Cystic Fibrosis and PGT

by | Jul 24, 2018
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If you and your partner are ready to have a child, your doctor is likely to bring up a cystic fibrosis screening, which determines if you are carriers of a mutation that causes the genetic disorder cystic fibrosis (CF). According to the Cystic Fibrosis Foundation (CFF), CF affects about 30,000 people in the United States and more than 70 million people worldwide.

The American College of Obstetricians and Gynecologists (ACOG) recommends that all couples who are considering having a child, or who are already pregnant, be offered this testing. If you and your partner carry a mutation that causes CF, or if you already have a child that has been diagnosed with the disease, you may want to consider PGT for CF.

What Is Cystic Fibrosis (CF)?

CF is a progressive disease that can cause chronic lung infections that, over time, limit the ability to breathe. The CF gene mutation causes mucus in the body to be thick and sticky. In the lungs, this can lead to infection and, eventually, lung damage. In the pancreas, the thick mucus clogs the duct leading to the small intestine, preventing digestive enzymes from getting where they’re needed to break down food, according to the CFF.

The severity and types of symptoms can vary greatly depending upon the individual. Many different factors also play a role, including the specific gene mutations the individual has and their age at diagnosis. Some of the most common symptoms include persistent cough, frequent lung infections, poor growth, greasy or bulky stools or other digestive issues, and shortness of breath.

What Does It Mean To Be a CF Carrier?

It’s quite common to be a CF carrier: about 1 in 31 people — or 10 million people — in the United States carry one CF mutation, according to the CFF. It takes two CF mutations to cause the disease, so carriers won’t have any symptoms. Those diagnosed with CF inherit one copy of the mutated gene from each parent.

Every time two CF carriers conceive a child, the chances of that child having CF are 25 percent, or 1 in 4. There is a 50 percent chance the child will be a carrier of a CF gene mutation but not have CF, while there is a 25 percent chance the child will not be a carrier and not have CF, explains the CFF.

We Both Carry CF Mutations — What Are Our Options ?

If the cystic fibrosis screening shows that you and your partner both carry a CF gene mutation, you could pursue in vitro fertilization (IVF) paired with preimplantation genetic testing (PGT) to test the embryos for CF before implantation. Then, only those embryos unaffected by CF are implanted for a potential pregnancy.

If IVF with PGT is not an option for you, you may discuss chorionic villi sampling (CVS) and amniocentesis with your physician or a genetic counselor. Both are prenatal diagnostic tests that can be performed during pregnancy to determine if the fetus has CF, notes ACOG. If the test is positive, your options are to prepare for a child with CF or to end the pregnancy.

How Does PGT Work for Couples Who Carry the CF Mutation?

The first step in using PGT for CF is to test your embryos by building a test specific to you, the parents. The carrier testing doesn’t give enough information to reliably test embryos for the specific CF mutations you both carry. If you already have a child with CF, DNA from your child may be used to help build your test, otherwise DNA from your parents is also a viable option. The test will look at the region of DNA around the CF gene mutation to determine if the embryo has two copies of the mutation, is a carrier or is unaffected.

While PGT is highly accurate, there is a small risk of an erroneous result. Thus, prenatal testing or newborn screening is recommended as a follow-up to ensure that the fetus doesn’t have CF.

Lauren Arcuri is a freelance writer in northern Vermont. She writes about science, health, and medicine, including genomics, neuroscience, and rare diseases. She has written for Pacific Standard, Proto, Genome, Yoga Journal, and many other publications.

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