Question

What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency.

Answer 1

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.

Treatment of ADA deficiency using gene therapy.

To do gene therapy, doctors take lymphocytes from the patient's bone marrow and use a retroviral vector to add a normal working copy of the human gene for ADA into those lymphocytes. 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, due to their limited lifespan and inability to divide, these lymphocytes require regular replenishment with engineered cells. Modifying stem cells during the early embryonic stage can solve this difficulty.