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Gene therapy and gene editing are not the same thing, and the difference is the single most useful distinction on this site. Gene therapy adds a working copy of a gene, usually carried in by a modified virus, and leaves the broken original exactly where it is. Gene editing changes the original. Adding is older, more established, and has many approved products; changing is newer and has one.
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Gene addition delivers a functional transgene via viral vectors — adeno-associated virus for non-integrating delivery to non-dividing tissue, lentivirus for integrating delivery to dividing cells such as haematopoietic stem cells — or by non-viral means. The endogenous locus is untouched. AAV episomes dilute out as cells divide, which limits durability in proliferating tissue; lentiviral integration is durable but semi-random, carrying insertional-mutagenesis risk.
Where it works better than editing
When the problem is a missing protein and the mutations causing it are scattered across the gene, adding one working copy treats everybody with the condition. Editing would need a different design per mutation. This is why approved therapies for spinal muscular atrophy, inherited retinal dystrophy and haemophilia are gene addition, not editing.
Where editing wins
When the problem is a protein that is actively harmful rather than absent — a toxic gain of function — adding another copy achieves nothing; the bad one has to be silenced or removed. Editing also preserves the gene's own regulation, which matters when the amount and timing of expression is important, and it does not run out as an AAV episome does in dividing cells.
Common questions
What is the difference between CRISPR and gene therapy?
Gene therapy adds a working copy of a gene and leaves the faulty one in place. CRISPR gene editing changes the existing DNA itself. Both are permanent for the cells they reach, both are administered once, and in ordinary speech they get used interchangeably — but they are different interventions with different risks, and regulators treat them differently.
Sources
- U.S. Food and Drug Administration
Approved cellular and gene therapy products ↗