Hidden Outcomes of CRISPR-Cas9 Genome Editing Revealed by Targeted Sequencing in Isogenic Human iPSC Clones

Advances in CRISPR-Cas9-based genome editing have simplified the generation of isogenic induced pluripotent stem cell (iPSC) pairs differing by a single genetic perturbation, minimizing interindividual variability in disease modeling. However, imprecise editing can cause unintended mutations that distort genotype-phenotype interpretation. Here, we investigated the molecular consequences of CRISPR-Cas9 editing in human iPSCs carrying a tandem duplication of the STAG2 locus. Using hybridization capture-based targeted next-generation sequencing of genomic regions surrounding Cas9-induced double-strand breaks, we identified inversions, plasmid DNA integrations, and complex structural rearrangements that had been missed by conventional PCR-based genotyping. The main advance of our study is the application of a practical hybridization capture-based workflow for resolving such hidden editing outcomes during the generation of isogenic iPSC models. In the selected clones subjected to detailed analysis, targeted sequencing enabled us to revise the initial interpretation of editing outcomes and resolve discrepancies between genotypic and transcriptomic data. Our results demonstrate that complex on-target alterations can remain undetected by conventional PCR-based genotyping and show that hybridization capture-based targeted sequencing can serve as a practical quality-control approach for the characterization of edited iPSC clones.