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CRISPR

Base editing, a refinement of CRISPR gene editing developed roughly a decade ago, has moved from a promising laboratory technique into a small but growing number of authorised clinical treatments. Unlike the original CRISPR-Cas9 approach, which cuts both strands of the DNA double helix and relies on the cell's repair machinery to fix the break, base editing chemically converts one DNA letter into another without cutting the helix at all. That distinction sounds technical, but it has meaningful consequences for safety and precision.

• First-generation CRISPR: cuts both DNA strands, relies on cellular repair, can produce larger unintended edits.
• Base editing: converts a single DNA letter without cutting both strands, generally produces smaller and more predictable changes.
• Both approaches still require careful off-target screening before and after treatment.
• Base editing is currently better suited to correcting single-letter mutations than to larger insertions or gene rearrangements.