What Is Gene Therapy?

A New Type of Therapy for Genetic Diseases

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Gene therapy is a type of treatment being developed to fight diseases that are caused by genetic defects. This is a relatively new medical intervention that is mainly in the experimental phase, including human trials and animal trials, for the treatment of some conditions, such as cystic fibrosis.

Gene therapy aims to change the unhealthy proteins that are produced as a result of disease-causing genes.

Gene therapy alters genetic material to treat diseases


What Is Gene Therapy? 

Some diseases are caused by a known genetic defect or a gene mutation. This means that there is a hereditary or acquired error in the DNA molecule that codes for producing a specific protein in the body. The altered protein doesn’t function as it should, resulting in a disease. 

The idea behind gene therapy is to direct the body to produce healthy proteins that do not cause disease.

This therapy involves the delivery of DNA or RNA. The RNA molecule is an intermediate molecule that is formed in the process of protein production. The genetic defect for some diseases has been identified, but many genetic mutations haven’t been identified (they might be in the future). 

Research is ongoing into ways to correct genetic defects that have been associated with certain diseases. There are different types and methods of gene therapy that are being investigated. 

Types of Gene Therapy 

Genetic mutations can be hereditary, which means that they are inherited from parents. Genetic defects can also be acquired, sometimes due to environmental factors, like smoking. 

Gene therapy is being evaluated as a potential treatment for both types of mutations. There are several ways of delivering the corrected DNA or RNA into a person’s body.

Most cells in your body are somatic cells. The only cells that are not somatic cells are the germline cells, which create the egg and sperm cells that can produce offspring.

Somatic gene therapy: Somatic gene therapy aims to correct a defect in the DNA of a somatic cell or to provide an RNA molecule to treat or prevent a genetic disease in the person who is undergoing the therapy. This treatment may be used if you have an inherited mutation or if the mutation developed due to environmental factors.

Germline gene therapy: Germline gene therapy aims to correct a defect in an egg or a sperm cell to prevent a hereditary disease from eventually affecting future offspring.

Bone Marrow 

Sometimes a person’s own cells can be removed from the bone marrow, genetically modified in a laboratory, and then reinserted into the body.

Viral Vector 

A viral vector is a virus that has been altered so that it will not cause a viral infection. It is then infused with the correct DNA or RNA sequence. The viral vector containing the correct gene may be injected into a person for delivery of gene therapy.

Stem Cells 

Stem cells are immature cells that have the potential to develop into different types of cells. Sometimes stem cells that have been genetically modified are transplanted into a person’s body to replace the defective cells as a way to treat disease. 


This technique uses a lipid (fat) to deliver the genetic DNA or RNA material. 

Why Is Gene Therapy Done? 

Some gene mutations direct the body to make disease-causing proteins. And some genetic mutations are not functional—they cause disease because the body lacks the healthy proteins that should be normally produced by the gene.

Gene therapy aims to direct the body to produce healthy proteins or to inhibit the production of defective proteins. This depends on the type of mutation that is causing the disease. 

Gene Augmentation Therapy: Replacing Mutated Genes

With gene augmentation, the goal is to help the body make a healthy protein.

Sometimes the DNA molecule can have a gene inserted into it. This is intended to permanently alter the DNA so that the body can make new cells with the correct DNA code. The new cells will then also make healthy products. 

Some research using gene augmentation therapy involves the insertion of a healthy DNA molecule or an RNA sequence into a cell, but not into the DNA of the recipient. This has been shown in experimental studies to trigger the production of healthy proteins, but future copies of the cell are not expected to contain the healthy gene. 

Gene Inhibition Therapy: Inactivating Mutated Genes 

Sometimes gene therapy aims to cancel out the activity of a mutated gene to prevent the production of a disease-causing protein. This is done by the insertion of a non-mutated gene DNA sequence into a DNA molecule. 

Making Diseases Cells Apparent to the Immune System 

Another type of gene therapy involves the body’s immune system. An example of this therapy is the use of checkpoint inhibitors. With this therapy, the immune system is modified to recognize material in the body that is produced by the mutated genes in order to destroy them and to prevent the illnesses they cause. 

Risks of Gene Therapy 

There are some known risks of gene therapy. So far, the most common problem associated with gene therapy is a lack of effectiveness. However, there are also adverse effects that may occur. 

Unwanted Immune System Reaction 

Gene therapy that involves the immune system may cause excess immune reactivity to healthy cells that resemble the disease cells, potentially causing damage to healthy cells.   

Wrong Target Cell

Potentially, the immune reaction that is mediated by gene therapy can affect the wrong cell type, instead of the intended target cells. 

Infection Caused by Viral Vector 

When a viral vector is used, there may be a risk that the virus could cause an infection. Depending on the primary disease that is being treated, a person receiving gene therapy may have a weak immune system and, therefore, could have difficulty fighting the virus. 

Possible Tumor

A new DNA sequence that’s inserted into a person’s genes could potentially lead to a mutation that could cause cancer to form. 

What to Expect From Gene Therapy 

If you are considering gene therapy, you will go through a process of diagnosis, treatment, and medical surveillance to assess the effects. 


This step will determine whether you have a medical condition that can be treated with gene therapy. This means that you would have a blood sample sent to a laboratory to identify treatable gene mutations that are associated with your medical condition.

Examples of conditions that may be treatable with gene therapy include:

  • Cystic fibrosis: An inherited disorder in which thick mucus is produced, clogging the airways and blocking the secretion of digestive enzymes
  • Sickle cell disease: An inherited disorder that results in abnormal hemoglobin production (the protein that carries oxygen in the red blood cells)
  • Leber's hereditary optic neuropathy (LHON): An inherited disorder that causes the death of cells in the optic nerve, resulting in damage to central vision
  • Inherited or acquired retinal disease: Conditions that damage to the retina, the light-sensing layer in the back of the eye
  • WW domain-containing oxidoreductase (WWOX) epileptic encephalopathy syndrome: A genetic condition resulting in severe epilepsy, developmental delays, and early death
  • Spinocerebellar ataxia and autosomal recessive 12 (SCAR12): An inherited disorder resulting in seizures in infancy, developmental delays, and inability to coordinate movement
  • Cancer: Many types of cancer


Your treatment may involve collection of your cells and delivery of the genes into your cells with a viral vector or liposome. The modified cells will be restored to your body after the treatment. 


The effects of your treatment will be assessed, and you will be monitored for adverse events (side effects). If this occurs, you may be treated again. 

Clinical Trials

You can find clinical trials for gene therapy by talking to your doctor or by searching for organizations that support your medical condition, such as the Cystic Fibrosis Foundation.


Gene therapy is a relatively new treatment designed to alleviate disease by modifying defective genes or altering the production of proteins by faulty genes. There are several ways that healthy genes can be inserted into the body, such as inside a deactivated virus or inside a fat particle.

Sometimes immature and healthy cells are transplanted to replace cells that have a disease-causing mutation. This type of therapy can cause side effects, and there is also a risk that it might not work. 

A Word From Verywell 

If you have a genetic disease with a known and identified gene mutation, you might be a candidate for gene therapy treatment in a clinical trial. This type of treatment is not a standard therapy, and you would need to be monitored closely so that you and your doctors would know if the therapy is working and whether you are having any side effects.

You can talk to your doctor about gene therapy. This treatment is not widespread, so there is a possibility that you may need to travel to be able to participate in a clinical trial if there is not a research study near you. 

Frequently Asked Questions

  • Is gene therapy safe?

    This therapy is considered safe, but there are risks and side effects. You may have an opportunity to participate in a clinical trial, and side effects and adverse effects would be monitored. 

  • What is an example of gene therapy?

    One example of this therapy is the use of a deactivated virus to insert a portion of a DNA molecule into the body’s cells so that the healthy DNA sequence can provide a blueprint for healthy proteins. 

  • What is the main goal of gene therapy?

    The main goal of gene therapy is to provide DNA or RNA to code for healthy proteins so the body will not be affected by a genetic disease. 

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Cystic Fibrosis Foundation. Gene therapy for cystic fibrosis.

  2. Food and Drug Administration. What is gene therapy?

  3. Jiang J, Sun G, Miao Q, Li B, Wang D, Yuan J, Chen C. Observation of peripapillary choroidal vascularity in natural disease course and after gene therapy for Leber's hereditary optic neuropathy. Front Med (Lausanne). 2021;8:770069. doi:10.3389/fmed.2021.770069

  4. Repudi S, Kustanovich I, Abu-Swai S, Stern S, Aqeilan RI. Neonatal neuronal WWOX gene therapy rescues Wwox null phenotypes. EMBO Mol Med. 2021;13(12):e14599. doi:10.15252/emmm.202114599

  5. Tan TE, Fenner BJ, Barathi VA, Tun SBB, Wey YS, Tsai ASH, Su X, Lee SY, Cheung CMG, Wong TY, Mehta JS, Teo KYC. Gene-based therapeutics for acquired retinal disease: Opportunities and progress. Front Genet. 2021;12:795010. doi:10.3389/fgene.2021.795010

  6. Lu Z, Chen H, Jiao X, et. al. Germline HLA-B evolutionary divergence influences the efficacy of immune checkpoint blockade therapy in gastrointestinal cancer. Genome Med. 2021;13(1):175. doi:10.1186/s13073-021-00997-6

By Heidi Moawad, MD
Heidi Moawad is a neurologist and expert in the field of brain health and neurological disorders. Dr. Moawad regularly writes and edits health and career content for medical books and publications.