Detection and Haplotype Construction of ring Chromosome 17 for Carrier Screening in Preimplantation Genetic Testing

Background : While preimplantation genetic testing (PGT) carrier screening has proven efficacious in improving assisted reproduction outcomes for individuals with balanced translocations and chromosome inversions, the accurate identification of embryos carrying ring chromosomes remains a substantial challenge, undermining the efficacy of PGT. This study aims to address this gap by pioneering an advanced proband-independent haplotyping technology based on Linked-Read Sequencing technology designed to overcome the limitations of traditional molecular approaches. Results : Our integrated approach resulted in the identification of an 804 kb copy number variation (CNV) deficiency in the 17q25.3 region by CMA. Pacbio HiFi and Nanopore sequencing techniques refined breakpoint characterization, confirming telomere fusion events in chromosome 17, validated by FISH analysis. Linked-Read Sequencing technology played a pivotal role in precisely detecting CNV breakpoints and confirming end-to-end connections on chromosome 17 by linked reads. This critical insight supported the construction of a specific ring chromosome 17 haplotype for Preimplantation Genetic Testing (PGT) applications. Conclusions : This study represents a significant advancement in accurately identifying carriers of ring chromosomes and elucidating their impact on Preimplantation Genetic Testing (PGT). Our results underscore the efficacy of Linked-Read Sequencing as a robust and superior method for detecting and precisely localizing ring chromosome breakpoints, offering relatively longer DNA sequences compared to both PacBio and Nanopore technologies. Through the integration of exact breakpoint identification with haplotype linkage analysis, we were able to distinguish embryos carrying ring chromosomes from those with normal karyotypes effectively. This approach is particularly vital for chromosomes with telomeric region fusion, facilitating the construction of distinct haplotypes for affected and unaffected embryos. The methodological advancements achieved in this research significantly enhance the capabilities of PGT, marking a pivotal contribution to genetic diagnostics.