Off-target genomic DNA sites with partial complementarity to single-guide RNA (Off-target sites)

Off-target genomic DNA sites are sequences within the genome that possess partial complementarity to a single-guide RNA (sgRNA) used in CRISPR-based gene editing systems (Zhang et al., 2015). While the CRISPR-Cas complex is designed to target a specific sequence, the Cas nuclease can occasionally bind and cleave these unintended sites if the mismatch is tolerated by the enzyme's binding kinetics. This phenomenon poses a significant challenge for therapeutic applications, as off-target mutations can lead to deleterious effects such as the activation of oncogenes or the disruption of essential tumor suppressor genes (Tsai et al., 2015). Minimizing off-target activity is a primary focus of genome engineering, involving the optimization of sgRNA design and the development of high-fidelity Cas variants. Monitoring these sites through specialized sequencing techniques like GUIDE-seq or CIRCLE-seq is crucial for ensuring the safety and precision of gene-editing therapies (FDA, 2023). These sites are not therapeutic targets themselves but represent a critical safety liability that must be characterized during drug development. The presence of these sites can lead to chromosomal translocations if multiple double-strand breaks occur simultaneously. Consequently, rigorous bioinformatic prediction and empirical validation are required for any CRISPR-based therapeutic candidate.

Other names

Off-target effectsCRISPR off-targetsNon-specific cleavage sitesMismatched DNA sequences

Unintended binding and enzymatic cleavage of DNA sequences that share high homology with the target single-guide RNA (sgRNA) sequence, leading to permanent genomic alterations.