It is the therapeutic treatment of defective heredity by the introduction healthy and functional gene which also silence the defective genes of an individual.
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The replacement of a nonfunctional or defective gene with a normal functional gene is called gene therapy. A person with defect in the gene for the enzyme adenosine deaminase (ADA) suffers with SC1D (Severe Combined Immuno Deficiency) The enzyme ADA is crucial for the immune system. Ideally gene therapy should be applied to the zygotes so that the progeny of defective individual also gets rid of effect. It is however, generally applied to somatic cells where the defect occurs.
At first step towards gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body. A functional ADA cDNA (using a retrovirus vector) is then introduced into these lymphocytes which are subsequently returned to the patient. Since these cells are not immortal, the patient requires periodic infusion of such genetically engineered lymphocytes.
