Is the primary AZFc duplication a potential risk for male infertility?: A systematic review and meta-analysis

Primary azoospermia factor C duplication associated with spermatogenic impariment: a case-control study based on Y-chromosome haplogrouping in a Han Chinese population

BACKGROUND

Azoospermia factor C (AZFc) in the male-specific region of Y-chromosome (MSY) presents wide structure variation mainly due to frequent non-allele homologous recombination, leading to significant copy number variation of the AZFc-linked coding sequences involving in spermatogenesis. A large number of studies had been conducted to investigate the association between AZFc deletions and male infertility in certain Y chromosome genetic backgrounds, however, the influence of primary AZFc duplication on spermatogenesis remained controversial and the cause of the discrepant outcomes is unknown.

METHODS

In the present study, a total of 1,102 unrelated Han Chinese males without any detectable AZF deletions were recruited from 2014 to 2019, including 411 controls with normozoospermia and 691 patients with idiopathic spermatogenic failure. Using multiple paralog ratio tests (PRTs), the structure duplications were classified by the copy number of the AZFc-linked amplicons and genes. The Y-chromosome haplogroup (Y-hg) was categorized by genetyping of MSY-linked polymorphism loci. The association of primary AZFc duplication with spermatogenic phenotype was investigated in males with the same Y-hg.

RESULTS

Within Y-hg O3* group, the frequency of the gr/gr duplication in patients is significantly higher than that of controls (P = 1.29×10-3 , odds ratio (OR) 7.64, 95% confidence interval (CI) 1.79-32.57). Moreover, Y-hg O3* males with the gr/gr duplication presented a significantly lower sperm production compared with non-AZFc duplicated ones (sperm concentration: P = 1.46×10-3 ; total sperm count: P = 1.82 ×10-3 ). The b2/b3 duplication were identified clustered in Y-hg Cα2*, and the significant difference in the distribution was not observed between patients with spermatogenic failure and controls.

CONCLUSION

The results suggest that, in the Han Chinese population, the gr/gr duplication is a predisposing genetic factor for spermatogenic impairment in males harboring Y-hg O3* . Meanwhile, the b2/b3 duplication may be fixed on a yet-unidentified subbranch of Y-hg Cα2* without significantly deleterious effect on spermatogenesis. Our findings provide evidence that the difference in the Y-hg composition may cause the discrepancy on the association of AZFc duplication with spermatogenic failure among the studied populations.

High incidence of AZF duplications in clan-structured Iranian populations detected through Y chromosome sequencing read depth analysis

The ampliconic region of the human Y chromosome consists of large duplicated sequences that can undergo non-allelic homologous recombination (NAHR), resulting in structural rearrangements that may cause infertility, especially when they occur in the azoospermia factor b/c (AZFb/c) region. Although AZF duplications have long been neglected due to the technical limitations of STS-based studies that focused mainly on deletions, recent next generation sequencing (NGS) technologies provided evidence for their importance in fertility. In this study, a NGS read depth approach was used to detect AZFb/c rearrangements in 87 Iranians from different ethnic groups. The duplication frequency in Iran proved to be twice as high as in the "1000 Genomes" dataset. Interestingly, most duplications were found in patrilineal ethnic groups, possibly as a consequence of their lower male effective population size which can counteract negative selection. Moreover, we found a large 8.0 Mb duplication, resulting in a fourfold increase in the copy number of AZFc genes, which to our knowledge is the largest duplication ever reported in this region. Overall, our results suggest that it is important to consider not only AZF deletions but also duplications to investigate the causes of male infertility, especially in patrilineal clan-based populations.

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.

An NGS-based approach to identify Y-chromosome variation in non-obstructive azoospermia

Copy number variations (CNVs), including deletions and duplications on the Y chromosome, are known genetic factors in azoospermia. Therefore, it is important to identify novel pathogenic CNVs related to azoospermia. In this study, we compared CNVs detected by STS-PCR and NGS in 107 individuals with nonobstructive azoospermia (NOA). STS-PCR analysis revealed that 8.14% (9/107) of patients had AZF deletions. The highest percentage of deletions was located in the AZFc region, followed by AZFa and AZFb+c. Positive CNVs, including four duplications, six deletions and three complex CNVs, were detected using NGS methods in 12.15% (13/107) of NOA patients. Both the duplications and deletions detected in q11.223 were confirmed to increase the genetic risk for NOA. A comparison between the STS-PCR results and NGS methods revealed concordant CNV-positive results in 4 of 107 cases (3.74%). The discrepancies included 6 cases with CNVs identified by NGS but not detected by STS-PCR, and two cases were detected by STS-PCR but not by NGS. Notably, four duplications were not identified and three complex CNVs were detected as simple deletions using STS-PCR analysis. The NGS method provides comprehensive results in detecting Y chromosome-linked CNVs, including deletions and duplications, which might broaden our understanding of NOA.

Y-Chromosome Microdeletions: A Review of Prevalence, Screening, and Clinical Considerations

Deletions within the male-specific region of the Y-chromosome, known as Y-Chromosome Microdeletions (YCMs), are present in as many as 5% and 10% of severe oligospermic and azoospermic men, respectively. These microdeletions are distinguished by which segment of the Y chromosome is absent, identified as AZFa (the most proximal segment), AZFb (middle), and AZFc (distal). The reported prevalence of YCMs within the world’s populations of infertile men displays vast heterogeneity, ranging from less than 2% to over 24% based on region and ethnicity. AZFc is the most commonly identified YCM, and its phenotypic presentation provides for the highest chance for fertility through artificial reproductive techniques. Conversely, deletions identified in the subregions of AZFa, AZFb, or any combination of regions containing these segments, are associated with low probabilities of achieving pregnancy. A putative mechanism explaining this discrepancy lies within the expression of autosomal, DAZ-like genes which could serve to “rescue” wild type AZFc gene expression and hence spermatogenesis. Nevertheless, recent reports challenge this dogma and stress the importance of further analysis when an AZFb deletion is detected. The screening thresholds to determine which oligospermic and azoospermic men are tested for potential YCMs has been recently contested. More recent literature supports lowering the threshold from 5 million sperm/mL of ejaculate to 1 million/mL as the frequency of YCMs in men with sperm concentrations between 1 and 5 million sperm/mL is very low (~0.8%). As such, subsequent guidelines should recommend a lower screening threshold. While YCMs are extremely common globally, the understanding of their clinical significance in the field remains scattered and without consensus. Furthermore, very little is currently known about partial deletions within the AZFc region, such as b1/b3, b2/b3, and gr/gr. Hence, this review aimed to summarize and discuss modern trends in the epidemiology, screening guidelines, and clinical considerations pertaining to YCMs.

Xp;Yq Unbalanced Translocation with Pseudoautosomal Region Aberrations in a Natural Two-Generation Transmission

Translocations involving X and Y chromosomes rarely occur in humans and may affect reproductive function. We investigated an Xp:Yq unbalanced translocation with pseudoautosomal region (PAR) aberrations in a natural two-generation transmission. We report the case of an azoospermic male and his fertile mother without any other abnormal clinical phenotypes, except for short stature. Cytogenetic methods, including karyotyping and fluorescence in situ hybridization (FISH), revealed the translocation. Chromosomal microarray comparative genomic hybridization (array-CGH) was used to investigate the regions of Xp partial deletion and Yq partial duplication. Final chromosome karyotypes in the peripheral blood of the infertile male and his mother were 46,Y,der(X)t(X;Y)(p22.33;q11.22) and 46,X,der(X)t(X;Y)(p22.33;q11.22), respectively. Short-stature-homeobox gene deletion was responsible for the short stature in both subjects. PAR aberrations and AZFc duplication may be a direct genetic risk factor for spermatogenesis. This report further supports the use of routine karyotype analysis, FISH-based technology, and array-CGH analysis to identify derivative chromosomes in a complex rearrangement.

Partial-AZFc deletions in Chilean men with primary spermatogenic impairment: gene dosage and Y-chromosome haplogroups

PURPOSE

To investigate the association of partial-AZFc deletions in Chilean men with primary spermatogenic failure and their testicular histopathological phenotypes, analyzing the contribution of DAZ dosage, CDY1 copies, and Y-chromosome haplogroups.

SUBJECTS AND METHODS

We studied 479 Chilean men: 334 infertile patients with histological examination (233 cases with spermatogenic defects and 101 normal spermatogenesis, obstructive controls, OC), and 145 normozoospermic controls (NC). AZFc subdeletions were detected by single-tagged sequences and single nucleotide variants analysis. DAZ-copy number was quantified by real-time qPCR. Y-chromosome haplogroups (Y-hg) were hierarchically genotyped through 16 biallelic-markers.

RESULTS

The prevalence of AZFc-partial deletions was increased in cases (6%) compared with NC (1.4%) (P = 0.035). There was no difference between 143 Sertoli-cell only syndrome, 35 maturation arrest, or 35 mix atrophy patients and controls. However, gr/gr deletions were more frequent in 16 subjects with hypospermatogenesis compared with NC (P = 0.003) and OC (P = 0.013). Y-hg R was the most prevalent (~ 50%), but decreased among gr/gr deletions (21%, P = 0.03). The prevalence of Y-hg M increased in cases versus controls, both in total and non-deleted men (3.9 and 3.7% versus 0.4%, P = 0.009 and P = 0.016, respectively). Among gr/gr deletions, Y-hg H increased compared with non-deleted men (14.3% versus 0.4%, P = 0.0047).

CONCLUSION

Partial-AZFc deletions in a Chilean admixed population are associated with secretory azo/oligozoospermia and might have a role in the development of hypospermatogenesis. Low represented haplogroups, Y-hg M and Y-hg H, show an association with the occurrence of spermatogenic failure and gr/gr deletions respectively; however, additional studies are required.