Why Edit RNA Instead of DNA?
Every gene editing technology discussed in mainstream science coverage — CRISPR-Cas9, base editing, prime editing — makes permanent changes to the genome. That permanence is a feature when correcting a clear-cut genetic defect, but it is also a risk. An off-target edit in DNA is irreversible: once a gene is mutated, it stays mutated in that cell and all its descendants.
RNA editing offers a fundamentally different paradigm. Because messenger RNA (mRNA) is a transient molecule — it is transcribed from DNA, translated into protein, and then degraded — edits made at the RNA level are inherently temporary. If something goes wrong, the cell simply makes fresh, unedited mRNA from the original, unaltered DNA. This reversibility has made RNA editing one of the most closely watched frontiers in genetic medicine.
ADAR Enzymes: Nature's RNA Editors
RNA editing is not a human invention. It occurs naturally in every human cell, carried out by a family of enzymes called ADARs (Adenosine Deaminases Acting on RNA). Humans have two catalytically active ADAR enzymes: ADAR1 and ADAR2.
The A-to-I Reaction
ADARs catalyze the deamination of adenosine (A) to inosine (I) in double-stranded RNA. Because the cellular machinery reads inosine as guanosine (G), the functional effect is an A-to-G change at the RNA level. This single chemical reaction can:
- Recode proteins: Change the amino acid specified by a codon, altering protein function.
- Alter splicing: Modify splice site recognition sequences, changing which exons are included in the mature mRNA.
- Regulate innate immunity: Extensive A-to-I editing of endogenous double-stranded RNA prevents the innate immune system from mistakenly recognizing the cell's own RNA as foreign. Loss of ADAR1 function triggers a severe autoinflammatory condition called Aicardi-Goutieres syndrome.
The human transcriptome contains millions of A-to-I editing sites, most of them in repetitive Alu elements within non-coding regions. However, dozens of sites in coding regions are functionally important, including a critical site in the GluA2 glutamate receptor subunit where editing is required for normal brain function.
Programmable RNA Editing
The therapeutic vision is to harness the cell's own ADAR enzymes — or deliver engineered versions — to edit specific RNA transcripts on demand. Several approaches are under development.
Endogenous ADAR Recruitment
The most elegant strategy is to recruit the cell's existing ADAR enzymes to a target RNA without delivering any foreign protein. This is done by introducing a short antisense oligonucleotide (ASO) or guide RNA that binds to the target mRNA, creating a double-stranded RNA structure that attracts endogenous ADAR.
The guide RNA is designed so that the target adenosine is positioned opposite a cytidine mismatch — a structural feature that ADAR recognizes and preferentially edits. Some designs incorporate chemically modified nucleotides or ADAR-recruiting domains to enhance efficiency.
Key advantage: No foreign protein is introduced into the cell, potentially reducing immunogenicity and simplifying the regulatory pathway.
Engineered ADAR Fusion Proteins
An alternative approach fuses a catalytically active ADAR deaminase domain to a programmable RNA-binding protein, such as the Cas13 enzyme (which targets RNA rather than DNA) or a PUF (Pumilio and FBF homology) domain. The RNA-binding protein directs the ADAR domain to the specific transcript, and the deaminase makes the A-to-I edit.
This approach offers potentially higher editing efficiency and greater control over site selectivity, but requires delivery of an exogenous protein.
CRISPR-Cas13 Systems
The Zhang laboratory at the Broad Institute demonstrated that catalytically inactive Cas13 (dCas13) fused to the ADAR2 deaminase domain can perform programmable A-to-I editing in mammalian cells. This system, called REPAIR (RNA Editing for Programmable A-to-I Replacement), achieves editing without affecting the DNA and avoids the permanent changes associated with Cas9.
A subsequent system called RESCUE (RNA Editing for Specific C-to-U Exchange) expanded the toolkit to include C-to-U editing by engineering the ADAR2 deaminase domain to accept cytidine as a substrate.
Advantages Over DNA Editing
Reversibility
The most important advantage is that RNA edits are temporary. mRNA has a half-life measured in hours to days. When the guide RNA or ASO is cleared from the cell, editing ceases, and normal mRNA is produced from the unchanged DNA. This creates an inherently safer therapeutic profile — dosing can be adjusted, and treatment can be stopped if adverse effects emerge.
No Double-Strand Breaks
RNA editing introduces no breaks in genomic DNA, eliminating the risk of large deletions, translocations, or chromothripsis that can accompany CRISPR-Cas9 cutting.
Harnessing Endogenous Machinery
By recruiting the cell's own ADAR enzymes, some RNA editing approaches avoid delivering any foreign protein, reducing immunogenicity — a significant challenge for repeated dosing of protein-based DNA editors.
Applicability to Dominant Negative Mutations
Some genetic diseases are caused by dominant negative mutations, where the mutant protein actively interferes with the normal protein. In these cases, simply knocking out the mutant gene with CRISPR is insufficient. RNA editing can correct the mutant transcript while leaving the normal allele untouched.
Limitations and Challenges
Restricted Edit Types
Endogenous ADAR enzymes can only make A-to-I (functionally A-to-G) changes. While engineered variants are expanding the repertoire, the current toolkit is far narrower than what DNA editing offers.
Efficiency
Editing rates for endogenous ADAR recruitment strategies are often in the 20-60% range, lower than what DNA editors routinely achieve. For therapeutic applications where near-complete correction is needed, this remains a challenge.
Durability
The transient nature of RNA editing is both its greatest strength and its greatest limitation. For chronic genetic diseases, patients would require repeated dosing — potentially for life — rather than the single curative treatment that DNA editing promises.
Off-Target Editing
ADAR enzymes are not perfectly specific. Transcriptome-wide off-target A-to-I editing has been observed with some approaches, though careful guide RNA design and optimized ADAR variants can reduce this substantially.
Wave Life Sciences and the Clinical Frontier
Wave Life Sciences has emerged as a leader in programmable RNA editing therapeutics. The company's ADAR-mediated editing platform uses stereopure antisense oligonucleotides — ASOs with precisely controlled stereochemistry at every phosphorothioate linkage — to recruit endogenous ADAR1 to specific RNA targets.
Wave's lead program, WVE-006, targets alpha-1 antitrypsin deficiency (AATD), a genetic liver disease caused by the PiZ mutation. The approach aims to correct the mutant transcript by converting a single adenosine to inosine, restoring production of functional alpha-1 antitrypsin protein. Early clinical data have shown measurable increases in functional protein levels.
The company is also developing RNA editing candidates for neurological and other hepatic diseases, leveraging the ability of ASOs to cross the blood-brain barrier when delivered intrathecally.
Other Players
- Korro Bio: Developing endogenous ADAR recruitment therapies, with programs in cardio-metabolic diseases.
- Shape Therapeutics: Using engineered ADAR-recruiting guide RNAs delivered via AAV for durable RNA editing.
- Ascidian Therapeutics: Focused on RNA exon editing, a distinct approach that replaces entire exons at the RNA level rather than making single-nucleotide changes.
Where the Field Is Heading
RNA editing is still in its early clinical stages, but the trajectory is promising. As guide RNA chemistry improves, editing efficiency rises, and delivery to diverse tissues matures, RNA editing could become the preferred approach for a significant subset of genetic diseases — particularly those where reversibility is valued, chronic dosing is acceptable, and the mutation involves a single A-to-G correctable change.
The ultimate vision is a complement to DNA editing, not a replacement. For diseases where a permanent one-time cure is possible and desirable, DNA editing will remain the tool of choice. For diseases where precise, tunable, reversible correction is preferable — or where the risk profile of permanent DNA changes is unacceptable — RNA editing offers a compelling alternative.
Sources & Further Reading
- Merkle, T. et al. "Precise RNA editing by recruiting endogenous ADARs with antisense oligonucleotides." Nature Biotechnology 37, 133–138 (2019).
- Wave Life Sciences Pipeline — WVE-006 for AATD in Phase 1/2.
Last updated: March 2026.
