Investigators as wellas patients with genetic diseases look forward to the day when itwill be possible to correct the effects of abnormal alleles by supplying the normal alleles. The hope is that the transferred genes will cure the basic defect rather than merely alleviate the resulting damage.
For single-gene defects, transplantation from a donor may sometimes effect a cure in this sense, but continuing treatment is usually needed to control the immunological side effects of other genes. Another procedure, gene therapy, cures a hereditary disease by transferring just single genes rather than whole genomes.
Only somatic gene therapy is considered in this argument. In a somatic gene therapy a patient's body cells, not the gametes, receive the corrected gene. Of course, if the gametes were also changed from mutant to normal, the cure could extend through future generations. However, there are objections to this gametic gene therapy due to the possibility of unwarranted or unwise tampering with another generation's genes.
Therefore, gene therapy techniques will probably always be limited to single-gene defects, rather than being used to treat chromosomal imbalance like Down's syndrome. Diseases expressed in bone marrow cells are good candidates for gene therapy because the tissue is accessible.
Possibilities include thalassemia, sickle-cell anemia, and especially severe combined immunodeficiency diseases due to a deficiency of the enzyme adenosine deaminase. This form of gene therapy calls for patients to donate their own bone marrow and receive it back after the gene defect is corrected.
*Illustrations credit: Biotechnology: Principles and Isuues, J. Weston Walch, Publisher, 1991.
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Last modified July 30th 1997