Why are off-target edits a concern in CRISPR experiments?

• A. They always improve editing accuracy.
• B. They can introduce unintended mutations with potential functional consequences.
• C. They speed up the editing reaction.
• D. They have no effect.

Answer: (B)

Off-target edits are a concern because the CRISPR system can cut DNA at unintended sites in the genome. The guide RNA is designed to match a specific sequence, but the genome contains many similar sequences, and the Cas9 enzyme can tolerate a few mismatches. When a cut happens at these near-match sites, the cell’s repair processes (like NHEJ or HDR) can introduce small or larger mutations at those locations. These unintended mutations can disrupt genes, alter regulatory elements, or cause unexpected changes in gene function, which is especially risky in therapeutic contexts where safety is critical. So, while off-target edits don’t typically speed up the process or improve accuracy, they pose real potential for harmful or confounding changes, which is why they’re a major focus of CRISPR risk assessment and optimization.