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What Is Gene Therapy?

Using genes to treat disease


Updated June 21, 2014

Gene therapy is an experimental way of using genes to treat or prevent disease. Disorders that are caused by mutations in a single gene are the best candidates for gene therapy. Gene therapy may be used to:
  • insert a normal gene into tissues to replace an abnormal disease-causing gene
  • shut down (inactivate) a mutated gene that is not working properly, or turn on (activate) a gene that should be working but is not
  • introduce a new gene into the body to treat or cure a disorder

How is gene therapy done?

In most gene therapy studies, a normal gene is inserted into the body to replace an abnormal gene that is causing disease. Getting the replacement gene into the body tissues where it is needed is a challenging and complex problem that researchers are trying to solve. A carrier called a vector is created to bring the new gene into the body's cells. Some carriers for gene therapy being investigated are:
  • a virus that has been made harmless
  • an artificial lipid sphere called a liposome
Other ways to get genes inside cells might include:
  • altering stem cells in the laboratory to make them accept new genes
  • having the new genes chemically linked to molecules being absorbed by body cells, so the gene is carried into the cells along with the molecules
  • introducing into cells a 47th (extra) artificial human chromosome that could have genes in it

Problems with gene therapy

There are a number of problems with gene therapy that need to be solved before this type of treatment becomes safe and effective. The FDA has not yet approved any human gene therapy product for sale. Factors influencing gene therapy include:
  • Diseases caused by more than one gene would be difficult to treat with gene therapy.
  • Studies using gene therapy have already shown that it can have serious health risks such as toxicity, inflammation, and cancer.
  • Because it is a new treatment, some of the risks of gene therapy may not yet be known.
  • Although gene therapy could potentially lessen or cure a disorder caused by a defective gene, the treatment would only be effective for that particular person; he or she could still pass the defective gene on to children.
  • The body’s immune system naturally attacks anything that invades it, so the body may attack the genes being introduced to it by gene therapy or may attack the carrier (vector) if it is a virus. This already happened in 1999, when 18-year-old Jesse Gelsinger died during a gene therapy study for ornithine transcarbamylase deficiency. His death is believed to have been triggered by a severe immune response to the gene therapy carrier virus.
  • An efficient way to deliver working copies of the needed gene into the cells where they are needed has not yet been found.
  • There is also the concern that viruses used to deliver genes might recover their ability to cause disease in the body.
No treatment is without risks, so the risks of gene therapy must be balanced against its potential benefits. Safety concerns are a priority in the planning and carrying out gene therapy research. Until gene therapy is proven safe and effective it will remain an experimental treatment only used in clinical studies.


"Gene Therapy." Human Genome Project Information. 06 Aug 2007. The Human Genome Program of the U.S. Department of Energy Office of Science. 22 Feb 2008

Barlow-Stewart, Kristine. "Fact Sheet 27: Gene Therapy." The Australasian Genetics Resource Book. June 2007. Centre for Genetics Education. 22 Feb 2008

"Gene Therapy." Genetics Home Reference. 29 Feb 2008. U.S. National Library of Medicine. 6 Mar 2008

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