Off-target genomic DNA loci

Off-target genomic DNA loci are sequences within the genome that are unintentionally modified by genome-editing technologies such as CRISPR-Cas9, Zinc Finger Nucleases (ZFNs), and Transcription Activator-Like Effector Nucleases (TALENs). These sites often share significant sequence homology with the intended target locus, allowing the editing machinery to bind and induce double-strand breaks or other modifications (Zhang et al., 2015). While these loci are not therapeutic targets themselves, their modification is a primary safety concern in the development of gene therapies. Unintended edits at these locations can result in permanent mutations, including gene disruptions or large-scale chromosomal translocations (Fu et al., 2013). Such alterations carry the risk of activating proto-oncogenes or inactivating tumor suppressor genes, potentially leading to tumorigenesis or other adverse cellular outcomes. Therefore, rigorous assessment of off-target activity using methods like GUIDE-seq or whole-genome sequencing is essential for ensuring the safety and specificity of genomic medicines (FDA, 2024).

Other names

Off-target sitesUnintended genomic modificationsNon-specific DNA binding sitesOff-target effectsGenomic off-targets

Unintended enzymatic modification or cleavage of DNA at sites with sequence homology to the guide RNA or DNA-binding domain of a genome editing tool.