Genetic Counseling
Most of the time our genes do their jobs so we take them for granted. However,
when a gene does not function normally, a person may have a genetic disorder. Just as
there are thousands of genes, there are thousands of genetic disorders. This story is
about a four year old girl, Laurie Ramsey, who has a genetic disorder called cystic
fibrosis. The Ramseys are thinking about having another baby and wonder what the
chances are of their next child having cystic fibrosis. They go to a genetic counselor who
will explain this to them.
When Laurie Was A Baby
Laurie had seemed healthy when she was born. She had been a small, goodnatured baby who seldom cried and loved to be held. Then, when she was about three
months old, she developed a cough. It wasn’t much of a cough, but since it wouldn’t go
away, the Ramseys had asked the doctor about it.
At first Dr. Jones had been more worried about Laurie’s size than about her
cough. The fact that she was smaller than other babies her age even though she ate well
was puzzling. How could a baby who ate all of the time gain so little weight?
Unknowingly, Mr. Ramsey provided an important clue when he mentioned that
he and his wife noticed a salty taste whenever they kissed Laurie.
“Oh,” Dr. Jones had said, “I’m glad that you mentioned that. It might help us
understand the problem. Laurie’s symptoms sound like cystic fibrosis. We’ll need to do
some laboratory tests to check out the possibility.”
The Ramseys had returned to Dr. Jones’ office when the results of the tests were
back. Dr. Jones’ suspicion had been right. Laurie had cystic fibrosis. The Ramseys had
heard of cystic fibrosis, but they didn’t know what it was, so the doctor explained.
“Cystic fibrosis is the most common genetic condition in Caucasian (white)
people. It affects one in every 2500 births with about 30,000 people living in the U.S.
that have cystic fibrosis. About 5% of the population has the recessive gene for this
condition but do not realize it. That was the situation in your case. Both of you have a
gene for cystic fibrosis but you’ve been unaware of it. We say that you’re carriers for
cystic fibrosis. Laurie inherited a cystic fibrosis gene from each of you and so, with a
double dose of the gene, she is affected.
“The main problem with cystic fibrosis seems to involve the body’s ducts and
glands. For example, the sweat glands usually are affected. For some reason that is not
completely understood, the body loses more salt than it should. That’s why Laurie’s skin
seems salty when you kiss her. Also, the glands in the digestive system are easily
clogged. When this happens, the enzymes needed for digestion can’t get to the food.
That’s why Laurie isn’t gaining weight even though she eats a lot.”
“Another serious problem involves the respiratory system. The small air passages
in the lungs become filled with a thick mucus. The mucus makes it hard to breathe.
Laurie coughs because she’s trying to clear this mucus out of her lungs.”
As you can imagine the Ramseys had been very concerned. Laurie had breathing
problems, she couldn’t digest her food properly, and her body was losing too much salt.
They had looked worriedly at Laurie but all they saw was a healthy, happy baby. It was
hard to believe that she had so many medical problem. “What,” they had asked, “can we
do to help her?”
Dr Jones explained, “At this time, cystic fibrosis cannot be cured since the gene
that causes cystic fibrosis is on Laurie’s two chromosomes #7’s in every cell of her body.
All we can do is try to manage her condition. It will be important for you to keep
Laurie’s lungs free of mucus. By gently thumping her chest and back, you can help her
cough up the mucus. This could be up to one liter per day. Think of it as a type of lung
exercise. However, because of this mucus, she’ll always have the cough so you’ll have to
learn to live with it. The mucus provides the right environment for bacterial growth.
That will put Laurie at risk for developing lung infections. Consequently, we’ll be using
antibiotics to help her fight these infections.”
“Because of her digestive problems, Laurie will need to take several other kinds
of pills. I’ll prescribe enzyme tablets to help her digest her food so that she can gain
weight and grow. She’ll also need to take vitamins to supply what her body can’t absorb
from her food. Even with all of this, Laurie will probably not live past 40.
“There are a few promising treatments of gene therapy where a correct form of
the gene is put in a virus and the virus is absorbed into the skin in the nose. There are
two problems with this. One is that the cells in the nose die every few months, so the
treatment would have to take place that often. Another is that the body builds up
antibodies, the body’s army, to fight viruses. After awhile the virus may be destroyed by
the body before it can get the corrected gene to the nose cells.”
This all happened more than four years ago. By now the Ramseys know all too
well how cystic fibrosis affects a person. Laurie also understands some things about
cystic fibrosis. For instance, she knows that her breathing problems may prevent her
from playing rough games or running as much as the other children. However, in most
ways she’s like other four year olds-she loves peanut butter sandwiches, chocolate milk,
and cookies and watching Big Bird on TV.
Mr. and Mrs. Ramsey love Laurie and would like for her to have a baby brother
or sister. But they need to know what their chances are for having another child with
cystic fibrosis.
Names______________
___________________
___________________
Hour_________
Genetic Counseling
Analysis Questions
1. List at least 3 symptoms of cystic fibrosis.
a.
b.
c.
2. List at least 3 ways that Laurie is being treated for cystic fibrosis.
a.
b.
c.
3. Do you think other children can catch cystic fibrosis from Laurie? Explain.
4. Could Laurie outgrow cystic fibrosis? Explain.
5. Describe how you would feel if you found out that you had cystic fibrosis.
6. Now consider the Ramsey family.
a. Draw the family's pedigree including the names of each person. Shade in half
of a square or circle to indicate carriers of cystic fibrosis. Shade a whole circle to
indicate a person with cystic fibrosis. If you do not know whether a person has it or not,
indicate this with a question mark.
b. Record the gene pair for each person in the pedigree above. If 2 stands for the gene
form for cystic fibrosis and 1stands for the normal form of the gene, then 1,1 would be
normal, 1,2 normal but a carrier, and 2,2 would have cystic fibrosis. Remember that you
need two genes for each person.
7. Consider a second Ramsey child’s chances of having cystic fibrosis.
a. What are the possible gene pairs combinations that he could have inherited from his
parents? (Use 1’s and 2’s.)
b. What do you think are the chances that a second child would get the gene pair for
cystic fibrosis? Use a punnett square to show your answer.
8. Would it be possible for Mr. or Mrs. Ramsey to come down with cystic fibrosis as
they grow older? Explain.
9. Imagine that Laurie is now grown up and has married a man named Larry. he is a
carrier of cystic fibrosis. They have a daughter named Lisa.
a. Draw a pedigree that includes Lisa, Laurie, and Larry.
b. Show which gene pair each person in the family has. Write this beneath their
numbers (1 or 2) on the pedigree.
c. What are the chances that Lisa has cystic fibrosis? Explain your answer using
a punnett square.
10. Why is cystic fibrosis said to be a recessive genetic condition and not a dominant
one? (Hint: How many cystic fibrosis genes do you need to have cystic fibrosis?)
11. Do you think that you could be carrying the gene for cystic fibrosis? Explain.