Novel and recurrent TUBB8 variants cause irreversible meiotic spindle defects and refractory ART failure in Chinese women with oocyte maturation arrest.

PURPOSE: Oocyte maturation arrest (OMA) is a major monogenic cause of unexplained female infertility and recurrent assisted reproductive technology (ART) failure. TUBB8, which encodes an oocyte-specific β-tubulin isoform essential for acentrosomal spindle assembly, represents the most common genetic etiology of metaphase I (MI) arrest. This study aimed to identify pathogenic TUBB8 variants and characterize their clinical phenotypes and molecular mechanisms in Chinese women with unexplained recurrent OMA.

METHODS

Six unrelated Chinese women with primary infertility and persistent OMA were enrolled. Whole-exome sequencing and Sanger sequencing were performed to identify and validate TUBB8 variants. Inheritance patterns, oocyte morphology, spindle integrity, and clinical ART outcomes were systematically evaluated. Three-dimensional structural modeling was used to predict the functional impact of the identified variants.

RESULTS

Five heterozygous missense variants were identified: c.292G > A (p.Gly98Arg), c.731G > A (p.Gly244Asp), c.735G > C (p.Gln245His), c.845G > C (p.Arg282Pro), and c.880 T > C (p.Phe294Leu). All variants mapped to evolutionarily conserved, functionally essential domains and were predicted to be deleterious. All patients exhibited normal ovarian reserve and endocrine profiles but uniform, irreversible MI arrest: 85.4% of retrieved oocytes arrested at MI, with only 5.7% reaching metaphase II. Polarization microscopy revealed absent or severely disorganized spindles. Despite ICSI combined with artificial oocyte activation, the fertilization rate was only 6.3%, with no blastocyst formation or clinical pregnancy. Structural modeling suggested that these variants may interfere with GTP hydrolysis, lateral protofilament interactions, and C-terminal hydrophobic networks, thereby exerting dominant-negative effects on spindle assembly.

CONCLUSIONS

This study expands the pathogenic mutational spectrum of TUBB8 and confirms that novel and recurrent TUBB8 missense variants cause irreversible MI arrest and complete ART refractoriness in Chinese women. Our findings support routine TUBB8 genetic screening as a valuable diagnostic tool for unexplained recurrent OMA, facilitating early diagnosis, avoidance of futile ART cycles, and personalized reproductive counseling.