Is There a Gene Test for Cystic Fibrosis?

Cystic fibrosis (CF) is a serious disease that runs in families. It’s caused by a gene that doesn’t work properly. Genetic tests can tell if you have this faulty gene.

These tests are used for different reasons. They can diagnose CF, or help your doctor prescribe a treatment. Genetic tests can also tell you your chances of having a child with the disease.

How Are Genetic Tests Done?

Genetic material, called DNA, is in your cells. Your doctor will take some of your cells by either drawing blood or gently swabbing the inside of your cheek.

He’ll send the sample to a lab. There, scientists will look for changes (mutations) to a gene called CFTR. They’ve found about 2,000 different mutations on the gene, but not all of them cause CF. Genetic tests for the disease are usually done in one of two ways:

  • Panel test: This screen checks for the most common mutations that cause CF. If your result is “positive,” that means it’s 99% certain you have the gene mutation. A “negative” result isn’t as solid as a positive. That’s because you might have a rare mutation that doesn’t show up on the test.
  • Gene sequencing: This test studies all 250,000 pairs that make up the CFTR gene. It spots rare mutations. But it’s more expensive, so doctors don’t use it as often.

Genetic Testing for Family Planning

Doctors offer genetic, or carrier, testing to all couples who are pregnant or thinking about becoming pregnant. This panel screen allows you to find out your chances of having a child with CF. It may help you make decisions when planning your family.

Genes come in pairs. To have CF, a child needs to inherit two flawed copies of the CFTR gene -- one from each parent. A child with only one copy is called a “carrier.” That means he doesn’t have the disease, but he can pass the gene on to his children.

If you’re a carrier but your partner isn’t, the odds of your having a child with the disease are very small. If both of you are carriers, there’s a 25% chance that your child will have CF.

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You may want to speak with a genetic counselor about your risk and options. If you’re pregnant, a follow-up genetic test can show if the fetus has CF. There are two types of tests:

If you’re planning to have kids in the future, your options include:

In vitro fertilization with an egg or sperm from a donor who’s not a carrier (or you may have your own fertilized egg tested for CF before it’s implanted)

Genetic Testing for Newborns

Newborns are screened for genetic diseases, including CF, in the hospital. A few days after your baby is born, a nurse will prick his heel for a blood sample, and it will be sent to a lab. There, doctors look for high levels of a chemical called IRT, which may mean CF. In some states, babies are also given a genetic test. If the result is positive, your doctor will order another test to confirm it. This is called a “sweat test.”

Genetic Testing for Cystic Fibrosis Patients

If you have CF symptoms, or if you’re a patient, your doctor may order a genetic test for one of a few reasons:

  • To diagnose CF: Most people who have it are diagnosed under the age of 2. But sometimes it is not found until later.
  • For more knowledge about your case: Some mutations on the CFTR gene cause different symptoms. For example, some cause more problems for your digestive system than for your lungs. A genetic screen may reveal the exact mutation you have. This can help your doctor find the right treatment for your disease.
  • To prescribe targeted therapies: This is a new line of drugs for CF. They treat the faulty proteins caused by specific mutations. Your doctor may order a genetic test to see if one of these medications can help you.
WebMD Medical Reference Reviewed by Dan Brennan, MD on May 07, 2019

Sources

SOURCES:

Patrick Sosnay, M.D., physician, Johns Hopkins Cystic Fibrosis Center; assistant professor of medicine, pulmonary and critical care department, Johns Hopkins University School of Medicine.

Cystic Fibrosis Foundation: “Carrier Testing for CF,” “Newborn Screening for CF,” “Know Your CF Mutations.”

Human Genome Variation: “p.G970D is the most frequent CFTR mutation in Chinese patients with cystic fibrosis.”

Journal of Biological Chemistry: “Antibody against a cystic fibrosis transmembrane conductance regulator-derived synthetic peptide inhibits anion currents in human colonic cell line T84.”

American College of Obstetrics and Gynecology: “Cystic Fibrosis: Prenatal Screening and Diagnosis.”

U.S. National Library of Medicine Genetics Home Reference: “Cystic Fibrosis.”

CDC: “Chorionic Villus Sampling and Amniocentesis: Recommendations for Prenatal Counseling.”

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