A Homozygous NUP210L Variant Is Associated With Severe Defects in Human Spermiogenesis.

Biallelic Truncating Variant in LRGUK Is Associated With Severe Multiple Morphological Abnormalities of the Sperm Flagella and Sperm Nuclear Defects in Humans.

Findings identify LRGUK as a novel gene involved in male infertility, essential for spermatid morphogenesis and flagellum assembly, essential for spermatid morphogenesis and flagellum assembly.

HIPK4 is a novel gene associated with teratozoospermia and male infertility

STUDY QUESTION: Are pathogenic variants in Homeodomain-interacting protein kinase (HIPK4) associated with sperm head abnormalities causing male infertility? SUMMARY ANSWER: HIPK4 is a novel candidate gene associated with sperm head defects and human male infertility. WHAT IS KNOWN ALREADY: Numerous genes causing male infertility due to Multiple Morphological Abnormalities of the sperm flagella (MMAF) have been described but the genetic basis of sperm head defects is less well understood. STUDY DESIGN, SIZE, DURATION: Four infertile brothers displaying varying degrees of quantitatively and/or qualitatively impaired spermatogenesis, their parents, and their fertile brother were included in the study. Further, the Male Reproductive Genomics (MERGE) cohort comprising exome/genome sequencing data of >3,300 men was queried. PARTICIPANTS/MATERIALS, SETTING, METHODS: We performed exome sequencing in all five brothers and their parents. To characterise the sperm phenotype, standard semen analysis, immunofluorescence staining, and transmission-electron microscopy (TEM) were carried out. Further, we evaluated the impact of the HIPK4 variant in cell culture experiments using HEK293T cells. MAIN RESULTS AND THE ROLE OF CHANCE: Analysing the exome data, we could not identify a common genetic cause in all four affected brothers. However, one of the affected brothers was compound heterozygous for two loss-of-function variants in DNAH17 (c.1076_1077dup p.(Lys360*) and c.7752+2T>A p.?) associated with markedly reduced sperm motility and MMAF. The variants' pathogenicity was further validated by TEM of flagellar cross-sections revealing an outer dynein arm defect and axonemal disruption. On the contrary, his three infertile brothers were homozygous for the start-loss variant c.1A>G in HIPK4. This gene is expressed during spermiogenesis and is reportedly involved in sperm head shaping in mice. Heterologous expression of (partial) HIPK4 variant cDNA elucidated the alternative use of an in frame start codon located 35 amino acids downstream, resulting in an N-terminally truncated protein p.(Met1_Glu35del). The truncated HIPK4 protein lacks parts of its kinase domain and shows reduced protein stability. In line with published mouse models, all three brothers displayed 100% abnormal sperm head morphology with variable defects. Importantly, one brother affected by HIPK4 variants fathered a child after successful intracytoplasmic sperm injection demonstrating that it is a treatment option for HIPK4-related teratozoospermia. No further men from the MERGE cohort were affected by biallelic HIPK4 variants. Taken together, HIPK4 is an autosomal-recessive candidate gene associated with sperm head defects and male infertility. LARGE SCALE DATA: The reported variants in DNAH17 and HIPK4 were submitted to ClinVar. LIMITATIONS, REASONS FOR CAUTION: Independent replication is required to assess the phenotypic spectrum and the reproductive outcome associated with biallelic HIPK4 variants and to formally establish the gene-disease relationship for male infertility. WIDER IMPLICATIONS OF THE FINDINGS: This study raises awareness of the significant genetic heterogeneity of male infertility. The described family highlights that distinct genetic causes may underlie a seemingly similar phenotype. Exome sequencing of families is helpful to efficiently disentangle individual causes among affected family members. STUDY FUNDING/COMPETING INTEREST(S): N.N., J.R., H.O., S.L., C.F., and F.T. were supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the Clinical Research Unit 'Male Germ Cells' (CRU326, project number 329621271). R.T.W., N.N., J.R., H.O., and F.T. were supported by the Federal Ministry of Research, Technology and Space (BMFTR) as part of the project ReproTrack.MS (grant 01GR2303). S.A.K. was supported by the DFG Clinician Scientist programme CareerS Munster (project number 493624047). A.S.G. was supported by the Medical Faculty Munster via an Innovative Medical Research (IMF) grant (GA-122104).

Biallelic FSIP2 variants are associated with sperm defective chromatin condensation beyond MMAF and acrosomal abnormalities.

Mutation Severity of FBXO43 Determines Spermatogenic Outcome and Informs Precision ART Strategies

Objective FBXO43 is a known inhibitor of the anaphase‐promoting complex/cyclosome (APC/C), a key E3 ubiquitin ligase that controls meiotic cell cycle progression. However, how different FBXO43 mutations affect APC/C inhibition and lead to divergent clinical phenotypes remains unclear. This study is aimed at clarifying how different FBXO43 mutations produce divergent clinical phenotypes in male infertility and to investigate their preliminary molecular mechanisms, thereby providing evidence‐based guidance for precision‐assisted reproduction in affected individuals. Methods Two infertile patients carrying distinct compound heterozygous FBXO43 variants—missense mutations in a macrozoospermia case and truncating mutations in a nonobstructive azoospermia (NOA) case—were identified through whole‐exome sequencing. Sperm morphology, chromatin status, and aneuploidy were assessed, and a testicular biopsy was performed for the NOA case. Functional consequences of each mutation were evaluated using in vitro HEK 293T cell models, including protein stability, ubiquitination, and APC/C subunit interactions. Clinical outcomes of assisted reproductive technology (ART) were also reviewed. Results Missense variants (NM_001029860, p.Pro641Leu/p.Arg660Gln) in the macrozoospermia patient allowed completion of meiosis but led to severe sperm head enlargement, chromatin condensation defects, and markedly elevated aneuploidy, resulting in repeated ICSI failure. In contrast, the truncating variants (p.Trp532 ∗/p.Ser577Leufs ∗11) in the NOA patient abolished the C‐terminal functional domain and caused meiotic arrest with complete absence of mature sperm. Mechanistically, all mutations reduced FBXO43 protein stability and disrupted its specific binding to the APC/C substrate recognition subunit APC3, whereas interactions with APC2/6/8 remained intact. Loss of APC3 binding likely impairs APC/C inhibition, disturbing meiotic chromosome segregation in a mutation‐severity–dependent manner. Conclusions Different types of FBXO43 mutations generate distinct infertility phenotypes through a dose‐dependent mechanism: Truncating mutations cause profound meiotic arrest and NOA, whereas hypomorphic missense mutations permit meiotic completion but result in severe teratozoospermia with high aneuploidy. These findings link FBXO43 to a continuous phenotypic spectrum and highlight its relevance for precision reproductive counseling. Based on the identified mutation‐specific risks, preimplantation genetic testing for aneuploidy (PGT‐A) is recommended for affected couples to improve embryo selection and optimize ART outcomes.

Loss of TMC7 causes male infertility with disrupted spermiogenesis in mice.

Spermatogenesis is a highly ordered developmental process that occurs in the seminiferous tubules and involves mitotic proliferation of spermatogonial stem cells, meiotic division of spermatocytes, and post-meiotic spermiogenesis, ultimately producing mature spermatozoa. Defects at any stage of this process can lead to male infertility. Large-scale transcriptomic and proteomic studies have identified thousands of testis-enriched genes in humans and mice, supporting the use of mouse models to uncover genetic regulators of male fertility. In this study, we focused on transmembrane channel-like protein 7 (TMC7), which is highly expressed in the testis. To investigate its physiological function, we generated a Tmc7 knockout (KO) mouse line using the CRISPR/Cas9 system. Tmc7 KO male mice were sterile, and no spermatozoa were observed in the epididymis. Instead, multinucleated giant cells containing multiple elongating spermatids were detected in the lumens of seminiferous tubules. We found that these abnormalities were associated with defective intercellular bridge (ICB) stabilization. Transmission electron microscopy further revealed that spermatid nuclei passed through gaps within the ICBs, leading to the formation of multinucleated giant cells. Given the Golgi localization of TMC7, ICB destabilization may occur secondarily due to blood-testis barrier disruption caused by alterations in the testicular microenvironment. Importantly, ectopic expression of TMC7 in Tmc7 KO mice rescued the defective spermiogenesis phenotype. Taken together, these findings demonstrate that TMC7 plays a critical role in spermiogenesis and indirectly contributes to the maintenance of ICB integrity.

Novel mutations in ZMYND15 expand the phenotypic spectrum to acephalic spermatozoa: abnormal sperm head-tail connection mediated by SUN5.

Acephalic spermatozoa syndrome (ASS) is a rare cause of male infertility characterized by sperm tails lacking heads. Although zinc finger MYND-type containing 15 (ZMYND15) mutations are linked to male infertility, their role in ASS is unknown. In this study, whole-exome sequencing identified novel homozygous truncating mutations, c.292C>T (p.Arg98Ter) and c.337G>T (p.Glu113Ter), in ZMYND15 from two infertile patients. These mutations caused protein truncation and impaired function, leading to extremely low sperm counts, poor motility, and numerous acephalic spermatozoa. Electron microscopy and sperm immunofluorescence revealed abnormal sperm neck structures, missing mitochondrial sheaths, failure of acrosome formation, and a lack of central microtubules. Experiments showed reduced mutant protein expression and high rates of degradation. Coimmunoprecipitation experiments indicated a direct interaction between ZMYND15 and Sad1 and UNC84 domain containing 5 (SUN5), crucial for forming the sperm head-tail connection. One patient achieved a live birth via intracytoplasmic sperm injection (ICSI), whereas the other had an early miscarriage. This study links ZMYND15 mutations directly to ASS, highlighting its role in spermatogenesis and offering insights for clinical diagnosis and treatment.