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What is Gene Therapy?

written by: Rafael•edited by: Paul Arnold•updated: 9/9/2009

Gene therapy is a technique that introduces an altered gene into a person's body to carry out the work of a mulfunctioning gene. The procedure aims to treat or cure diseases that have been caused by faulty genes.

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    Importance of Curing Genetic Disease

    There are more than 4000 genetic disorders, and that number is likely to increase as we discover more about our DNA. Many of these diseases are incurable.

    So, what is gene therapy?

    Gene therapy attempts to cure genetic disorders by replacing a defective gene in the human body with a properly functioning gene.

    The first FDA-approved gene therapy procedure was performed by Dr. French Anderson in September 1994, on a child born with a rare genetic disorder, known as severe combined immunodeficiency. This caused her to have no effective immune system, resulting in frequent infections, and a poor quality of life.

    The procedure consisted of removing the child’s white blood cells, inserting the good functional copies of the desired gene into some of the cells, and then putting them back into her body. The procedure is not a permanent fix, and needs to be performed every few months. But she's alive and well and has a strengthened immune system.

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    Types of Gene Therapy

    There are two types of gene therapy; somatic cell gene therapy and germ line gene therapy.

    Somatic cells are those cells within the body that are not involved in the hereditary process. Basically, any cell in your body, except sperm or egg cells, are somatic cells. This type of gene therapy is not heritable and would not be passed on to later generations. Somatic cell gene therapy is designed for treating specific symptoms of specific genetic disorders. For example, if a patient has a disease of the liver, the therapy would be aimed at restoring the affected liver cells.

    Germ line gene therapy would involve sperm or eggs cells. It is currently prohibited in humans.

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    How to Replace Genes

    So how do you get your desired genes into a person's body? One way is by using viruses, and hijacking their cellular machinery.

    A virus has the ability to introduce its own DNA into cells. This is its natural way to colonize and infect a host. For years scientists have been able to modify viruses, such that they are able to introduce beneficial genes. At the same time they are changed so as not to cause infection.

    Among the viruses used for gene therapy are adenoviruses and retroviruses.

    Adenoviruses introduce their DNA molecule into the host. The viral DNA is not incorporated into the host cell DNA but remains free in the host nucleus, and it is expressed like any host's DNA. The viral DNA will not be duplicated when the host cell undergoes cell division.

    Retroviruses introduce RNA and eventually the DNA becomes incorporated into the host DNA. So when the host cell divides the new genes appear in its descendants.

    There are also non-viral vectors such as using naked DNA or a chain of DNA bases bonded together known as oligonucleotides.

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    Gene therapy is not without controversy or problems. The introduction of anything foreign into a body can cause problems, and gene therapy is no exception, with reports of toxic shock and severe immune system reaction. In 1999 Jesse Gelsinger became the first person to die whilst undergoing gene therapy.

    The technology is also tricky to get right. It is incredibly difficult to introduce a desired gene into a cell and get it to do what you want it to. 

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    The Future

    Gene therapy is a rapidly evolving field of research and study. It holds out much promise for the future if some of the major technical hurdles can be overcome. Those hurdles though present opportunities and encourage others to look for either viable alternatives to gene therapy or new ways of modifying the techniques for the benefit of all; one such technique scientists are excited about is DNA scissors.