The association of four SNPs in DNA mismatch repair genes with idiopathic male infertility in northwest China

Male Fertility as a Proxy for Health

Male fertility is affected by a wide range of medical conditions that directly and indirectly affect spermatogenesis. As such, it can be useful as both an indicator of current health and a predictive factor for future health outcomes. Herein, we discuss the current literature regarding the association between male fertility and systemic health conditions and exposures. We review the connection between male fertility and genetics, medications, diet, and environmental pollutants, as well as its effects on future oncologic, cardiovascular, and autoimmune conditions. Understanding this interplay will allow more health care providers to engage in health counseling that will not only improve men's reproductive outcomes but also their overall health.

Reproduction as a window for health in men

Male factor infertility is widely considered a harbinger for a man's general health. Failure of reproduction often accompanies other underlying processes, with growing evidence suggesting that a diagnosis of infertility increases the likelihood of developing future cardiac, metabolic, and oncologic diseases. The goal of this review is to provide a comprehensive overview of the research on male fertility as a marker for current and future health. A multidisciplinary approach is essential, and there is growing consensus that the male fertility evaluation offers an opportunity to better men's wellness beyond their immediate reproductive ambitions.

Genomic instability and the link to infertility: A focus on microsatellites and genomic instability syndromes

Infertility is associated to multiple types of different genomic instabilities and is a genetic feature of genomic instability syndromes. While the mismatch repair machinery contributes to the maintenance of genome integrity, surprisingly its potential role in infertility is overlooked. Defects in mismatch repair mechanisms contribute to microsatellite instability and genomic instability syndromes, due to the inability to repair newly replicated DNA. This article reviews the literature to date to elucidate the contribution of microsatellite instability to genomic instability syndromes and infertility. The key findings presented reveal microsatellite instability is poorly researched in genomic instability syndromes and infertility.

Genom-wide analysis identifies single nucleotide polymorphism variations and altered pathways associated with poor semen quality in breeding bulls

The reason for poor semen quality among the breeding bulls is not well understood. In the present study, we performed high-throughput RNAseq analysis of spermatozoa to identify the SNPs present in good and poor-quality semen-producing Holstein Friesian breeding bulls. A total of 21,360 and 44,650 SNPs were identified in good and poor-quality semen with a minimum read depth of 20, among which 4780 and 8710 novel variants were observed in good and poor-quality semen, respectively. Greater SNPs and indels variations were observed in poor compared to good-quality semen. In poor-quality semen, SNP variations were observed in ZNF280B, SLC26A2, DMXL1, OR52A1, MACROD2 and REV1 genes, which are associated with regulation of spermatogenesis, post-testicular maturation, Cl^- channel activity, V-ATPase-mediated intracellular vesicle acidification, a mono-ADP-ribosyl hydrolase and ATR-Chk1 checkpoint activation. GO analysis of filtered genes with significant variations between good and poor-quality semen showed enrichment in important pathways related to semen quality such as MAPK signalling pathway, Akt signalling pathway, focal adhesion, cAMP signalling pathway, and Rap1 signalling pathway. Network analysis of filtered genes in poor-quality semen showed variations in pathways of purine metabolism, pyrimidine metabolism, prolactin signalling pathway and RNA cap-binding complex. It is inferred that SNP in genes involved in maintaining sperm functions could be the reason for poor-quality semen production in bulls, and the identified SNPs hold potential to be used as biomarkers for semen quality in bulls.

Idiopathic Infertility as a Feature of Genome Instability

Genome instability may play a role in severe cases of male infertility, with disrupted spermatogenesis being just one manifestation of decreased general health and increased morbidity. Here, we review the data on the association of male infertility with genetic, epigenetic, and environmental alterations, the causes and consequences, and the methods for assessment of genome instability. Male infertility research has provided evidence that spermatogenic defects are often not limited to testicular dysfunction. An increased incidence of urogenital disorders and several types of cancer, as well as overall reduced health (manifested by decreased life expectancy and increased morbidity) have been reported in infertile men. The pathophysiological link between decreased life expectancy and male infertility supports the notion of male infertility being a systemic rather than an isolated condition. It is driven by the accumulation of DNA strand breaks and premature cellular senescence. We have presented extensive data supporting the notion that genome instability can lead to severe male infertility termed “idiopathic oligo-astheno-teratozoospermia.” We have detailed that genome instability in men with oligo-astheno-teratozoospermia (OAT) might depend on several genetic and epigenetic factors such as chromosomal heterogeneity, aneuploidy, micronucleation, dynamic mutations, RT, PIWI/piRNA regulatory pathway, pathogenic allelic variants in repair system genes, DNA methylation, environmental aspects, and lifestyle factors.

Telomere Length and Male Fertility

Over the past decade, telomeres have attracted increasing attention due to the role they play in human fertility. However, conflicting results have been reported on the possible association between sperm telomere length (STL) and leukocyte telomere length (LTL) and the quality of the sperm parameters. The aim of this study was to run a comprehensive study to investigate the role of STL and LTL in male spermatogenesis and infertility. Moreover, the association between the sperm parameters and 11 candidate single nucleotide polymorphisms (SNPs), identified in the literature for their association with telomere length (TL), was investigated. We observed no associations between sperm parameters and STL nor LTL. For the individual SNPs, we observed five statistically significant associations with sperm parameters: considering a p < 0.05. Namely, ACYP2˗rs11125529 and decreased sperm motility (p = 0.03); PXK˗rs6772228 with a lower sperm count (p = 0.02); NAF1˗rs7675998 with increased probability of having abnormal acrosomes (p = 0.03) and abnormal flagellum (p = 0.04); ZNF208˗rs8105767 and reduction of sperms with normal heads (p = 0.009). This study suggests a moderate involvement of telomere length in male fertility; however, in our analyses four SNPs were weakly associated with sperm variables, suggesting the SNPs to be pleiotropic and involved in other regulatory mechanisms independent of telomere homeostasis, but involved in the spermatogenic process.

A loss-of-function variant in DNA mismatch repair gene MLH3 underlies severe oligozoospermia

Male infertility pertains to male's inability to cause pregnancy in a fertile female. It accounts for 40-50% of infertility in human. In the study, presented here, a large consanguineous family of Pakistani origin segregating male infertility in autosomal recessive manner was investigated. Exome sequencing revealed a homozygous frameshift variant [NM_001040108: c.3632delA, p.(Asn1211Metfs*49)] in DNA mismatch repair gene MLH3 (MutL Homolog) that segregated with male infertility within the family. This is the first loss-of-function homozygous variant in the MLH3 gene causing severe oligozoospermia leading to male infertility. Previous studies have demonstrated association of infertility with gene knockout in the mice.

The association of rs11457523 in HSP90AA1 with idiopathic male infertility in the Chinese population

The association of single nucleotide polymorphisms (SNPs) in heat shock protein 90 (HSP90) genes with idiopathic male infertility remains unclear. In this study, the five selected SNPs in HSP90AA1 namely rs10133307, rs10873531, rs11547523, rs11621560 and rs7145597 were genotyped in 116 idiopathic infertile males and 185 ethnically matched fertile males using the Sequenom MassARRAY assay. The role of these SNPs in male infertility was then studied using multiple genetic models. We observed that genotype distribution (p = .028) and allelic frequency (p = .032) of rs11547523 were significantly different between the infertile and fertile groups. In particular, A genotype of rs11547523 was associated with an increased risk of infertility in the allele (OR = 2.508, p = .048), dominant (OR = 2.733, p = .030) and additive models (OR = 0.366, p = .031). However, there were no significant differences in semen parameters including seminal volume (p = .452), sperm concentration (p = .727), total sperm number (p = .588), motility (p = .282) and morphology (p = .975) between A and A/G genotypes of rs11547523. These results indicate that rs11547523 in HSP90AA1 may be associated with idiopathic male infertility in the Chinese population. The outcome of this study contributes to the development of the diagnosis of male infertility.

Genetic Landscape of Nonobstructive Azoospermia and New Perspectives for the Clinic

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