Bi-allelic Mutations in TTC29 Cause Male Subfertility with Asthenoteratospermia in Humans and Mice

ZMYND12 serves as an IDAd subunit that is essential for sperm motility in mice

Inner dynein arms (IDAs) are formed from a protein complex that is essential for appropriate flagellar bending and beating. IDA defects have previously been linked to the incidence of asthenozoospermia (AZS) and male infertility. The testes-enriched ZMYND12 protein is homologous with an IDA component identified in Chlamydomonas. ZMYND12 deficiency has previously been tied to infertility in males, yet the underlying mechanism remains uncertain. Here, a CRISPR/Cas9 approach was employed to generate Zmynd12 knockout (Zmynd12-/-) mice. These Zmynd12-/- mice exhibited significant male subfertility, reduced sperm motile velocity, and impaired capacitation. Through a combination of co-immunoprecipitation and mass spectrometry, ZMYND12 was found to interact with TTC29 and PRKACA. Decreases in the levels of PRKACA were evident in the sperm of these Zmynd12-/- mice, suggesting that this change may account for the observed drop in male fertility. Moreover, in a cohort of patients with AZS, one patient carrying a ZMYND12 variant was identified, expanding the known AZS-related variant spectrum. Together, these findings demonstrate that ZMYND12 is essential for flagellar beating, capacitation, and male fertility.

Deficiency of MFSD6L, an acrosome membrane protein, causes oligoasthenoteratozoospermia in humans and mice

Oligoasthenoteratozoospermia is an important factor affecting male fertility and has been found to be associated with genetic factors. However, there are still a proportion of oligoasthenoteratozoospermia cases that cannot be explained by known pathogenic genetic variants. Here, we perform genetic analyses and identify bi-allelic loss-of-function variants of MFSD6L from an oligoasthenoteratozoospermia-affected family. Mfsd6l knock-out male mice also present male subfertility with reduced sperm concentration, motility, and deformed acrosomes. Further mechanistic analyses reveal that MFSD6L, as an acrosome membrane protein, plays an important role in the formation of acrosome by interacting with the inner acrosomal membrane protein SPACA1. Moreover, poor embryonic development is consistently observed after intracytoplasmic sperm injection treatment using spermatozoa from the MFSD6L-deficient man and male mice. Collectively, our findings reveal that MFSD6L is required for the anchoring of sperm acrosome and head shaping. The deficiency of MFSD6L affects male fertility and causes oligoasthenoteratozoospermia in humans and mice.

Bi-allelic variants in chromatoid body protein TDRD6 cause spermiogenesis defects and severe oligoasthenoteratozoospermia in humans

BACKGROUND

The association between the TDRD6 variants and human infertility remains unclear, as only one homozygous missense variant of TDRD6 was found to be associated with oligoasthenoteratozoospermia (OAT).

METHODS

Whole-exome sequencing and Sanger sequencing were employed to identify potential pathogenic variants of TDRD6 in infertile men. Histology, immunofluorescence, immunoblotting and ultrastructural analyses were conducted to clarify the structural and functional abnormalities of sperm in mutated patients. Tdrd6-knockout mice were generated using the CRISPR-Cas9 system. Total RNA-seq and single-cell RNA-seq (scRNA-seq) analyses were used to elucidate the underlying molecular mechanisms, followed by validation through quantitative RT-PCR and immunostaining. Intracytoplasmic sperm injection (ICSI) was also used to assess the efficacy of clinical treatment.

RESULTS

Bi-allelic TDRD6 variants were identified in five unrelated Chinese individuals with OAT, including homozygous loss-of-function variants in two consanguineous families. Notably, besides reduced concentrations and impaired motility, a significant occurrence of acrosomal hypoplasia was detected in multiple spermatozoa among five patients. Using the Tdrd6-deficient mice, we further elucidate the pivotal role of TDRD6 in spermiogenesis and acrosome identified. In addition, the mislocalisation of crucial chromatoid body components DDX4 (MVH) and UPF1 was also observed in round spermatids from patients harbouring TDRD6 variants. ScRNA-seq analysis of germ cells from a patient with TDRD6 variants revealed that TDRD6 regulates mRNA metabolism processes involved in spermatid differentiation and cytoplasmic translation.

CONCLUSION

Our findings strongly suggest that TDRD6 plays a conserved role in spermiogenesis and confirms the causal relationship between TDRD6 variants and human OAT. Additionally, this study highlights the unfavourable ICSI outcomes in individuals with bi-allelic TDRD6 variants, providing insights for potential clinical treatment strategies.

Conserved genes regulating human sex differentiation, gametogenesis and fertilization

The study of the functional genome in mice and humans has been instrumental for describing the conserved molecular mechanisms regulating human reproductive biology, and for defining the etiologies of monogenic fertility disorders. Infertility is a reproductive disorder that includes various conditions affecting a couple's ability to achieve a healthy pregnancy. Recent advances in next-generation sequencing and CRISPR/Cas-mediated genome editing technologies have facilitated the identification and characterization of genes and mechanisms that, if affected, lead to infertility. We report established genes that regulate conserved functions in fundamental reproductive processes (e.g., sex determination, gametogenesis, and fertilization). We only cover genes the deletion of which yields comparable fertility phenotypes in both rodents and humans. In the case of newly-discovered genes, we report the studies demonstrating shared cellular and fertility phenotypes resulting from loss-of-function mutations in both species. Finally, we introduce new model systems for the study of human reproductive biology and highlight the importance of studying human consanguineous populations to discover novel monogenic causes of infertility. The rapid and continuous screening and identification of putative genetic defects coupled with an efficient functional characterization in animal models can reveal novel mechanisms of gene function in human reproductive tissues.

Genetic Causes of Qualitative Sperm Defects: A Narrative Review of Clinical Evidence

Several genes are implicated in spermatogenesis and fertility regulation, and these genes are presently being analysed in clinical practice due to their involvement in male factor infertility (MFI). However, there are still few genetic analyses that are currently recommended for use in clinical practice. In this manuscript, we reviewed the genetic causes of qualitative sperm defects. We distinguished between alterations causing reduced sperm motility (asthenozoospermia) and alterations causing changes in the typical morphology of sperm (teratozoospermia). In detail, the genetic causes of reduced sperm motility may be found in the alteration of genes associated with sperm mitochondrial DNA, mitochondrial proteins, ion transport and channels, and flagellar proteins. On the other hand, the genetic causes of changes in typical sperm morphology are related to conditions with a strong genetic basis, such as macrozoospermia, globozoospermia, and acephalic spermatozoa syndrome. We tried to distinguish alterations approved for routine clinical application from those still unsupported by adequate clinical studies. The most important aspect of the study was related to the correct identification of subjects to be tested and the correct application of genetic tests based on clear clinical data. The correct application of available genetic tests in a scenario where reduced sperm motility and changes in sperm morphology have been observed enables the delivery of a defined diagnosis and plays an important role in clinical decision-making. Finally, clarifying the genetic causes of MFI might, in future, contribute to reducing the proportion of so-called idiopathic MFI, which might indeed be defined as a subtype of MFI whose cause has not yet been revealed.

Gene-knockout by iSTOP enables rapid reproductive disease modeling and phenotyping in germ cells of the founder generation

Cytosine base editing achieves C•G-to-T•A substitutions and can convert four codons (CAA/CAG/CGA/TGG) into STOP-codons (induction of STOP-codons, iSTOP) to knock out genes with reduced mosaicism. iSTOP enables direct phenotyping in founders' somatic cells, but it remains unknown whether this works in founders' germ cells so as to rapidly reveal novel genes for fertility. Here, we initially establish that iSTOP in mouse zygotes enables functional characterization of known genes in founders' germ cells: Cfap43-iSTOP male founders manifest expected sperm features resembling human "multiple morphological abnormalities of the flagella" syndrome (i.e., MMAF-like features), while oocytes of Zp3-iSTOP female founders have no zona pellucida. We further illustrate iSTOP's utility for dissecting the functions of unknown genes with Ccdc183, observing MMAF-like features and male infertility in Ccdc183-iSTOP founders, phenotypes concordant with those of Ccdc183-KO offspring. We ultimately establish that CCDC183 is essential for sperm morphogenesis through regulating the assembly of outer dynein arms and participating in the intra-flagellar transport. Our study demonstrates iSTOP as an efficient tool for direct reproductive disease modeling and phenotyping in germ cells of the founder generation, and rapidly reveals the essentiality of Ccdc183 in fertility, thus providing a time-saving approach for validating genetic defects (like nonsense mutations) for human infertility.

Coiled-coil domain-containing 38 is required for acrosome biogenesis and fibrous sheath assembly in mice

During spermiogenesis, haploid spermatids undergo dramatic morphological changes to form slender sperm flagella and cap-like acrosomes, which are required for successful fertilization. Severe deformities in flagella cause a male infertility syndrome, multiple morphological abnormalities of the flagella (MMAF), while acrosomal hypoplasia in some cases leads to sub-optimal embryonic developmental potential. However, evidence regarding the occurrence of acrosomal hypoplasia in MMAF is limited. Here, we report the generation of base-edited mice knocked out for coiled-coil domain-containing 38 (Ccdc38) via inducing a nonsense mutation and find that the males are infertile. The Ccdc38-KO sperm display acrosomal hypoplasia and typical MMAF phenotypes. We find that the acrosomal membrane is loosely anchored to the nucleus and fibrous sheaths are disorganized in Ccdc38-KO sperm. Further analyses reveal that Ccdc38 knockout causes a decreased level of TEKT3, a protein associated with acrosome biogenesis, in testes and an aberrant distribution of TEKT3 in sperm. We finally show that intracytoplasmic sperm injection overcomes Ccdc38-related infertility. Our study thus reveals a previously unknown role for CCDC38 in acrosome biogenesis and provides additional evidence for the occurrence of acrosomal hypoplasia in MMAF.

Genome-Wide DNA Methylation Analysis and Functional Validation of Litter Size Traits in Jining Grey Goats

DNA methylation (DNAm) is associated with the reproductive system. However, the genetic mechanism through which DNAm regulates gene expression and thus affects litter size in goats is unclear. Therefore, in the present work, genome-wide DNAm profiles of HP and LP Jining Grey goat ovary tissues were comprehensively analyzed via WGBS, and RNA-Seq data were combined to identify candidate genes associated with litter size traits in the Jining Grey goat. Finally, BSP and RT-qPCR were used to verify the sequencing results of the key genes. Notably, the DNMT genes were downregulated at the expression level in the HP group. Both groups exhibited comparable levels of methylation. A total of 976 differentially methylated regions (DMRs) (973 DMRs for CG and 3 DMRs for CHG) and 310 differentially methylated genes (DMGs) were identified in this study. Through integration of WGBS and RNA-Seq data, we identified 59 differentially methylated and differentially expressed genes (DEGs) and ultimately screened 8 key DMGs (9 DMRS) associated with litter size traits in Jining Grey goats (SERPINB2: chr24_62258801_62259000, NDRG4: chr18_27599201_27599400, CFAP43: chr26_27046601_27046800, LRP1B. chr2_79720201_79720400, EPHA6: chr1_40088601_40088800, TTC29: chr17_59385801_59386000, PDE11A: chr2_117418601_117418800 and PGF: chr10_ 16913801_16914000 and chr10_16916401_16916600). In summary, our research comprehensively analyzed the genome-wide DNAm profiles of HP and LP Jining Grey goat ovary tissues. The data findings suggest that DNAm in goat ovaries may play an important role in determining litter size.

Male reproductive phenotypes of genetically altered laboratory mice (Mus musculus): a review based on pertinent literature from the last three decades

Laboratory mice (Mus musculus) are preferred animals for biomedical research due to the close relationship with humans in several aspects. Therefore, mice with diverse genetic traits have been generated to mimic human characteristics of interest. Some genetically altered mouse strains, on purpose or by accident, have reproductive phenotypes and/or fertility deviating from wild-type mice. The distinct reproductive phenotypes of genetically altered male mice mentioned in this paper are grouped based on reproductive organs, beginning with the brain (i.e., the hypothalamus and anterior pituitary) that regulates sexual maturity and development, the testis where male gametes and sex steroid hormones are produced, the epididymis, the accessory sex glands, and the penis which involve in sperm maturation, storage, and ejaculation. Also, distinct characteristics of mature sperm from genetically altered mice are described here. This repository will hopefully be a valuable resource for both humans, in terms of future biomedical research, and mice, in the aspect of the establishment of optimal sperm preservation protocols for individual mouse strains.

From TgO/GABA-AT, GABA, and T-263 Mutant to Conception of Toxoplasma

Toxoplasma gondii causes morbidity, mortality, and disseminates widely via cat sexual stages. Here, we find T. gondii ornithine aminotransferase (OAT) is conserved across phyla. We solve TgO/GABA-AT structures with bound inactivators at 1.55 Å and identify an inactivator selective for TgO/GABA-AT over human OAT and GABA-AT. However, abrogating TgO/GABA-AT genetically does not diminish replication, virulence, cyst-formation, or eliminate cat's oocyst shedding. Increased sporozoite/merozoite TgO/GABA-AT expression led to our study of a mutagenized clone with oocyst formation blocked, arresting after forming male and female gametes, with "Rosetta stone"-like mutations in genes expressed in merozoites. Mutations are similar to those in organisms from plants to mammals, causing defects in conception and zygote formation, affecting merozoite capacitation, pH/ionicity/sodium-GABA concentrations, drawing attention to cyclic AMP/PKA, and genes enhancing energy or substrate formation in TgO/GABA-AT-related-pathways. These candidates potentially influence merozoite's capacity to make gametes that fuse to become zygotes, thereby contaminating environments and causing disease.

Functional and structural significance of the inner-arm-dynein subspecies d in ciliary motility

Motile cilia play various important physiological roles in eukaryotic organisms including cell motility and fertility. Inside motile cilia, large motor-protein complexes called "ciliary dyneins" coordinate their activities and drive ciliary motility. The ciliary dyneins include the outer-arm dyneins, the double-headed inner-arm dynein (IDA f/I1), and several single-headed inner-arm dyneins (IDAs a, b, c, d, e, and g). Among these single-headed IDAs, one of the ciliary dyneins, IDA d, is of particular interest because of its unique properties and subunit composition. In addition, defects in this subspecies have recently been associated with several types of ciliopathies in humans, such as primary ciliary dyskinesia and multiple morphologic abnormalities of the flagellum. In this mini-review, we discuss the composition, structure, and motor properties of IDA d, which have been studied in the model organism Chlamydomonas reinhardtii, and further discuss the relationship between IDA d and human ciliopathies. In addition, we provide future perspectives and discuss remaining questions regarding this intriguing dynein subspecies.

Dnali1 is required for sperm motility and male fertility in mice

BACKGROUND

The sperm flagellum is an evolutionarily conserved specialized organelle responsible for sperm motility and male fertility. Deleterious mutations in genes involved in the sperm flagellum assembly can often cause sperm motility defects and male infertility. The murine Dnali1 gene encodes a protein that is known to interact with the cytoplasmic dynein heavy chain 1.

RESULTS

A Dnali1-mutated mouse model was generated by inducing a nonsense mutation in the Dnali1 gene. The Dnali1-mutated male mice presented impaired sperm motility and were completely infertile. Although no obviously abnormal sperm morphology was observed in Dnali1-mutated male mice, the ultrastructural structure of sperm flagellum was disrupted, displaying as an asymmetrical distribution of the longitudinal columns (LCs). Notably, infertile Dnali1-mutated male mice were able to obtain offspring via ICSI.

CONCLUSIONS

Our results uncover a role of DNALI1 in sperm motility and male fertility in mice, and demonstrate that ICSI overcomes Dnali1-associated male infertility, thus providing guidance for the diagnosis and genetic counseling of DNALI1-associated human infertility.

Novel axonemal protein ZMYND12 interacts with TTC29 and DNAH1, and is required for male fertility and flagellum function

Male infertility is common and complex, presenting a wide range of heterogeneous phenotypes. Although about 50% of cases are estimated to have a genetic component, the underlying cause often remains undetermined. Here, from whole-exome sequencing on samples from 168 infertile men with asthenoteratozoospermia due to severe sperm flagellum, we identified homozygous ZMYND12 variants in four unrelated patients. In sperm cells from these individuals, immunofluorescence revealed altered localization of DNAH1, DNALI1, WDR66, and TTC29. Axonemal localization of ZMYND12 ortholog TbTAX-1 was confirmed using the Trypanosoma brucei model. RNAi knock-down of TbTAX-1 dramatically affected flagellar motility, with a phenotype similar to the sperm from men bearing homozygous ZMYND12 variants. Co-immunoprecipitation and ultrastructure expansion microscopy in T. brucei revealed TbTAX-1 to form a complex with TTC29. Comparative proteomics with samples from Trypanosoma and Ttc29 KO mice identified a third member of this complex: DNAH1. The data presented revealed that ZMYND12 is part of the same axonemal complex as TTC29 and DNAH1, which is critical for flagellum function and assembly in humans, and Trypanosoma. ZMYND12 is thus a new asthenoteratozoospermia-associated gene, bi-allelic variants of which cause severe flagellum malformations and primary male infertility.

Biallelic mutations in CFAP54 cause male infertility with severe MMAF and NOA

BACKGROUND

Spermatogenic impairments can lead to male infertility by different pathological conditions, such as multiple morphological abnormalities of the sperm flagella (MMAF) and non-obstructive azoospermia (NOA). Genetic factors are involved in impaired spermatogenesis.

METHODS AND RESULTS

Here, we performed genetic analyses through whole-exome sequencing in a cohort of 334 Han Chinese probands with severe MMAF or NOA. Biallelic variants of CFAP54 were identified in three unrelated men, including one homozygous frameshift variant (c.3317del, p.Phe1106Serfs*19) and two compound heterozygous variants (c.878G>A, p.Arg293His; c.955C>T, p.Arg319Cys and c.4885C>T, p.Arg1629Cys; c.937G>A, p.Gly313Arg). All of the identified variants were absent or extremely rare in the public human genome databases and predicted to be damaging by bioinformatic tools. The men harbouring CFAP54 mutations exhibited abnormal sperm morphology, reduced sperm concentration and motility in ejaculated semen. Significant axoneme disorganisation and other ultrastructure abnormities were also detected inside the sperm cells from men harbouring CFAP54 mutations. Furthermore, immunofluorescence assays showed remarkably reduced staining of four flagellar assembly-associated proteins (IFT20, IFT52, IFT122 and SPEF2) in the spermatozoa of CFAP54-deficient men. Notably, favourable clinical pregnancy outcomes were achieved with sperm from men carrying CFAP54 mutations after intracytoplasmic sperm injection treatment.

CONCLUSION

Our genetic analyses and experimental observations revealed that biallelic deleterious mutations of CFAP54 can induce severe MMAF and NOA in humans.

A novel frameshift mutation in DNAH6 associated with male infertility and asthenoteratozoospermia

Introduction

Asthenoteratozoospermia is one of the most common causes of male infertility. Several genes have been identified as genetic causative factors, but there is a considerable genetic heterogeneity underlying asthenoteratozoospermia. In this study, we performed a genetic analysis of two brothers from a consanguineous Uighur family in China to identify gene mutations causative for asthenoteratozoospermia-related male infertility.

Methods

Two related patients with asthenoteratozoospermia from a large consanguineous family were sequenced by whole-exome sequencing and Sanger sequencing to identify disease-causing genes. Scanning and transmission electron microscopy analysis revealed ultrastructural abnormalities of spermatozoa. Quantitative real-time PCR (qRT-PCR) analysis and immunofluorescence (IF) analysis were used to assess the expression of the mutant messenger RNA (mRNA) and protein.

Results

A novel homozygous frameshift mutation (c.2823dupT, p.Val942Cysfs*21) in DNAH6 was identified in both affected individuals and was predicted to be pathogenic. Papanicolaou staining and electron microscopy revealed multiple morphological and ultrastructural abnormalities of affected spermatozoa. qRT-PCR and IF analysis showed abnormal expression of DNAH6 in affected sperm, probably due to premature termination code and decay of abnormal 3' untranslated region (UTR) region of mRNA. Furthermore, intracytoplasmic sperm injection could achieve successful fertilization in infertile men with DNAH6 mutations.

Discussion

The novel frameshift mutation identified in DNAH6 may contribute to asthenoteratozoospermia. These findings expand the spectrum of genetic mutations and phenotypes associated with asthenoteratozoospermia and may be useful for genetic and reproductive counseling in male infertility.

CFAP70 is a solid and valuable target for the genetic diagnosis of oligo-astheno-teratozoospermia in infertile men

BACKGROUND

Male infertility is a worldwide population health concern, but its aetiology remains largely understood. Although CFAP70 variants have already been reported in two oligo-astheno-teratozoospermia (OAT) individuals by sequencing, animal evidence to support CFAP70 as a credible OAT-pathogenic gene is lacking.

METHOD

Cfap70-KO mice were generated to explore the physiological role of CFAP70. CFAP70 variants were detected in infertile men with OAT by whole exome sequencing and Sanger sequencing confirmation. Cfap70-truncated mice were further generated to explore the pathogenicity of the nonsense variant of CFAP70 identified in the proband.

FINDINGS

Here, we demonstrate that Cfap70-KO mice are sterile mainly due to OAT and further identify a Chinese infertile man carrying a homozygous nonsense variant (c.2962C > T/p.R988X) of CFAP70. Cfap70-truncated mice lacking 5-8 tetratricopeptide repeats (TPRs) mimic the patient's symptoms. CFAP70 is required for the biogenesis of spermatid flagella partially by regulating the expression of OAT-associated proteins (e.g., QRICH2), assisting the cytoplasmic preassembly of the calmodulin- and radial spoke-associated complex (CSC), and controlling the manchette localization of axoneme-related proteins. Moreover, we suggest that CFAP70-associated male infertility could be overcome by intracytoplasmic sperm injection (ICSI) treatment.

INTERPRETATION

Overall, we demonstrate that CFAP70 is necessary to assemble spermatid flagella and that CFAP70 gene could be used as a diagnostic target for male infertility with OAT in the clinic.

FUNDING

This study was supported by the National Key Research and Development Project (2019YFA0802101 to S.C), Open Fund of Key Laboratory of Cell Proliferation and Regulation Biology, Ministry of Education (to S.C), Central Government to Guide Local Scientific and Technological Development (ZY21195023 to B.W), and Basic Research Projects of Central Scientific Research Institutes (to B.W).

BBOF1 is required for sperm motility and male fertility by stabilizing the flagellar axoneme in mice

The sperm flagellum is a specialized type of motile cilium composed of a typical "9 + 2" axonemal structure with peri-axonemal structures, such as outer dense fibers (ODFs). This flagellar arrangement is crucial for sperm movement and fertilization. However, the association of axonemal integrity with ODFs remains poorly understood. Here, we demonstrate that mouse BBOF1 could interact with both MNS1, an axonemal component, and ODF2, an ODF protein, and is required for sperm flagellar axoneme maintenance and male fertility. BBOF1 is expressed exclusively in male germ cells from the pachytene stage onwards and is detected in sperm axoneme fraction. Spermatozoa derived from Bbof1-knockout mice exhibit a normal morphology, however, reduced motility due to the absence of certain microtubule doublets, resulting in the failure to fertilize mature oocytes. Furthermore, BBOF1 is found to interact with ODF2 and MNS1 and is also required for their stability. Our findings in mice suggest that Bbof1 could also be essential for human sperm motility and male fertility, thus is a novel potential candidate gene for asthenozoospermia diagnosis.

Deficiency of primate-specific SSX1 induced asthenoteratozoospermia in infertile men and cynomolgus monkey and tree shrew models

Primate-specific genes (PSGs) tend to be expressed in the brain and testis. This phenomenon is consistent with brain evolution in primates but is seemingly contradictory to the similarity of spermatogenesis among mammals. Here, using whole-exome sequencing, we identified deleterious variants of X-linked SSX1 in six unrelated men with asthenoteratozoospermia. SSX1 is a PSG expressed predominantly in the testis, and the SSX family evolutionarily expanded independently in rodents and primates. As the mouse model could not be used for studying SSX1, we used a non-human primate model and tree shrews, which are phylogenetically similar to primates, to knock down (KD) Ssx1 expression in the testes. Consistent with the phenotype observed in humans, both Ssx1-KD models exhibited a reduced sperm motility and abnormal sperm morphology. Further, RNA sequencing indicated that Ssx1 deficiency influenced multiple biological processes during spermatogenesis. Collectively, our experimental observations in humans and cynomolgus monkey and tree shrew models highlight the crucial role of SSX1 in spermatogenesis. Notably, three of the five couples who underwent intra-cytoplasmic sperm injection treatment achieved a successful pregnancy. This study provides important guidance for genetic counseling and clinical diagnosis and, significantly, describes the approaches for elucidating the functions of testis-enriched PSGs in spermatogenesis.

Copy Number Variation and Structural Genomic Findings in 116 Cases of Sudden Unexplained Death between 1 and 28 Months of Age

In sudden unexplained death in pediatrics (SUDP) the cause of death is unknown despite an autopsy and investigation. The role of copy number variations (CNVs) in SUDP has not been well-studied. Chromosomal microarray (CMA) data are generated for 116 SUDP cases with age at death between 1 and 28 months. CNVs are classified using the American College of Medical Genetics and Genomics guidelines and CNVs in our cohort are compared to an autism spectrum disorder (ASD) cohort, and to a control cohort. Pathogenic CNVs are identified in 5 of 116 cases (4.3%). Variants of uncertain significance (VUS) favoring pathogenic CNVs are identified in 9 cases (7.8%). Several CNVs are associated with neurodevelopmental phenotypes including seizures, ASD, developmental delay, and schizophrenia. The structural variant 47,XXY is identified in two cases (2/69 boys, 2.9%) not previously diagnosed with Klinefelter syndrome. Pathogenicity scores for deletions are significantly elevated in the SUDP cohort versus controls (p = 0.007) and are not significantly different from the ASD cohort. The finding of pathogenic or VUS favoring pathogenic CNVs, or structural variants, in 12.1% of cases, combined with the observation of higher pathogenicity scores for deletions in SUDP versus controls, suggests that CMA should be included in the genetic evaluation of SUDP.

Homozygous variants in AKAP3 induce asthenoteratozoospermia and male infertility

BACKGROUND

As a common type of asthenoteratozoospermia, multiple morphological abnormalities of the sperm flagella (MMAF) can cause male infertility. Previous studies have revealed genetic factors as a major cause of MMAF. The known MMAF-associated genes are involved in the mitochondrial sheath, outer dense fibre or axoneme of the sperm flagella. These findings indicate the genetic heterogeneity of MMAF.

METHODS AND RESULTS

Here, we conducted genetic analyses using whole-exome sequencing in a cohort of 150 Han Chinese men with asthenoteratozoospermia. Homozygous deleterious variants of AKAP3 (A-kinase anchoring protein 3) were identified in two MMAF-affected men from unrelated families. One AKAP3 variant was a frameshift (c.2286_2287del, p.His762Glnfs*22) and the other variant was a missense mutation (c.44G>A, p.Cys15Tyr), which was predicted to be damaging by multiple bioinformatics tools. Further western blotting and immunofluorescence assays revealed the absence of AKAP3 in the spermatozoa from the man harbouring the homozygous frameshift variant, whereas the expression of AKAP3 was markedly reduced in the spermatozoa of the man with the AKAP3 missense variant p.Cys15Tyr. Notably, the clinical outcomes after intracytoplasmic sperm injection (ICSI) were divergent between these two cases, suggesting a possibility of AKAP3 dosage-dependent prognosis of ICSI treatment.

CONCLUSIONS

Our study revealed AKAP3 as a novel gene involved in human asthenoteratozoospermia.

Novel FSIP2 Variants Induce Super-Length Mitochondrial Sheath and Asthenoteratozoospermia in Humans

Asthenoteratozoospermia is one of the major factors for male infertility, whereas the causes of large numbers of cases are still unknown. We identified compound heterozygous variants of FSIP2 in three unrelated individuals from a cohort of 105 patients with asthenoteratozoospermia by exome sequencing. Deleterious FSIP2 variations caused severe disassembly of the fibrous sheath and axonemal defects. Intriguingly, spermatozoa in our study manifested "super-length" mitochondrial sheaths, increased levels of the mitochondrial sheath outer membrane protein TOMM20 and decreased mitochondrial ATP consumption. Dislocation or deletion of the annulus and reduction or dislocation of the annulus protein SEPT4 were also observed. While the lengthened mitochondrial sheaths were not presented in men harboring SEPT4 variants. Furthermore, female partners of two of three men achieved successful pregnancies following intracytoplasmic sperm injection (ICSI). Overall, we presume that FSIP2 may not only serve as a structural protein of the fibrous sheath but also as an intra-flagellar transporter involving in the axonemal assembly, mitochondrial selection and the termination of mitochondrial sheath extension during spermatogenesis, and ICSI is an effective treatment for individuals with FSIP2-associated asthenoteratozoospermia.

Clinical detection, diagnosis and treatment of morphological abnormalities of sperm flagella: A review of literature

Sperm carries male genetic information, and flagella help move the sperm to reach oocytes. When the ultrastructure of the flagella is abnormal, the sperm is unable to reach the oocyte and achieve insemination. Multiple morphological abnormalities of sperm flagella (MMAF) is a relatively rare idiopathic condition that is mainly characterized by multiple defects in sperm flagella. In the last decade, with the development of high-throughput DNA sequencing approaches, many genes have been revealed to be related to MMAF. However, the differences in sperm phenotypes and reproductive outcomes in many cases are attributed to different pathogenic genes or different pathogenic mutations in the same gene. Here, we will review information about the various phenotypes resulting from different pathogenic genes, including sperm ultrastructure and encoding proteins with their location and functions as well as assisted reproductive technology (ART) outcomes. We will share our clinical detection and diagnosis experience to provide additional clinical views and broaden the understanding of this disease.

Novel biallelic mutations in TTC29 cause asthenoteratospermia and male infertility

BACKGROUND

Multiple morphological abnormalities of the sperm flagella (MMAF), which is characterized as asthenoteratospermia involving absent, short, bent, coiled, and/or irregular-caliber flagella, is a rare recessive inherited disorder associated with male infertility. To date, genetic causes of MMAF cases are not fully explored.

METHODS

Whole-exome sequencing was conducted to identify pathogenic variants in a patient with MMAF. The functional effect of the identified mutations was investigated by immunofluorescence staining and western blotting. Intracytoplasmic sperm injection was used to assist fertilization for the patient with MMAF.

RESULTS

We identified novel biallelic mutations, a splicing variant NC_000004.12:g.146937593C>T (c.254+1G>A), and a nonsense mutation NM_001300761.4:c.1185C>G (NP_001287690.1:p.Tyr395*), in TTC29 from an infertile patient. In addition to the typical MMAF phenotype, the patient also presented aberrant morphology of sperm heads. Further functional experiments confirmed the absence of TTC29 expression in the spermatozoa. We also explored the specific expression pattern of TTC29 in human and mouse spermatogenesis. The outcome of intracytoplasmic sperm injection in the patient was unsuccessful, while additional female risk factors should not be excluded.

CONCLUSIONS

Our study revealed the novel biallelic mutations in TTC29 in a MMAF patient, which findings expand the mutational spectrum of TTC29 and further contribute to the diagnosis, genetic counseling, and prognosis of male infertility.

LRRC46 Accumulates at the Midpiece of Sperm Flagella and Is Essential for Spermiogenesis and Male Fertility in Mouse

The sperm flagellum is essential for male fertility. Multiple morphological abnormalities of the sperm flagella (MMAF) is a severe form of asthenoteratozoospermia. MMAF phenotypes are understood to result from pathogenic variants of genes from multiple families including AKAP, DANI, DNAH, RSPH, CCDC, CFAP, TTC, and LRRC, among others. The Leucine-rich repeat protein (LRRC) family includes two members reported to cause MMAF phenotypes: Lrrc6 and Lrrc50. Despite vigorous research towards understanding the pathogenesis of MMAF-related diseases, many genes remain unknown underlying the flagellum biogenesis. Here, we found that Leucine-rich repeat containing 46 (LRRC46) is specifically expressed in the testes of adult mice, and show that LRRC46 is essential for sperm flagellum biogenesis. Both scanning electron microscopy (SEM) and Papanicolaou staining (PS) presents that the knockout of Lrrc46 in mice resulted in typical MMAF phenotypes, including sperm with short, coiled, and irregular flagella. The male KO mice had reduced total sperm counts, impaired sperm motility, and were completely infertile. No reproductive phenotypes were detected in Lrrc46-/- female mice. Immunofluorescence (IF) assays showed that LRRC46 was present throughout the entire flagella of control sperm, albeit with evident concentration at the mid-piece. Transmission electron microscopy (TEM) demonstrated striking flagellar defects with axonemal and mitochondrial sheath malformations. About the important part of the Materials and Methods, SEM and PS were used to observe the typical MMAF-related irregular flagella morphological phenotypes, TEM was used to further inspect the sperm flagellum defects in ultrastructure, and IF was chosen to confirm the location of protein. Our study suggests that LRRC46 is an essential protein for sperm flagellum biogenesis, and its mutations might be associated with MMAF that causes male infertility. Thus, our study provides insights for understanding developmental processes underlying sperm flagellum formation and contribute to further observe the pathogenic genes that cause male infertility.

Bi-allelic variants in human TCTE1/DRC5 cause asthenospermia and male infertility

Asthenozoospermia (AZS) is a common male infertility phenotype, accounting for 18% of infertile patients. The N-DRC (Nexin-dynein Regulatory Complex) complex is the motor regulating device in the flagellum, which is found in most eukaryotic organisms with flagellum. The deletion of TCTE1 (T-Complex-Associated Testis-Expressed 1), a component of the N-DRC complex also known as DRC5 (Dynein regulatory complex subunit 5), has been shown to cause asthenospermia in mice. This study mainly introduces a clinical case of male infertility with normal sperm count, normal morphological structure, but low motility and weak forward movement. By whole-exome sequencing, we found that TCTE1 became a frameshift mutant, ENST00000371505.5: c.396_397insTC (p.Arg133Serfs*33), resulting in the rapid degradation of TCTE1 protein and male infertility. This phenotype is similar to the Tcte1^-/- (Tcte1 knockout) mice, which showed structural integrity but reduced motility. Further, different from mice, in vitro Fertilization (IVF) could successfully solve the patient's problem of infertility. Our data provides a better understanding of the biological functions of TCTE1 in human flagellum assembly and male fertility.

Patient with multiple morphological abnormalities of sperm flagella caused by a novel ARMC2 mutation has a favorable pregnancy outcome from intracytoplasmic sperm injection

PURPOSE

To investigate the potential genetic cause in a primary infertility patient with multiple morphological abnormalities of sperm flagella (MMAF).

METHODS

The patient's sperm was observed by light and electron microscopy. Whole-exome sequencing (WES) was carried out to identify candidate genes. Then, the mutation found by WES was verified by Sanger sequencing. The proteins interacting with ARMC2 were revealed by co-immunoprecipitation (co-IP) and mass spectrometry. Intracytoplasmic sperm injection (ICSI) was carried out to achieve successful pregnancy.

RESULTS

Typical MMAF phenotype (absent, short, coiled, bent irregular flagella) was shown in the patient's sperm. A novel homozygous mutation in ARMC2 (c.1264C > T) was identified. The proteins interacting with ARMC2 we found were CEP78, PGAM5, RHOA, FXR1, and SKIV2L2. The ICSI therapy was successful, and boy-girl twins were given birth.

CONCLUSION

We found a novel mutation in ARMC2 which led to MMAF and male infertility. This is the first report of ICSI outcome of patient harboring ARMC2 mutation. The interacting proteins indicated that ARMC2 might be involved in multiple processes of spermatogenesis.

Homozygous SPAG6 variants can induce nonsyndromic asthenoteratozoospermia with severe MMAF

BACKGROUND

Multiple morphological abnormalities of the sperm flagella (MMAF) is a subtype of severe asthenoteratozoospermia with poorly understood genetic etiology. SPAG6 is a core axonemal component that plays a critical role in the formation of cilia and sperm flagella. Previous studies have reported that mutations in SPAG6 cause primary ciliary dyskinesia (PCD), but the association between SPAG6 gene variants and the MMAF phenotype has not yet been described.

METHODS

We performed whole-exome sequencing (WES) in two unrelated Han Chinese men with MMAF. Sanger sequencing was used to validate the candidate variants. Routine semen analysis was carried out according to the WHO guidelines (5^th Edition). Sperm morphology was assessed using modified Papanicolaou staining. Scanning and transmission electron microscopy (S/TEM) was performed to observe the ultrastructural defects of the sperm flagella. Western blot analysis and immunofluorescence (IF) of spermatozoa were performed to examine the expression of SPAG6 protein. Assisted fertilization with intracytoplasmic sperm injection (ICSI) was applied.

RESULTS

Two homozygous SPAG6 variants were identified by WES and Sanger validation in two patients with MMAF phenotype (F1 II-1: c.308C > A, p. A103D; F2 II-1: c. 585delA, p. K196Sfs*6). Semen analysis showed progressive rates of less than 1%, and most of the spermatozoa presented MMAF by Papanicolaou staining. TEM revealed that the overall axonemal ultrastructure was disrupted and primarily presented an abnormal "9 + 0" configuration. No other PCD-related symptoms were found on physical examination and medical consultations, as well as lung CT screening. The level of SPAG6 protein was significantly decreased in the spermatozoa, and IF analysis revealed that SPAG6 staining was extremely weak and discontinuous in the sperm flagella of the two patients. Notably, F1 II-1 and his wife conceived successfully after undergoing ICSI.

CONCLUSIONS

Our research provides new evidence for a potential correlation between SPAG6 variants and the MMAF phenotype.

Successful Results of Intracytoplasmic Sperm Injection of a Chinese Patient With Multiple Morphological Abnormalities of Sperm Flagella Caused by a Novel Splicing Mutation in CFAP251

Asthenospermia is one of the most important causes of male infertility. Among asthenospermia, multiple morphological abnormalities of sperm flagella (MMAF) are relatively rare idiopathic conditions characterized by multiple defects in sperm flagella. Although many studies focusing on the genetic factors of MMAF have been conducted, its pathogenesis and treatment effect remain largely unknown. Here, we report a male patient from a nonconsanguineous Chinese family who exhibited a typical MMAF phenotype revealed by morphological analysis. We identified splicing mutations in CFAP251 (c.1192-3C>G), and the mutation was proven to cause exon skipping. In addition, western blotting and immunofluorescence analysis of the spermatozoa from the proband and a control subject revealed a significantly lower expression of CFAP251 protein due to pathogenic mutation. Interestingly, the patient’s mother was a heterozygous carrier for the mutation, but his father was not, and finally, the inheritance pattern was proven to be maternal uniparental disomy. We applied an intracytoplasmic sperm injection and achieved a successful pregnancy. Above all, our findings expand the spectrum of CFAP251 pathogenic mutations and provide more indications for clinical genetic counseling and assisted reproductive treatment for such patients.

Mitochondrial regulation during male germ cell development

Mitochondria tailor their morphology to execute their specialized functions in different cell types and/or different environments. During spermatogenesis, mitochondria undergo continuous morphological and distributional changes with germ cell development. Deficiencies in these processes lead to mitochondrial dysfunction and abnormal spermatogenesis, thereby causing male infertility. In recent years, mitochondria have attracted considerable attention because of their unique role in the regulation of piRNA biogenesis in male germ cells. In this review, we describe the varied characters of mitochondria and focus on key mitochondrial factors that play pivotal roles in the regulation of spermatogenesis, from primordial germ cells to spermatozoa, especially concerning metabolic shift, stemness and reprogramming, mitochondrial transformation and rearrangement, and mitochondrial defects in human sperm. Further, we discuss the molecular mechanisms underlying these processes.

Bi-allelic variants in DNHD1 cause flagellar axoneme defects and asthenoteratozoospermia in humans and mice

Asthenoteratozoospermia, defined as reduced sperm motility and abnormal sperm morphology, is a disorder with considerable genetic heterogeneity. Although previous studies have identified several asthenoteratozoospermia-associated genes, the etiology remains unknown for the majority of affected men. Here, we performed whole-exome sequencing on 497 unrelated men with asthenoteratozoospermia and identified DNHD1 bi-allelic variants from eight families (1.6%). All detected variants were predicted to be deleterious via multiple bioinformatics tools. Hematoxylin and eosin (H&E) staining revealed that individuals with bi-allelic DNHD1 variants presented striking abnormalities of the flagella; transmission electron microscopy (TEM) further showed flagellar axoneme defects, including central pair microtubule (CP) deficiency and mitochondrial sheath (MS) malformations. In sperm from fertile men, DNHD1 was localized to the entire flagella of the normal sperm; however, it was nearly absent in the flagella of men with bi-allelic DNHD1 variants. Moreover, abundance of the CP markers SPAG6 and SPEF2 was significantly reduced in spermatozoa from men harboring bi-allelic DNHD1 variants. In addition, Dnhd1 knockout male mice (Dnhd1^‒/‒) exhibited asthenoteratozoospermia and infertility, a finding consistent with the sperm phenotypes present in human subjects with DNHD1 variants. The female partners of four out of seven men who underwent intracytoplasmic sperm injection therapy subsequently became pregnant. In conclusion, our study showed that bi-allelic DNHD1 variants cause asthenoteratozoospermia, a finding that provides crucial insights into the biological underpinnings of this disorder and should assist with counseling of affected individuals.

Homozygous mutation in SLO3 leads to severe asthenoteratozoospermia due to acrosome hypoplasia and mitochondrial sheath malformations

BACKGROUND

Potassium channels are important for the structure and function of the spermatozoa. As a potassium transporter, the mSlo3 is essential for male fertility as Slo3 knockout male mice were infertile with the series of functional defects in sperm cells. However, no pathogenic variant has been detected in human SLO3 to date. Here we reported a human case with homozygous SLO3 mutation. The function of SLO3 in human sperm and the corresponding assisted reproductive strategy are also investigated.

METHODS

We performed whole-exome sequencing analysis from a large cohort of 105 patients with asthenoteratozoospermia. The effects of the variant were investigated by quantitative RT-PCR, western blotting, and immunofluorescence assays using the patient spermatozoa. Sperm morphological and ultrastructural studies were conducted using haematoxylin and eosin staining, scanning and transmission electron microscopy.

RESULTS

We identified a homozygous missense variant (c.1237A > T: p.Ile413Phe) in the sperm-specific SLO3 in one Chinese patient with male infertility. This SLO3 variant was rare in human control populations and predicted to be deleterious by multiple bioinformatic tools. Sperm from the individual harbouring the homozygous SLO3 variant exhibited severe morphological abnormalities, such as acrosome hypoplasia, disruption of the mitochondrial sheath, coiled tails, and motility defects. The levels of SLO3 mRNA and protein in spermatozoa from the affected individual were reduced. Furthermore, the acrosome reaction, mitochondrial membrane potential, and membrane potential during capacitation were also afflicted. The levels of acrosome marker glycoproteins and PLCζ1 as well as the mitochondrial sheath protein HSP60 and SLO3 auxiliary subunit LRRC52, were significantly reduced in the spermatozoa from the affected individual. The affected man was sterile due to acrosome and mitochondrial dysfunction; however, intra-cytoplasmic sperm injection successfully rescued this infertile condition.

CONCLUSIONS

SLO3 deficiency seriously impact acrosome formation, mitochondrial sheath assembly, and the function of K⁺ channels. Our findings provided clinical implications for the genetic and reproductive counselling of affected families.

Deleterious variants in TAF7L cause human oligoasthenoteratozoospermia and its impairing histone to protamine exchange inducing reduced in vitro fertilization

INTRODUCTION

Oligoasthenoteratozoospermia (OAT) is a major cause of infertility in males. Only a few pathogenic genes of OAT have been clearly identified till now. A large number of OAT-affected cases remain largely unknown.

METHODS

Here, Whole-exome sequencing (WES) in 725 idiopathic OAT patients was performed. Ejaculated spermatozoa by OAT patients were microinjected into mouse oocytes to estimate fertilization potential. Diff-quick staining and transmission electron microscopy were performed to evaluate sperm morphology and ultrastructure. The protein expression level and localization In vitro were detected by Western Blotting and Immunocytochemistry.

RESULTS

We identified four X-linked hemizygous deleterious variants of TAF7L-namely, c.1301_1302del;(p.V434Afs*5), c.699G>T;(p.R233S), c.508delA; (p. T170fs), c.719dupA;(p.K240fs) -in five probands. Intracytoplasmic sperm injection (ICSI) were carried out in M1, M2-1and M3 patient's wife. However only M1 patient's wife became pregnant after embryo transfer. In vitro study demonstrated significantly reduced fertilization ability in patient with TAF7L mutation. The TAF7L mutation let to abnormal sperm head and impaired histone-to protamine exchange. Variant 719dupA (p. K240fs) resulted in producing a truncated TAF7L protein and localized massively within the nucleus. In addition, TAF7L expression were not able to be detected due to variants c.1301_1302del (p. V434Afs*5) and c.508delA (p. T170fs) In vitro.

CONCLUSION

Our findings support that TAF7L is one of pathogenic genes of OAT and deleterious mutations in TAF7L may cause impaired histone-to-protamine affected the chromatin compaction of sperm head.

Novel biallelic mutations in SLC26A8 cause severe asthenozoospermia in humans owing to midpiece defects: Insights into a putative dominant genetic disease

To investigate the genetic cause of male infertility characterized by severe asthenozoospermia, two unrelated infertile men with severe asthenozoospermia from nonconsanguineous Chinese families were enrolled, and whole exome sequencing were performed to identify the potential pathogenic mutations. Novel compound heterozygous mutations (NK062 III-1: c.290T>C, p.Leu97Pro; c.1664delT, p.Ile555Thrfs*11/NK038 III-1: c.212G>T, p.Arg71Leu; c.290T>C, p.Leu97Pro) in SLC26A8 were identified. All mutations were inherited from their heterozygous parents and are predicted to be disease-causing by sorts intolerant from tolerant, PolyPhen-2, Mutation Taster, and Combined Annotation Dependent Depletion. In silico mutant SLC26A8 models predict that mutations p.Leu97Pro and p.Arg71Leu cause changes in the α-helix, which may result in functional defects in the protein. Notably, heterozygous male carriers of each mutation in both families were able to reproduce naturally, which is inconsistent with previous reports. Ultrastructural analysis revealed severe asthenozoospermia associated with absence of the mitochondrial sheath and annulus in spermatozoa from both the probands, and both structural defects were verified by HSP60 and SEPT4 immunofluorescence analysis. SLC26A8 levels were significantly reduced in spermatozoa from patients harboring biallelic SLC26A8 mutations, and both patients achieved good prognosis following intracytoplasmic sperm injection. Our findings indicate that mutations in SLC26A8 could manifest as a recessive genetic cause of severe asthenozoospermia and male infertility.

CFAP61 is required for sperm flagellum formation and male fertility in human and mouse

Defects in the structure or motility of cilia and flagella may lead to severe diseases such as primary ciliary dyskinesia (PCD), a multisystemic disorder with heterogeneous manifestations affecting primarily respiratory and reproductive functions. We report that CFAP61 is a conserved component of the calmodulin- and radial spoke-associated complex (CSC) of cilia. We find that a CFAP61 splice variant, c.143+5G>A, causes exon skipping/intron retention in human, inducing a multiple morphological abnormalities of the flagella (MMAF) phenotype. We generated Cfap61 knockout mice that recapitulate the infertility phenotype of the human CFAP61 mutation, but without other symptoms usually observed in PCD. We find that CFAP61 interacts with the CSC, radial spoke stalk and head. During early stages of Cfap61-/- spermatid development, the assembly of radial spoke components is impaired. As spermiogenesis progresses, the axoneme in Cfap61-/- cells becomes unstable and scatters, and the distribution of intraflagellar transport proteins is disrupted. This study reveals an organ-specific mechanism of axoneme stabilization that is related to male infertility.

Bi-allelic variants in human WDR63 cause male infertility via abnormal inner dynein arms assembly

Inner dynein arm (IDA), composed of a series of protein complex, is necessary to cilia and flagella bend formation and beating. Previous studies indicated that defects of IDA protein complex result in multiple morphological abnormalities of the sperm flagellum (MMAF) and male infertility. However, the genetic causes and molecular mechanisms in the IDAs need further exploration. Here we identified two loss-of-function variants of WDR63 in both MMAF and non-obstructive azoospermia (NOA) affected cohorts. WDR63 encodes an IDA-associated protein that is dominantly expressed in testis. We next generated Wdr63-knockout (Wdr63-KO) mice through the CRISPR-Cas9 technology. Remarkably, Wdr63-KO induced decreased sperm number, abnormal flagellar morphology and male infertility. In addition, transmission electron microscopy assay showed severely disorganized "9 + 2" axoneme and absent inner dynein arms in the spermatozoa from Wdr63-KO male mice. Mechanistically, we found that WDR63 interacted with WDR78 mainly via WD40-repeat domain and is necessary for IDA assembly. Furthermore, WDR63-associated male infertility in human and mice could be overcome by intracytoplasmic sperm injection (ICSI) treatment. In conclusion, the present study demonstrates that bi-allelic variants of WDR63 cause male infertility via abnormal inner dynein arms assembly and flagella formation and can be used as a genetic diagnostic indicator for infertility males.

Genetic diagnosis, sperm phenotype and ICSI outcome in case of severe asthenozoospermia with multiple morphological abnormalities of the flagellum

STUDY QUESTION

Are ICSI outcomes impaired in cases of severe asthenozoospermia with multiple morphological abnormalities of the flagellum (MMAF phenotype)?

SUMMARY ANSWER

Despite occasional technical difficulties, ICSI outcomes for couples with MMAF do not differ from those of other couples requiring ICSI, irrespective of the genetic defect.

WHAT IS KNOWN ALREADY

Severe asthenozoospermia, especially when associated with the MMAF phenotype, results in male infertility. Recent findings have confirmed that a genetic aetiology is frequently responsible for this phenotype. In such situations, pregnancies can be achieved using ICSI. However, few studies to date have provided detailed analyses regarding the flagellar ultrastructural defects underlying this phenotype, its genetic aetiologies, and the results of ICSI in such cases of male infertility.

STUDY DESIGN, SIZE, DURATION

We performed a retrospective study of 25 infertile men exhibiting severe asthenozoospermia associated with the MMAF phenotype identified through standard semen analysis. They were recruited at an academic centre for assisted reproduction in Paris (France) between 2009 and 2017. Transmission electron microscopy (TEM) and whole exome sequencing (WES) were performed in order to determine the sperm ultrastructural phenotype and the causal mutations, respectively. Finally 20 couples with MMAF were treated by assisted reproductive technologies based on ICSI.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Patients with MMAF were recruited based on reduced sperm progressive motility and increased frequencies of absent, short, coiled or irregular flagella compared with those in sperm from fertile control men. A quantitative analysis of the several ultrastructural defects was performed for the MMAF patients and for fertile men. The ICSI results obtained for 20 couples with MMAF were compared to those of 378 men with oligoasthenoteratozoospermia but no MMAF as an ICSI control group.

MAIN RESULTS AND THE ROLE OF CHANCE

TEM analysis and categorisation of the flagellar anomalies found in these patients provided important information regarding the structural defects underlying asthenozoospermia and sperm tail abnormalities. In particular, the absence of the central pair of axonemal microtubules was the predominant anomaly observed more frequently than in control sperm (P < 0.01). Exome sequencing, performed for 24 of the 25 patients, identified homozygous or compound heterozygous pathogenic mutations in CFAP43, CFAP44, CFAP69, DNAH1, DNAH8, AK7, TTC29 and MAATS1 in 13 patients (54.2%) (11 affecting MMAF genes and 2 affecting primary ciliary dyskinesia (PCD)-associated genes). A total of 40 ICSI cycles were undertaken for 20 MMAF couples, including 13 cycles (for 5 couples) where a hypo-osmotic swelling (HOS) test was required due to absolute asthenozoospermia. The fertilisation rate was not statistically different between the MMAF (65.7%) and the non-MMAF (66.0%) couples and it did not differ according to the genotype or the flagellar phenotype of the subjects or use of the HOS test. The clinical pregnancy rate per embryo transfer did not differ significantly between the MMAF (23.3%) and the non-MMAF (37.1%) groups. To date, 7 of the 20 MMAF couples have achieved a live birth from the ICSI attempts, with 11 babies born without any birth defects.

LIMITATIONS, REASONS FOR CAUTION

The ICSI procedure outcomes were assessed retrospectively on a small number of affected subjects and should be confirmed on a larger cohort. Moreover, TEM analysis could not be performed for all patients due to low sperm concentrations, and WES results are not yet available for all of the included men.

WIDER IMPLICATIONS OF THE FINDINGS

An early and extensive phenotypic and genetic investigation should be considered for all men requiring ICSI for severe asthenozoospermia. Although our study did not reveal any adverse ICSI outcomes associated with MMAF, we cannot rule out that some rare genetic causes could result in low fertilisation or pregnancy rates.

STUDY FUNDING/COMPETING INTEREST(S)

No external funding was used for this study and there are no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

The mutation c.346-1G > a in SOHLH1 impairs sperm production in the homozygous but not in the heterozygous condition

Non-obstructive azoospermia (NOA) is an important cause of male infertility, and the genetic pathogenesis is still incompletely understood. The previous study reported that heterozygous mutation of c.346-1G > A in spermatogenesis and oogenesis specific basic helix–loop–helix 1 (SOHLH1) was identified in two NOA patients and suggested it is the pathogenic factor for NOA. However, in our research, this heterozygous mutation was confirmed in three Chinese infertile patients who suffered from teratozoospermia, but they had normal sperm number. Intriguingly, a homozygous mutation of c.346-1G > A in SOHLH1 was detected in a severe oligozoospermia (SOZ) patient, characterized with severely decreased sperm count. Notably, we unprecedently revealed that this homozygous mutation of c.346-1G > A in SOHLH1 leads to the sharp decrease in various germ cells and spermatogenesis dysfunction, which is similar to the phenotype of SOHLH1 knockout male mice. Moreover, western blotting confirmed that the homozygous mutation declined SOHLH1 protein expression. Additionally, we correlated the good prognosis of intracytoplasmic sperm injection (ICSI) in the patients carrying the mutation of c.346-1G > A in SOHLH1. Thus, we suggested that the heterozygous mutation of c.346-1G > A in SOHLH1 is responsible for teratozoospermia, and this homozygous mutation in SOHLH1 impairs spermatogenesis and further leads to the reduced sperm count, eventually causing male infertility, which unveils a new recessive-inheritance pattern of SOHLH1-associated male infertility initially.

Bi-allelic mutations of DNAH10 cause primary male infertility with asthenoteratozoospermia in humans and mice

Multiple morphological abnormalities of the sperm flagella (MMAF)-induced asthenoteratozoospermia is a common cause of male infertility. Previous studies have identified several MMAF-associated genes, highlighting the condition's genetic heterogeneity. To further define the genetic causes underlying MMAF, we performed whole-exome sequencing in a cohort of 643 Chinese MMAF-affected men. Bi-allelic DNAH10 variants were identified in five individuals with MMAF from four unrelated families. These variants were either rare or absent in public population genome databases and were predicted to be deleterious by multiple bioinformatics tools. Morphological and ultrastructural analyses of the spermatozoa obtained from men harboring bi-allelic DNAH10 variants revealed striking flagellar defects with the absence of inner dynein arms (IDAs). DNAH10 encodes an axonemal IDA heavy chain component that is predominantly expressed in the testes. Immunostaining analysis indicated that DNAH10 localized to the entire sperm flagellum of control spermatozoa. In contrast, spermatozoa from the men harboring bi-allelic DNAH10 variants exhibited an absence or markedly reduced staining intensity of DNAH10 and other IDA components, including DNAH2 and DNAH6. Furthermore, the phenotypes were recapitulated in mouse models lacking Dnah10 or expressing a disease-associated variant, confirming the involvement of DNAH10 in human MMAF. Altogether, our findings in humans and mice demonstrate that DNAH10 is essential for sperm flagellar assembly and that deleterious bi-allelic DNAH10 variants can cause male infertility with MMAF. These findings will provide guidance for genetic counseling and insights into the diagnosis of MMAF-associated asthenoteratozoospermia.

Homozygous mutations in CCDC34 cause male infertility with oligoasthenoteratozoospermia in humans and mice

BACKGROUND

Oligoasthenoteratozoospermia is a typical feature of sperm malformations leading to male infertility. Only a few genes have been clearly identified as pathogenic genes of oligoasthenoteratozoospermia.

METHODS AND RESULTS

Here, we identified a homozygous frameshift variant (c.731dup, p.Asn244Lysfs*3) in CCDC34, which is preferentially expressed in the human testis, using whole-exome sequencing in a cohort of 100 Chinese men with multiple morphological abnormalities of the sperm flagella (MMAF). In an additional cohort of 167 MMAF-affected men from North Africa, Iran and France, we identified a second subject harbouring a homozygous CCDC34 frameshift variant (c.799_817del, p.Glu267Lysfs*72). Both affected men presented a typical MMAF phenotype with an abnormally low sperm concentration (ie, oligoasthenoteratozoospermia). Transmission electron microscopy analysis of the sperm flagella affected by CCDC34 deficiency further revealed dramatic disorganisation of the axoneme. Immunofluorescence assays of the spermatozoa showed that CCDC34 deficiency resulted in almost absent staining of CCDC34 and intraflagellar transport-B complex-associated proteins (such as IFT20 and IFT52). Furthermore, we generated a mouse Ccdc34 frameshift mutant using CRISPR-Cas9 technology. Ccdc34-mutated (Ccdc34^mut/mut ) male mice were sterile and presented oligoasthenoteratozoospermia with typical MMAF anomalies. Intracytoplasmic sperm injection has good pregnancy outcomes in both humans and mice.

CONCLUSIONS

Our findings support that CCDC34 is crucial to the formation of sperm flagella and that biallelic deleterious mutations in CCDC34/Ccdc34 cause male infertility with oligoasthenoteratozoospermia in humans and mice.

Bi-allelic truncating variants in CFAP206 cause male infertility in human and mouse

Spermatozoa are polarized cells with a head and a flagellum joined together by the connecting piece. Flagellum integrity is critical for normal sperm function, and flagellum defects consistently lead to male infertility. Multiple morphological abnormalities of the flagella (MMAF) is a distinct sperm phenotype consistently leading to male infertility due to a reduced or absent sperm motility associated with severe morphological and ultrastructural flagellum defects. Despite numerous genes recently described to be recurrently associated with MMAF, more than half of the cases analyzed remain unresolved, suggesting that many yet uncharacterized gene defects account for this phenotype. By performing a retrospective exome analysis of the unsolved cases from our initial cohort of 167 infertile men with a MMAF phenotype, we identified one individual carrying a homozygous frameshift variant in CFAP206, a gene encoding a microtubule-docking adapter for radial spoke and inner dynein arm. Immunostaining experiments in the patient's sperm cells demonstrated the absence of WDR66 and RSPH1 proteins suggesting severe radial spokes and calmodulin and spoke-associated complex defects. Using the CRISPR-Cas9 technique, we generated homozygous Cfap206 knockout (KO) mice which presented with male infertility due to functional, structural and ultrastructural sperm flagellum defects associated with a very low rate of embryo development using ICSI. Overall, we showed that CFAP206 is essential for normal sperm flagellum structure and function in human and mouse and that bi-allelic mutations in CFAP206 cause male infertility in man and mouse by inducing morphological and functional defects of the sperm flagellum that may also cause ICSI failures.

Novel Mutations in X-Linked, USP26-Induced Asthenoteratozoospermia and Male Infertility

Male infertility is a multifactorial disease with a strong genetic background. Abnormal sperm morphologies have been found to be closely related to male infertility. Here, we conducted whole-exome sequencing in a cohort of 150 Han Chinese men with asthenoteratozoospermia. Two novel hemizygous mutations were identified in USP26, an X-linked gene preferentially expressed in the testis and encoding a deubiquitinating enzyme. These USP26 variants are extremely rare in human population genome databases and have been predicted to be deleterious by multiple bioinformatics tools. Hematoxylin-eosin staining and electron microscopy analyses of the spermatozoa from men harboring hemizygous USP26 variants showed a highly aberrant morphology and ultrastructure of the sperm heads and flagella. Real-time quantitative PCR and immunoblotting assays revealed obviously reduced levels of USP26 mRNA and protein in the spermatozoa from men harboring hemizygous deleterious variants of USP26. Furthermore, intracytoplasmic sperm injections performed on infertile men harboring hemizygous USP26 variants achieved satisfactory outcomes. Overall, our study demonstrates that USP26 is essential for normal sperm morphogenesis, and hemizygous USP26 mutations can induce X-linked asthenoteratozoospermia. These findings will provide effective guidance for the genetic and reproductive counseling of infertile men with asthenoteratozoospermia.

Loss of DRC1 function leads to multiple morphological abnormalities of the sperm flagella and male infertility in human and mouse

Motile cilia and flagellar defects can result in primary ciliary dyskinesia, which is a multisystemic genetic disorder that affects roughly 1:10 000 individuals. The nexin-dynein regulatory complex (N-DRC) links neighboring doublet microtubules within flagella, serving as a central regulatory hub for motility in Chlamydomonas. Herein, we identified two homozygous DRC1 variants in human patients that were associated with multiple morphological abnormalities of the sperm flagella (MMAF) and male infertility. Drc1^−/−, Drc1^R554X/R554X and Drc1^W244X/W244X mice on the C57BL/6 background suffered from pre-pubertal mortality. However, when the ICR background was introduced, some of these mice were able to survive and recapitulate the MMAF phenotypes detected in human patients. By analyzing these animals, we determined that DRC1 is an essential regulator of N-DRC assembly in cilia and flagella. When DRC1 is absent, this results in the shortening of cilia and consequent impairment of their motility. Damage associated with DRC1 deficiency in sperm flagella was more pronounced than in cilia, as manifested by complete axoneme structural disorder in addition to the loss of the DRC structure. Altogether, these findings suggest that DRC1 is required for the structural stability of flagella but not cilia, emphasizing the key role of this protein in mammalian species.

Towards Post-Meiotic Sperm Production: Genetic Insight into Human Infertility from Mouse Models

Declined quality and quantity of sperm is currently the major cause of patients suffering from infertility. Male germ cell development is spatiotemporally regulated throughout the whole developmental process. While it has been known that exogenous factors, such as environmental exposure, diet and lifestyle, et al, play causative roles in male infertility, recent progress has revealed abundant genetic mutations tightly associated with defective male germline development. In mammals, male germ cells undergo dramatic morphological change (i.e., nuclear condensation) and chromatin remodeling during post-meiotic haploid germline development, a process termed spermiogenesis; However, the molecular machinery players and functional mechanisms have yet to be identified. To date, accumulated evidence suggests that disruption in any step of haploid germline development is likely manifested as fertility issues with low sperm count, poor sperm motility, aberrant sperm morphology or combined. With the continually declined cost of next-generation sequencing and recent progress of CRISPR/Cas9 technology, growing studies have revealed a vast number of disease-causing genetic variants associated with spermiogenic defects in both mice and humans, along with mechanistic insights partially attained and validated through genetically engineered mouse models (GEMMs). In this review, we mainly summarize genes that are functional at post-meiotic stage. Identification and characterization of deleterious genetic variants should aid in our understanding of germline development, and thereby further improve the diagnosis and treatment of male infertility.

Exome sequencing reveals variants in known and novel candidate genes for severe sperm motility disorders

STUDY QUESTION

What are the causative genetic variants in patients with male infertility due to severe sperm motility disorders?

SUMMARY ANSWER

We identified high confidence disease-causing variants in multiple genes previously associated with severe sperm motility disorders in 10 out of 21 patients (48%) and variants in novel candidate genes in seven additional patients (33%).

WHAT IS KNOWN ALREADY

Severe sperm motility disorders are a form of male infertility characterised by immotile sperm often in combination with a spectrum of structural abnormalities of the sperm flagellum that do not affect viability. Currently, depending on the clinical sub-categorisation, up to 50% of causality in patients with severe sperm motility disorders can be explained by pathogenic variants in at least 22 genes.

STUDY DESIGN, SIZE, DURATION

We performed exome sequencing in 21 patients with severe sperm motility disorders from two different clinics.

PARTICIPANTS/MATERIALS, SETTING, METHOD

Two groups of infertile men, one from Argentina (n = 9) and one from Australia (n = 12), with clinically defined severe sperm motility disorders (motility <5%) and normal morphology values of 0–4%, were included. All patients in the Argentine cohort were diagnosed with DFS-MMAF, based on light and transmission electron microscopy. Sperm ultrastructural information was not available for the Australian cohort. Exome sequencing was performed in all 21 patients and variants with an allele frequency of <1% in the gnomAD population were prioritised and interpreted.

MAIN RESULTS AND ROLE OF CHANCE

In 10 of 21 patients (48%), we identified pathogenic variants in known sperm assembly genes: CFAP43 (3 patients); CFAP44 (2 patients), CFAP58 (1 patient), QRICH2 (2 patients), DNAH1 (1 patient) and DNAH6 (1 patient). The diagnostic rate did not differ markedly between the Argentinian and the Australian cohort (55% and 42%, respectively). Furthermore, we identified patients with variants in the novel human candidate sperm motility genes: DNAH12, DRC1, MDC1, PACRG, SSPL2C and TPTE2. One patient presented with variants in four candidate genes and it remains unclear which variants were responsible for the severe sperm motility defect in this patient.

LARGE SCALE DATA

N/A

LIMITATIONS, REASONS FOR CAUTION

In this study, we described patients with either a homozygous or two heterozygous candidate pathogenic variants in genes linked to sperm motility disorders. Due to unavailability of parental DNA, we have not assessed the frequency of de novo or maternally inherited dominant variants and could not determine the parental origin of the mutations to establish in all cases that the mutations are present on both alleles.

WIDER IMPLICATIONS OF THE FINDINGS

Our results confirm the likely causal role of variants in six known genes for sperm motility and we demonstrate that exome sequencing is an effective method to diagnose patients with severe sperm motility disorders (10/21 diagnosed; 48%). Furthermore, our analysis revealed six novel candidate genes for severe sperm motility disorders. Genome-wide sequencing of additional patient cohorts and re-analysis of exome data of currently unsolved cases may reveal additional variants in these novel candidate genes.

STUDY FUNDING/COMPETING INTEREST(S)

This project was supported in part by funding from the Australian National Health and Medical Research Council (APP1120356) to M.K.O.B., J.A.V. and R.I.M.L., The Netherlands Organisation for Scientific Research (918-15-667) to J.A.V., the Royal Society and Wolfson Foundation (WM160091) to J.A.V., as well as an Investigator Award in Science from the Wellcome Trust (209451) to J.A.V. and Grants from the National Research Council of Argentina (PIP 0900 and 4584) and ANPCyT (PICT 9591) to H.E.C. and a UUKi Rutherford Fund Fellowship awarded to B.J.H.

Essential Role of CFAP53 in Sperm Flagellum Biogenesis

The sperm flagellum is essential for male fertility. Despite vigorous research progress toward understanding the pathogenesis of flagellum-related diseases, much remains unknown about the mechanisms underlying the flagellum biogenesis itself. Here, we show that the cilia and flagella associated protein 53 (Cfap53) gene is predominantly expressed in testes, and it is essential for sperm flagellum biogenesis. The knockout of this gene resulted in complete infertility in male mice but not in the females. CFAP53 localized to the manchette and sperm tail during spermiogenesis, the knockout of this gene impaired flagellum biogenesis. Furthermore, we identified two manchette and sperm tail-associated proteins that interacted with CFAP53 during spermiogenesis. Together, our results suggest that CFAP53 is an essential protein for sperm flagellum biogenesis, and its mutations might be associated with multiple morphological abnormalities of the flagella (MMAF).

A novel mutation in DNAH17 is present in a patient with multiple morphological abnormalities of the flagella

RESEARCH QUESTION

Asthenoteratospermia is characterized by malformed spermatozoa with motility defects, which results in male infertility. Multiple morphological abnormalities of the sperm flagella (MMAF) is a hallmark of asthenoteratospermia. The genetic causes of MMAF, however, are unknown in about one-third of cases. Which other MMAF-associated genes are waiting to be discovered?

DESIGN

Whole-exome sequencing was conducted to identify causative genes in a man with MMAF. Immunofluorescence staining and western blot were applied to assess the pathogenicity of the identified variant. Intracytoplasmic sperm injection (ICSI) was used to assist fertilization for the patient with MMAF.

RESULT

Sanger sequencing of the family demonstrated that the infertile man carried a homozygous DNAH17 variant (c. 4810C>T [p.R1604C]). The obviously decreased DNAH17 expression was observed in HEK293T cells transfected with MUT-DNAH17 plasmid compared with cells with WT-DNAH17 plasmid. Immunofluorescence analysis showed that this mutation induced significant decrease in DNAH17 expression, which negatively affected the DNAH8 expression in the patient's spermatozoa. Moreover, the outcome of ICSI in the patient was unsuccessful.

CONCLUSION

Our study revealed a novel homozygous missense mutation in DNAH17 involved in MMAF phenotype. The finding of the novel mutation in DNAH17 enriches the gene variant spectrum of MMAF, further contributing to diagnosis, genetic counselling and prognosis for male infertility.

Composition and function of ciliary inner-dynein-arm subunits studied in Chlamydomonas reinhardtii

Motile cilia (also interchangeably called "flagella") are conserved organelles extending from the surface of many animal cells and play essential functions in eukaryotes, including cell motility and environmental sensing. Large motor complexes, the ciliary dyneins, are present on ciliary outer-doublet microtubules and drive movement of cilia. Ciliary dyneins are classified into two general types: the outer dynein arms (ODAs) and the inner dynein arms (IDAs). While ODAs are important for generation of force and regulation of ciliary beat frequency, IDAs are essential for control of the size and shape of the bend, features collectively referred to as waveform. Also, recent studies have revealed unexpected links between IDA components and human diseases. In spite of their importance, studies on IDAs have been difficult since they are very complex and composed for several types of IDA motors, each unique in composition and location in the axoneme. Thanks in part to genetic, biochemical, and structural analysis of Chlamydomonas reinhardtii, we are beginning to understand the organization and function of the ciliary IDAs. In this review, we summarize the composition of Chlamydomonas IDAs particularly focusing on each subunit, and discuss the assembly, conservation, and functional role(s) of these IDA subunits. Furthermore, we raise several additional questions/challenges regarding IDAs, and discuss future perspectives of IDA studies.

Novel mutations in FSIP2 lead to multiple morphological abnormalities of the sperm flagella and poor ICSI prognosis

Multiple morphological abnormalities of the sperm flagella (MMAF) is defined as deformities that cause sperm motility disorders, further resulting in male infertility. However, the reported genes related to sperm flagellar defects can only explain approximately 60% of human MMAF cases. Here, we report two novel compound heterozygous mutations, c.16246_16247insCCCAAATATCACC (p. T5416fs*7) and c.17323C > T (p.Q5774*), in the fibrous sheath-interacting protein 2 gene (FSIP2; OMIM: 615796) in an infertile patient by whole-exome sequencing (WES). Western blotting and immunofluorescence staining confirmed that the compound heterozygous mutations abrogated FSIP2 protein expression. Notably, our staining revealed that FSIP2 is expressed in the cytoplasm of primary germ cell and flagella of spermatids during the spermiogenesis. Moreover, intracytoplasmic sperm injection (ICSI) was carried out using sperm from this patient; however, pregnancy failed after embryo transfer through one cycle. Our findings may be helpful in establishing a genetic diagnosis for MMAF, as well as provide additional beneficial knowledge for genetic counseling and infertility treatment.

Deleterious variants in X-linked CFAP47 induce asthenoteratozoospermia and primary male infertility

Asthenoteratozoospermia characterized by multiple morphological abnormalities of the flagella (MMAF) has been identified as a sub-type of male infertility. Recent progress has identified several MMAF-associated genes with an autosomal recessive inheritance in human affected individuals, but the etiology in approximately 40% of affected individuals remains unknown. Here, we conducted whole-exome sequencing (WES) and identified hemizygous missense variants in the X-linked CFAP47 in three unrelated Chinese individuals with MMAF. These three CFAP47 variants were absent in human control population genome databases and were predicted to be deleterious by multiple bioinformatic tools. CFAP47 encodes a cilia- and flagella-associated protein that is highly expressed in testis. Immunoblotting and immunofluorescence assays revealed obviously reduced levels of CFAP47 in spermatozoa from all three men harboring deleterious missense variants of CFAP47. Furthermore, WES data from an additional cohort of severe asthenoteratozoospermic men originating from Australia permitted the identification of a hemizygous Xp21.1 deletion removing the entire CFAP47 gene. All men harboring hemizygous CFAP47 variants displayed typical MMAF phenotypes. We also generated a Cfap47-mutated mouse model, the adult males of which were sterile and presented with reduced sperm motility and abnormal flagellar morphology and movement. However, fertility could be rescued by the use of intra-cytoplasmic sperm injections (ICSIs). Altogether, our experimental observations in humans and mice demonstrate that hemizygous mutations in CFAP47 can induce X-linked MMAF and asthenoteratozoospermia, for which good ICSI prognosis is suggested. These findings will provide important guidance for genetic counseling and assisted reproduction treatments.

Novel bi-allelic variants in DNAH2 cause severe asthenoteratozoospermia with multiple morphological abnormalities of the flagella

RESEARCH QUESTION

Multiple morphological abnormalities of the flagella (MMAF) is characterized by excessive immotile spermatozoa with severe flagellar abnormalities in the ejaculate. Previous studies have reported a heterogeneous genetic profile associated with MMAF. What other genetic variants might explain the cause of MMAF?

DESIGN

Whole-exome sequencing was conducted in a cohort of 90 Chinese patients with MMAF. The pathogenicity of identified mutations was assessed through electron microscopy and immunofluorescent examinations.

RESULTS

Three unrelated men with bi-allelic DNAH2 variants were identified. Sanger sequencing verified that the six novel variants originated from every parent. All these variants were located at the conserved domains of DNAH2 and predicted to be deleterious by bioinformatic tools. Haematoxylin and eosin staining and scanning electron microscopy revealed that spermatozoa harbouring DNAH2 variants displayed severely aberrant morphology mainly with absent and short flagella (≥78%). Moreover, transmission electron microscopy revealed the obvious absence of a central pair of microtubules and inner dynein arms in the spermatozoa with mutated DNAH2. Immunofluorescence data further validated these findings, showing reduced DNAH2 protein expression in the spermatozoa with DNAH2 variants, compared with normal spermatozoa. Intracytoplasmic sperm injection using spermatozoa from the three men with mutated DNAH2 resulted in blastocyst formation in all cases. Embryo transfer was carried out in two couples, both resulting in clinical pregnancy.

CONCLUSIONS

These experimental and clinical data suggest that bi-allelic DNAH2 variants might induce MMAF-associated asthenoteratozoospermia, which can be overcome through intracytoplasmic sperm injection. These findings contribute to the knowledge of the genetic landscape of asthenoteratozoospermia and clinical counselling of male infertility.