GENE THERAPY

Attention has been focussed on the genetic metabolic diseases in which a defective gene causes an enzyme to be either absent or ineffective in catalyzing a particular metabolic reaction effectively. A potential approach to the treatment of genetic disorders in man is gene therapy. This is a technique where the absent or faulty gene is replaced by a working gene, so that the body can make the correct enzyme or protein and consequently eliminate the root cause of the disease.

The first clinical gene therapy was given in 1990 to a 4 years old with Adenosine Deaminase (ADA) deficiency. This enzyme is crucial for the immune system to function. The disorder is caused due to the deletion of the gene for Adenosine Deaminase. In some children, ADA deficiency can be cured by bone marrow transplantation; in others, it can be cured by enzyme replacement therapy in which functional ADA is given to the patient by injection. The demerit in both of these approaches is that they are not completely curative so gene therapy is the only alternative solution.

The first step towards gene therapy is the growth of lymphocytes in a culture outside the body extracted from the blood of patient. A functional ADA cDNA (Circular DNA) by using a retroviral vector is then introduced into these lymphocytes which are subsequently returned to the patient’s body. However, as these are not immortal, the patient needs periodic infusion of such genetically engineered lymphocytes but if the gene isolated from the bone marrow cells producing ADA is introduced into cells at early embryonic stages then it could be a permanent cure.

Before treatment for a genetic disease can begin, an accurate diagnosis of the genetic defects needs to be made. It is here that biotechnology is likely to have a great impact in near future. Genetic Engineering research has produced a powerful tool for pinpointing specific diseases rapidly and accurately. Short pieces of DNA (Deoxyribonucleic Acid) called DNA probe can be designed to stick very specifically to certain other pieces of DNA. The technique relies upon the fact that complementary pieces of DNA stick together. DNA probes are more specific and have potential to be more specific than conventional diagnostic methods and it should be possible in near future to distinguish between defective genes and their normal counterparts, an important development towards Genetic Enginnering.

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