Off-target genomic DNA adenine bases at partially matched sgRNA sites (DNA off-target sites)

Off-target genomic DNA adenine bases at partially matched sgRNA sites refer to unintended genomic loci where adenine base editors (ABEs) induce mutations (Gaudelli et al., 2017, Nature). These events occur when the single guide RNA (sgRNA) directs the CRISPR-Cas complex to DNA sequences that share high homology with the intended target, allowing for mismatch tolerance (Rees & Liu, 2018, Nature Reviews Genetics). At these sites, the deoxyadenosine deaminase component of the ABE converts adenine to inosine, which is subsequently replicated or repaired as guanine, resulting in permanent A-to-G transitions (Kim et al., 2019, Nature Biotechnology). Such off-target activity is a primary safety concern in genome editing because it can lead to genotoxicity, the activation of oncogenes, or the disruption of tumor suppressor genes (Zuo et al., 2019, Science). Consequently, identifying and minimizing these off-target effects is essential for the clinical development of base editing therapies. Advanced sequencing methods like CIRCLE-seq and GOTI are employed to detect these unintended modifications across the genome to ensure therapeutic precision (Zuo et al., 2019, Science).

Other names

Off-target adenine deaminationsgRNA-dependent DNA off-targetsUnintended A-to-G transitionsCRISPR-Cas9 off-target sites

Adenine base editors (ABEs) utilize a guide RNA to target a Cas9 nickase fused to a deoxyadenosine deaminase (e.g., TadA) to a specific DNA sequence. At partially matched off-target sites, the deaminase converts adenine to inosine, which is read as guanine during DNA replication, resulting in an A-to-G transition (Gaudelli et al., 2017, Nature).