Identification of a complex chromosomal insertion using the chromosome conformation based karyotyping technique for the implementation of PGT-SR.

OBJECTIVE: This study completed the karyotyping of a patient with a complex chromosomal insertion and identified the location of the breakpoint for implementing preimplantation genetic testing for chromosomal structural rearrangements (PGT-SR) to differentiate between normal and carrier embryos, aiming to assess the clinical outcome of PGT-SR in couples with complex chromosome rearrangements (CCRs). METHOD: The Chromosome conformation based Karyotyping technique (C-Moka) was implemented to identify karyotypes and analyze chromosomal breakpoints, with subsequent verification of karyotype results by fluorescence in situ hybridization (FISH). Whole genome sequencing (WGS) of embryos followed by copy number variation and second-generation sequencing (NGS) based single nucleotide polymorphism (SNP) haplotyping to discriminate between normal and carrier embryos were carried out in PGT-SR cycles. RESULTS: Based on the precise breakpoint sequences identified by C-Moka, mapping allele with resolved carrier status (MaReCs) was used to distinguish a normal embryo from a carrier embryo among two balanced euploidy embryos, resulting in the birth of a healthy baby after transfer of the normal embryo. CONCLUSION: This case demonstrates the feasibility of C-Moka technique in assisting CCRs diagnosis and directly identifying breakpoints to construct haplotypes without family lineage or reference embryo pre-tests.