA haplogroup M8a influences the penetrance of m.8684C>T in Han Chinese men with non-obstructive azoospermia

RESEARCH QUESTION

What is the role of mitochondrial DNA (mtDNA) in the pathogenesis of non-obstructive azoospermia (NOA)?

DESIGN

mtDNA genome sequencing followed by an independent population validation were performed in 628 NOA cases and 584 healthy controls. Antioxidant capacity of serum was evaluated in 54 randomly selected cases out of 536 and 49 out of 489 controls.

RESULTS

In the screening stage, 13 mtDNA haplogroups (hg) were ascertained, and 10 susceptible variants were observed. In the validation stage, hg M8* in individuals was found to be associated with increased risk of NOA [odds ratio (OR) 2.61, 95% confidence interval (CI) 1.47-4.61] (P=0.001). Unexpectedly, the frequency of m.8684C>T, the defining marker for hg M8a, was also higher in NOA (OR 4.14, 95% CI 1.56-11.03) (P=0.002). Subsequently, the frequency distributions were compared among the sub-hg of hg M8* (including hg M8a, C and Z) and, intriguingly, no significance was found in hg C and Z. Additionally, the level of total antioxidant capacity was significantly decreased (P<0.05) compared with the control group.

CONCLUSIONS

hg M8a background in general played an active role in the penetrance of 8684C>T in NOA, and mtDNA genetic variants (causing low antioxidant levels) might increase mtDNA damage and impair normal spermatogenesis.

Temporal trends in sperm count: a systematic review and meta-regression analysis

BACKGROUND

Reported declines in sperm counts remain controversial today and recent trends are unknown. A definitive meta-analysis is critical given the predictive value of sperm count for fertility, morbidity and mortality.

OBJECTIVE AND RATIONALE

To provide a systematic review and meta-regression analysis of recent trends in sperm counts as measured by sperm concentration (SC) and total sperm count (TSC), and their modification by fertility and geographic group.

SEARCH METHODS

PubMed/MEDLINE and EMBASE were searched for English language studies of human SC published in 1981-2013. Following a predefined protocol 7518 abstracts were screened and 2510 full articles reporting primary data on SC were reviewed. A total of 244 estimates of SC and TSC from 185 studies of 42 935 men who provided semen samples in 1973-2011 were extracted for meta-regression analysis, as well as information on years of sample collection and covariates [fertility group ('Unselected by fertility' versus 'Fertile'), geographic group ('Western', including North America, Europe Australia and New Zealand versus 'Other', including South America, Asia and Africa), age, ejaculation abstinence time, semen collection method, method of measuring SC and semen volume, exclusion criteria and indicators of completeness of covariate data]. The slopes of SC and TSC were estimated as functions of sample collection year using both simple linear regression and weighted meta-regression models and the latter were adjusted for pre-determined covariates and modification by fertility and geographic group. Assumptions were examined using multiple sensitivity analyses and nonlinear models.

OUTCOMES

SC declined significantly between 1973 and 2011 (slope in unadjusted simple regression models -0.70 million/ml/year; 95% CI: -0.72 to -0.69; P < 0.001; slope in adjusted meta-regression models = -0.64; -1.06 to -0.22; P = 0.003). The slopes in the meta-regression model were modified by fertility (P for interaction = 0.064) and geographic group (P for interaction = 0.027). There was a significant decline in SC between 1973 and 2011 among Unselected Western (-1.38; -2.02 to -0.74; P < 0.001) and among Fertile Western (-0.68; -1.31 to -0.05; P = 0.033), while no significant trends were seen among Unselected Other and Fertile Other. Among Unselected Western studies, the mean SC declined, on average, 1.4% per year with an overall decline of 52.4% between 1973 and 2011. Trends for TSC and SC were similar, with a steep decline among Unselected Western (-5.33 million/year, -7.56 to -3.11; P < 0.001), corresponding to an average decline in mean TSC of 1.6% per year and overall decline of 59.3%. Results changed minimally in multiple sensitivity analyses, and there was no statistical support for the use of a nonlinear model. In a model restricted to data post-1995, the slope both for SC and TSC among Unselected Western was similar to that for the entire period (-2.06 million/ml, -3.38 to -0.74; P = 0.004 and -8.12 million, -13.73 to -2.51, P = 0.006, respectively).

WIDER IMPLICATIONS

This comprehensive meta-regression analysis reports a significant decline in sperm counts (as measured by SC and TSC) between 1973 and 2011, driven by a 50-60% decline among men unselected by fertility from North America, Europe, Australia and New Zealand. Because of the significant public health implications of these results, research on the causes of this continuing decline is urgently needed.

Partial Deletions of Y-Chromosome in Infertile Men with Non-obstructive Azoospermia and Oligoasthenoteratozoospermia in a Turkish Population

Many genetic alterations have been identified to aid in understanding the genetic basis of male infertility, however, the cause of 30% of male infertility remains unknown. Some studies indicated that subdeletions of Y chromosome may be a reason for male infertility caused by testicular failure. In this regard, we aimed to investigate frequency of AZFc region subdeletions and their clinical effects in patients with idiopathic infertility. A total of 333 male infertile patients with non-obstructive azoospermia (NOA) or oligoasthenoteratozoospermia (OAT), and 87 normozoospermic controls were screened to detect gr/gr, b1/b3 and b2/b3 subdeletions. We recorded higher gr/gr deletion frequency in normozoospermic controls compared NAO and OAT groups (p=0.026). There were no significant differences in b2/b3 subdeletion rates among groups (p=0.437). In the OAT group, follicle-stimulating hormone levels of cases with b2/b3 deletion were statistically lower than cases without b2/b3 deletion (p=0.047). No statistical correlations were indicated among subdeletions, sperm count and assisted reproductive technology (ART) outcomes. These data demonstrate that gr/gr and b2/b3 subdeletions may not play a significant role in the etiopathogenesis of male infertility and ART outcomes in the studied population.

Efficient generation of functional haploid spermatids from human germline stem cells by three-dimensional-induced system

Generation of functional spermatids from human spermatogonial stem cells (SSCs) in vitro is of utmost importance for uncovering mechanisms underlying human germ cell development and treating infertility. Here we report a three-dimensional-induced (3D-I) system by which human SSCs were efficiently differentiated into functional haploid spermatids. Human SSCs were isolated and identified phenotypically. Meiotic chromatin spreads and DNA content assays revealed that spermatocytes and haploid cells were effectively generated from human SSCs by 3D-I system. Haploid cells derived from human SSCs harbored normal chromosomes and excluded Y chromosome microdeletions. RNA sequencing and bisulfite sequencing analyses reflected similarities in global gene profiles and DNA methylation in human SSCs-derived spermatids and normal round spermatids. Significantly, haploid spermatids generated from human SSCs via 3D-I system were capable of fertilizing mouse oocytes, which subsequently enabled the development of hybrid embryos. This study thus provides invaluable human male gametes for treating male infertility.

Examination of Y-Chromosomal Microdeletions and Partial Microdeletions in Idiopathic Infertility in East Hungarian Patients

Purpose

The aim of this study was to establish the Y chromosome microdeletion and partial AZFc microdeletion/duplication frequency firstly in East Hungarian population and to gain information about the molecular mechanism of the heterogeneous phenotype identified in males bearing partial AZFc deletions and duplications.

Materials and Methods

Exactly determined sequences of azoospermia factor (AZF) region were amplified. Lack of amplification was detected for deletion. To determine the copy number of DAZ and CDY1 genes, we performed a quantitative analysis. The primers flank an insertion/deletion difference, which permitted the polymerase chain reaction products to be separated by polyacrylamide gel electrophoresis.

Statistical Analysis Used

Mann-Whitney/Wilcoxon two-sample test, Kruskal-Wallis test, and two-sample t-probe were used for statistical analysis.

Results

AZFbc deletion was detected only in the azoospermic cases; AZFc deletion occurred significantly more frequently among azoospermic patients, than among oligozoospermic males. The frequency of gr/gr deletions was significantly higher in the oligozoospermic patients than in the normospermic group. The b2/b3 deletion and partial duplications were not different among our groups, while b1/b3 deletion was found only in the azoospermic group. In infertile males and in normozoospermic controls, similar Y haplogroup distribution was detected with the highest frequency of haplogroup P. The gr/gr deletion with P haplogroup was more frequent in the oligozoospermic group than in the normozoospermic males. The b2/b3 deletion with E haplogroup was the most frequent, found only in the normozoospermic group.

Conclusions

Y microdeletion screening has prognostic value and can affect the clinical therapy. In case of Y chromosome molecular genetic aberrations, genetic counseling makes sense also for other males in the family because these types of aberrations are transmittable (from father to son 100% transmission).

Interaction between Y chromosome haplogroup O3* and 4-n-octylphenol exposure reduces the susceptibility to spermatogenic impairment in Han Chinese

Certain genetic background (mainly Y chromosome haplogroups, Y-hg) may modify the susceptibility of certain environmental exposure to some diseases. Compared with respective main effects of genetic background or environmental exposure, interactions between them reflect more realistic combined effects on the susceptibility to a disease. To identify the interactions on spermatogenic impairment, we performed Y chromosome haplotyping and measurement of 9 urinary phenols concentrations in 774 infertile males and 520 healthy controls in a Han Chinese population, and likelihood ratio tests were used to examine the interactions between Y-hgs and phenols. Originally, we observed that Y-hg C and Y-hg F^* might modify the susceptibility to male infertility with urinary 4-n-octylphenol (4-n-OP) level (P_inter = 0.005 and 0.019, respectively). Subsequently, based on our results, two panels were tested to identify the possible protective sub-branches of Y-hg F^* to 4-n-OP exposure, and Y-hg O3^* was uncovered to interact with 4-n-OP (P_inter = 0.019). In conclusion, while 4-n-OP shows an adverse effect on spermatogenesis, Y-hg O3^* makes individuals more adaptive to such an effect for maintaining basic reproductive capacity.

Genetic diagnostics of male infertility in clinical practice

Approximately 15% of couples are infertile. Male factors contribute to infertility in over 50% of cases. Identifiable genetic abnormalities contribute to 15%-20% of the most severe forms of male infertility, azoospermia. In this chapter, we explore known genetic causes of male infertility such as Klinefelter syndrome, XYY men, Kallmann syndrome, y-microdeletions, Robertsonian translocations, autosomal inversions, mixed gonadal dysgenesis, x-linked and autosomal gene mutations, and cystic fibrosis transmembrane conductance regulator abnormalities. We also briefly comment on novel biomarkers for male infertility.

Spermatogenic failure and the Y chromosome

The Y chromosome harbors a number of genes essential for testis development and function. Its highly repetitive structure predisposes this chromosome to deletion/duplication events and is responsible for Y-linked copy-number variations (CNVs) with clinical relevance. The AZF deletions remove genes with predicted spermatogenic function en block and are the most frequent known molecular causes of impaired spermatogenesis (5-10% of azoospermic and 2-5% of severe oligozoospermic men). Testing for this deletion has both diagnostic and prognostic value for testicular sperm retrieval in azoospermic men. The most dynamic region on the Yq is the AZFc region, presenting numerous NAHR hotspots leading to partial losses or gains of the AZFc genes. The gr/gr deletion (a partial AZFc deletion) negatively affects spermatogenic efficiency and it is a validated, population-dependent risk factor for oligozoospermia. In certain populations, the Y background may play a role in the phenotypic expression of partial AZFc rearrangements and similarly it may affect the predisposition to specific deletions/duplication events. Also, the Yp contains a gene array, TSPY1, with potential effect on germ cell proliferation. Despite intensive investigations during the last 20 years on the role of this sex chromosome in spermatogenesis, a number of clinical and basic questions remain to be answered. This review is aimed at providing an overview of the role of Y chromosome-linked genes, CNVs, and Y background in spermatogenesis.

Azoospermia Factor C Subregion of the Y Chromosome

The azoospermia factor (AZF) region on the Y chromosome consists of genes required for spermatogenesis. Among the three subregions, the AZFc subregion located at the distal portion of AZF is the driver for genetic variation in Y chromosome. The candidate gene of AZFc is known as deleted in azoospermia gene, which is studied with interest because it is involved in germ cell development and most frequently deleted genes leading to oligozoospermia and azoospermia. Recently, two partial deletions in AZFc gr/gr and b2/b3 are characterized at the molecular level which showed homologous recombination between amplicons, affecting spermatogenesis process. There are novel methods and commercially available kits for accurate screening and characterization of microdeletions. It is important to detect the AZFc microdeletions through genetic screening and counseling those infertile men who planned to avail assisted reproduction techniques such as undergoing intracytoplasmic sperm injection or in vitro fertilization.

Relationship between AZFc deletions and testicular histology in infertile South Chinese men with azoospermia and severe oligospermia

BACKGROUND

The AZFc deletion has been associated with wide range of phenotypes including complete absence of germ cells in the testes (SCOS), reduction in germ cells hypospermatogenesis, and maturation arrest. The main objective of this study was to evaluate the relationship between AZFc microdeletions and testicular histology in South Chinese men with azoospermia or severe oligospermia.

FINDINGS

338 men presenting with idiopathic non-obstructive azoospermia or severe oligospermia were evaluated between March 2012 and April 2015. Thirty-nine of the patients examined had an AZFc deletion (10.9 %). Testicular cytopathology was examined in 25 patients with an AZFc microdeletion and 14 with an AZFc deletion. There was no significant difference in the testicular histology of patients with partial or complete AZFc deletions (Mann-Whitney U = 152.500, p = 0.515). There was an association between testicular histology and gr/gr, b1/b3 or b2/b3 deletion (Fisher's exact test, p = 0.013).

CONCLUSIONS

Men with a gr/gr partial deletion were at higher risk of having hypospermatogenesis or maturation arrest. Men with a b1/b3 partial deletion were at higher risk of having maturation arrest. Men with a b2/b3 partial deletion were at higher risk of having maturation arrest or complete absence of germ cells in the testes.

Y chromosome b2/b3 deletions and male infertility: A comprehensive meta-analysis, trial sequential analysis and systematic review

The correlation of Y-chromosome b2/b3 partial deletions with spermatogenic failure remains dubious. We undertook a systematic review of the literature followed by meta-analyses and trial sequential analyses in order to compare the frequency of b2/b3 deletions between oligo/azoospermic infertile and normozoospermicmen. Out of twenty-four studies reviewed for meta-analysis, twenty reported no correlation between this deletion and male infertility and two studies each reported a direct and inverse correlation. In the collective analysis, 241 out of 8892 (2.71%) oligo/azoospermic individuals and 118 out of 5842 (2.02%) normozoospermic controls had a b2/b3 deletion, suggesting a relatively higher frequency of deletions in the cases. Eventually, meta-analysis showed a significant correlation between b2/b3 deletions and the risk of spermatogenic loss/infertility (Fixed model: OR=1.313, 95% CI=1.04-1.65, p=0.02; Random model: OR=1.315, 95% CI=1.02-1.70, p=0.037). Further meta-analysis on studies grouped by ethnicity and geographic regions showed that the b2/b3 deletions are significantly associated with spermatogenic loss/infertility in Mongolians, Nigro-Caucasians, East Asians and Africans, but not in Caucasians, Europeans, South Asians and Dravidians. In summary, the Y-chromosome b2/b3 deletions increase infertility risk; however, it may be significant only in the Mongolian populations and the East Asian region.

Gr/gr deletions on Y-chromosome correlate with male infertility: an original study, meta-analyses, and trial sequential analyses

We analyzed the AZFc region of the Y-chromosome for complete (b2/b4) and distinct partial deletions (gr/gr, b1/b3, b2/b3) in 822 infertile and 225 proven fertile men. We observed complete AZFc deletions in 0.97% and partial deletions in 6.20% of the cases. Among partial deletions, the frequency of gr/gr deletions was the highest (5.84%). The comparison of partial deletion data between cases and controls suggested a significant association of the gr/gr deletions with infertility (P = 0.0004); however, the other partial deletions did not correlate with infertility. In cohort analysis, men with gr/gr deletions had a relatively poor sperm count (54.20 ± 57.45 million/ml) in comparison to those without deletions (72.49 ± 60.06), though the difference was not statistically significant (p = 0.071). Meta-analysis also suggested that gr/gr deletions are significantly associated with male infertility risk (OR = 1.821, 95% CI = 1.39–2.37, p = 0.000). We also performed trial sequential analyses that strengthened the evidence for an overall significant association of gr/gr deletions with the risk of male infertility. Another meta-analysis suggested a significant association of the gr/gr deletions with low sperm count. In conclusion, the gr/gr deletions show a strong correlation with male infertility risk and low sperm count, particularly in the Caucasian populations.

Copy number variation and microdeletions of the Y chromosome linked genes and loci across different categories of Indian infertile males

We analyzed 34 azoospermic (AZ), 43 oligospermic (OS), and 40 infertile males with normal spermiogram (INS) together with 55 normal fertile males (NFM) from the Indian population. AZ showed more microdeletions in the AZFa and AZFb regions whereas oligospermic ones showed more microdeletions in the AZFc region. Frequency of the AZF partial deletions was higher in males with spermatogenic impairments than in INS. Significantly, SRY, DAZ and BPY2 genes showed copy number variation across different categories of the patients and much reduced copies of the DYZ1 repeat arrays compared to that in normal fertile males. Likewise, INS showed microdeletions, sequence and copy number variation of several Y linked genes and loci. In the context of infertility, STS deletions and copy number variations both were statistically significant (p = 0.001). Thus, semen samples used during in vitro fertilization (IVF) and assisted reproductive technology (ART) must be assessed for the microdeletions of AZFa, b and c regions in addition to the affected genes reported herein. Present study is envisaged to be useful for DNA based diagnosis of different categories of the infertile males lending support to genetic counseling to the couples aspiring to avail assisted reproductive technologies.

A genome-wide association study of mitochondrial DNA in Chinese men identifies two risk single nucleotide substitutions for idiopathic oligoasthenospermia

Mitochondrial DNA (mtDNA) is believed to be both the source and target of reactive oxygen species (ROS), and mtDNA genetic alterations have been reported to be associated with molecular defects in the oxidative phosphorylation (OXPHOS) system. In order to investigate the potentially susceptible mtDNA genetic variants to oligoasthenospermia, we conducted a two-stage study in 921 idiopathic infertile men with oligoasthenospermia and 766 healthy controls using comprehensive molecular analysis. In the screen stage, we used next generation sequencing (NGS) in 233 cases and 233 controls to screen oligoasthenospermia susceptible mitochondrial genetic variants. In total, seven variants (C5601T, T12338C, A12361G, G13928C, A15235G, C16179T and G16291A) were screened to be potentially associated with idiopathic oligoasthenospermia. In the validation stage, we replicated these variants in 688 cases and 533 healthy controls using SNPscan. Our results demonstrated that the genetic alteration of C16179T was associated with idiopathic male infertility (odds ratio (OR) 3.10, 95% CI 1.41-6.79) (p=3.10×10(-3)). To elucidate the exact role of the genetic variants in spermatogenesis, two main sperm parameters (sperm count and motility) were taken into account. We found that C16179T was associated with both low sperm count and motility, with ORs of 4.18 (95% CI 1.86-9.40) (p=1.90×10(-4)) and 3.17 (95% CI 1.40-7.16) (p=3.50×10(-3)), respectively. Additionally, A12361G was found to be associated with low sperm count, with an OR of 3.30 (95% CI 1.36-8.04) (p=5.50×10(-3)). These results indicated that C16179T influenced both the process of spermatogenesis and sperm motility, while A12361G may just only participate in the process of spermatogenesis. Further investigation in larger populations and functional characterizations are needed to validate our findings.

Impact of Y chromosome AZFc subdeletion shows lower risk of fertility impairment in Siddi tribal men, Western Ghats, India

Background

India is characterized by the presence of a large number of endogamous castes, tribes and religions, having second largest concentration of tribal population in the World with differed genetic ethnicity, lifestyle and environmental habitat from those of mainstream population. Lack of data is constraint when it comes to tracking the tribal population health status, specifically reproductive health aspects by experimental approaches. The male fertility impairment depends on Y chromosome azoospermia factor c (AZFc) subdeletions, which varies highly in different geographical populations and in an Indian admixed population the frequency and effect of deletion on fertility is relatively poorly documented. Therefore, the current study has been initiated to enumerate and characterize the strength of association between Yq11 AZFc subdeletions and fertility impairment among Siddi tribal men of Western Ghats, India.

Methods

Here, using predesigned performa we collected personal as well as familial information of 200 volunteered male subjects and grouped them into: (i) 104 married individuals with proven fertility, and (ii) 96 unmarried men with unknown fertility status. Quantification of reproductive hormones such as follicle stimulating hormone (FSH), leutinizing hormone (LH) and testosterone were studied. Oxidative stress markers like total antioxidant capacity (TAC) and super oxide dismutase (SOD) along with analysis of five sequence tagged site (STS) hotspot markers were employed for mapping of Y chromosome AZFc subdeletions. Statistical analyses were performed using SPSS software.

Results

Hormonal analysis and estimation of oxidative stress markers showed normal values with no significant differences between two subgroups. However, the Y chromosome AZFc subdeletion mapping revealed evident results as an individual displayed absence of STS sY1191 marker indicating b2/b3 deletion, whereas rest of the subjects exhibited no deletion for all the five STS markers. While, the individual has fathered two children, at this point it is difficult to draw a causal link between the observed deletion and its effect on fertility.

Conclusion

Thus, our current study suggests that the association between AZFc subdeletions with its effect on infertility varies highly in this study cohort compared to other Indian ethnic groups, exhibiting lower risk factor and non-association reaching insignificance among Siddi tribal men.

Electronic supplementary material

The online version of this article (doi:10.1186/s12610-014-0017-5) contains supplementary material, which is available to authorized users.

Screening for AZFc partial deletions in Dravidian men with nonobstructive azoospermia and oligozoospermia

CONTEXT

Dravidians are the predominant population residing in South India with a diverse genetic structure. Considering various genetic discoveries taking place today, it is evident that deletions in the AZFc region are the most common cause of severe spermatogenic failure (SSF) in various populations studied. However, it is significant to note that there is a paucity of scientific literature on AZFc subdeletion screening among the Dravidian population.

OBJECTIVE

To investigate the prevalence and association of AZFc subdeletion patterns among Dravidian men with nonobstructive azoospermia (NOA) and oligozoospermia.

METHODS

A population of 354 subjects, including 120 patients with NOA, 109 with oligozoospermia, and 125 normal male controls, were screened using locus-specific sequence tag site markers.

RESULTS

We found 21 (9.17%) patients with classical AZF deletion, while no deletions were observed in controls. After excluding the samples with AZF deletions, the remaining 208 infertile and 125 control samples were screened for partial AZFc deletions using a standardized multiplex polymerase chain reaction and on analysis revealed that 13 (6.25%) of the infertile samples possessed gr/gr subdeletions and 15 (7.21%) of the infertile samples possessed b2/b3 subdeletions. Six (4.8%) of the normal samples were found to carry gr/gr subdeletions and two (1.6%) had b2/b3 deletions. The b1/b3 deletion was not observed in any of the patient and control samples screened.

CONCLUSION

Our finding shows that there is a strong association between b2/b3 subdeletion and SSF in the Dravidian population (odds ratio, 4.78; 95% confidence interval 1.07-21.26) (p=0.018). Further studies, including gene copy typing for DAZ and CDY genes and a comprehensive haplogrouping analysis, are recommended in a large and well-selected patient group to elude the genetic mechanism behind this association.

Association of single nucleotide polymorphisms in the USF1, GTF2A1L and OR2W3 genes with non-obstructive azoospermia in the Chinese population

PURPOSE

To research the association between the single nucleotide polymorphisms (SNPs) of three spermatogenesis-related genes (USF1, GTF2A1L and OR2W3) and non-obstruction azoospermia (NOA).

METHODS

We investigated 361 NOA cases and 368 controls from the Chinese Han population, and we used Sequenom iplex technology to analyze the candidate 9 SNPs from the USF1, GTF2A1L and OR2W3 genes.

RESULTS

In this study, we found that the variant rs2516838 of USF1 was associated with NOA susceptibility (P = 0.020, OR = 1.436), and the haplotype TCG of the variants rs1556259, rs2516838, and rs2774276 of USF1 conferred an increased risk of NOA (P = 0.019, OR = 1.436). Furthermore, we found that the rs11204546 genotype of OR2W3 and the rs11677854 genotype of GTF2A1L were correlated with the FSH level in the patients (P = 0.004 and P = 0.018, respectively).

CONCLUSIONS

Our results provided a new insight into susceptibility of USF1 variant with male infertility. Clinically, the SNPs (rs11204546 of OR2W3 and rs11677854 of GTF2A1L ) might be additional valuable molecular predictive markers for assessing the treatment of NOA patients.

Analysis of DAZ gene expression in a partial AZFc deletion of the human Y chromosome

The azoospermia factor c (AZFc) region of the Y chromosome consists of repetitive amplicons and is therefore highly susceptible to structural rearrangements, such as deletions and duplications. The b2/b3 deletion is a partial AZFc deletion that is conventionally determined by the selective absence of sY1191 in sequence-tagged site polymerase chain reaction (PCR) and is generally believed to retain two of the four deleted in azoospermia (DAZ) genes on the Y chromosome. In the present study we determined the copy number and expression of DAZ genes in sY1191-negative individuals. Using a DAZ dosage PCR assay and Southern blot analysis we evaluated the expression of four DAZ genes in five of six sY1191-negative individuals. Furthermore, cloning and immunoblot analyses revealed that three or more DAZ genes are expressed in sY1191-negative testes with germ cells. The results indicate that the selective absence of sY1191 not only means b2/b3 deletion with two DAZ genes, but also includes another AZFc configuration with four DAZ genes. These results exemplify the prevalence of variations in the AZFc region of the human Y chromosome.

Oxygen free radicals and mitochondrial signaling in oligospermia and asthenospermia

The aim of this study was to investigate the roles of oxygen free radicals and mitochondrial signaling in semen disorders, in particular, how this induces low concentrations and reduced motility of sperm. Ejaculate samples were obtained from 120 young adult males (mean age, 28.7±5.3 years) with normal semen (n=30), oligospermia (n=30), asthenospermia (n=30) and oligoasthenozoospermia (n=30). The malondialdehyde (MDA) content, total superoxide dismutase (T‑SOD) activity and glutathione peroxidase (GSH‑Px) activity of the sperm samples were determined by enzymatic assays. Mitochondrial membrane potential (MMP) was determined by flow cytometric detection of accumulated membrane‑permeable JC‑1 fluorescent dye. The mRNA and protein expression levels of apoptosis-associated genes [Bcl‑2, Bax, cytochrome c (Cyt C) and caspase-3] were measured by quantitative polymerase chain reaction and western blotting. Intergroup differences were evaluated by Student's t‑test. The sperm samples from all semen disorder groups exhibited significantly lower T‑SOD content and GSH‑Px activity (all P<0.05 versus normal sperm), and the extent of reduction revealed a disorder-associated trend (asthenospermia < oligospermia ≈ oligoasthenozoospermia). By contrast, the semen disorder groups had significantly higher MDA content (all P<0.05 versus normal sperm); the extent of this increase also revealed a disorder-associated trend (asthenospermia > oligospermia ≈ oligoasthenozoospermia). The sperm from patients with semen disorders also exhibited significantly lower MMP than normal sperm, as evidenced by lower mean ratios of JC‑1+ sperm per group. The semen disorder groups had significantly higher Bax, Cyt C and caspase-3 mRNA and protein expression levels in the sperm samples, but significantly lower levels of Bcl‑2 (all P<0.05 versus normal sperm). However, only the extent of increases in Cyt C and caspase-3 exhibited a disorder-associated trend (oligospermia > asthenospermia). In conclusion, oxygen free radicals may be involved in reduced sperm concentration and motility, possibly through effects on the mitochondrial apoptotic signaling pathway. Perturbed mitochondrial release of Cyt C may be the distinguishing molecular feature between oligospermia and asthenospermia.

CREM variants rs4934540 and rs2295415 conferred susceptibility to nonobstructive azoospermia risk in the Chinese population

To evaluate the association of variants related to spermatogenesis with susceptibility to Chinese idiopathic nonobstructive azoospermia (NOA), seventeen tag single-nucleotide polymorphisms (SNPs) in CREM, ACT, KIF17b, and SPAG8 were analyzed in 361 NOA patients and 368 controls by Sequenom iplex technology. The results showed that two CREM SNPs, rs4934540 and rs22954152, were significantly associated with NOA and played protective roles against the disease (P value with Bonferroni correction = 0.00017, odds ratio [OR] = 0.624 and P = 0.012, OR = 0.686, respectively). Haplotype analysis of CREM gene variants suggested that haplotype CGTG of the SNPs, rs4934540, rs2295415, rs11592356, and rs1148247, exhibited significant protective effect against the occurrence of NOA (P = 0.001, OR = 0.659). The haplotype TATG conferred a significantly increased risk of NOA (P = 0.011, OR = 1.317). Furthermore, making use of quantitative RT-PCR, we demonstrated that relative mRNA expression of CREM in NOA patients with maturation arrest was only one-third of that in the controls with normal spermatogenesis (P < 0.0001). Our findings indicated that the polymorphisms of CREM gene were associated with NOA in the Chinese population and low CREM expression might be involved in the pathogenesis of spermatogenesis maturation arrest.

Gene copy number alterations in the azoospermia-associated AZFc region and their effect on spermatogenic impairment

The azoospermia factor c (AZFc) region in the long arm of human Y chromosome is characterized by massive palindromes. It harbors eight multi-copy gene families that are expressed exclusively or predominantly in testis. To assess systematically the role of the AZFc region and these eight gene families in spermatogenesis, we conducted a comprehensive molecular analysis (including Y chromosome haplogrouping, AZFc deletion typing and gene copy quantification) in 654 idiopathic infertile men and 781 healthy controls in a Han Chinese population. The b2/b3 partial deletion (including both deletion-only and deletion-duplication) was consistently associated with spermatogenic impairment. In the subjects without partial AZFc deletions, a notable finding was that the frequency of DAZ and/or BPY2 copy number alterations in the infertile group was significantly higher than in the controls. Combined patterns of DAZ and/or BPY2 copy number abnormality were associated with spermatogenic impairment when compared with the pattern of all AZFc genes with common level copies. In addition, in Y chromosome haplogroup O1 (Y-hg O1), the frequency of copy number alterations of all eight gene families was significantly higher in the case group than that in the control group. Our findings indicate that the DAZ, BPY2 genes may be prominent players in spermatogenesis, and genomic rearrangements may be enriched in individuals belonging to Y-hg O1. Our findings emphasize the necessity of routine molecular analysis of AZFc structural variation during the workup of azoospermia and/or oligozoospermia, which may diminish the genetic risk of assisted reproduction.

Partial AZFc duplications not deletions are associated with male infertility in the Yi population of Yunnan Province, China

OBJECTIVE

There are many reports on associations between spermatogenesis and partial azoospermia factor c (AZFc) deletions as well as duplications; however, results are conflicting, possibly due to differences in methodology and ethnic background. The purpose of this study is to investigate the association of AZFc polymorphisms and male infertility in the Yi ethnic population, residents within Yunnan Province, China.

METHODS

A total of 224 infertile patients and 153 fertile subjects were selected in the Yi ethnic population. The study was performed by sequence-tagged site plus/minus (STS+/-) analysis followed by gene dosage and gene copy definition analysis. Y haplotypes of 215 cases and 115 controls were defined by 12 binary markers using single nucleotide polymorphism on Y chromosome (Y-SNP) multiplex assays based on single base primer extension technology.

RESULTS

The distribution of Y haplotypes was not significantly different between the case and control groups. The frequencies of both gr/gr (7.6% vs. 8.5%) and b2/b3 (6.3% vs. 8.5%) deletions do not show significant differences. Similarly, single nucleotide variant (SNV) analysis shows no significant difference of gene copy definition between the cases and controls. However, the frequency of partial duplications in the infertile group (4.0%) is significantly higher than that in the control group (0.7%). Further, we found a case with sY1206 deletion which had two CDY1 copies but removed half of DAZ genes.

CONCLUSIONS

Our results show that male infertility is associated with partial AZFc duplications, but neither gr/gr nor b2/b3 deletions, suggesting that partial AZFc duplications rather than deletions are risk factors for male infertility in Chinese-Yi population.

Y chromosome gr/gr subdeletion is associated with lower semen quality in young men from the general Japanese population but not in fertile Japanese Men

Several case-control studies have investigated whether Y chromosome haplogroups or deletions are associated with spermatogenic failure. However, the relationships between Y chromosome haplogroups or deletions and semen quality in general population have not been elucidated. In this study, we assessed relationships between Y chromosome haplogroups or deletions and semen parameters in 791 fertile Japanese men and 1221 young men from the general Japanese population. We found that the haplogroup D2 (M55 lineage) was significantly associated with lower semen parameters, especially total motile sperm count (P = 0.00051, beta = -0.097), in men from the general population but not in fertile men. In addition, we found that the gr/gr subdeletion was associated with semen quality and in particular, strongly associated with decreased sperm motility (P = 0.00041, beta = -3.14) and total motile sperm count (P = 0.00031, beta = -0.099) in men from the general population but not in fertile men. The combined analysis of fertile Japanese men and men from the general Japanese population showed that the haplogroup D2 (M55 lineage) and the gr/gr subdeletion were strongly associated with reduced sperm motility (P = 0.00056, beta = -2.71, and P = 7.7 × 10(-5), beta = -3.05, respectively) and that haplogroup O2b1 was strongly associated with elevated sperm motility (P = 0.00089, beta = 2.94). These observations add further support for the view that the gr/gr subdeletion diminishes sperm motility that consequently may result in male infertility.

Evaluation of five candidate genes from GWAS for association with oligozoospermia in a Han Chinese population

Background

Oligozoospermia is one of the severe forms of idiopathic male infertility. However, its pathology is largely unknown, and few genetic factors have been defined. Our previous genome-wide association study (GWAS) has identified four risk loci for non-obstructive azoospermia (NOA).

Objective

To investigate the potentially functional genetic variants (including not only common variants, but also less-common and rare variants) of these loci on spermatogenic impairment, especially oligozoospermia.

Design, Setting, and Participants

A total of 784 individuals with oligozoospermia and 592 healthy controls were recruited to this study from March 2004 and January 2011.

Measurements

We conducted a two-stage study to explore the association between oligozoospermia and new makers near NOA risk loci. In the first stage, we used next generation sequencing (NGS) in 96 oligozoospermia cases and 96 healthy controls to screen oligozoospermia-susceptible genetic variants. Next, we validated these variants in a large cohort containing 688 cases and 496 controls by SNPscan for high-throughput Single Nucleotide Polymorphism (SNP) genotyping.

Results and Limitations

Totally, we observed seven oligozoospermia associated variants (rs3791185 and rs2232015 in PRMT6, rs146039840 and rs11046992 in Sox5, rs1129332 in PEX10, rs3197744 in SIRPA, rs1048055 in SIRPG) in the first stage. In the validation stage, rs3197744 in SIRPA and rs11046992 in Sox5 were associated with increased risk of oligozoospermia with an odds ratio (OR) of 4.62 (P  =  0.005, 95%CI 1.58-13.4) and 1.82 (P  =  0.005, 95%CI 1.01-1.64), respectively. Further investigation in larger populations and functional characterizations are needed to validate our findings.

Conclusions

Our study provides evidence of independent oligozoospermia risk alleles driven by variants in the potentially functional regions of genes discovered by GWAS. Our findings suggest that integrating sequence data with large-scale genotyping will serve as an effective strategy for discovering risk alleles in the future.

Pathogenic variants screening in five non-obstructive azoospermia-associated genes

Non-obstructive azoospermia (NOA) is one of the most severe forms of male infertility and a recent, genome-wide association study (GWAS) has identified four risk loci associated with NOA. However, a large portion of the heritability of NOA has not been well explained by GWAS. By hypothesizing that rare, low-frequency and common genetic variants might point toward a causal relation between candidate genes and NOA, we performed a two-stage study including deep exon sequencing in 96 NOA cases and 96 healthy controls and a replication study in a larger population containing 522 NOA cases and 484 healthy controls. In the solexa sequencing stage, a total of two rare mutations (chr20. 1902132 and chr20. 1902301 in SIRPA), four common mutations (rs1048055 and rs2281807 in SIRPG, rs11046992 and rs146039840 in SOX5) were identified by using next generation sequencing (NGS). In the validation stage, subjects in the NOA group had a significantly decreased frequency of the heterozygous GA genotype in SIRPA (4.23%, 22 out of 520) than that in the control group (8.60%, 41 out of 477) [odds ratios (OR) 0.47, 95% confidence intervals (CI) 0.28-0.80] (P = 6.00 × 10(-3)). The rs1048055 in SIRPG was associated with a significantly increased risk of spermatogenic impairment, compared with the CC genotype (OR 3.93, 95% CI 1.59-9.70) (P = 3.00 × 10(-3)). Our study provides evidence of independent NOA risk alleles driven by variants in the protein-coding sequence of two of the genes (SIRPA and SIRPG) discovered by GWAS. Further investigation in larger populations and functional characterizations are needed to validate our findings.

Bulky DNA adducts in human sperm associated with semen parameters and sperm DNA fragmentation in infertile men: a cross-sectional study

BACKGROUND

DNA adducts are widely used marker of DNA damage induced by environmental pollutants. The present study was designed to explore whether sperm polycyclic aromatic hydrocarbon-DNA adducts were associated with sperm DNA integrity and semen quality.

METHODS

A total of 433 Han Chinese men were recruited from an infertility clinic. Immunofluorescence was applied to analyze sperm PAH-DNA adducts. Sperm DNA fragmentation was detected by terminal deoxynucleotidyl transferase (Tdt)-mediated dUTP nick end labelling (TUNEL) assay.

RESULTS

After adjustment for potential confounders using linear regression, sperm PAH-DNA adducts were negatively associated with sperm concentration, total sperm count, sperm motility, and curvilinear velocity (VCL). In addition, a positive relationship between sperm PAH-DNA adducts and sperm DNA fragmentation was found.

CONCLUSIONS

Our findings suggested an inverse association between sperm PAH-DNA adducts and semen quality, and provided the first epidemiologic evidence of an adverse effect of PAH-DNA adducts on sperm DNA integrity.

DAZ duplications confer the predisposition of Y chromosome haplogroup K* to non-obstructive azoospermia in Han Chinese populations

STUDY QUESTION

What are the genetic causes for the predisposition of certain Y chromosome haplogroups (Y-hgs) to spermatogenic impairment?

SUMMARY ANSWER

The AZFc(azoospermia factor c)/DAZ (deleted in azoospermia) duplications might underlie the susceptibility of Y-hg K* to spermatogenic impairment.

WHAT IS KNOWN ALREADY

The roles of Y chromosomal genetic background in spermatogenesis are controversial and vary among human populations. Individuals in predisposed Y-hgs may carry some genetic factors, which might be a potential genetic modifier for the Y-hg-specific susceptibility to spermatogenic impairment.

STUDY DESIGN, SIZE, DURATION

A total of 2444 individuals with azoospermia or oligozoospermia and 2456 healthy controls were recruited to this study from March 2004 and January 2011.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We performed a two-stage association study to investigate the risk and/or protective Y-hgs for spermatogenic impairment. In addition, the genetic causes for the predisposition of certain Y-hg to spermatogenic impairment were investigated. Deletion typing and DAZ gene copy number quantification were performed for individuals in predisposed Y-hgs.

MAIN RESULTS AND THE ROLE OF CHANCE

Y-hgs K* and O3e* showed significantly different distribution between cases and controls consistently in two-stage studies. Combined analyses identified significant predisposition to non-obstructive azoospermia in Y-hg K* [odds ratio (OR) 8.58; 95% confidence interval (CI) 3.31-22.28; P = 1.40 × 10⁻⁵], but a protecting effect in Y-hg O3e* (OR 0.64; 95% CI 0.53-0.78; P = 4.20 × 10⁻⁵). Based on the dynamic nature of the Y chromosome, we hypothesized that Y-hgs K* and O3e* may be accompanied by modifying genetic factors for their predisposing or protecting effects in spermatogenesis. Accordingly, we quantified the multi-copy DAZ gene, which has variable copy numbers between individuals and plays an important role in spermatogenesis. In combined analysis, we found that the over-dosage of DAZ was significantly more frequent in Y-hg K* than in O3e* (OR 4.79; 95% CI 1.67-13.70; P = 6 × 10⁻³).

LIMITATIONS, REASONS FOR CAUTION

Owing to the inconsistency of genetic background, it remains to be determined whether the results derived from Han Chinese populations are applicable to other ethnic groups.

WIDER IMPLICATIONS OF THE FINDINGS

The findings of this study can advance the etiology of spermatogenic impairment, and also shed new light on Y chromosome evolution in human populations. Y-hg-specific genetic factors of modifying spermatogenic phenotypes deserve further investigation in larger and diverse populations.

Polymorphisms in double-strand breaks repair genes are associated with impaired fertility in Chinese population

The DNA double-strand breaks (DSBs) repair pathway plays a critical role in repairing double-strand breaks, and genetic variants in DSBs repair pathway genes are potential risk factors for various diseases. To test the hypothesis that polymorphisms in DSBs genes are associated with susceptibility to male infertility, we examined 11 single nucleotide polymorphisms in eight key DSBs genes (XRCC3, XRCC2, BRCA2, RAG1, XRCC5, LIG4, XRCC4 and ATM) in 580 infertility cases and 580 controls from a Chinese population-based case-control study (NJMU Infertility Study). Genotypes were determined using the OpenArray platform, and sperm DNA fragmentation was detected using the TUNEL assay. The adjusted odds ratio (OR) and 95% CI were estimated using logistic regression. The results indicate that LIG4 rs1805388 (Ex2+54C>T, Thr9Ile) T allele could increase the susceptibility to male infertility (adjusted OR=2.78; 95% CI, 1.77-4.36 for TT genotype; and adjusted OR=1.58; 95% CI, 1.77-4.36 for TC genotype respectively). In addition, the homozygous variant genotype GG of RAG1 rs2227973 (A>G, K820R) was associated with a significantly increased risk of male infertility (adjusted OR, 1.44; 95% CI, 1.01-2.04). Moreover, linear regression analysis revealed that carriers of LIG4 rs1805388 or RAG1 rs2227973 variants had a significantly higher level of sperm DNA fragmentation and that T allele carriers of LIG4 rs1805388 also had a lower level of sperm concentration when compared with common homozygous genotype carriers. This study demonstrates, for the first time, to our knowledge, that functional variants of RAG1 rs2227973 and LIG4 rs1805388 are associated with susceptibility to male infertility.

Expansion and de novo occurrence of Y chromosome microdeletions occurring via natural vertical transmission in northeastern China

OBJECTIVE

To determine characteristics of classical and partial deletions of the Y chromosome azoospermia factor (AZF) region transmitted from father to son by natural fertilization.

METHODS

Patients from northeastern China with primary male infertility (n = 10) and their fathers were investigated. Healthy fertile men and women were recruited as positive and negative controls, respectively. The Y chromosome microdeletions were detected by polymerase chain reaction. Serum concentrations of reproductive hormones were determined by electrochemiluminescence immunoassay and enzyme-linked immunosorbent assay.

RESULTS

Expansions of microdeletions were observed in seven father–son pairs; de novo microdeletions were found in the remaining three father–son pairs. The Y chromosome microdeletions were larger in sons than in their fathers. Patients with infertility had significantly higher levels of follicle stimulating hormone and lower levels of inhibin B than fertile men.

CONCLUSIONS

The Y chromosome microdeletions were transmitted from father to son via natural transmission. These microdeletions may expand during transmission or arise de novo, possibly resulting in reduced fertility.

Analysis of partial AZFc deletions in Malaysian infertile male subjects

Complete deletions in the AZF (a, b, and c) sub-regions of the Y-chromosome have been shown to contribute to unexplained male infertility. However, the role of partial AZFc deletions in male infertility remains to be verified. Three types of partial AZFc deletions have been identified. They are gr/gr, b1/b3, and b2/b3 deletions. A recent meta-analysis showed that ethnic and geographical factors might contribute to the association of partial AZFc deletions with male infertility. This study analyzed the association of partial AZFc deletions in Malaysian infertile males. Fifty two oligozoospermic infertile males and 63 fertile controls were recruited to this study. Screening for partial AZFc deletions was done using the two sequence-tagged sites approach (SY1291 and SY1191) which were analyzed using both the conventional PCR gel-electrophoresis and the high resolution melt, HRM method. Gr/gr deletions were found in 11.53% of the cases and 9.52% of the controls (p = 0.725). A B2/b3 deletion was found in one of the cases (p = 0.269). No B1/b3 deletions were identified in this study. The results of HRM analysis were consistent with those obtained using the conventional PCR gel-electrophoresis method. The HRM analysis was highly repeatable (95% limit of agreement was -0.0879 to 0.0871 for SY1191 melting temperature readings). In conclusion, our study showed that partial AZFc deletions were not associated with male infertility in Malaysian subjects. HRM analysis was a reliable, repeatable, fast, cost-effective, and semi-automated method which can be used for screening of partial AZFc deletions.

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 217 controls 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.

Organizational and functional status of the Y-linked genes and loci in the infertile patients having normal spermiogram

Male fertility is an orchestrated interplay of loci on the Y chromosome with a number of genes from across the other chromosomes. In this context, micro-deletions in the Y chromosome have been correlated with spermatogenic failure often leading to infertility. However, causes of infertility in the patients with the normal spermiogram have remained unclear and therefore pose another level of challenge. In the present study, we analyzed 64 STSs, studied different Y-linked genes and loci and conducted single nucleotide variant (SNV) analyses in 31 infertile males with normal spermiogram along with 67 normal fertile males (NFMs) to gain an insight into the organization of their Y chromosome. Further, employing quantitative real-time PCR (qPCR), we studied copy number variation of DYZ1 arrays and three genes and mutational status of SRY by direct sequence analyses. STS analyses of the AZFa, b and c regions in these patients showed known and new mutations. Further, copies of DAZ and BPY2 in the patients were found to be affected compared to those in NFMs. All the patients had normal copy number of the SRY however its sequence analysis (in silico) showed mutations in eight patients. In four of these eight patients, SRY mutations resulted into truncated proteins. Similarly, DYZ1 analysis showed micro-deletions and it's much reduced copy number as compared to those in NFMs. Present study in males with unexplained infertility revealed deletions similar to those observed in oligospermic and azoospermic patients. Thus, there are some common but still unknown factors underlying infertility in these patients irrespective of their spermatogenic status. This work is envisaged to augment DNA diagnosis, proving beneficial in the context of in vitro fertilization (IVF) and genetic counselling.

Genetic variants in TP53 and MDM2 associated with male infertility in Chinese population

The TP53, a transcriptional regulator and tumor suppressor, is functionally important in spermatogenesis. MDM2 is a key regulator of the p53 pathway and modulates p53 activity. Both proteins have been functionally linked to germ cell apoptosis, which may affect human infertility, but very little is known on how common polymorphisms in these genes may influence germ cell apoptosis and the risk of male infertility. Thus, this study was designed to test whether three previously described polymorphisms 72Arg>Pro (rs1042522) and the Ex2+19C>T (rs2287498) in TP53, and the 5' untranslated region (5' UTR) 309T>G (rs937283) in MDM2, are associated with idiopathic male infertility in a Chinese population. The three polymorphisms were genotyped using OpenArray assay in a hospital-based case-control study, including 580 infertile patients and 580 fertile controls. Our analyses revealed that TP53 Ex2+19C>T and MDM2 309T>G polymorphisms are associated with male infertility. Furthermore, we detected a nearly statistically significant additive interaction between TP53 rs2287498 and MDM2 rs937283 for the development of male infertility (P(interaction)=0.055). In summary, this study found preliminary evidence, demonstrating that genetic variants in genes of the TP53 pathway are risk factors for male infertility.