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Gene Editing: News and Plain-Language Guide
How CRISPR, base editing and prime editing differ, which are used in patients today, and what is still in trials. Sources linked.
Get the newsletter →Gene editing tools let scientists change DNA at a chosen spot. Here we track what is in the lab, what is in clinical trials, and what is approved, and explain the differences in plain language.
Quick answer: CRISPR-Cas9 cuts both strands of DNA and relies on the cell to repair the break. Base editing changes a single DNA letter without a double-strand break. Prime editing can write small insertions, deletions or letter swaps, also without a double-strand break. (Sources: PMC reviews listed below.)
What is base editing?
A base editor joins a modified Cas9 that nicks rather than cuts DNA to an enzyme that chemically converts one DNA letter into another. Cytosine base editors change C to T; adenine base editors change A to G. Because many disease-linked variants are single-letter changes, base editing is being tested as a way to correct or switch off genes. (PMC8819410)
Base editing vs prime editing vs CRISPR
| Tool | DNA break | What it can do |
|---|---|---|
| CRISPR-Cas9 | Double-strand cut | Disrupt genes; insert DNA with a template |
| Base editing | No double-strand break | Four single-letter changes (transitions) |
| Prime editing | Single-strand nick | All 12 letter changes plus small insertions and deletions |
Is gene editing used in patients today?
Yes, for a small number of conditions. On December 8, 2023 the US FDA approved Casgevy, a CRISPR-based cell therapy for sickle cell disease in patients 12 and older. Most other uses, including in vivo editing inside the body, are in clinical trials. Trials are listed on ClinicalTrials.gov.
Is gene editing safe?
Safety is still being studied. Double-strand breaks can cause unintended insertions, deletions or larger rearrangements, which is one reason newer tools avoid them. Each therapy is judged on its own trial data. (PMC9838544)
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Frequently asked questions
What is the difference between base editing and prime editing?
Base editing makes four kinds of single-letter DNA changes without a double-strand break. Prime editing uses a nicking Cas9 joined to a reverse transcriptase and a special guide RNA to make all 12 letter changes plus small insertions and deletions.
How does CRISPR work, in simple terms?
A guide RNA leads the Cas9 enzyme to a matching DNA sequence. Cas9 cuts both strands there, and the cell repairs the cut, which can disrupt a gene or, with a template, insert new DNA.
What is in vivo gene editing?
In vivo editing delivers the editing tool into the body, for example to the liver through lipid nanoparticles, instead of editing cells outside the body and returning them.
Is there an approved CRISPR treatment?
Yes. The FDA approved Casgevy for sickle cell disease on December 8, 2023.
Sources
- Basic Principles and Clinical Applications of CRISPR-Based Genome Editing (PMC)
- Assessing and advancing the safety of CRISPR-Cas tools (PMC)
- Prime Editing: An All-Rounder for Genome Editing (PMC)
- FDA: FDA Approves First Gene Therapies to Treat Patients with Sickle Cell Disease (Dec 8, 2023)
- ClinicalTrials.gov
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Darwi is for education only and is not medical advice. Talk with a qualified clinician about your health. Medical disclaimer.