Yue-Qiu Tan

STUDY QUESTION: In best-prognosis preimplantation genetic testing (PGT) cycles—defined by the availability of multiple transferable embryos—can polygenic embryo screening (PES) provide meaningful, context-dependent stratification that may influence embryo prioritization? SUMMARY ANSWER: In a sister-pair breast cancer validation cohort, the polygenic risk score (PRS) showed modest predictive performance, and when applied retrospectively to embryos, differences in modelled susceptibility were context-dependent, primarily influenced by the number of available embryos, parental polygenic risk profile, the limited discriminative power of the PRS, and the presence of disease-related monogenic variants. WHAT IS KNOWN ALREADY: The use of PES as an embryo-ranking tool within PGT remains controversial. Its potential utility depends on embryo availability and clinical context, yet empirical evaluations in real-world PGT settings remain limited. STUDY DESIGN, SIZE, DURATION: This retrospective study combined (i) family-based validation using 184 affected–unaffected sisters, and (ii) embryo-level analysis of 310 PGT for monogenic disorders (PGT-M) cycles comprising 1722 embryos. Simulation modelling estimated differences in modelled embryo-level PRS percentile ranking under varying clinical and genetic scenarios. PARTICIPANTS/MATERIALS, SETTING, METHODS: Family-based performance of a breast cancer PRS was evaluated using affected and unaffected sister pairs. Embryo genotype data from PGT-M cycles were used to model PES under varying conditions, including the number of transferable embryos, the presence of pathogenic monogenic variants, and parental PRS percentile strata. MAIN RESULTS AND THE ROLE OF CHANCE: Within-family PRS discrimination was modest: sisters in the top 10% of the PRS distribution had 4.07-fold higher breast cancer odds than their siblings (95% CI: 1.55–6.33). In the PGT-M cohort, 55% of cycles produced ≥3 transferable embryos, with a median within-cycle spread of approximately 25 PRS percentiles. In BRCA1/2-related cycles, PRS did not introduce distinct risk strata but revealed dispersion in modelled susceptibility among embryos sharing the same monogenic background. Embryo PRS distributions were concordant with parental profiles: 71% of embryos from couples with parental PRS ≥80th percentile were classified as high-PRS, compared with 7% when at least one parent was ≤20th percentile. Simulation analyses indicated that PRS-based embryo prioritization was associated with a 12-point lower mean embryo PRS percentile compared with morphology-based embryo prioritization in PGT-M cycles, attenuating to 10 points when PGT-A was incorporated. These differences reflect a statistical surrogate outcome only and do not demonstrate reduction in lifetime disease incidence or other clinical benefits. LARGE SCALE DATA: N/A LIMITATIONS, REASONS FOR CAUTION: These findings derive from high-prognosis PGT-M cycles and may not generalize to other PGT settings. Current PRS models have modest performance and variable transferability across ancestries. The retrospective design, limited subgroup sizes, and modelling assumptions (e.g. aneuploidy and sex distribution) further constrain interpretation. The primary simulation outcome—PRS percentile shift—is a hypothesis-generating surrogate endpoint, not a clinical outcome; clinical benefit was not assessed or demonstrated. These findings should not be interpreted as supporting routine clinical implementation of PES; premature use may increase parental anxiety, inequitable access, and pressure to rank embryos using predictions that remain unvalidated at the embryo level. WIDER IMPLICATIONS OF THE FINDINGS: This study provides an empirical framework for evaluating the current limits of PES within PGT. The observed PRS percentile shifts appear concentrated in best-prognosis cycles with multiple transferable embryos and elevated parental PRS, whereas little change is observed when embryo numbers are limited or risk is dominated by high-penetrance monogenic variants. These findings are hypothesis-generating and may inform future prospective research and ethical discussion, while underscoring that clinical utility and implementation require further validation within appropriately governed settings. FUNDING: This study was funded by Major Scientific Program of CITIC Group (No. 2023ZXKYB34100), the Science Foundation of Hunan Province (Grant 2023JJ30422), and Health Research Project of Hunan Provincial Health Commission (grant number: W20243089). DISCLOSURES: The authors declare no conflicts of interest.

The precise assembly of the sperm flagellum is essential for male fertility and has long been ascribed to kinesin‐2–driven intraflagellar transport (IFT) of protein cargoes. However, during late spermiogenesis, when transcription activity is largely silenced, how the spatiotemporally regulated delivery of flagellar components remains poorly understood. Here, we systematically screened kinesin genes in asthenozoospermic patients and identified two homozygous deleterious KIF6 variants in unrelated men characterized by complete sperm immotility. Mouse models carrying the corresponding mutations recapitulated the human infertility phenotypes. Multi‐omics analyses revealed that most testicular mRNAs remained largely unchanged in Kif6 ^M1/M1 mice, whereas proteins involved in axonemal organization and energy metabolism were markedly reduced. Mechanistically, KIF6 interacts with the RNA‐binding proteins (RBPs) FMRP and FXR1 to assemble mRNP transport complexes that ferry transcripts encoding flagellar structural proteins (e.g., DNALI1) and metabolic enzymes (e.g., HK1). Impaired KIF6 function compromises mRNP trafficking to the developing flagellum, reducing flagellar transcript levels and ultimately causing decreased protein abundance and defective flagellar function. Collectively, we identify KIF6 as a key regulator of mRNA transport during spermiogenesis. It interacts with RBPs through a novel IFT‐like pathway to deliver mRNAs essential for flagellar biogenesis, redefining the traditional protein‐centric IFT paradigm.

STUDY QUESTION: What is the genetic etiology of recurrent blastulation failure, particularly in morphologically good-quality cleavage-stage embryos? SUMMARY ANSWER: Variants in meiotic genes may contribute to gamete-derived complex aneuploidy and impaired embryonic genome activation, which are strongly associated with recurrent blastulation failure in good-quality cleavage-stage embryos (R-GQBF). WHAT IS KNOWN ALREADY: Successful blastocyst formation is critical for implantation. Embryonic development undergoes a major transition around the 8‑cell stage, shifting from reliance on maternal transcripts to embryonic genome activation. While pathogenic variants in maternal-effect genes have been linked to developmental arrest before the 8-cell stage, the genetic basis of failure occurring between the 8-cell stage and blastulation remains unclear. STUDY DESIGN, SIZE, DURATION: From 2018 to 2023, 707 couples who met the R-GQBF criteria were recruited. After rigorous exclusion, 204 couples remained, of whom 97 were ultimately included for genetic etiology analysis. PARTICIPANTS/MATERIALS, SETTING, METHODS: A total of 109 individuals from 97 selected couples (93 females and 16 males, including 13 couples with both partners) underwent whole-exome sequencing (WES). Genetic variants were compared with those from 1000 fertile controls (500 females and 500 males). The chromosomal constitutions of 103 blastulation-failure embryos from 50 R-GQBF couples were analyzed via WES. Copy number variation (CNV) parental origin analysis was performed on 13 aneuploid embryos. Paternally derived chromosomal anomalies were further investigated using single-sperm chromosome analysis. Additionally, single-cell RNA sequencing was carried out on 15 arrested embryos. MAIN RESULTS AND THE ROLE OF CHANCE: Twenty-five variants in 10 meiotic genes were identified in 20 patients (18.3%). Female carriers predominantly harbored prophase I variants (SPO11, MEI1, REC114, ANKRD31, DMC1, CNTD1, MLH3, SYCE1, and SYCP2), while three male patients carried MEIKIN variants. Female carriers generally had preserved ovarian reserve, whereas male carriers showed severe oligoasthenoteratozoospermia. Chromosomal analysis revealed a high prevalence of complex aneuploidy in blastulation-failure embryos (63.1%). CNV tracing confirmed the parental origin of abnormalities from the meiotic variant carrier in analyzed case, and sperm from all MEIKIN carriers also exhibited severe chromosomal abnormalities. Single-cell transcriptomics revealed defective embryonic genome activation, impaired lineage specification, and activation of stress pathways. These consistent findings minimize the likelihood of chance associations. LARGE SCALE DATA: N/A. LIMITATIONS, REASONS FOR CAUTION: Direct evaluation of oocyte chromosomal integrity was not feasible. Larger cohorts may reveal additional genes, and functional studies in animal models are required to validate genotype–phenotype relationships. WIDER IMPLICATIONS OF THE FINDINGS: This study identifies biparental meiotic variants as an underrecognized cause of R-GQBF. Clinically, beyond routine extended embryo culture, chromosomal analysis should be recommended for etiological investigation. For couples experiencing recurrent complex aneuploidy in good-quality cleavage-stage embryos, genetic screening for meiotic variants may aid in diagnosis, counseling, and personalized treatment planning. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the National Natural Science Foundation of China (32270911, 82371672, 82471697, 62588301), the Natural Science Foundation of Hunan Province (2024JJ2083, 2023JJ30714, 2023JJ10084), the Science and Technology Innovation Program of Hunan Province (2023RC3233), the Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (JYB2025XDXM117), the National Key R&D Program of China (2023YFC2705504), and the project of the Reproductive and Genetic Hospital of CITIC-XIANGYA (YNXM-202221, YNXM-202402, and YNXM-202505). The authors declare no competing interests.

Oligoasthenoteratozoospermia (OAT) is a prevalent phenotype among infertile males, yet its underlying genetic etiology remains largely undefined. In this study, we found Spem2 deficiency did not affect the development of spermatogenic cells or the eventual generation of elongated spermatids within the testis, but affected the normal formation of residual bodies during the late stage of spermiation, which led to incomplete cytoplasmic removal of spermatids, abnormal sperm release and caused OAT. Affected sperm exhibited severely bent heads, cytoplasmic remnants encasing the head, and multiple sperm gathered. We further found SPEM2 may be involved in maintaining spermiation and cell polarity through interactions with cell polar molecules VANGL2, PRICKLE3, and DVL3. In vitro experiments showed that the transmembrane region of SPEM2 was its key functional domain and the binding domain for interactions between SPEM2 and VANGL2. Importantly, Spem2-deficient sperm enabled successful fertilization via intracytoplasmic sperm injection. Three novel SPEM2 heterozygous pathogenic variants were identified in four OAT patients by the whole-exome sequencing. Our findings revealed key roles of SPEM2 in spermiation, explored the potential pathogenesis of male infertility caused by SPEM2 deficiency, and provided essential information for genetic and reproductive counseling for such patients.

Structural variants (SVs) underlie genomic diversity and human diseases; however, current short-read sequencing-based methods experience challenges in precisely identifying and determining SV composition, which often lead to incorrect interpretation and/or missing detection of clinically significant variants. Here, we introduce SCARD (split-read, chimeric read-pairs, and read-depth difference), an integrated approach optimized for the detection and characterization of rare SVs using short-read genome sequencing data. Firstly, we evaluated rare SV (with minor allele frequency <1%) detection performance using 16 clinical cases with 18 previously ascertained exonic deletions/duplications in dominant/recessive conditions. SCARD accurately detected all 18 exonic deletions/duplications, ranging from 490 bp to 24.5 kb, confirmed by gap-PCR and/or Sanger sequencing, outperforming other methods that only achieved 15/18 at best. In addition, SCARD characterized rare SVs from 2,504 unrelated individuals and 477 trios/probands from the 1000 Genomes Project, and compared them to those from 13 SV detection methods (13callers). Among the 2,504 genomes analyzed, we identified 429,259 rare simple deletions/duplications and 7,795 structural rearrangements, with 10.7% of deletions/duplications (46,032/429,259) and 40.1% of structural rearrangements (3,126/7,795) being novel to those from the 13callers. Notably, 45.2% (1,133/2,504) of the subjects carried likely loss-of-function SVs involving autosomal recessive disorders related genes. In 477 trios, the overall de novo rate for rare SVs was 0.5% (383/77,349). Finally, to evaluate the accuracy of rare SV calling, we compared our SVs in 15 cases to those of high-quality long-read sequencing datasets. The accuracies of detecting deletions/duplications, structural rearrangements, and all SVs by SCARD were 98.0% (2,858/2,917), 94% (47/50), and 97.9% (2,905/2,967), respectively. In comparison, 13callers missed or misinterpreted 325 of 2,905 validated rare SVs (11.2%) reported by SCARD. Overall, our study demonstrates that SCARD enables comprehensive, genome-wide identification and precise delineation of rare SVs, particularly for those affecting exons, to reveal a high carrier rate of autosomal recessive disorders contributed by rare SVs.