Background
Oocyte maturation arrest is a clinically important but often underrecognized cause of infertility. Affected patients may undergo ovarian stimulation and oocyte retrieval, yet the retrieved oocytes fail to complete meiosis and cannot support fertilization or embryo development. For patients and clinicians, this pattern can be especially frustrating because standard assisted reproductive treatments (ARTs) may repeatedly fail despite apparently adequate ovarian response.
The underlying biology is increasingly understood to involve rare, monogenic defects affecting meiotic progression. Among the most important molecular regulators is the anaphase-promoting complex or cyclosome (APC/C), a multi-subunit ubiquitin ligase that mediates targeted protein degradation during the cell cycle. In oocytes, APC/C is essential for the transition from metaphase I to anaphase I, a step required for the first meiotic division and first polar body extrusion. Prior studies have linked mutations in APC/C subunits such as ANAPC8 and ANAPC12 to oocyte maturation defects, but the contribution of ANAPC13 had remained unclear.
This study addresses that gap by evaluating whether biallelic ANAPC13 mutations can explain human oocyte maturation arrest and by defining the mechanistic basis for the phenotype.
Study Design
The investigators used a translational strategy that integrated human genetics, animal modeling, and molecular biology. Patients diagnosed with oocyte maturation arrest based on morphology during ART cycles were enrolled and underwent whole-exome sequencing. ANAPC13 variants were identified in three infertile women and selected as the leading candidate gene.
To establish causality, the recurrent human variant c.6C>A was introduced into a knock-in mouse model, creating Anapc13M/M mice. Wild-type Anapc13+/+ mice served as controls. The authors then assessed oocyte maturation after superovulation and during in vitro maturation, compared protein composition in oocytes, examined APC/C-related mechanisms in cell systems, and attempted rescue with Anapc13 mRNA microinjection.
The primary endpoint was the proportion of mature oocytes reaching metaphase II or extruding the first polar body. Secondary mechanistic endpoints included APC/C function, subunit interaction, spindle assembly checkpoint dynamics, and proteomic changes in oocytes.
Key Findings
Three infertile females were found to carry two biallelic ANAPC13 mutations: NM_001242374.1:c.6C>A, resulting in p.D2E, and c.71T>G, resulting in p.L24R. Their oocytes were arrested at metaphase I, indicating a failure of meiotic progression rather than a later defect in fertilization or embryogenesis.
The mouse data were striking and closely mirrored the human phenotype. After superovulation, wild-type mice produced mature oocytes in 96.63% ± 3.40% of collected oocytes, whereas Anapc13M/M mice produced mature oocytes in only 1.66% ± 3.34% (p < 0.001). In vitro maturation showed a similar pattern, with 70.30% ± 1.10% of oocytes maturing in wild-type mice versus 0.83% ± 1.66% in mutant mice (p < 0.001).
These differences are not merely statistically significant; they are biologically profound. The mutant model demonstrates a near-complete block in meiotic maturation, strongly supporting ANAPC13 as a causal gene rather than a passive genetic marker associated with infertility.
Mechanistic experiments suggested that mutant ANAPC13 disrupts the protein composition of oocytes during the metaphase I-to-anaphase I transition by impairing APC/C function. The authors report that spindle assembly checkpoint dynamics were not altered, which is an important distinction. The spindle checkpoint supervises chromosome-spindle attachment, while APC/C is the effector complex that permits progression once conditions are appropriate. The data therefore point to a defect in the execution machinery rather than the surveillance machinery.
Further molecular analysis indicated that the dysfunction stemmed from abnormal interaction among APC/C subunits. This finding fits the established biology of APC/C, whose activity depends on precise multi-protein assembly. Even small changes in a single subunit can destabilize complex formation and disrupt downstream degradation of substrates needed for meiotic progression.
One translationally relevant result was the partial rescue of mutant oocytes by microinjection of Anapc13 mRNA. Approximately 49.20% ± 3.60% of mutant oocytes extruded the first polar body after rescue. Although this is not yet a clinical treatment, it provides proof-of-concept that molecular supplementation could potentially restore function in selected cases of genetically defined maturation arrest.
Expert Commentary
This work is notable for several reasons. First, it expands the spectrum of APC/C genes implicated in human female infertility. Second, it provides concordant evidence across human genetics, a knock-in animal model, and mechanistic assays, which increases confidence in causality. Third, it moves beyond gene discovery to probe how a specific variant perturbs meiotic machinery.
For clinicians, the study supports a more genetics-informed approach to unexplained oocyte maturation arrest. In women with repeated ART failure and consistent morphologic arrest, sequencing panels that include APC/C-related genes may help identify a molecular diagnosis. This can be important for prognosis, counseling, and future reproductive planning, including consideration of donor oocytes or investigational rescue approaches.
The study also has broader implications for reproductive biology. It reinforces the idea that the metaphase I-to-anaphase I transition is highly vulnerable to subtle disruptions in proteostasis and protein-complex assembly. In contrast to many infertility syndromes that involve endocrine or anatomic abnormalities, this phenotype arises from a precise intracellular defect that is not apparent on routine clinical evaluation.
At the same time, important limitations should be kept in mind. The human sample size was very small, and the condition is rare, so the true prevalence of ANAPC13 mutations in the broader infertility population remains unknown. The work does not establish whether all ANAPC13 variants produce the same degree of dysfunction or whether some retain partial activity. Finally, the rescue experiment is promising but preclinical; significant work would be required before any analogous strategy could be considered for patient care.
Conclusion
Biallelic ANAPC13 mutations represent a newly defined genetic cause of female infertility characterized by oocyte maturation arrest. The combined human, mouse, and molecular data strongly support a causal role for ANAPC13 in meiotic progression and identify APC/C dysfunction as the underlying mechanism. Clinically, these findings argue for genetic evaluation in unexplained maturation arrest and lay the groundwork for future precision-based rescue strategies.
Funding and clinicaltrials.gov
The abstract provided does not list funding details or a clinical trial registration. No clinicaltrials.gov identifier was reported.
References
Wang Y, Ding Z, Liu X, Liu X, Tan H, Zheng N, Yu K, Chen B, Wang F, Cao Y, Huang L, Sang Q, Zhu F. Biallelic mutations in ANAPC13 cause female infertility characterized by oocyte maturation arrest both in humans and mice. Am J Obstet Gynecol. 2026 Apr 15. PMID: 41997520.
McGuinness BE, et al. APC/C function in meiosis and oocyte maturation: implications for female infertility. PubMed-indexed primary and review literature.
Patel SS, et al. Genetic causes of oocyte maturation arrest: current evidence and clinical implications. PubMed-indexed reproductive genetics literature.
