Cystic Fibrosis Genetic Testing Basics

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Cystic Fibrosis Genetic Testing Basics

Genetic Testing Guide
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Putting Knowlege To Work
Cystic Fibrosis Genetic Testing Basics
Cystic Fibrosis Genetic Testing Basics
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Cystic Fibrosis Genetic Testing Basics
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InteliHealth
2011-06-28
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InteliHealth Medical Content
2014-06-28

Reviewed by the Faculty of Harvard Medical School

Cystic Fibrosis Genetic Testing Basics

Cystic Fibrosis

What is cystic fibrosis?
Cystic fibrosis is a lifelong disease that primarily affects the lungs and digestive system. People who have CF look no different from anyone else. Symptoms include a buildup of thick mucus in the lungs, digestive tract and pancreas. This mucus can provide a haven for bacterial and viral infections in the lungs that can lead to tissue damage and pneumonia. Some people die from these infections; some require lung transplants. If the pancreas becomes damaged it will not produce enzymes needed for the digestion of food. People with CF often take enzyme pills when they eat to help their bodies digest food and absorb nutrients.

How common is cystic fibrosis?
Cystic fibrosis is one of the most common inherited diseases. It affects approximately one out of every 3,200 Caucasian people in the United States, with smaller numbers affected in other ethnic groups.

Who is at risk of cystic fibrosis?
Every couple has a chance of having a child with cystic fibrosis. High-risk populations include people with a family history of CF (meaning someone in the family has or had CF) and/or those with European ancestry. About one in every 25 Caucasians carries a mutation in the CF gene. However, because most people who are carriers have no family history of CF (meaning no one in the family has or had the disease) and because they themselves are healthy, they often do not realize they are carriers until they have a child affected with CF. Although Caucasians are at highest risk of being CF carriers, it occurs in every population throughout the world.

Ethnicity Chance Of Being A CF Carrier
African-American 1 in 60-65
Non-Hispanic Caribbean, West Indian 1 in 60-65
Southern European 1 in 25-29
Northern European 1 in 25-29
Eastern European Jewish (Ashkenazi) 1 in 26-29
Hispanic Caribbean 1 in 46
Hispanic Mexican, Central American 1 in 46
Asian 1 in 90
Southeast Asian Southeast Asian 1 in 90
Asian Subcontinent (India, Pakistan), Middle Eastern Variable
French Canadian, Cajun 1 in 25-29
 
Ethnicity CF Carrier Testing Detection Rate
Ashkenazi Jewish 97%
Non-Hispanic Caucasian 88%
African-American 69%
Hispanic-American 57%
Asian-American Uncertain
Other Populations Uncertain

Is there a cure for cystic fibrosis?
No. Different treatments can alleviate some of the symptoms of cystic fibrosis, but there is no cure. For example, antibiotics can help to prevent some common lung infections that damage lung tissue, and daily physical therapy can help to move some of the mucus out of the lungs. Enzymes in pill form taken with every meal help someone with a poorly functioning pancreas. The enzymes help with the digestion and absorption of nutrients. While there is yet no cure for CF, there is a great deal of research in this area with hope for the future.

Related Reading
Cystic Fibrosis

The CFTR Gene

How do you get cystic fibrosis?
Cystic fibrosis is an inherited disease. Everyone has two copies of the CF gene: one inherited from the mother and one from the father. CF occurs when both copies of the inherited cystic fibrosis transmembrane receptor (CFTR) gene are mutated or altered. Scientists know more than one thousand types of mutations in the CFTR gene, and new mutations are still being found. Most of these mutations are rare and only occur in one family, but there are many common mutations.

How do I know if I carry cystic fibrosis?
Because there are typically no symptoms when you are a carrier, the only way to find out if you carry an altered cystic fibrosis gene is to have a DNA test that detects the most common mutations (or changes) in the CF gene. Generally, these tests look for only the most common mutations and not for all of the rare mutations. DNA for this test comes from a blood sample or a scraping of tissue from the inside of your mouth.

No one in my family has cystic fibrosis, so I can't be a carrier, right?
You could be a carrier. The vast majority of people who are cystic fibrosis carriers have never had anyone in their family with the disease. Most children with CF are born to couples who had no family history of the disease. Remember, a mutation in a CF gene can be passed down for many generations without anyone in the family ever having symptoms or any children being affected.

What if I have a family history of cystic fibrosis?
You are more likely to be a cystic fibrosis carrier. Review your family history of CF with a genetic counselor, a medical professional specially trained to evaluate your risk due to a family history of genetic disease. Depending on who is affected in your family, and how closely this person is related to you, the genetic counselor can tell you what the chance is that you are a CF carrier. Because there are so many mutations in the CFTR gene, it is helpful to know which mutation or mutations your relative has. Not every lab tests for the same mutations, and it is important to test for the mutation(s) known to be running in the family as well as other common mutations.

Should You Be Tested?

Should you (and your future baby) be tested?
First, it is helpful to know what your chance is of being a carrier and the chance the DNA test will be positive (meaning you are a carrier of a common mutation). If there is a family history of cystic fibrosis, find out what mutation(s) the relative has and try to get a lab report. You then can meet with a genetic counselor to review the records and your family history to determine your risk of being a CF carrier. A genetic counselor can also help you decide if testing is right for you.

If I don't have a family history of cystic fibrosis, should I be tested?
The chance that you are a carrier depends on your family's ethnic background. Because the standard DNA screening test only detects the most common mutations, some people who have a negative result will actually be carriers of more rare mutations of cystic fibrosis that were not detected by the DNA test. The carrier detection rate of the DNA screening test depends on your ethnic background.

What happens if a test reveals the fetus has cystic fibrosis?
Some people use this knowledge as a way of preparing for the birth of a child with cystic fibrosis. Parents can meet with others who are raising children with CF. Parents can meet with specialists who treat cystic fibrosis. Some people make plans to deliver the baby in a hospital with the facilities needed to treat an infant that may have complications from CF. Some couples decide not to continue the pregnancy.

Are all babies tested at birth for cystic fibrosis?
Every state, and the District of Columbia, now offers testing of all newborns for cystic fibrosis as part of newborn screening for various conditions. Even if the newborn screen was normal, ask your baby's doctor if he/she has any symptoms of CF because newborn screening is not perfect.

Learn more about newborn screening by state.

Understanding Test Results And Options

How Do You Make Sense Of The Results?

Your genetic counselor or the doctor who ordered the test will be able to explain the results. There are several possible outcomes:

Positive
This means you are a carrier of a common cystic fibrosis mutation. For example, DeltaF508 is the most common mutation (by far). If you are a DeltaF508 carrier, your partner should be tested. If he or she also carries a mutation in the CF gene, it means there is a 25 percent (one in four) chance for each pregnancy you have together to be affected. If your partner tests negative, there is still a small chance, less than 0.1 percent (one in 1,000), of having an affected child.

False Positive
This is extremely rare (in fact, it virtually never happens). The only way this could happen is if there is an accidental mix-up of samples. For this reason, it is important to use a reputable lab to avoid a mix-up.

Negative/False Negative
You have tested negative for the most common mutations. The number of mutations tested varies from lab to lab. This does not completely eliminate the chances of having a CF mutation, but it makes the chances much lower.

If I test negative for cystic fibrosis, does that mean I am definitely not a carrier?
No. There is still a chance you could carry a rare mutation that was not tested for by the lab. There is no way to guarantee you are not a carrier. There is always a small chance that you are a carrier.

Personal Questions

Why would I want to know if I am a cystic fibrosis carrier?
You may want to know that you are a carrier because:

  • You are from a high-risk population.
  • Your partner is also a CF carrier, giving you a 25-percent risk of having an affected child. You may consider using an egg or sperm donor who is not a carrier.
  • If you are not a carrier of a common CF mutation, it might reduce anxiety or worry about having a child with CF.
  • You want to know your chance of having a child with CF. Prenatal testing is available, so if you and your partner are carriers, you can learn whether the fetus is affected. (Remember, even if both parents are carriers there is a 75 percent chance the baby is unaffected.)
  • Some people want to know the baby's status prior to birth so they can prepare medically, emotionally and financially. Some people want to know so they can decide whether to continue the pregnancy or not.
  • You want to test the baby right at birth so treatment can begin before symptoms develop.

Why would I not want to know if I am a cystic fibrosis carrier?
You may not want to know that you are a carrier because:

  • You prefer not to know if your future children or current pregnancy could be affected because that may force you to make a decision about whether or not to pursue prenatal testing, which carries some risk.
  • You would not change any decisions about becoming pregnant or terminating a pregnancy.
  • It would make you feel anxious or worried to learn you are a carrier.
  • It may make you feel guilty about being a carrier and putting your children at risk of being affected or of being carriers as well. (Even a negative test result may make you worry since it cannot rule out the possibility that you are a carrier — it only rules out your being a carrier for a common mutation.)
  • The test may not be covered by your insurance, or you may worry that insurance coverage for your children may be affected.
  • It may give information to family members that they did not want to hear. For instance, if you learn that you are a CF carrier, it means your sister is at 50-percent risk of being a carrier. She may not want to know this.

Test Details

How do I find out if I am a carrier?
With a blood test. The test usually requires drawing about one teaspoon of blood from your arm and sending it to a lab that does cystic fibrosis testing. Your doctor, obstetrician or midwife can arrange this for you. If your doctor is uncertain about which lab to use, contact a genetic counselor.

Should I be tested before or after a pregnancy?
It is ideal to be tested for cystic fibrosis before beginning a pregnancy. This provides you more options (such as using an egg or sperm donor) if you and your partner are both carriers. It typically takes about two weeks to get results back. Waiting those two weeks is often very stressful, but is even more stressful while a pregnancy is ongoing.

You may want to check with your insurance company first. Some insurers only cover CF carrier screening if you are already pregnant.

How is a baby diagnosed with cystic fibrosis prior to birth?
If both the mother and father are carriers of cystic fibrosis, prenatal testing can determine if the baby is affected. There are two ways to do this:

  • Chorionic villus sample is performed between 10 to 12 weeks. Guided by ultrasound, a doctor inserts a very thin needle through the mother's abdomen to retrieve a tiny amount of tissue from the placenta. (Sometimes the small amount of tissue is obtained with a very thin tube inserted through the mother's vagina.) The procedure carries a risk of about 1 percent (1 in 100) of miscarriage.
  • Amniocentesis is typically performed between 15 to 22 weeks. Guided by ultrasound, a doctor inserts a very thin needle into the uterus to retrieve one or two tablespoons of amniotic fluid. The needle does not touch the fetus. There is a 0.5 percent (1 in 200) risk of miscarriage with this procedure.

Prenatal ultrasound cannot reveal if your baby has cystic fibrosis. But sometimes a doctor will see an "echogenic bowel" on the ultrasound. This means the baby's bowel appears more dense than usual. A dense bowel increases the chances of cystic fibrosis, although it can also occur in other conditions and in normal babies. If your doctor detects an echogenic bowel, you should ask about the risks and benefits of amniocentesis, which may be able to give you a clearer answer about cystic fibrosis.

If the baby inherits a mutation from its mother and from its father it will have cystic fibrosis. If the baby inherits a single mutation from the mother or father the baby will be a carrier, but will not have cystic fibrosis. If the baby didn't inherit any mutations, then it is neither a carrier of cystic fibrosis nor affected with it.

Are there different types of cystic fibrosis genetic testing?
Yes, there is a mutation panel test to look for the common changes. This is most appropriate as a general screening test for carriers. If a child is affected, and the mutation panel test does not identify both changes in the gene, then complete gene sequencing is an option. This test has a better chance of finding a rare mutation, but is also more expensive. If two rare mutations can be found in the affected child, that information can be used to test the parents or other family members even when the standard screening test doesn’t work.

Does insurance pay for cystic fibrosis testing?
Most health-insurance companies pay for "diagnostic testing," which means the test is being done to confirm a diagnosis in a person who already has symptoms. However, there are many different plans, and you should check whether diagnostic genetic testing is a covered service before having the test performed. Many insurance companies cover carrier testing for cystic fibrosis, but it is best to check with your individual policy prior to testing. Some insurers only cover CF carrier screening if you are already pregnant. The cost varies from lab to lab, but most are in the $200 to $400 range for the common mutation panel. The complete gene sequencing is more expensive (over $1,000).

Are there any laws that protect me against genetic discrimination?
In 2008, the U.S. government passed a law called GINA (Genetic Information Nondiscrimination Act). This law prohibits discrimination by health insurers and employers on the basis of genetic information. Learn more here.

Also, this may depend on whether you have group insurance or are self-employed. Both federal and state laws usually cover people with group insurance, while state laws only cover people who are self-employed. Also, the Federal Health Insurance Portability and Accountability Act (HIPAA) of 1996 prohibits health insurance discrimination based on any "health status-related factor" (including genetic information) by group health plans. Unfortunately, this act does not apply to the self-employed.

Life insurance, long-term care and disability insurance are generally not covered by these laws. People with life and disability coverage provided by their employers are unlikely to have this insurance affected by a genetic test result.

For information about laws in individual states, click on the following links:

Learn more about life insurance, disability insurance and long-term-care insurance laws.

Learn more about health-insurance laws.

How do I find a genetic counselor?
Your primary-care physician or obstetrician can refer you to a local genetic counselor. Find genetic counselors in your area.

 

 

cystic fibrosis,gene,dna,bowel,prenatal,lung,ultrasound,amniocentesis,digestion,gene sequencing,gene.,miscarriage,obstetrician,sperm
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Last updated June 28, 2011


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