Gene therapy is an experimental technique that uses genes to treat or prevent disease. In the future, this technique may allow doctors to treat a disorder by inserting a gene into a patients cells instead of using drugs or surgery. Researchers are testing several approaches to gene therapy, including replacing a mutated gene that causes disease with a healthy copy of the gene, inactivating, or knocking out, a mutated gene that is functioning improperly, and introducing a new gene into the body to help fight a disease.

Although gene therapy is a promising treatment option for a number of diseases (including inherited disorders, some types of cancer, and certain viral infections), the technique remains risky and is still under study to make sure that it will be safe and effective. Gene therapy is currently only being tested for the treatment of diseases that have no other cures.

But gene therapy is not a simple solution - it's not a molecular bandage that will automatically fix a disorder. Although scientists and physicians have made progress in gene therapy research, they have much more work to do before they can realize its full potential. In this module, you'll explore several approaches to gene therapy, try them out yourself, and figure out why creating successful gene-based therapies is so challenging.

In one of the eye disease trials, done by researchers at the University of Pennsylvania and elsewhere, all three young adults treated so far have shown apparent improvements in central vision and in night vision. They started reporting better ability to see in the dark within two weeks after treatment, and their central vision also improved about three lines on an eye chart, although their sight was still highly impaired.

In the second trial, researchers at the University College London and the Seattle biotech firm Targeted Genetics used a similar treatment and found that one of the first three young adults treated improved. His ability to navigate an indoor maze without bumping into walls improved after the treatment.

Martin Friedlander, chief of the retina service at the Scripps Clinic in San Diego, calls the new results tremendously exciting." But given the small number of patients it is too early to have any sense of efficacy.

The more important finding, Friedlander says, is that the gene therapy appeared to be safe in the first few patients, which should allow the researchers to expand the trials into younger patients who have more remaining retina cells, and are thus more likely to benefit from a gene therapy treatment. The gene therapy can restore a missing enzyme, but it cannot bring back dead retina cells.

To avoid the safety problems that have hampered previous studies, researchers in the two new studies have turned to adeno-associated virus, which doesn't cause any known disease in humans. It also does not insert genetic material into unpredictable locations in the human genome sequence, as does the so-called retrovirus used in the French study in which some children got leukemia.

Targeted Genetics also had a death in one of its trials using adeno-associated virus to treat inflammatory arthritis last summer. However, the federal Food and Drug Administration let the trial resume last fall as a federal advisory panel concluded that the death was the result of an opportunistic infection, and was not due to the gene-therapy virus. The patient that died was also taking an immune-suppressing drug.