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Question
What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency.
Solution
Gene therapy is a genetic engineering approach that involves replacing a faulty gene with a normal, functional gene. In 1990, a 4-year-old child suffering from adenosine deaminase deficiency received the first clinical gene therapy. This enzyme is essential for the immune system to operate. Severe combined immunodeficiency (SCID) is caused by a gene abnormality in the enzyme adenosine deaminase. SCID patients lack functioning T-lymphocytes and cannot fight bacteria and other microorganisms.
To perform gene therapy, lymphocytes are taken from the patient's bone marrow, and a normal functional copy of the human gene coding for ADA is inserted into the lymphocytes using a retroviral vector. The treated cells are reintroduced into the patient's bone marrow. These cells create lymphocytes that contain the functioning ADA gene, which reactivates the victim's immune system. However, because these lymphocytes can not divide and have a short lifespan, they must be supplied on a regular basis with engineered cells. This difficulty can be solved by modifying stem cells during the early embryonic stage.
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