When does gene therapy not work?

          The Human Genome Project cites four main criteria that keeps gene therapy from becoming an effective treatment (http://www.ornl.gov/sci/
techresources/Human_Genome/medicine/genetherapy.shtml).

   1) The short lived nature of gene therapy. Before gene therapy and become a viable treatment the DNA introduced into the target cells must remain functional and the and the host cells must be long lived and stable.

   2) Immune response. Since gene therapy involves introducing a foreign molecule (either the retrovirus, liposome, or the DNA itself) into the body it is likely to trigger an immune response that will lessen the effectiveness of the therapy and which could be harmful to the patient. This coupled with the increased effectiveness of the immune system in recognizing foreign molecules it has seen before makes the long term use of gene therapy impractical at this point in time.

3) Problems with viral vectors. Viral vectors, while the preferred choice for gene therapy, present many complications. These complications include toxicity, immune and inflammatory response, and gene control and targeting issues. There is also the possibility that once inside the patient the virus will regain its ability to cause disease.

4) Multigene disorders. Discussed in "When does gene therapy works" we saw that single gene disorders should be the easiest to threat. Disorders that arise from the combined interactions of several genes are said to be multigene disorders. Disorders of this type include heart disease, arthritis, and diabetes. The reason these disorders are harder to treat is because each gene would have to be modified according each other gene involved. This makes the process exponentially more difficult and increases the amount of foreign DNA that must be inserted into the host's genome.

To view a presentation of adisorder that is mutligenic click here

	What are some other dangers associated with Gene Therapy?
	There is the danger of inserting the "donor" DNA into an existing gene and disrupting the function of that gene. There is the danger of the virus becoming virulent once inside the patient and infecting that patient with a potentially fatal illness. The inserted gene may enhance the transcription of an unrelated gene and lead to over expression. In extreme circumstances this may lead to cancer.