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.
- 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.
- 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.
- 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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Resource Book Index: Promises and Perils
