Putting DNA to Work
  INHERITED DISEASES

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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