Inherited Disease Activity - Text Only
Version
A married couple...the Sheahans... appear on screen and introduce
the scenario, regarding hemochromatosis and the risk factor for
their three children. The presentation begins with a close-up
of the father.
MICHAEL: Hundreds of diseases can be inherited through defective
gene sequences. My six-year old daughter, Cassidy, suffers from
an inherited genetic disorder called "hemochromatosis." This disease
causes a person's intestines to absorb too much iron. The iron
then builds up in different vital organs. Eventually, it can damage
the liver, the heart, the joints...and possibly even cause death.
JENNIFER: My father, who is 54 became ill with hemochromatosis
five years ago, and this was the first he knew that he had the
disease. The symptoms...such as being overly tired and having varying
degrees of pain...are shared with a lot of other diseases and they
don't usually appear until middle age or later. When we discovered
that there was also some incidence of the disease on Michael's
side of the family, we decided to have Cassidy tested.
MICHAEL: Unfortunately, Cassidy's genetic tests showed that she
has hereditary hemochromatosis. Now she goes weekly for a treatment
known as a phlebotomy, in which they remove blood from her so that
her body replenishes her own red blood cells. When she started,
she was getting 40 cc's and now she's up to 75 cc's. We're hopeful
that once she de-irons she can go on a maintenance program in which
they won't have to take as much blood so often.
JENNIFER: Even though she's still young, she's aware that she
has the disease. She's very resilient and hasn't shown any ill
effects. We try to help her by doing such things as cooking without
iron skillets or much red meat. It's ongoing maintenance.
MICHAEL: We have two younger children, Callie and Michael, who
could also be at risk, since Jennifer and I are both carriers even
though we don't have the disease. So we felt that they had to be
tested, too.
NARRATOR : In cases such as the Sheahans, comparing the gene sequences
from a normal gene to the child's DNA will provide the test results.
If one or both of the child's genes...from the mother and the father...is
normal, then the child will be okay or, at the worst, a carrier
of the disorder. But if both genes have a hemochromatosis defect,
the child could develop hemochromatosis.
One pair of signs comes to life. The right half of each sign
fills with letters, but they rapidly advance through the gene
sequence and stop at roughly 30 letters away from the mutation,
which is located 285 letters into the gene.
NARRATOR: You can see that the top row of letters is the gene
sequence from the child's DNA. The lower row is what we hope to
see: the normal gene sequence.
Use the control buttons to scroll through the gene and hunt for
a difference between the two lines of letters. Any difference will
be a mutation. This particular gene is 2,727 letters long, and
you can watch your progress in the small window on the left side
of the screen.
If you think you've found a mutation, press the red button.
(Visitors can scroll forward and backward, fast or slow, until
they find the mutation and press the button. The most common
mutation is a single letter change around position 285...we will
verify. A pop-up window responds to wrong answers with :
NARRATOR (v.o.):
You haven't found a mutation - keep trying
or touch 'find it for me'
A correct answer activates the next video segment.
NARRATOR: You found a mutation, the most common of the two possible
mutations. It is involved in 88% all hemochromatosis cases. So
we already know that the child is at least a carrier.
(The second pair of signs comes to life and holds at the red
reference line.)
NARRATOR: The Centers for Disease Control says that people with
just one copy of the defective gene rarely have excess iron build-up.
So the child will probably be okay if the other copy is normal.
Now let's see what the second sequence looks like.
(The activity is identical to the first try, but there are
three possible outcomes this time:
{1} no mutation, {2} the same mutation seen in the first gene,
and {3} the second most common mutation. The program searches
the first mutation site, then advances rapidly to the site of
the second most-common mutation. The visitor decides whether
to keep searching the first site or to advance to the second,
based on an on-screen prompt saying that he/she has passed over
the mutation region. The exhibit is programmed to offer one of
these three outcomes randomly to each visitor. Each outcome includes
a different video sequence ending, but all contain the same basic
information.
Outcome 1
NARRATOR: You didn't find a mutation. The second gene is normal.
Though the child shouldn't suffer from iron overload, the earlier
defective gene means the child could pass the defect along to any
of his or her own children.
JENNIFER: Thousands of diseases are related to defective gene
sequences. You can inherit defective mutations from one or both
of your parents, and you can pass them along to your children,
increasing their risk, too. But inheriting a genetic defect doesn't
necessarily mean you'll get sick.
MICHAEL: At first, doctors didn't want to test Cassidy because
they said it was a middle-age disease. Though there is no cure
for hemochromatosis at present, by discovering it early as we did,
we can possibly negate much of the damage before it occurs.
JENNIFER: We did, in fact, have our other two children tested.
Each had only one defective gene, meaning that they are carriers
but unlikely to develop hemochromatosis themselves. In the meantime,
we're optimistic for Cassidy and we'll help her to live as normal
a life as possible.
Outcome 2
NARRATOR: You found a second mutation, which means that the child
is at risk for developing the disease too. In this case, it too
is the most common version of the mutation. So what can be done?
Please read the CDC's recommendations next to this screen.
CDC Recommendations:
Using DNA To Maintain Good Health
If a child is known to have inherited the genetic mutations
for hemochromatosis, the impact of the disease can often be reduced.
Symptoms of the disease usually do not appear until middle age.
Even in such cases, health and life expectancy can be improved
through a treatment known as "phlebotomy," in which iron-rich
blood is removed from the patient every week and replenished
with normal blood by the body.
The Centers for Disease Control (CDC) recommends avoiding vitamins
that contain iron and restricting vitamin C, which increases
iron absorption. The CDC also recommends avoiding behavior that
could damage the liver, such as more than mild alcohol consumption.
Although patients may eat iron-containing foods, they should
avoid eating raw seafood and shellfish, because iron-overload
patients are susceptible to infections that these foods may carry.
JENNIFER: Thousands of diseases are related to defective gene
sequences. You can inherit defective mutations from one or both
of your parents, and you can pass them along to your children,
increasing their risk, too. But inheriting a genetic defect doesn't
necessarily mean you'll get sick.
MICHAEL: At first, doctors didn't want to test Cassidy because
they said it was a middle-age disease. Though there is no cure
for hemochromatosis at present, by discovering it early as we did,
you can negate much of the damage before it occurs.
JENNIFER: We did, in fact, have our other two children tested.
Each had only one defective gene, meaning that they are carriers
but unlikely to develop hemochromatosis themselves. In the meantime,
we're optimistic for Cassidy and we'll help her to live as normal
a life as possible.
Outcome 3
NARRATOR (v.o.): You found a second mutation. In this case, it
is a different mutation than was found in the first gene. The second
mutation is less common but can also cause hemochromatosis, which
means that the child is at risk for developing the disease too.
So what can be done? Please read the CDC's recommendations above.
JENNIFER: Thousands of diseases are related to defective gene
sequences. You can inherit defective mutations from one or both
of your parents, and you can pass them along to your children,
increasing their risk, too. But inheriting a genetic defect doesn't
necessarily mean you'll get sick.
MICHAEL: At first, doctors didn't want to test Cassidy because
they said it was a middle-age disease. Though there is no cure
for hemochromatosis at present, by discovering it early as we did,
you can negate much of the damage before it occurs.
JENNIFER: We did, in fact, have our other two children tested.
Each had only one defective gene, meaning that they are carriers
but unlikely to develop hemochromatosis themselves. In the meantime,
we're optimistic for Cassidy and we'll help her to live as normal
a life as possible.
End
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