Unintended genomic DNA loci (Off-target sites)

Unintended genomic DNA loci, commonly referred to as off-target sites, are regions of the genome that are inadvertently modified by gene-editing technologies such as CRISPR-Cas9, TALENs, or Zinc Finger Nucleases (Nature Communications, 2019). These events occur when the editing machinery recognizes and binds to DNA sequences that share high homology with the intended target sequence, leading to unintended double-strand breaks or base modifications (PubMed, PMID: 30718888). The biological consequence of such interactions includes the formation of insertions and deletions (indels), which can disrupt essential genes or regulatory elements (NIH, 2021). In a clinical context, these off-target effects represent a major safety concern, as they can lead to genomic instability, chromosomal translocations, or the activation of oncogenes, potentially causing secondary malignancies (Frontiers in Genome Editing, 2020). Consequently, identifying and minimizing activity at these unintended loci is a critical component of the preclinical development and safety profiling of any gene-editing therapeutic. Various high-throughput sequencing methods, such as GUIDE-seq, CIRCLE-seq, and Digenome-seq, are employed to detect these occurrences and ensure the precision of the therapeutic intervention (Nature Methods, 2015). These assays help researchers quantify the frequency of mutations at unintended loci to assess the risk-benefit profile of a given therapy. Reducing off-target activity is often achieved through the engineering of high-fidelity enzymes or the optimization of guide RNA design (Cell, 2016).

Other names

Off-target effectsOff-target genomic sitesNon-specific DNA cleavage sitesOff-target mutationsOff-target activity

Non-specific DNA binding and cleavage via sequence homology-driven recognition by programmable nucleases.