What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency.
Gene therapy is a collection of methods that allows correction of a gene defect that has been diagnosed in a child or embryo. It involves insertion of genes into a person's cells and tissues to treat hereditary diseases by delivering a normal gene to take over the function of and compensate for the non-functional gene.
The first clinical gene therapy was given in 1990 to a 4-year-old girl with adenosine deaminase (ADA) deficiency. This disorder is caused by deletion of the gene for adenosine deaminase, an enzyme crucial for the immune system to function. In this therapy, lymphocytes from the patient's blood are grown in a culture outside the body. A functional ADA cDNA (using a retroviral vector) is introduced into these lymphocytes, which are subsequently returned to the patient. However, since these cells are not immortal, the patient requires periodic infusion of such genetically engineered lymphocytes. If the gene is introduced into cells at early embryonic stages, it could be a permanent cure.
Explanation
This answer defines gene therapy and then illustrates it with the ADA deficiency example as asked. Key points covered: definition of gene therapy, the 1990 milestone, cause of ADA deficiency, the step-by-step procedure using lymphocytes and retroviral vector, and the limitation requiring periodic infusion. The textbook also mentions that introducing the gene at early embryonic stages could provide a permanent cure.
Solution Steps
Step 1: Define gene therapy as a corrective method for gene defects
Step 2: Explain the ADA deficiency disorder and its cause
Step 3: Describe the gene therapy procedure - lymphocyte culture, cDNA insertion via retroviral vector, and reinfusion
Step 4: Mention the limitation of periodic infusion and possibility of permanent cure at embryonic stage