Development of a high-resolution Y-chromosome microarray for improved male infertility diagnosis

Uncovering the Association Between Complete AZFc Microduplications and Spermatogenic Ability: The First Reported Series

Purpose This article aims to report the first series of men with complete AZFc microduplications and their clinical and reproductive characteristics. Methods We sampled 3000 men who presented for reproductive urology evaluation from 2012-2020, of which 104 men underwent high-resolution Y-chromosome microarray testing, and five men were identified to have complete AZFc microduplications. Medical, surgical, and reproductive histories were obtained. Semen and hormonal parameters as well as response to fertility therapies were recorded. Results Five men were identified as having complete AZFc microduplications. The mean age was 33.75 years, representing 0.2% (5/3000) of men presenting for fertility investigation, 4.8% (5/104) of men undergoing microarray testing, and 21% (5/24) of men with AZFc abnormalities. Two of the men had prior undescended testicles and one had several autoimmune processes. The mean follicle-stimulating hormone (FSH) was 5.5 IU/L, luteinizing hormone (LH) 3.6 IU/L, and testosterone 14.56 nmol/L. One man was azoospermic, one man alternated between severe oligospermia and rare non-motile sperm, one had variable parameters, with one semen analysis demonstrating azoospermia and a second demonstrating a total motile sperm count (TMSC) of 4 ×106, one man was persistently oligospermic with TMSCs ranging 3.96-12.6 ×106, and one man initially had severe oligospermia, with a mean TMSC of 1.5 ×106, which increased to 21.7 ×106 after intervention (varicocele embolization, clomiphene citrate). This last man then fathered a spontaneous pregnancy. Conclusion AZFc complete microduplications are a rare cause of spermatogenic failure but not an uncommon form of AZFc abnormality. Clinically, they represent a heterogeneous group, having a variable reproductive potential. Cases should be managed on an individual basis.

Impact of Advanced Paternal Age on Fertility and Risks of Genetic Disorders in Offspring

The average age of fathers at first pregnancy has risen significantly over the last decade owing to various variables, including a longer life expectancy, more access to contraception, later marriage, and other factors. As has been proven in several studies, women over 35 years of age have an increased risk of infertility, pregnancy problems, spontaneous abortion, congenital malformations, and postnatal issues. There are varying opinions on whether a father's age affects the quality of his sperm or his ability to father a child. First, there is no single accepted definition of old age in a father. Second, much research has reported contradictory findings in the literature, particularly concerning the most frequently examined criteria. Increasing evidence suggests that the father's age contributes to his offspring's higher vulnerability to inheritable diseases. Our comprehensive literature evaluation shows a direct correlation between paternal age and decreased sperm quality and testicular function. Genetic abnormalities, such as DNA mutations and chromosomal aneuploidies, and epigenetic modifications, such as the silencing of essential genes, have all been linked to the father's advancing years. Paternal age has been shown to affect reproductive and fertility outcomes, such as the success rate of in vitro fertilisation (IVF), intracytoplasmic sperm injection (ICSI), and premature birth rate. Several diseases, including autism, schizophrenia, bipolar disorders, and paediatric leukaemia, have been linked to the father's advanced years. Therefore, informing infertile couples of the alarming correlations between older fathers and a rise in their offspring's diseases is crucial, so that they can be effectively guided through their reproductive years.

Infertility in Men: Advances towards a Comprehensive and Integrative Strategy for Precision Theranostics

Male infertility is an increasing and serious medical concern, though the mechanism remains poorly understood. Impaired male reproductive function affects approximately half of infertile couples worldwide. Multiple factors related to the environment, genetics, age, and comorbidities have been associated with impaired sperm function. Present-day clinicians rely primarily on standard semen analysis to diagnose male reproductive potential and develop treatment strategies. To address sperm quality assessment bias and enhance analysis accuracy, the World Health Organization (WHO) has recommended standardized sperm testing; however, conventional diagnostic and therapeutic options for male infertility, including physical examination and semen standard analysis, remain ineffective in relieving the associated social burden. Instead, assisted reproductive techniques are becoming the primary therapeutic approach. In the post-genomic era, multiomics technologies that deeply interrogate the genome, transcriptome, proteome, and/or the epigenome, even at single-cell level, besides the breakthroughs in robotic surgery, stem cell therapy, and big data, offer promises towards solving semen quality deterioration and male factor infertility. This review highlights the complex etiology of male infertility, especially the roles of lifestyle and environmental factors, and discusses advanced technologies/methodologies used in characterizing its pathophysiology. A comprehensive combination of these innovative approaches in a global and multi-centric setting and fulfilling the suitable ethical consent could ensure optimal reproductive and developmental outcomes. These combinatorial approaches should allow for the development of diagnostic markers, molecular stratification classes, and personalized treatment strategies. Since lifestyle choices and environmental factors influence male fertility, their integration in any comprehensive approach is required for safe, proactive, cost-effective, and noninvasive precision male infertility theranostics that are affordable, accessible, and facilitate couples realizing their procreation dream.

Y-chromosome genes associated with sertoli cell-only syndrome identified by array comparative genome hybridization

BACKGROUND

The precise contribution of each chromosome gene or gene family in achieving male fertility is still the subject of debate. Most studies have examined male populations with heterogeneous causes of infertility, and have therefore reached controversial or uncertain conclusions. This study uses Y-chromosome array-based comparative genomic hybridization (aCGH) to examine a population of males with a uniform sertoli cell-only syndrome (SCOS) infertility phenotype.

METHODS

Initial analysis of gene copy number variations in 8 SCOS patients, with determination of the log-ratio of probe signal intensity against a DNA reference, was performed using the Y-chromosome NimbleGen aCGH. To confirm the role of candidate genes, real-time quantitative RT-PCR was used to compare 19 patients who had SCOS non-obstructive azoospermia with 15 patients who had obstructive azoospermia but normal spermatogenesis.

RESULTS

Our initial aCGH experiments identified CDY1a and CDY1b double deletions in all 8 patients who had total germ cell depletion. However, 5 patients had DAZ1/2 and DAZ3/4 deletions, 1 patient had a DAZ2 and DAZ3/4 deletion, and 2 patients had no DAZ1/2 or DAZ3/4 deletions. Examination of testicular mRNA expression in another 19 patients with SCOS indicated all patients had no detectable levels of CDY1.

CONCLUSIONS

Our findings indicate that CDY1 deletion in SCOS patients, and analysis of the expression of DAZ and CDY1 genes using aCGH and quantitative RT-PCR, may be useful to predict the presence of mature spermatozoa.

Genome medicine in male infertility: From karyotyping to single-cell analysis

Male infertility is a multifactorial pathological condition that affects half of infertile couples. The majority of cases are categorized as idiopathic, especially in cases of nonobstructive azoospermia (NOA). An increasing number of genetic abnormalities have been shown to cause spermatogenic impairment with the development of microarray technologies and next-generation sequencing (NGS), moving beyond classical karyotype and polymerase chain reaction analyses of targeted genes. However, the majority of gene mutations, such as Klinefelter syndrome, azoospermia factor microdeletion, or congenital bilateral absence of the vas deferens, fail to function in a one gene-one phenotype manner. Single-cell transcriptome analysis performed using human testicular samples has begun to be published, which has brought about a more comprehensive understanding of testicular pathology. NGS also enables omics approaches, which provide more powerful tools to interrogate the genome, epigenome, transcriptome, and proteome. Simultaneously, the involvement of environmental factors and comorbidities, which may potentially regulate epigenetic factors, has been shown, resulting in a more complex understanding of the pathophysiology of spermatic disorders, especially NOA. The combination of phenotypic data and large amounts of bioinformatical data obtained by NGS may provide a more comprehensive understanding of the pathophysiology of male infertility, which will contribute not only to a diagnosis but also to the proper selection of infertility treatment and the development of new treatment modalities for male infertility.

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

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

Genetic testing for men with infertility: techniques and indications

Genetic testing is an integral component in the workup of male infertility as genetic conditions may be responsible for up to 15% of all cases. Currently, three genetic tests are commonly performed and recommended by major urologic associations: karyotype analysis (KA), Y-chromosome microdeletion testing, and CFTR mutation testing. Despite widespread adoption of these tests, an etiology for infertility remains elusive in up to 80% of cases. Recent work has identified intriguing new targets for genetic testing which may soon see clinical relevance. This review will discuss the indications and techniques for currently offered genetic tests and briefly explore ongoing research directions within this field.

Deletion of b1/b3 shows risk for expanse of Yq microdeletion in male offspring: Case report of novel Y chromosome variations

RATIONALE

This study aimed to report 1 family case with novel Y chromosome structural variations by an established next-generation sequencing (NGS) method using unique STSs.

PATIENT CONCERNS

The case studied was from a family with a father and son (the proband). G-band staining was used for karyotype analysis. Y chromosome microdeletions were detected by sequence-tagged site (STS)-PCR analysis and a new NGS screening strategy.

DIAGNOSES

Semen analysis showed that the proband was azoospermic. The patient had an abnormal karyotype (45,X[48%]/46,XY[52%]). His father exhibited a normal karyotype. STS-PCR analysis showed that the proband had a deletion of the AZFb+c region, and his father had no deletion of STS markers examined. The sequencing method revealed that the patient had DNA sequence deletions from nt 20099846 to nt 28365090 (8.3 Mb), including the region from yel4 to the Yq terminal, and his father exhibited a deletion of b1/b3 and duplication of gr/gr.

INTERVENTIONS

The proband was advised to undergo genetic counseling, and consider the use of sperm from a sperm bank or adoption to become a father.

OUTCOMES

The proband was azoospermic. AZFc partial deletions may produce a potential risk for large AZFb+c deletions or abnormal karyotypes causing spermatogenic failure in men.

LESSONS

The NGS method can be considered a clinical diagnostic tool to detect Y chromosome microdeletions. The partial AZFc deletions and/or duplications can be a risk of extensive deletions in offspring.

Cytogenetic and molecular study of 370 infertile men in South India highlighting the importance of copy number variations by multiplex ligation-dependent probe amplification

Male infertility is a common and severe problem affecting 7% of population. The main objective of this study is to identify the chromosomal abnormalities, Y microdeletions in infertile men and also to access the frequency of abnormal sperm count. Based on the sperm count and viability, the infertile men were grouped as Azoospermia, Asthenospermia, Oligospermia and the remaining as Idiopathic infertility. A total of 370 infertile men and 60 normal control men were recruited. Chromosomal abnormalities were identified in 3 men (3/370). The prevalence of Y microdeletions in the infertile group is 8/370 in the Azoospermia factor (AZF) region with four AZFc deletion/duplication, two AZFa deletion, one AZF b & AZFc deletion and one case of total AZF a, AZFb & AZFc deletion. However, only five cases of Y microdeletions were identified by Multiplex PCR but an additional three cases by MLPA (Multiplex ligation-dependent probe amplification). Fluorescence in situ hybridisation also confirmed the deletions. Here, we performed MLPA post-multiplex PCR, and our study revealed good yield of the Y microdeletion identification. The partial duplications which are difficult to be identified can now be easily identified by MLPA, and hence, we recommend MLPA as the choice of investigation compared to multiplex PCR for infertile men.

Methodology for Y Chromosome Capture: A complete genome sequence of Y chromosome using flow cytometry, laser microdissection and magnetic streptavidin-beads

This study is a comparison of the efficiency of three technologies used for Y chromosome capture and the next-generation sequencing (NGS) technologies applied for determining its whole sequence. Our main findings disclose that streptavidin-biotin magnetic particle-based capture methodology offers better and a deeper sequence coverage for Y chromosome capture, compared to chromosome sorting and microdissection procedures. Moreover, this methodology is less time consuming and the most selective for capturing only Y chromosomal material, in contrast with other methodologies that result in considerable background material from other, non-targeted chromosomes. NGS results compared between two platforms, NextSeq 500 and SOLID 5500xl, produce the same coverage results. This is the first study to explore a methodological comparison of Y chromosome capture and genetic analysis. Our results indicate an improved strategy for Y chromosome research with applications in several scientific fields where this chromosome plays an important role, such as forensics, medical sciences, molecular anthropology and cancer sciences.

The control of male fertility by spermatid-specific factors: searching for contraceptive targets from spermatozoon's head to tail

Male infertility due to abnormal spermatozoa has been reported in both animals and humans, but its pathogenic causes, including genetic abnormalities, remain largely unknown. On the other hand, contraceptive options for men are limited, and a specific, reversible and safe method of male contraception has been a long-standing quest in medicine. Some progress has recently been made in exploring the effects of spermatid-specifical genetic factors in controlling male fertility. A comprehensive search of PubMed for articles and reviews published in English before July 2016 was carried out using the search terms 'spermiogenesis failure', 'globozoospermia', 'spermatid-specific', 'acrosome', 'infertile', 'manchette', 'sperm connecting piece', 'sperm annulus', 'sperm ADAMs', 'flagellar abnormalities', 'sperm motility loss', 'sperm ion exchanger' and 'contraceptive targets'. Importantly, we have opted to focus on articles regarding spermatid-specific factors. Genetic studies to define the structure and physiology of sperm have shown that spermatozoa appear to be one of the most promising contraceptive targets. Here we summarize how these spermatid-specific factors regulate spermiogenesis and categorize them according to their localization and function from spermatid head to tail (e.g., acrosome, manchette, head-tail conjunction, annulus, principal piece of tail). In addition, we emphatically introduce small-molecule contraceptives, such as BRDT and PPP3CC/PPP3R2, which are currently being developed to target spermatogenic-specific proteins. We suggest that blocking the differentiation of haploid germ cells, which rarely affects early spermatogenic cell types and the testicular microenvironment, is a better choice than spermatogenic-specific proteins. The studies described here provide valuable information regarding the genetic and molecular defects causing male mouse infertility to improve our understanding of the importance of spermatid-specific factors in controlling fertility. Although a male contraceptive 'pill' is still many years away, research into the production of new small-molecule contraceptives targeting spermatid-specific proteins is the right avenue.

Association and meta-analysis of HLA and non-obstructive azoospermia in the Han Chinese population

The exact aetiology and pathogenesis of most non-obstructive azoospermia (NOA) are still unknown. The previous two genomewide association studies (GWASs) have identified three different loci within the HLA region for NOA in the Han Chinese population, including rs3129878, rs498422 and rs7194. To further validate the risk of three GWAS-linked loci for NOA, we conducted a case-control study of these three risk loci in an independent Han Chinese male population, with 603 NOA patients and 610 controls. Furthermore, we also performed a meta-analysis of five studies on these three NOA-risk loci. The case-control study strongly suggested a significant association between loci rs3129878, rs498422 and rs7194 and NOA (P = 6.75 × 10^-21 (OR = 2.2586), P = 0.0060 (OR = 1.4013) and P = 0.0128 (OR = 1.2626) respectively). Our meta-analyses also supported the susceptibility of these three risk loci to NOA (P < 0.01). The risk variants within the HLA region potentially have a strong effect on males at risk of NOA, and may serve as diagnostic markers for male infertility. However, considering genetic difference between different populations, future validating studies in larger independent samples and animal experiments are suggested.

Novel Y-chromosomal microdeletions associated with non-obstructive azoospermia uncovered by high throughput sequencing of sequence-tagged sites (STSs)

Y-chromosomal microdeletion (YCM) serves as an important genetic factor in non-obstructive azoospermia (NOA). Multiplex polymerase chain reaction (PCR) is routinely used to detect YCMs by tracing sequence-tagged sites (STSs) in the Y chromosome. Here we introduce a novel methodology in which we sequence 1,787 (post-filtering) STSs distributed across the entire male-specific Y chromosome (MSY) in parallel to uncover known and novel YCMs. We validated this approach with 766 Chinese men with NOA and 683 ethnically matched healthy individuals and detected 481 and 98 STSs that were deleted in the NOA and control group, representing a substantial portion of novel YCMs which significantly influenced the functions of spermatogenic genes. The NOA patients tended to carry more and rarer deletions that were enriched in nearby intragenic regions. Haplogroup O2* was revealed to be a protective lineage for NOA, in which the enrichment of b1/b3 deletion in haplogroup C was also observed. In summary, our work provides a new high-resolution portrait of deletions in the Y chromosome.

Testis-Specific Y-Centric Protein-Protein Interaction Network Provides Clues to the Etiology of Severe Spermatogenic Failure

Pinpointing causal genes for spermatogenic failure (SpF) on the Y chromosome has been an ever daunting challenge with setbacks during the past decade. Since complex diseases result from the interaction of multiple genes and also display considerable missing heritability, network analysis is more likely to explicate an etiological molecular basis. We therefore took a network medicine approach by integrating interactome (protein-protein interaction (PPI)) and transcriptome data to reconstruct a Y-centric SpF network. Two sets of seed genes (Y genes and SpF-implicated genes (SIGs)) were used for network reconstruction. Since no PPI was observed among Y genes, we identified their common immediate interactors. Interestingly, 81% (N = 175) of these interactors not only interacted directly with SIGs, but also they were enriched for differentially expressed genes (89.6%; N = 43). The SpF network, formed mainly by the dys-regulated interactors and the two seed gene sets, comprised three modules enriched for ribosomal proteins and nuclear receptors for sex hormones. Ribosomal proteins generally showed significant dys-regulation with RPL39L, thought to be expressed at the onset of spermatogenesis, strongly down-regulated. This network is the first global PPI network pertaining to severe SpF and if experimentally validated on independent data sets can lead to more accurate diagnosis and potential fertility recovery of patients.

A PLK4 mutation causing azoospermia in a man with Sertoli cell-only syndrome

About 15% of couples wishing to have children are infertile; approximately half these cases involve a male factor. Polo-like kinase 4 (PLK-4) is a member of the polo protein family and a key regulator of centriole duplication. Male mice with a point mutation in the Plk4 gene show azoospermia associated with germ cell loss. Mutational analysis of 81 patients with azoospermia and Sertoli cell-only syndrome (SCOS) identified one man with a heterozygous 13-bp deletion in the Ser/Thr kinase domain of PLK4. Division of centrioles occurred in wild-type PLK4-transfected cells, but was hampered in PLK-4-mutant transfectants, which also showed abnormal nuclei. Thus, this PLK4 mutation might be a cause of human SCOS and nonobstructive azoospermia.

Microarray Analysis of Copy Number Variants on the Human Y Chromosome Reveals Novel and Frequent Duplications Overrepresented in Specific Haplogroups

BACKGROUND

The human Y chromosome is almost always excluded from genome-wide investigations of copy number variants (CNVs) due to its highly repetitive structure. This chromosome should not be forgotten, not only for its well-known relevance in male fertility, but also for its involvement in clinical phenotypes such as cancers, heart failure and sex specific effects on brain and behaviour.

RESULTS

We analysed Y chromosome data from Affymetrix 6.0 SNP arrays and found that the signal intensities for most of 8179 SNP/CN probes in the male specific region (MSY) discriminated between a male, background signals in a female and an isodicentric male containing a large deletion of the q-arm and a duplication of the p-arm of the Y chromosome. Therefore, this SNP/CN platform is suitable for identification of gain and loss of Y chromosome sequences. In a set of 1718 males, we found 25 different CNV patterns, many of which are novel. We confirmed some of these variants by PCR or qPCR. The total frequency of individuals with CNVs was 14.7%, including 9.5% with duplications, 4.5% with deletions and 0.7% exhibiting both. Hence, a novel observation is that the frequency of duplications was more than twice the frequency of deletions. Another striking result was that 10 of the 25 detected variants were significantly overrepresented in one or more haplogroups, demonstrating the importance to control for haplogroups in genome-wide investigations to avoid stratification. NO-M214(xM175) individuals presented the highest percentage (95%) of CNVs. If they were not counted, 12.4% of the rest included CNVs, and the difference between duplications (8.9%) and deletions (2.8%) was even larger.

CONCLUSIONS

Our results demonstrate that currently available genome-wide SNP platforms can be used to identify duplications and deletions in the human Y chromosome. Future association studies of the full spectrum of Y chromosome variants will demonstrate the potential involvement of gain or loss of Y chromosome sequence in different human phenotypes.

Effects of increased paternal age on sperm quality, reproductive outcome and associated epigenetic risks to offspring

Over the last decade, there has been a significant increase in average paternal age when the first child is conceived, either due to increased life expectancy, widespread use of contraception, late marriages and other factors. While the effect of maternal ageing on fertilization and reproduction is well known and several studies have shown that women over 35 years have a higher risk of infertility, pregnancy complications, spontaneous abortion, congenital anomalies, and perinatal complications. The effect of paternal age on semen quality and reproductive function is controversial for several reasons. First, there is no universal definition for advanced paternal ageing. Secondly, the literature is full of studies with conflicting results, especially for the most common parameters tested. Advancing paternal age also has been associated with increased risk of genetic disease. Our exhaustive literature review has demonstrated negative effects on sperm quality and testicular functions with increasing paternal age. Epigenetics changes, DNA mutations along with chromosomal aneuploidies have been associated with increasing paternal age. In addition to increased risk of male infertility, paternal age has also been demonstrated to impact reproductive and fertility outcomes including a decrease in IVF/ICSI success rate and increasing rate of preterm birth. Increasing paternal age has shown to increase the incidence of different types of disorders like autism, schizophrenia, bipolar disorders, and childhood leukemia in the progeny. It is thereby essential to educate the infertile couples on the disturbing links between increased paternal age and rising disorders in their offspring, to better counsel them during their reproductive years.

Individualized medicine enabled by genomics in Saudi Arabia

The biomedical research sector in Saudi Arabia has recently received special attention from the government, which is currently supporting research aimed at improving the understanding and treatment of common diseases afflicting Saudi Arabian society. To build capacity for research and training, a number of centres of excellence were established in different areas of the country. Among these, is the Centre of Excellence in Genomic Medicine Research (CEGMR) at King Abdulaziz University, Jeddah, with its internationally ranked and highly productive team performing translational research in the area of individualized medicine. Here, we present a panorama of the recent trends in different areas of biomedical research in Saudi Arabia drawing from our vision of where genomics will have maximal impact in the Kingdom of Saudi Arabia. We describe advances in a number of research areas including; congenital malformations, infertility, consanguinity and pre-implantation genetic diagnosis, cancer and genomic classifications in Saudi Arabia, epigenetic explanations of idiopathic disease, and pharmacogenomics and personalized medicine. We conclude that CEGMR will continue to play a pivotal role in advances in the field of genomics and research in this area is facing a number of challenges including generating high quality control data from Saudi population and policies for using these data need to comply with the international set up.

Y chromosome azoospermia factor region microdeletions and transmission characteristics in azoospermic and severe oligozoospermic patients

Spermatogenesis is an essential reproductive process that is regulated by many Y chromosome specific genes. Most of these genes are located in a specific region known as the azoospermia factor region (AZF) in the long arm of the human Y chromosome. AZF microdeletions are recognized as the most frequent structural chromosomal abnormalities and are the major cause of male infertility. Assisted reproductive techniques (ART) such as intra-cytoplasmic sperm injection (ICSI) and testicular sperm extraction (TESE) can overcome natural fertilization barriers and help a proportion of infertile couples produce children; however, these techniques increase the transmission risk of genetic defects. AZF microdeletions and their associated phenotypes in infertile males have been extensively studied, and different AZF microdeletion types have been identified by sequence-tagged site polymerase chain reaction (STS-PCR), suspension array technology (SAT) and array-comparative genomic hybridization (aCGH); however, each of these approaches has limitations that need to be overcome. Even though the transmission of AZF microdeletions has been reported worldwide, arguments correlating ART and the incidence of AZF microdeletions and explaining the occurrence of de novo deletions and expansion have not been resolved. Using the newest findings in the field, this review presents a systematic update concerning progress in understanding the functions of AZF regions and their associated genes, AZF microdeletions and their phenotypes and novel approaches for screening AZF microdeletions. Moreover, the transmission characteristics of AZF microdeletions and the future direction of research in the field will be specifically discussed.