Gene therapy is the addition of new genes to a patient's cells to replace missing or malfunctioning genes. The treatment, which was first tested in humans in , can be performed inside or outside of the body. This approach is also being used to treat eye diseases and hemophilia, an inherited disease that leads to a high risk for excess bleeding, even from minor cuts.
Early in-the-body gene therapies used a virus called adenovirus—the virus behind the common cold—but the agent can cause an immune response from the body, putting a patient at risk of further illness. Today, researchers use a virus called adeno-associated virus, which is not known to cause any disease in humans. In nature, this agent needs to hitch a ride with an adenovirus, because it lacks the genes required to spread itself on its own.
To produce an adeno-associated virus that can carry a therapeutic gene and live on its own, researchers add innocuous DNA from adenovirus during preparation. In-the-body gene therapies often take advantage of the natural tendency of viruses to infect certain organs. Adeno-associated virus, for example, goes straight for the liver when it is injected into the bloodstream. Because blood-clotting factors can be added to the blood in the liver, this virus is used in gene therapies to treat hemophilia.
In out-of-the-body gene therapy, researchers take blood or bone marrow from a patient and separate out immature cells. They then add a gene to those cells and inject them into the bloodstream of the patient; the cells travel to the bone marrow, mature and multiply rapidly, eventually replacing all of the defective cells. Sometimes the whole or part of a gene is defective or missing from birth, or a gene can change or mutate during adult life. Any of these variations can disrupt how proteins are made, which can contribute to health problems or diseases.
In gene therapy, scientists can do one of several things depending on the problem that is present. Viruses, for example, have a natural ability to deliver genetic material into cells, and therefore, can be used as vectors. Before a virus can be used to carry therapeutic genes into human cells, however, it is modified to remove its ability to cause an infectious disease.
Gene therapy can be used to modify cells inside or outside the body. In gene therapy that is used to modify cells outside of the body, blood, bone marrow, or another tissue can be taken from a patient, and specific types of cells can be separated out in the lab. The technique was first developed in but has, so far, had limited success in treating human diseases.
Gene therapy may be a promising treatment option for some genetic diseases , including muscular dystrophy and cystic fibrosis. Germline gene therapy: transfer of a section of DNA to cells that produce eggs or sperm. Gene therapy techniques There are several techniques for carrying out gene therapy. These include: Gene augmentation therapy This is used to treat diseases caused by a mutation that stops a gene from producing a functioning product, such as a protein.
This therapy adds DNA containing a functional version of the lost gene back into the cell. The new gene produces a functioning product at sufficient levels to replace the protein that was originally missing.
This is only successful if the effects of the disease are reversible or have not resulted in lasting damage to the body. For example, this can be used to treat loss of function disorders such as cystic fibrosis by introducing a functional copy of the gene to correct the disease see illustration below.
Related Content:. What is muscular dystrophy? What is cystic fibrosis? Treating the bubble babies: gene therapy in use.
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