Promises and Perils
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Handout 8: Gene Therapy Project Summaries

 

You are part of a committee that oversees the development of new genetic therapies--treatments for disorders that involve the use of manipulated DNA. You have received several proposals for new therapies; however, there is only enough money to fund the development of one treatment. Carefully read through the proposal summaries below. Then do a risk/benefit analysis to help you decide which proposal, if any, should be the one that is funded.

  1. Severe combined immune deficiency (SCID) is an extremely rare and life-threatening disease that affects approximately 25 children a year. Many children with this disease lack an enzyme, called adenosine deaminase (ADA), which is critically needed by cells of the immune system, which fights disease and infections. Without the ADA enzyme the person's immune system does not develop. He or she is defenseless against even the most harmless viruses, bacteria, and fungi. A new therapy is being developed that involves removing white blood cells from an afflicted child, modifying a single gene in the cell DNA, and then transferring the modified DNA back into the blood. The modified DNA allows the body to produce the ADA enzyme. The modification only affects a specific DNA sequence, and the changed cells can be accurately reinserted into the body. In addition, the modified cells have a fixed lifetime, and are not inheritable. Repeated applications of the therapy will be needed every few months. Alternate treatments include lifetime care inside a germ-free environment, and bone marrow transplant, which requires a genetically compatible donor.

  2. Sickle cell anemia is a blood disorder in which the red blood cells lose their round shape and collapse into sickle shapes. The sickle-shaped cells cannot carry oxygen to the body cells as normal blood cells do. In addition, the sickle cells tend to clog up small blood vessels, causing reduced circulation and severe pain that can last weeks or months. Damage may also result to major organs such as the heart, lungs, and brain. The disease affects approximately 1 out of every 500 African Americans, though the severity of the disease varies. A new therapy is being developed that involves removing cells from the bone marrow of an afflicted person, modifying a single gene in the cell DNA, and then transferring the modified DNA back into the bone marrow. The modified gene allows the body to produce normal hemoglobin, which is needed to prevent the red blood cells from collapsing. The modification affects only a specific DNA sequence, and the modified genes have a fixed lifetime and are not inheritable. However, it may be difficult to insert the modified cells into the stem cells where they are needed. Repeated applications of the therapy will be needed every few months. Alternate treatments for severe cases of the disease include frequent blood transfusions to relieve the symptoms, and bone marrow transplant, which requires a compatible donor. Treatments for less severe cases include increased attention to diet and nutrition.

  3. Type 1 diabetes mellitus affects approximately 1 out of every 500 people, particularly those of northern European descent. The disease occurs when the pancreas stops producing insulin. Without insulin, the body is unable to metabolize, or use, food correctly. The symptoms of the disease include excessive thirst, weight loss, abdominal pain, tiredness, and increased likelihood of infection. A new therapy is being developed that involves modifying the genes that produce insulin so that they produce insulin when the concentration of sugar in the blood is high and do not produce insulin when the concentration of sugar in the blood is low. This requires modifying several genes, and may affect other DNA sequences near each gene. However, the modified cells will have a fixed lifetime and will not be inheritable. Repeated applications of the therapy will be needed every few months. Alternative treatments include daily shots of insulin.


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