Gene therapy may have the potential to fix or replace genetic mutations, which are changes in your DNA that affect how your body works.

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Doctors use gene therapy, also called “gene editing” to directly alter your genes.

This approach may help treat diseases caused by a single mutation, such as beta-thalassemia or spinal muscular atrophy (SMA). Gene editing may also help treat certain cancers.

Gene editing tools such as CRISPR-Cas9 are very new and are rapidly changing. Researchers continue to study their full potential along with any risks they may pose.

Here’s what experts know so far about gene therapy.

Genes are small segments of DNA that instruct your cells to make certain proteins when specific conditions are met.

Mutated genes, on the other hand, may cause your cells to make too much or too little of the necessary protein. Even small changes can have a domino effect across your body — just as tiny changes in computer code can affect an entire program.

Gene therapy can address this issue by:

  • replacing a missing or ”broken” gene with a working copy
  • turning off malfunctioning genes
  • adding genes to immune cells to help them better target diseased cells

Viral vectors

Scientists don’t have tweezers small enough to edit your DNA by hand. Instead, they recruit a surprising ally to work on their behalf: viruses.

Typically, a virus would enter your cells and alter your DNA to create more copies of itself. But scientists can switch out this programming with their own, hijacking the virus to heal instead of harm. These vectors, as they’re called, don’t have the parts they need to cause disease, so they can’t make you sick the way a regular virus could.

Do nonviral vectors exist?

Experts continue to study gene therapies that use nonviral vectors, such as lipid molecules or magnetic nanoparticles. None have been approved yet, though.

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There are two types of gene therapy:

  • In vivo (inside your body): Scientists put the vector carrying the new genes directly into your body via an injection or intravenous (IV) infusion.
  • Ex vivo (outside your body): Scientists extract cells from your body and introduce them to the vector inside a petri dish. Then, your altered cells are returned to your body, where they’ll hopefully multiply.

Each type has its own benefits:

Benefits of in vivo therapiesBenefits of ex vivo therapies
can deliver vectors across the body, which is useful for bone or blood diseasesbetter at targeting specific organs and cell types
quicker and less invasivetend to pose fewer safety risks

Gene therapy is different from genetic engineering, which means changing otherwise healthy DNA for the purpose of enhancing specific traits. Hypothetically, genetic engineering could potentially reduce a child’s risk of certain diseases or change the color of their eyes. But the practice remains highly controversial since it hovers very close to eugenics.

Gene therapy may be used to treat a variety of genetic conditions, including:

Inherited vision loss

When the RPE65 gene in your retinas doesn’t work, your eyeballs can’t convert light to electrical signals.

The gene therapy Luxturna, approved by the Food and Drug Administration (FDA) in 2017, can deliver a functional replacement of the RPE64 gene to your retinal cells.

Blood disorders

The FDA-approved Hemgenix can treat the bleeding disorder hemophilia B. The viral vector instructs your liver cells to create more of the factor IX protein, which helps your blood clot.

Meanwhile, the gene therapy Zynteglo, approved by the FDA in 2022, treats beta-thalassemia by giving your bone marrow stem cells correct instructions for creating hemoglobin.

This blood disorder can lower the oxygen in your body because it decreases your body’s hemoglobin production.

Spinal muscular atrophy (SMA)

In infantile-onset SMA, an infant’s body can’t make enough of the “survival of motor neuron” (SMN) proteins necessary to build and repair motor neurons. Without these neurons, infants gradually lose their ability to move and breathe.

The gene therapy Zolgensma, approved by the FDA in 2019, replaces faulty SMN1 genes in an infant’s motor cells with genes that can create enough SMN proteins.

Cerebral adrenoleukodystrophy (CALD)

Your ABCD1 gene produces an enzyme that breaks down fatty acids in your brain. If you have cerebral adrenoleukodystrophy, this gene is either broken or missing.

Skysona, FDA approved as of 2022, delivers a functional ABCD1 gene so that fatty acids don’t build up and cause brain damage.


The FDA has approved gene therapies to treat multiple types of cancer, such as non-Hodgkin’s lymphoma and multiple myeloma.

Most cancer gene therapies work indirectly by inserting new genes into a powerful antibody called a T cell. Your changed T cells can then latch on to cancerous cells and eliminate them, similar to how they attack viruses.

The therapy Adstiladrin, approved by the FDA in 2022, can treat nonmuscle-invasive bladder cancer by altering the DNA in your bladder cells themselves.

Some people considering gene therapy may feel uneasy about putting viruses in their body.

Keep in mind, though, that gene therapies undergo extensive testing before approval. The viruses in gene therapies are also fixed so they can’t replicate — similar to many vaccines.

That said, gene therapies may pose other risks:

  • Immune response: Your immune system may mistake viral vectors as an invading threat. The resulting rush of white blood cells can trigger side effects such as fever, inflammation, and fatigue.
  • Off-target editing: There’s some risk the viral vector could insert its genetic package in the wrong stretch of DNA, essentially creating a new mutation. In one case in 2002, such mutations led to cancer. That said, scientists have since developed “smarter” vectors that make fewer targeting mistakes.
  • Unknown long-term effects: Because gene therapies are so new, scientists don’t yet know how they might affect your body in the long term. Some experts have expressed concerns that viral vectors may pass mutations on to the next generation if they accidentally edit egg or sperm cells.

Despite these issues, experts generally believe gene therapy offers more benefits than risks.

Most of the conditions treated with gene therapy are life threatening. The dangers of leaving them untreated often outweigh the risks of potential side effects.

Gene therapy does come with a few drawbacks that keep it from becoming a widespread treatment.

Limited targets

Gene therapy can only target certain mutations. This means it may not work for everyone with a specific condition.

For example, two people may have inherited vision loss. Currently, gene therapy can only treat vision loss caused by the RPE64 mutation.

Time to approval

Because gene therapy research is so new, experts do extensive safety testing before introducing their treatments to the public. It can take years to get FDA approval for each new therapy.


As you might imagine, gene therapies are expensive to manufacture and administer. This not only affects funding for clinical trials but also the price of the drug.

For example, the gene therapy Zolgensma is the most expensive drug in the United States at $2.1 million per dose. Even with insurance, that kind of price tag remains out of reach for the average American.

Scientists are trying to find ways to make the development process safer, cheaper, and more efficient so more people can access gene therapy.

Gene therapy works to treat several different genetic diseases by editing the mutations that cause them. As researchers further refine and expand this technology, they may find even more conditions that could be treated with it.

Experts are also continuing to explore options to make gene therapy more affordable so people who need these treatments have an easier time getting them.

Emily Swaim is a freelance health writer and editor who specializes in psychology. She has a BA in English from Kenyon College and an MFA in writing from California College of the Arts. In 2021, she received her Board of Editors in Life Sciences (BELS) certification. You can find more of her work on GoodTherapy, Verywell, Investopedia, Vox, and Insider. Find her on Twitter and LinkedIn.