Sperm mitochondrial DNA deletion in Iranian infertiles with asthenozoospermia

Genetics of male infertility

PURPOSE OF REVIEW

The aim of this study was to outline the role of genetic abnormalities, including chromosomal anomalies, single-gene mutations, epigenetic changes, and mitochondrial DNA (mtDNA) defects, in male factor infertility.

RECENT FINDINGS

Recent advances in genetic research have brought incredible new perspectives to understanding male infertility, thanks in large part to next-generation sequencing. Chromosomal abnormalities like Klinefelter syndrome and Y chromosome microdeletions remain key contributors, with new insights into their variable presentations and impact on sperm retrieval. Advanced discoveries in genes such as CFTR and ADGRG2 have reframed our approach to conditions like CBAVD, while epigenetic disruptions and mitochondrial DNA mutations are revealing previously unrecognized mechanisms behind impaired spermatogenesis and sperm motility. Rare copy number variations and genetic syndromes like Kallmann and Noonan further underscore the complex interplay between systemic disorders and male fertility.

SUMMARY

The field of genetic infertility is rapidly evolving, offering new insights into the molecular mechanisms behind impaired spermatogenesis and fertility. These findings highlight the importance of integrating genetic testing into infertility evaluations to guide personalized management strategies.

A lack of a definite correlation between male sub-fertility and single nucleotide polymorphisms in sperm mitochondrial genes MT-CO3, MT-ATP6 and MT-ATP8

BACKGROUND

An inability of a man to conceive a potentially fertile woman after a year of unprotected intercourse is defined as male infertility. It is reported that 30-40% of males in their reproductive years have abnormalities in sperm production, either qualitatively or quantitatively, or both. However, genetic factors result in up to 15% of male infertility cases. The present study aimed to analyze the possible correlations between sub-fertility and polymorphisms in sperm mitochondrial CO3, ATP6 and ATP8 genes in sub-fertile men.

METHODS AND RESULTS

For 67 sub-fertile and 44 fertile male samples, Sanger sequencing of selected mitochondrial DNA genes was done. A total of twelve SNPs in the MT-CO3 gene: rs2248727, rs7520428, rs3134801, rs9743, rs28358272, rs2853824, rs2856985, rs2854139, rs41347846, rs28380140, rs3902407, and 28,411,821, fourteen SNPs in the MT-ATP6: rs2001031, rs2000975, rs2298011, rs7520428, rs9645429, rs112660509, rs6650105, rs6594033, rs6594034, rs6594035, rs3020563, rs28358887, rs2096044, and rs9283154, and ten SNPs in the MT-ATP8: rs9285835, rs9285836, rs9283154, rs8179289, rs121434446, rs1116906, rs2153588, rs1116905, rs1116907, and rs3020563 were detected in the case and control groups at different nucleotide positions. Only the rs7520428 in the MT-CO3 and MT-ATP6 showed a statistically significant difference between sub-fertile and fertile groups in the genotype's and allele's frequency test (P < 0.0001 for both).

CONCLUSION

The results of our study suggest that male sub-fertility is linked with rs7520428 SNP in MT-CO3 and MT-ATP6. The studied polymorphic variations in the MT-ATP8 gene, on the contrary, did not reveal any significant association with male sub-fertility.

Associations of Sperm mtDNA Copy Number, DNA Fragmentation Index, and Reactive Oxygen Species With Clinical Outcomes in ART Treatments

Recent studies have suggested that sperm mitochondrial DNA copy number (mtDNA-CN), DNA fragmentation index (DFI), and reactive oxygen species (ROS) content are crucial to sperm function. However, the associations between these measurements and embryo development and pregnancy outcomes in assisted reproductive technology (ART) remain unclear. Semen samples were collected from 401 participants, and seminal quality, parameters of sperm concentration, motility, and morphology were analyzed by a computer-assisted sperm analysis system. DFI, mtDNA-CN, and ROS levels were measured using sperm chromatin structure assay, real-time quantitative polymerase chain reaction, and ROS assay, respectively. Among the participants, 126 couples underwent ART treatments, including in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), and 79 of the couples had embryos transferred. In 401 semen samples, elevated mtDNA-CN and DFI were associated with poor seminal quality. In 126 ART couples, only mtDNA-CN was negatively correlated with the fertilization rate, but this correlation was not significant after adjusting for male age, female age, seminal quality, ART strategy, number of retrieved oocytes, controlled stimulation protocols, and cycle rank. Regarding pregnancy outcomes, sperm mtDNA-CN, ROS, and DFI were not associated with the clinical pregnancy rate or live birth rate in 79 transferred cases. In conclusion, increased mtDNA-CN and DFI in sperm jointly contributed to poor seminal quality, but sperm mtDNA-CN, ROS, and DFI were not associated with clinical outcomes in ART.

Lack of association between single polymorphic variants of the mitochondrial nicotinamide adenine dinucleotide dehydrogenase 3, and 4L (MT-ND3 and MT-ND4L) and male infertility

Male infertility is a multifactorial condition associated with different genetic abnormalities in at least 15%-30% of cases. The purpose of this study was to identify suspected correlations between infertility and polymorphisms in mitochondrial NADH dehydrogenase subunits 3 and 4L (MT-ND3 and MT-ND4L) in subfertile male spermatozoa. Sanger sequencing of the mitochondrial DNA target genes was performed on 68 subfertile and 44 fertile males. Eight single nucleotide polymorphisms (SNPs) in MT-ND3 (rs2853826, rs28435660, rs193302927, rs28358278, rs41467651, rs3899188, rs28358277 and rs28673954) and seven SNPs in MT-ND4L (rs28358280, rs28358281, rs28358279, rs2853487, rs2853488, rs193302933 and rs28532881) were detected and genotyped. The genotypes and allele frequencies of the study population have shown a lack of statistically significant association between MT-ND3 and MT-ND4L SNPs and male infertility. However, no statistically significant association was found between the asthenozoospermia, oligozoospermia, teratozoospermia, asthenoteratozoospermia, oligoasthenoteratozoospermia and oligoteratozoospermia subgroups of subfertile males. However, rs28358278 genotype of the MT-ND3 gene was reported in the subfertile group but not in the fertile group, which implies a possible role of this SNP in male infertility. In conclusion, the investigated polymorphic variants in the MT-ND3 and MT-ND4L genes did not show any significant association with the occurrence of male infertility. Further studies are required to evaluate these findings. Moreover, the subfertile individuals who exhibit a polymorphism at rs28358278 require further monitoring and evaluation.

Mitochondrial nicotinamide adenine dinucleotide hydride dehydrogenase (NADH) subunit 4 (MTND4) polymorphisms and their association with male infertility

PURPOSE

The purpose of the present study was to determine the relationship between infertility and the polymorphisms of mitochondrial NADH dehydrogenase subunit 4 (MTND4) by spermatozoa analysis in fertile and subfertile men.

METHODS

Samples were divided into 68 subfertile men (case group) and 44 fertile men (control group). After semen analysis, samples were purified. The whole genome was extracted using a QIAamp DNA Mini Kit and the mitochondrial DNA was amplified by using the REPLI-g Mitochondrial DNA Kit. Polymerase chain reaction (PCR) was used to amplify the MT-ND4 gene. Then, samples were purified and sequenced using the Sanger method.

RESULTS

Twenty-five single-nucleotide polymorphisms (SNPs) were identified in the MTND4 gene. The genotype frequencies of the study population showed a statistically significant association between rs2853495 G>A (Gly320Gly) and male infertility (P = 0.0351). Similarly, the allele frequency test showed that rs2853495 G>A (Gly320Gly) and rs869096886 A>G (Leu164Leu) were significantly associated with male infertility (adjusted OR = 2.616, 95% CI = 1.374-4.983, P = 0.002; adjusted OR = 2.237, 95% CI = 1.245-4.017, P = 0.007, respectively).

CONCLUSION

In conclusion, our findings suggested that male infertility was correlated with rs2853495 and rs869096886 SNPs in MTND4.

Potential of Mitochondrial Genome Editing for Human Fertility Health

Mitochondrial DNA (mtDNA) encodes vital proteins and RNAs for the normal functioning of the mitochondria. Mutations in mtDNA leading to mitochondrial dysfunction are relevant to a large spectrum of diseases, including fertility disorders. Since mtDNA undergoes rather complex processes during gametogenesis and fertilization, clarification of the changes and functions of mtDNA and its essential impact on gamete quality and fertility during this process is of great significance. Thanks to the emergence and rapid development of gene editing technology, breakthroughs have been made in mitochondrial genome editing (MGE), offering great potential for the treatment of mtDNA-related diseases. In this review, we summarize the features of mitochondria and their unique genome, emphasizing their inheritance patterns; illustrate the role of mtDNA in gametogenesis and fertilization; and discuss potential therapies based on MGE as well as the outlook in this field.

Correlation of Sperm Mitochondrial DNA 7345 bp and 7599 bp Deletions with Asthenozoospermia in Jordanian Population

BACKGROUND

Alterations in sperm mitochondrial DNA (mtDNA) affect the functions of some OXPHOS proteins which will affect sperm motility and may be associated with asthenozoospermia. The purpose of this study was to investigate the correlation between 7599-bp and 7345-bp sperm mtDNA deletions and asthenozoospermia in Jordan.

METHODS

Semen specimens from 200 men including 121 infertile and 79 healthy individuals were collected at the Royal Jordanian Medical Services In-vitro fertilization (IVF) units. The mtDNA was extracted followed by mtDNA amplification. Polymerase chain reaction (PCR) was conducted for the target sequences, then DNA sequencing was performed for the PCR products. Chi-square, Fisher's and Spearman's tests were used to calculate the correlation.

RESULTS

The results showed a significant correlation between the presence of 7599-bp mtDNA deletion and infertility where the frequency of the 7599-bp deletion was 63.6% in the infertile group compared to the fertile 34.2% (p<0.001, (OR=3.37, 95% CI=1.860 to 6.108)). Additionally, the sperm motility showed a significant association with the frequency of the 7599-bp deletion (p=0.001, r=-0.887). The 7345-bp mtDNA deletion showed no assoctiation with the infertility (p=0.65, (OR=0.837, 95% CI= 0.464-1.51)) or asthenozoospermia (p=0.98, r=0.008).

CONCLUSION

We demonstrated a significant correlation between asthenozoospermia and the 7599-bp mtDNA deletion but not the 7345-bp mtDNA deletion in the infertile men in Jordan. Screening for deletions in sperm mtDNA can be used as a pre-diagnostic molecular marker for male infertility.

Attenuation of aquaporin-3 may be contributing to low sperm motility and is associated with activated caspase-3 in asthenozoospermic individuals

Aquaporins play a crucial in transportation of water and solutes across cell membranes but their roles in male fertility are controversial. This study aimed to determine association of the expression level of aquaporin-3 (AQP3) and caspase-3 (CASP3) activity with sperm motility in asthenozoospermic individuals. Thirty-five asthenozoospermic and 35 normozoospermic individuals, participated in this study. Sperm chromatin structure assay (SCSA) for estimating of the DNA-damaged spermatozoa and Fluorescein-labelled inhibitors of caspases for assessment of active CASP3 were used by flow cytometry. Gene and protein expressions of AQP3 and CASP3 were assessed by real-time PCR and flow cytometry respectively. The AQP3 gene expression level in asthenozoospermic individuals was significantly lower than that of normozoospermic group whereas it was higher for the CASP3 gene expression (p < .01). The SCSA data in asthenozoospermic was significantly higher than that of normozoospermic group (p < .01). There was a negative and significant correlation between attenuated AQP3 protein level with activated CASP3 and SCSA in the asthenozoospermic group. We showed that the attenuated AQP3 level may contribute to low sperm motility via reducing glycerol for energy production in sperm tails of asthenozoospermia. Increasing CASP3 activity could indirectly show the status of active apoptosis in individuals with asthenozoospermia.

Mitochondria: their role in spermatozoa and in male infertility

BACKGROUND

The best-known role of spermatozoa is to fertilize the oocyte and to transmit the paternal genome to offspring. These highly specialized cells have a unique structure consisting of all the elements absolutely necessary to each stage of fertilization and to embryonic development. Mature spermatozoa are made up of a head with the nucleus, a neck, and a flagellum that allows motility and that contains a midpiece with a mitochondrial helix. Mitochondria are central to cellular energy production but they also have various other functions. Although mitochondria are recognized as essential to spermatozoa, their exact pathophysiological role and their functioning are complex. Available literature relative to mitochondria in spermatozoa is dense and contradictory in some cases. Furthermore, mitochondria are only indirectly involved in cytoplasmic heredity as their DNA, the paternal mitochondrial DNA, is not transmitted to descendants.

OBJECTIVE AND RATIONAL

This review aims to summarize available literature on mitochondria in spermatozoa, and, in particular, that with respect to humans, with the perspective of better understanding the anomalies that could be implicated in male infertility.

SEARCH METHODS

PubMed was used to search the MEDLINE database for peer-reviewed original articles and reviews pertaining to human spermatozoa and mitochondria. Searches were performed using keywords belonging to three groups: 'mitochondria' or 'mitochondrial DNA', 'spermatozoa' or 'sperm' and 'reactive oxygen species' or 'calcium' or 'apoptosis' or signaling pathways'. These keywords were combined with other relevant search phrases. References from these articles were used to obtain additional articles.

OUTCOMES

Mitochondria are central to the metabolism of spermatozoa and they are implicated in energy production, redox equilibrium and calcium regulation, as well as apoptotic pathways, all of which are necessary for flagellar motility, capacitation, acrosome reaction and gametic fusion. In numerous cases, alterations in one of the aforementioned functions could be linked to a decline in sperm quality and/or infertility. The link between the mitochondrial genome and the quality of spermatozoa appears to be more complex. Although the quantity of mtDNA, and the existence of large-scale deletions therein, are inversely correlated to sperm quality, the effects of mutations seem to be heterogeneous and particularly related to their pathogenicity.

WIDER IMPLICATIONS

The importance of the role of mitochondria in reproduction, and particularly in gamete quality, has recently emerged following numerous publications. Better understanding of male infertility is of great interest in the current context where a significant decline in sperm quality has been observed.

Mitochondria, spermatogenesis, and male infertility - An update

The incorporation of mitochondria in the eukaryotic cell is one of the most enigmatic events in the course of evolution. This important organelle was thought to be only the powerhouse of the cell, but was later learnt to perform many other indispensable functions in the cell. Two major contributions of mitochondria in spermatogenesis concern energy production and apoptosis. Apart from this, mitochondria also participate in a number of other processes affecting spermatogenesis and fertility. Mitochondria in sperm are arranged in the periphery of the tail microtubules to serve to energy demand for motility. Apart from this, the role of mitochondria in germ cell proliferation, mitotic regulation, and the elimination of germ cells by apoptosis are now well recognized. Eventually, mutations in the mitochondrial genome have been reported in male infertility, particularly in sluggish sperm (asthenozoospermia); however, heteroplasmy in the mtDNA and a complex interplay between the nucleus and mitochondria affect their penetrance. In this article, we have provided an update on the role of mitochondria in various events of spermatogenesis and male fertility and on the correlation of mitochondrial DNA mutations with male infertility.

Genetic aspects of idiopathic asthenozoospermia as a cause of male infertility

Infertility is a worldwide problem affecting about 15% of couples trying to conceive. Asthenozoospermia (AZS) is one of the major causes of male infertility, diagnosed by reduced sperm motility, and has no effective therapeutic treatment. To date, a few genes have been found to be associated with AZS in humans and mice, but in most of cases its molecular aetiology remains unknown. Genetic causes of AZS may include chromosomal abnormalities, specific mutations of nuclear and mitochondrial genes. However recently, epigenetic factors, altered microRNAs expression signature, and proteomics have shed light on the pathophysiological basis of AZS. This review article summarises the reported genetic causes of AZS.

Large-scale mtDNA deletions as genetic biomarkers for susceptibility to male infertility: A systematic review and meta-analysis

Several complex rearrangements such as deletions in mitochondrial DNA (mtDNA) have been identified in sperm deficiencies. This study aimed to investigate the association of common mtDNA deletions with male infertility using a meta-analysis approach. Standard databases were systematically searched to discover relevant studies. Pooled odds ratios (ORs) with corresponding 95% confidence intervals (CI) were estimated to analyze the association of mtDNA deletions with male infertility. Our data revealed a significant association between a common 4977-bp deletion and an increased risk of male infertility. A similar association was observed in an Asian population. Stratified analysis by infertility phenotype showed significant associations between the 4977-bp deletion and increased risk of asthenozoospermia, oligoasthenoteratozoospermia, and asthenoteratozoospermia. In addition, significant associations were found in studies with sample sizes >100, age of participants <45 years, subject selection according to WHO criteria, and studies of moderate to high quality. Regarding the other common mtDNA deletions, significant associations were observed between 7436-bp, 7599-bp, and 4866-bp deletions and the risk of male infertility. Our findings suggest that the 4977-bp deletion might be a risk factor for male infertility, especially in an ethnic and infertility phenotype dependent manner.

Molecular Changes Induced by Oxidative Stress that Impair Human Sperm Motility

A state of oxidative stress (OS) and the presence of reactive oxygen species (ROS) in the male reproductive tract are strongly correlated with infertility. While physiological levels of ROS are necessary for normal sperm functioning, elevated ROS production can overwhelm the cell's limited antioxidant defenses leading to dysfunction and loss of fertilizing potential. Among the deleterious pleiotropic impacts arising from OS, sperm motility appears to be particularly vulnerable. Here, we present a mechanistic account for how OS contributes to altered sperm motility profiles. In our model, it is suggested that the abundant polyunsaturated fatty acids (PUFAs) residing in the sperm membrane serve to sensitize the male germ cell to ROS attack by virtue of their ability to act as substrates for lipid peroxidation (LPO) cascades. Upon initiation, LPO leads to dramatic remodeling of the composition and biophysical properties of sperm membranes and, in the case of the mitochondria, this manifests in a dissipation of membrane potential, electron leakage, increased ROS production and reduced capacity for energy production. This situation is exacerbated by the production of cytotoxic LPO byproducts such as 4-hydroxynonenal, which dysregulate molecules associated with sperm bioenergetic pathways as well as the structural and signaling components of the motility apparatus. The impact of ROS also extends to lesions in the paternal genome, as is commonly seen in the defective spermatozoa of asthenozoospermic males. Concluding, the presence of OS in the male reproductive tract is strongly and positively correlated with reduced sperm motility and fertilizing potential, thus providing a rational target for the development of new therapeutic interventions.

4,977-bp human mitochondrial DNA deletion is associated with asthenozoospermic infertility in Jordan

Male infertility is commonly associated with sperm abnormalities including asthenozoospermia. The molecular basis of asthenozoospermia was linked to mitochondrial DNA (mtDNA) mutations. The 4,977-bp human mtDNA deletion is one of the most common mutations of spermatozoa and results in loss of about 33% of the mitochondrial genome. In this preliminary study, we aimed to investigate the presence of 4,977-bp mtDNA deletion in asthenozoospermic infertile men in Jordan. Semen specimens of 120 asthenozoospermic infertile men and 80 normozoospermic individuals were collected at the in vitro fertilization unit. MtDNA was extracted after the enrichment of spermatozoa; then, polymerase chain reaction was performed using 4,977-bp mtDNA deletion-specific primers. The deletion of 4,977-bp mtDNA was detected in 79.2% of asthenozoospermic patients compared to 10% in normozoospermic controls. The results showed a significant association between the presence of 4,977-bp mtDNA deletion and the asthenozoospermia and infertility (OR = 34.2000, 95% CI = 14.57-80.26, p-value < .001). In conclusion, our findings underscored a strong association between 4,977-bp mtDNA deletion and asthenozoospermia in the Jordanian population.

Associations of sperm mitochondrial DNA copy number and deletion rate with fertilization and embryo development in a clinical setting

STUDY QUESTION

Are sperm mitochondrial DNA copy number (mtDNAcn) and deletion rate (mtDNAdel) associated with odds of fertilization and high embryo quality at Days 3 and 5?

SUMMARY ANSWER

Higher sperm mtDNAcn and mtDNAdel were associated with lower odds of high quality Day 3 embryos and transfer quality Day 5 embryos, both of which were primarily driven by lowered odds of fertilization.

WHAT IS KNOWN ALREADY

Sperm mtDNAcn and mtDNAdel have been previously associated with poor semen parameters and clinical male infertility. One prior study has shown that mtDNAdel is associated with lower fertilization rates. However, it is unknown whether these characteristics are linked with ART outcomes.

STUDY DESIGN, SIZE, DURATION

This prospective observational study included 119 sperm samples collected from men undergoing ART in Western Massachusetts. ART outcomes were observed through to Day 5 post-insemination.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

As part of the Sperm Environmental Epigenetics and Development Study (SEEDS), 119 sperm samples were collected from men undergoing ART in Western Massachusetts. Sperm mtDNAcn and mtDNAdel were measured via triplex probe-based qPCR. Fertilization, Day 3 embryo quality and Day 5 embryo quality measures were fitted with mtDNAcn and mtDNAdel using generalized estimating equations.

MAIN RESULTS AND THE ROLE OF CHANCE

After adjusting for male age and measurement batches, higher sperm mtDNAcn and mtDNAdel were associated with lower odds of fertilization (P = 0.01 and P < 0.01), high quality Day 3 embryos (P = 0.02 for both) and transfer quality Day 5 embryos (P = 0.01 and P = 0.09). However, the associations of mtDNAcn and mtDNAdel with Day 3 high quality status and Day 5 transfer quality status were attenuated in models restricted to fertilized oocytes. Sperm mtDNAcn and mtDNAdel remained statistically significant in models adjusted for both male age and semen parameters, although models including both mtDNA markers generally favoured mtDNAdel.

LIMITATIONS, REASONS FOR CAUTION

Our sample only included oocytes and embryos from 119 couples and thus large diverse cohorts are necessary to confirm the association of sperm mtDNA biomarkers with embryo development.

WIDER IMPLICATIONS OF THE FINDINGS

To our knowledge, our study is the first to assess the associations of sperm mtDNAcn and mtDNAdel with fertilization and embryo quality. The biological mechanism(s) underlying these associations are unknown. Multivariable models suggest that sperm mtDNAcn and mtDNAdel provide discrimination independent of age and semen parameters; therefore, future investigation of the utility of sperm mtDNA as a biomarker for ART outcomes is warranted.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by Grant (K22-ES023085) from the National Institute of Environmental Health Sciences. The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Comparison of large-scale deletions of the sperm mitochondrial DNA in normozoospermic and asthenoteratozoospermic men

BACKGROUND AND OBJECTIVE

Mitochondria play a crucial role in energy metabolism for the survival and motility of sperm during fertilization. The aim of this study was to determine the association of large-scale mitochondrial DNA deletions with abnormal sperm motility and morphology in asthenoteratozoospermic patients.

MATERIALS AND METHODS

In this case-control study, 41 semen samples were collected from 18 normozoospermic healthy men and 23 asthenoteratozoospermic patients, according to the WHO guidelines. The swim-up technique was used for separation of spermatozoa on the basis of their motility. Long-range polymerase chain reaction (PCR) was used for screening of mitochondrial DNA (mtDNA) large-scale deletions, and primer shift PCR was used for confirmation of deletions.

RESULTS

The mean sperm motility, normal morphology, and progressive motility in asthenoteratozoospermic patients were significantly lower than in the normozoospermic group (P < 0.0001). There was a positive significant correlation between motility and normal sperm morphology ( P < 0.0001, r = 0.741). The results of long-range PCR revealed the existence of 4866-bp deletion along with the two common 4977-bp and 7436-bp deleted mtDNA in both groups. However, the frequency of multiple mtDNA deletions in the asthenoteratozoospermic group (15/23, 65.22%) was significantly higher than that in the normozoospermic group (7/18, 38.89%). Direct sequencing of the 534-bp PCR product revealed that it was amplified from the mtDNA with a 4866-bp deletion flanked by a seven-nucleotide direct repeat (5'-ACCCCCT-3').

CONCLUSIONS

Our findings suggested that these large-scale deletions of mtDNA may be genetic risk factors for poor sperm quality in asthenoteratozoospermia-induced male infertility. Thus, it is necessary to understand the mechanisms behind the generation of these deletions.

Sperm mitochondrial DNA measures and semen parameters among men undergoing fertility treatment

RESEARCH QUESTION

To examine associations between sperm mitochondrial DNA copy number (mtDNAcn), sperm mitochondrial DNA deletions (mtDNAdel), semen parameters and clinical infertility in an IVF setting.

DESIGN

A total of 125 sperm samples were collected from men undergoing assisted reproductive procedures in an IVF clinic in Western Massachusetts, USA. Sperm mtDNAcn and mtDNAdel were measured by probe-based quantitative polymerase chain reaction. Semen parameters, clinical diagnoses of infertility, and infertility based on consecutive semen parameters, were fitted with mtDNAcn and mtDNAdel in linear models. The utility of sperm mtDNAcn and mtDNAdel to predict infertility was assessed by receiver operating characteristic curves.

RESULTS

Adjusting for relevant covariates, both sperm mtDNAcn and mtDNAdel were associated with lower sperm concentration, count, motility and morphology (P ≤ 0.03). Sperm mtDNAcn and mtDNAdel were also associated with increased risks of clinical infertility based on current and consecutive semen samples. Sperm mtDNAcn had high predictive accuracy for consecutive diagnoses of clinical infertility (C-statistic: 0.91), whereas sperm mtDNAdel had moderate predictive accuracy (C-statistic: 0.75).

CONCLUSIONS

Sperm mtDNAcn is a measure of consecutive abnormal semen parameters and has promise as a diagnostic test.

Mitochondrial DNA sequencing and large-scale genotyping identifies MT-ND4 gene mutation m.11696G>A associated with idiopathic oligoasthenospermia

Genetic variants of mitochondrial DNA (mtDNA) were implicated to be associated with male infertility. Our previous whole mitochondrial genome sequencing and association study has identified two susceptibility mtDNA variants for oligoasthenospermia in Han Chinese men. In this study, we tested promising associations in an extended validation using 670 idiopathic oligoasthenospermia cases and 793 healthy controls to identify additional risk variants. We found that the genetic variant of m.11696G>A showed significantly higher frequency in the case group than that in the control group (odds ratio (OR) 2.21, 95% CI 1.21-4.04) (P=7.90×10-3). 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 m.11696G>A was associated with low sperm motility, with the OR of 2.38 (95 % CI 1.27-4.46) (P =5.22×10-3). These results advance our understanding of the genetic susceptibility to oligoasthenospermia and more functional studies are needed to provide insights into its pathogenic mechanism.