Download Case Study - cK-12

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Standards: 5c
A. Learning Objectives
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Students will think critically about potential applications of gene therapy.
Students will distinguish between the use of gene therapy to cure disease and the use of gene therapy for
enhancement.
Students will construct their own definitions of enhancement and treatment.
Students will consider bioethical issues related to gene therapy.
B. Background Information
Note: It is important to remind students throughout this activity that the gene therapy applications discussed do
not, as of yet, exist. This activity is meant to encourage critical thought about what additional applications
might arise from successful gene therapy techniques and the bioethical issues those applications may entail.
Many medical conditions result from mutations in one or more of a person’s genes. Such mutations cause the
protein encoded by that gene to malfunction. When this happens, cells that rely on the protein’s function cannot
behave normally, causing problems for whole tissues or organs. Medical conditions related to gene mutations
are also called genetic disorders. If successful, gene therapy provides a way to fix a problem at its source.
Adding a corrected copy of the gene may help the affected cells, tissues or organs work properly. In this way,
gene therapy differs from traditional drug based approaches which may effectively treat the problem but do not
repair the underlying genetic fl aw. However, gene therapy is far from being a simple solution that will
automatically fi x a disorder. While scientists and physicians have made progress in gene therapy research,
much work remains before its full potential is realized.
Success in gene therapy depends on the efficient delivery of the correct gene to the correct cells in the correct
tissue. Scientists refer to DNA delivery vehicles as vectors. These vectors are designed to target specific cells.
Traditionally, vectors have been derived from modified viruses, including retroviruses, adenoviruses, adenoassociated viruses, and herpes simplex viruses. Other gene delivery approaches being examined include the use
of liposomes, (lipidbased pockets that can carry plasmid DNA) or simply naked DNA with no carrier.
Each vector and method of delivery varies depending on the specific disorder the therapy aims to treat.
The only possible way to alter a gene in every cell in a human would be at the earliest stages of development,
through germ line or embryonic gene delivery. Germ line gene delivery refers to the transfer of a gene into the
cells that make sperm or egg cells. Embryonic gene delivery refers to the transfer of a gene into the cells of an
early embryo, just after the sperm and egg unite. In both cases, the delivered gene would become a permanent
part of all cells in the resulting adult.
Scientists are looking to gene therapy as a way to treat genetic disorders. But what if the same gene delivery
techniques, once established, could be used to change other traits, such as physical or behavioral traits? In the
future, these techniques may open the door to genetic enhancement and the creation of so called “designer
babies.” In theory, scientists could someday alter any physical or behavioral trait that is controlled by genes.
The reality of genetic enhancement is far less likely, however. To date, scientists know very little about the
specific genes that contribute to any given trait. In fact, most human traits are controlled by multiple genes.
Secondly, no human trait is determined solely by genes. Environmental factors play a large role in determining
how traits develop in a person. So, even if the genes to alter were known, the outcome could not be reliably
predicted. In sum, most traits are so complex that the concept of enhancement will likely remain in the science
fiction realm for all time.
Case Study: Skin Cancer
A couple in Kansas is very concerned about the high incidence of skin cancer
and skin cancer-related deaths in their family. It has been known for some time
now that ultraviolet radiation from sunlight is a major contributing factor to
developing skin cancer. Working the fields of the family farm means spending a
lot of time outdoors constantly exposed to this type of radiation. A family
history of skin cancer is also considered a risk factor for developing such
cancers.
Through pre-natal genetic screening, the couple has discovered that the child
they are expecting carries the forms of genes that have been linked to skin
cancer. Specifically, the child is carrying mutated forms of genes thought to be
responsible for maintaining the normal cell division cycle. They wish to pursue
pre-natal gene therapy to reduce the risk of skin cancer in their child.
Case Study: Malignant Melanoma
A 36-year-old mother of three has been diagnosed with malignant melanoma.
Although malignant melanoma only accounts for approximately 4% of all skin
cancers, it is the most deadly. Melanoma begins in the cells of the epidermis
that are responsible for making pigment (melanocytes).It shuts down the
process that regulates normal cell division, causing cells to divide and
reproduce at a higher rate and form tumors. The DNA of genes involved in the
cell division cycle is often damaged in melanoma cells, probably caused by
ultraviolet radiation. Gene therapy could be used to insert an antigen-producing
gene into the woman’s melanoma cells, triggering an immune response that
would destroy the cancer cells.
Case Study: Height
A couple who are fans of professional basketball are planning on having a baby.
They would like for the child to b at least 6 feet 7 inches tall and extremely
muscular by the time he is 16 years old. This, according to the couple, will
guarantee him a spot in the NBA.
Height is a polygenic trait(a trait influenced by several genes) that can be
influenced by human growth hormone. Gene therapy could be used to add
multiple genes that control height to the embryo.
Case Study: Achondroplasia
A couple’s newborn son has just been diagnosed with achondroplasia, the most
common form of dwarfism. Achondroplasia is caused by a mutation in the
FGFR3 gene, which controls bone growth. This mutation causes a decrease in
the rate at which cartilage turns to bone during development and particularly
affects long bones in the body
Characteristics of this disorder include an average sized torso with
disproportionately short limbs and a slightly enlarged head with a prominent
forehead. In more than 80% of cases, achondroplasia is the result of a new
mutation, not inheritance. In cases where it is not caused by a new mutation,
achondroplasia is an autosomal dominant disorder. Prenatal screening for
achondroplasia is available. Gene therapy could be used to add a normallyfunctioning copy of the FGFR3 gene to the child’s bone cells.
Case Study: Transgenic Art
The gene that codes for a Green Fluorescent Protein (GFP) found in jellyfish
has been isolated, copied and used by scientists to mark gene expression in a
wide variety of studies. The protein glows when exposed to the proper light
source. By tacking the GFP gene onto genes of interest, scientists can easily see
where these genes are expressed in an organism. In April of 2000, artist
Eduardo Kac commissioned a French lab to inject the GFP gene into rabbit
eggs. This produced an animal named “Alba” the GFP Bunny. Alba appears
normal but glows green from every cell when placed under blue light. Alba is
an example of what is known as “transgenic art”.
Case Study: Cystic Fibrosis
A six-month old girl has been diagnosed with cystic fibrosis. This disease is
characterized by a buildup of very thick mucus in the lungs, making it difficult
to breathe and causing frequent infections. Additionally, a buildup of mucus in
the digestive tract blocks necessary digestive enzymes, leading to malnutrition.
Cystic fibrosis (CF) is caused by a defect in the gene that codes for the protein
that is responsible for chloride ion transport across cell membranes. The life
span of people with this autosomal recessive disorder is shorter than average approximately 30 years. Gene therapy could be used to add a normal copy of
the CF gene to the girl’s affected tissues.
Case Study: Immunity
Firemen, emergency medical technicians, policemen, doctors, nurses, dentists, and
other health care workers are constantly exposed to infectious diseases while
transporting and caring for people who have been hurt or fallen ill. These diseases
range from minor to life threatening and are an obvious concern for all involved.
Gene therapy could be used to enhance these people’s immune systems
Case Study: SCID
A two-month old boy is brought into the emergency room with
a severe respiratory infection. The infant’s blood work reveals few B and Tlymphocytes,
the white blood cells responsible for fighting infection. Further tests reveal that the infant
has Severe Combined Immune Deficiency (SCID), a genetic disorder that affects B and T
lymphocyte production in the body. SCID, commonly referred to as “bubble boy disease”,
is usually an X-linked recessive disorder, but can also be autosomal recessive in some
cases.
Common infectious diseases such as a cold, fl u and chicken pox are
life threatening to patients with SCID. Because people with SCID lack
the necessary immune response, many die within the first year of
life as a result of complications from these illnesses. Current treatment
for SCID includes bone marrow transplants and monthly injections of
antibodies collected from human blood. Gene therapy could be used to add the gene
responsible for producing T and B lymphocytes to the boy’s white blood cells.
Case Study: Sickle Cell
A seven-year old girl feels fatigued most of the time and even the mildest forms of
exercise, such as walking up a flight of stairs, leave her breathless. She periodically
complains about bone, joint andabdominal pain. After conducting tests, her doctors have
determinedthat she has sickle cell disorder. In this disorder, red blood cells
contain a mutated form of hemoglobin that causes them to collapse into a sickle shape
under low oxygen conditions, such as exercise. The sickled cells can clog blood vessels
and do not do a proper job of delivering oxygen to tissues. This is an autosomal recessive
disorder. Gene therapy could be used to add a normal copy of the gene that codes for
hemoglobin tothe girl’s bone marrow, where blood cells are made.
Case Study: Retinis Pigmentoso
Your neighbor has been complaining that he is having difficulty seeing at night and that
his peripheral (side) vision is beginning tonblur. Thinking that he needs a different
eyeglass or contact lens prescription, he visits his opthamologist. He is diagnosed with
retinitis pigmentosa, a disorder that will cause him to lose his vision until he becomes
blind. Retinitis pigmentosa causes cellsnin the retina to degenerate. It may be inherited
through a variety of ways, including autosomal dominant, autosomal recessive, or Xlinked. Gene therapy could be used to add genes to cells in the man’s retina so that the
cells will produce substances that have been shown to slow the loss of vision.
Case Study:
A girl in your class usually comes to school completelybandaged from the neck down.
You have been instructed to be very careful about pushing or bumping into her and you
notice that she moves very carefully and deliberately. You learn that this student suffers
from a severe blistering disorder called epidermolysis bullosa. People with this disorder
have very fragile skin and mucous membranes that blister after the slightest amount of
pressure or friction. The blisters fill with fluid and then scar when they heal, reducing the
ability to move. People with epidermolysis bullosa lack a particular type of collagen fibril
that anchors skin in place. The disorder is inherited; some forms are autosomal dominant
while others are autosomal recessive. Occasionally, the disorder may also arise as a new
mutation. Gene therapy could be used to insert a normal copy of the collagen-producing
gene into the girl’s skin cells.
Case Study:
A toddler you baby sit after school is having trouble walking and seems to fall more than
other children his age. After extensive medical
tests, the toddler is diagnosed with Duchenne muscular dystrophy. Muscular dystrophy
causes a slow degeneration of the voluntary muscles until the muscles have little to no
function. This degeneration is caused by the lack of a protein called dystrophin that aids in
proper muscle function. Duchenne muscular dystrophy, the most common form is an Xlinked disorder and begins to affect children at a very early age. Gene therapy could be
used to add a normal copy of the dystrophin-producing gene to the boy’s muscle cells.
Case Study:
A world-champion body builder notices that he must work harder and harder to keep his
physique as he ages. His muscles just are not retaining mass and bulk like they used to.He
also feels a very slight weakening of muscle performance as he is lifting weights. Body
building competitions are a way of life for him and he hopes to compete for at least
another 5 years before retiring. He would like to use gene therapy to add an additional
dystrophin-producing gene to his muscle cells, which would improve and maintain muscle
mass and performance.
Answer the questions below:
1. Look at the treatment portion of your diagram. For you, what are the characteristics of the
conditions for which gene therapy qualifi ed as a “treatment”?
2. Look at the “enhancement” portion of your diagram. For you, what are the characteristics of
the conditions for which gene therapy qualifi ed as an “enhancement”?
3. Agree or Disagree: “Most conceivable gene therapy treatments could potentially have an
application as an enhancement.” Explain your answer using an example.
4. What other categories (such as preventative measure) could you add to your diagram? List
Them and describe the characteristics of the conditions that they would contain.
Case Study:
Achondraplasia
A couple’s newborn son has just been diagnosed with
achondroplasia, the most common form of dwarfi sm.
Achondroplasia is caused by a mutation in the FGFR3 gene,
which controls bone growth. This mutation causes a decrease in
the rate at which cartilage turns to bone during development and
particularly affects long bones in the body.
Characteristics of this disorder include an average sized torso
with disproportionately short limbs and a slightly enlarged head
with a prominent forehead. In more than 80% of cases,
achondroplasia is the result of a new mutation, not inheritance. In
cases where it is not caused by a new mutation, achondroplasia
is an autosomal dominant disorder. Prenatal screening for
achondroplasia is available. Gene therapy could be used to add
a normally-functioning copy of the FGFR3
gene to the child’s bone cells.