Comprehensive preimplantation genetic testing by massively parallel sequencing

STUDY QUESTION: Can whole genome sequencing (WGS) offer a relatively cost-effective approach for embryonic genome-wide haplotyping and preimplantation genetic testing (PGT) for monogenic disorders (PGT-M), aneuploidy (PGT-A) and structural rearrangements (PGT-SR)? SUMMARY ANSWER: Reliable genome-wide haplotyping, PGT-M, PGT-A and PGT-SR could be performed by WGS with 10 x depth of parental and 4x depth of embryonic sequencing data. WHAT IS KNOWN ALREADY: Reduced representation genome sequencing with a genome-wide next-generation sequencing haplarithmisis-based solution has been verified as a generic approach for automated haplotyping and comprehensive PGT. Several low-depth massively parallel sequencing (MPS)-based methods for haplotyping and comprehensive PGT have been developed. However, an additional family member, such as a sibling, or a proband, is required for PGT-M haplotyping using low-depth MPS methods. STUDY DESIGN, SIZE, DURATION: In this study, 10 families that had undergone traditional IVF-PGT and 53 embryos, including 13 embryos from two PGT-SR families and 40 embryos from eight PGT-M families, were included to evaluate a WGS-based method. There were 24 blastomeres and 29 blastocysts in total. All embryos were used for PGT-A. Karyomapping validated the WGS results. Clinical outcomes of the 10 families were evaluated. PARTICIPANTS/MATERIALS, SETTING, METHODS: A blastomere or a few trophectoderm cells from the blastocyst were biopsied, and multiple displacement amplification (MDA) was performed. MDA DNA and bulk DNA of family members were used for library construction. Libraries were sequenced, and data analysis, including haplotype inheritance deduction for PGT-M and PGT-SR and read-count analysis for PGT-A, was performed using an in-house pipeline. Haplotyping with a proband and parent-only haplotyping without additional family members were performed to assess the WGS methodology. Concordance analysis between the WGS results and traditional PGT methods was performed. MAIN RESULTS AND THE ROLE OF CHANCE: For the 40 PGT M and 53 PGT A embryos, 100% concordance between the WGS and single nucleotide polymorphism (SNP) array results was observed, regardless of whether additional family members or a proband was included for PGT-M haplotyping. For the 13 embryos from the two PGT-SR families, the embryonic balanced translocation was detected and 100% concordance between WGS and MicroSeq with PCR-seq was demonstrated. LIMITATIONS, REASONS FOR CAUTION: The number of samples in this study was limited. In some cases, the reference embryo for PGT M or PGT SR parent only haplotyping was not available owing to failed direct genotyping. WIDER IMPLICATIONS OF THE FINDINGS: WGS-based PGT-A, PGT-M and PGT-SR offered a comprehensive PGT approach for haplotyping without the requirement for additional family members. It provided an improved complementary method to PGT methodologies, such as low-depth MPS- and SNP array-based methods.

Automated summary

WGS offers a cost-effective and reliable approach for genome-wide haplotyping and PGT for monogenic disorders, aneuploidy, and structural rearrangements without the need for additional family members, showing 100% concordance with traditional PGT methods.