Sometimes it is All in the Genes

Jake gripped Nancy's hand as they sat in the office waiting for the genetic counselor.  When Jake tested positive as a CF carrier, Dr. Kwin had set up an appointment with the counselor for the next day.  What had first seemed like a helpful thing to do for science had suddenly developed into a problem that Dr. Kwin did not feel qualified to handle.  Just being in a specialist's office made the couple nervous.

They both jumped a little when the door opened.  "Hello.  I'm Dr. Joon Park."  The counselor shook hands with them as he continued.  "I understand that you both tested positive as carriers for cystic fibrosis, but neither of you had any family history of the disease."

"Yes,"  said Nancy.  "That's one of the questions that bothers me.  How could we both be carriers yet we don't even know anyone with cystic fibrosis?"

"Good question,"  Dr. Park replied reassuringly.  "On the surface that might seem unusual, but it is actually quite common with recessive genetic disorders.  In fact, around 80 percent of children born with cystic fibrosis are born to parents with no family history of the disease."

Dr. Park paused, then continued.  "I'm glad that you are already comfortable asking questions.  One part of my job is to answer any questions you might have about inherited diseases and CF in particular.  The other goal for us today is to discuss your current options."

Jake entered the conversation.  "Yeah.  What are our options?  I want to know if our baby is going to have cystic fibrosis, but we can't just do a blood test now.  Can we?"

"No.  You are right.  We can't do a blood test."

Before Dr. Park could finish, Nancy jumped in to add, "But we can do a genetic test through amniocentesis, can't we?"  She looked at Jake with an expression that told him he should have read the pre-natal baby books as she had asked him to do.

"Yes, Nancy, we can do amniocentesis."  Dr. Park went on to explain for Jake's benefit.  "Using ultrasound to guide them, doctors insert a small needle through the abdomen and into the uterus.  A small amount of the amniotic fluid that surrounds the fetus is removed.  Fetal cells that have sloughed off are found in that fluid and from those cells, DNA can be isolated and checked for the presence of two bad copies of the gene that cause cystic fibrosis."

"What are we waiting for?"  an anxious Jake questioned.  "Let's get the test done."

"There is a chance that the amniocentesis will cause a miscarriage.  However, here at People's Best Hospital, miscarriage occurs less than 0.5 percent of the time."

"Point five percent; that still amounts to 1 in 200."  Jake did not lack intelligence, he just thought he would have another four and a half months before he really had to worry about anything related to babies.

Nancy interrupted.  "Dr. Park, what exactly causes cystic fibrosis?  What sort of life do people with CF lead?"

"Cystic fibrosis is caused by a mutation in a gene called CFTR.  A normal CFTR gene carries the instructions to make a protein that allows chloride to pass out of a cell.  When chloride moves, it causes water to follow and secretions are formed outside the cells.  When a person has cystic fibrosis, both alleles of their CFTR gene are mutated.  The mutant genes create defective CFTR proteins or no CFTR protein at all.  The lack of a functional CFTR protein means that not enough chloride moves out of the cells, in turn causing less water to move.  The reduced water content causes the secretions to be thicker than normal.  This thick, sticky mucus usually has its worst effects on the lungs and the pancreas. 

"Normally, a thin layer of mucus coats the bronchioles and bronchial tubes in our lungs.  This mucus traps dirt and germs and continually travels to the throat.  Thus, the mucus removes the bad stuff from our lungs.  In CF patients, the thicker mucus in the lungs can't be moved out as easily.  This accumulation of mucus can block the air passageways.  Worse yet, it allows bacteria to get trapped in the lungs where they can cause debilitating infections.  While most of the symptoms of CF can be treated pretty effectively now, the continual stress and recurring infections in the lungs means that patients today still die in their 30s or earlier."

"If our baby tests positive for cystic fibrosis, what sort of treatments can we do before she is born?"  Although a boy would be a joy, Nancy really wanted a girl.

"Unfortunately, there is nothing that we can do to help her before birth.  Currently, we can only treat the symptoms, and she won't have symptoms until after she is born."  As long as he had been at his job, Dr. Park hated being the bearer of bad news.  However, he felt that the simple truth was the best approach.  "Of course, there are many promising new technologies that are being investigated to treat CF.  Still, even the most promising of those would not help before she is born."  Inwardly, Dr.  Park cursed the technologies for not delivering yet what they promised.

There was a long silence. Finally, Jake decided to find out what his wife was thinking.  "I think I'd still like to know if our baby has CF or not.  But I'm not sure about the risk.  What do you think, honey?"

Questions:

1. How do mutant CFTR genes lead to thicker mucus in cystic fibrosis patients?
2. How would testing their unborn baby for CF help Nancy and Jake?  Their baby?
3. What are their options if they find out their baby does have two bad CFTR genes?
4. Should they have the amniocentesis procedure?  Provide your reasons for reaching this decision.

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