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Gene therapy


Related terms
Future research
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Related Terms
  • ADA deficiency, adenosine deaminase deficiency, cancer, faulty genes, genetic disease, genetic disorder, genetic mutation, Huntington's disease, inherited disorder, oncogene, p53, Parkinson's disease, retrovirus, sickle cell anemia, therapeutic genes, vector, viral vector.

  • Gene therapy is an experimental procedure that may help treat or prevent inherited disorders and some types of cancer. Although early research is promising, additional research is needed to determine if gene therapy is a safe and effective treatment.
  • Gene therapy involves inserting human genes into a patient in order to treat or prevent an illness.
  • Genes (DNA) are considered the building blocks of life because they provide instructions for all of the cells in the body. Genes, which are located inside of cells, control an organism's development and functions by instructing cells to make new molecules (usually proteins). Genes are passed down from parents to their children.
  • A genetic or inherited medical disorder is a condition that is caused by an abnormal expression of one or more genes. This occurs when the chemicals that make up an individual's genes are incorrectly deleted, added, or substituted. If the mutation causes the cells in the body to stop functioning properly, the person may develop a disease or disorder.
  • Researchers hope that gene therapy can be used instead of medications or surgery to treat or prevent inherited disorders that are currently incurable. Scientists also hope that gene therapy can prevent the growth of cancerous tumors and help kill cancer that has already developed.
  • There are several different methods of gene therapy that are currently being studied. Gene therapy is being studied as a possible way to either replace or inactivate the mutated gene that is causing the disorder. Other gene therapy studies involve inserting a new gene to help the body fight against a specific disease.
  • Because the safety of gene therapy remains unknown, it is only being studied for the treatment of diseases that have no known cures, such as Parkinson's disease and Huntington's disease.
  • No gene therapy products that introduce genetic material into the body have been approved for sale in the United States. Currently, gene therapy is only available through clinical trials. Gene therapy is a growing area of research, and hundreds of trials are ongoing.

  • General: In order for the new genes to enter the patient's cells, they must be delivered inside a carrier, called a vector. Viruses that are grown in a laboratory are the most commonly used vectors.
  • Scientists change the genetic makeup of a viral vector so it carries normal human DNA instead of viral DNA. In other words, the virus' disease-causing genes are removed, and normal human genes are inserted.
  • Once the genes are inserted, the virus can be injected into the patient. Since the disease-causing genes are removed, the virus will not cause an infection in the patient. In some cases, a piece of tissue from the patient may be removed and exposed to the vector in a laboratory. The tissue cells that contain the vector are then put back into the patient's body.
  • When the vector enters the human body, it enters the body's cells. The normal genes in the virus replace the mutated genes in the patient. As a result, the new gene functions appropriately, and the patient's disorder or illnesses is treated.
  • Replacing a gene: In most gene therapy studies, a normal gene is inserted into a patient to replace either a missing gene or a mutated gene that is causing an inherited disorder. For instance, a common tumor suppressor gene, called p53, normally prevents tumors from growing in the body. Several types of cancer have been linked to either a missing or inactive p53 gene. Researchers hope that by replacing this specific gene, it may help treat or prevent cancer. This is because researchers believe the p53 gene will help the body fight against tumors.
  • Inactivating a gene: Researchers have performed studies to determine if mutated genes can be turned off, or inactivated, to treat or prevent certain diseases. For example, certain genes, called oncogenes, are abnormal genes that have been shown to promote cancerous growths. It has been suggested that inactivating these genes may help treat or prevent cancer.
  • Man-made segments of DNA (called oligonucleotides) have been used to inactivate certain genes known to cause diseases. The oligonucleotides interfere with the patient's mutated gene, preventing or limiting its expression.
  • Inserting a new gene: Researchers have also studied inserting a new gene to help the body fight against certain diseases. For instance, cancer cells often mutate and become resistant to chemotherapy and radiation therapy. Researchers hope that by inserting genes that cannot mutate to become resistant to chemotherapy, cancer treatment may be more effective because the cells start responding to treatment again.
  • It has also been suggested that cancer cells could be given new genes that make them more vulnerable to anti-cancer drugs. Theoretically, this would allow the patient to receive an inactive form of toxic chemotherapy drugs. This is because the chemotherapy drugs would only become toxic if they came into contact with these specific genes inside the cancer cells. If proven to be effective, this type of gene therapy would reduce side effects of treatment because healthy cells would not be destroyed.
  • It has also been suggested that new genes could be inserted into cancer cells to make them easier for the immune system to identify and destroy. If the immune system is able to recognize the cancer cells as harmful, then they could be destroyed.

  • General: Gene therapy has been suggested as a possible treatment for many inherited disorders and various cancers. Gene therapy is a growing area of research, and hundreds of trials are underway. Below are some of the most common diseases and disorders that are being studied with gene therapy.
  • Adenosine deaminase (ADA) deficiency: The first gene therapy study in humans was performed in 1990 in patients with a rare genetic disorder called adenosine deaminase (ADA) deficiency. ADA is an enzyme that breaks down adenosine from foods. Without this enzyme, a toxic substance called deoxyadenosine builds up in the body and destroys important immune cells. As a result, patients with ADA deficiency are vulnerable to infections and diseases that are often life-threatening.
  • Researchers were interested in studying gene therapy for ADA deficiency because this disease is caused by a single gene. Also, the new gene that is inserted into the patient is easily regulated because the amount of ADA that is needed for proper immune function does not have to be precisely controlled. Gene therapy can be easily applied in patients with ADA deficiency because small amounts have been shown to be beneficial, and larger doses have not caused serious adverse effects. Also, unlike many other genes, the gene that helps treat ADA deficiency is always on.
  • Although research has shown that gene therapy may improve ADA deficiency, it is still considered an experimental procedure. Additional research is needed before gene therapy can be considered a conventional treatment for ADA deficiency.
  • Cancer: Many different types of gene therapy have been studied as possible ways to treat or prevent various types of cancer. Hundreds of human medical trials are currently underway to evaluate the safety and effectiveness of gene therapy in a wide variety of cancer patients. Although early research in this area is promising, additional research is needed to determine its safety and effectiveness.
  • Parkinson's disease: Gene therapy has also been studied as a possible treatment for Parkinson's disease, a degenerative nervous system disease. Researchers have recently figured out a way to transfer genes into the brain. Viruses cannot be used as vectors because they are too big to make it across the protective membrane that separates circulating blood from brain cells (called the blood-brain barrier). So, instead of using viral vectors, researchers have used fat molecules (called liposomes) that are coated in a polymer, called polyethylene glycol (PEG), to deliver the new genes. This allows billions of copies of a gene to be inserted into the brain to calm overactive connections in the brain. Researchers are hopeful that this method may be an effective treatment for Parkinson's disease in the future.
  • Some studies have involved inserting genes that increase the production of an enzyme that converts levodopa into dopamine. Patients with Parkinson's disease have half the amount of dopamine in their brains than healthy individuals.
  • Huntington's disease: Gene therapy may also help treat patients with Huntington's disease, a debilitating neurodegenerative disorder. Early research suggests that turning off, or inactivating, specific genes that are associated with the disease may treat or prevent Huntington's disease.
  • Sickle cell anemia: Researchers have successfully used gene therapy to treat sick cell anemia in mice. Sickle cell anemia is an inherited disorder that causes blood cells to have an abnormal shape that may lead to blood clots. Researchers have inserted a new gene in mice that counteracts the mutated gene that causes sickle cell anemia. However, additional research is needed to determine if this therapy is safe and effective in humans.

  • If proven to be safe and effective, gene therapy may one day be used to treat or prevent some types inherited disorders and cancer.
  • Gene therapy raises many ethical concerns because it involves changing the body's genetic makeup. Although gene therapy research currently focuses on treating and preventing disease, it could theoretically be used in the future to improve basic human traits, such as intelligence. It has been suggested that widespread use of gene therapy for such uses may make individuals less accepting of people who are different.
  • In addition, some individuals are concerned that not everyone will have access to gene therapy because of its cost.

  • Gene therapy is short-lived: In order to achieve long-term benefits of gene therapy, the genes that are inserted into the patient must remain functional after treatment. However, most types of cells that receive new genes during gene therapy eventually die and are replaced by new ones. Currently, researchers have not discovered an effective way to integrate therapeutic genes into a patient's genome. As a result, patients need to undergo multiple treatments of gene therapy in order for it to be effective.
  • Immune reactions: When genes are introduced into a patient, there is a risk of an immune response. The patient's immune system may identify the vector that is carrying the new genes as a harmful invader such as bacteria. The immune system may then launch an attack to destroy the cells that contain new genes. If an immune response occurs, the effectiveness of gene therapy is limited, and it may be more difficult to repeat therapy in the future.
  • Multifactorial genetic disorders: Most disorders, including Alzheimer's disease and arthritis, occur when there are mutations or problems with multiple genes. These types of disorders are especially difficult to treat with gene therapy because doctors would have to correct all of the mutated genes.
  • Viral vectors: Although most types of gene therapy involve viral vectors, there are several health risks associated with this method. The vector may cause toxicity or stimulate an immune and inflammatory response in the patient. There is also a slight chance that the virus may recover its ability to cause disease in the patient, even if researchers think that they have removed all of its disease-causing genes.


Future research
  • Gene therapy is a growing area of research, and hundreds of trials are ongoing for incurable medical conditions, such as Parkinson's disease and Huntington's disease. Because the safety of gene therapy remains unknown, it is only available through clinical trials.

Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (

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Copyright © 2011 Natural Standard (

The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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