Cystic fibrosis is an inherited disease that affects the lungs, pancreas, digestive system, and many other organs. It is caused by a defect in the cystic fibrosis transmembrane conductance regulator (CFTR) gene.
The CFTR protein controls transport of salt in and out of the cell, and mutations in the gene result in an imbalance in that transport system, leading to a build-up of thick, sticky mucus in the tissues. This leads to symptoms and complications, particularly in the lungs, where the thick mucus obstructs airways and traps bacteria, causing frequent infections.
Cystic fibrosis occurs in 1 out of every 2,500 to 3,500 live births, and among people of Northern European descent, about 1 in 25 are carriers.
.jpg "Cystic fibrosis. Image Credit: Alila Medical Media / Shutterstock")
Cystic fibrosis. Image Credit: Alila Medical Media / Shutterstock
Prenatal Diagnosis
Cystic fibrosis can be diagnosed during pregnancy by obtaining genetic material from the fetus through chorionic villus sampling or amniocentesis. For couples who are carriers of cystic fibrosis, testing during pregnancy allows them to plan or make decisions about termination. A genetic test for cystic fibrosis is virtually 100 percent accurate. However, it cannot predict how the disease will manifest.
The test is invasive and carries a risk of miscarriage. Non-invasive prenatal diagnosis is a new approach being developed to test for cystic fibrosis without the risk of harm to the fetus that is involved in currently available tests. One method of testing non-invasively is based on analysis of cell-free fetal DNA in maternal plasma. These tests use PCR to amplify the DNA. A drawback of this approach is that multiple mutations cannot be screened simultaneously.
Another strategy for non-invasive testing uses next-generation sequencing to test the mother’s plasma. This test can be used for multiple mutations at the same time.
Carrier Testing
Cystic fibrosis results when a person receives a copy of a CFTR mutation from each parent. Either or both parents can be carriers of cystic fibrosis without being aware of it or having any symptoms, but they can potentially pass the disease to their child.
Pregnant women may choose to be tested to find out if they are carriers of cystic fibrosis. The results of this decision may help in deciding whether to have the fetus tested for cystic fibrosis.
Cystic fibrosis carrier testing (CFCT) covers the most common cystic fibrosis mutations in the U.S. population. The CFCT is not diagnostic, either for the fetus or the parents, but it does indicate the potential risk that the fetus will carry one copy of the abnormal gene.
The American College of Obstetricians and Gynecologists (ACOG) recommends that CFCT be offered to:
- Couples with a family history of cystic fibrosis
- Partners of individuals with cystic fibrosis
- Caucasian couples of European or Ashkenazi Jewish descent
It is recommended that couples of other racial or ethnic groups be offered information about carrier testing, since cystic fibrosis carrier frequency and CFCT sensitivity vary based on ethnicity.
Economic Considerations
The costs and benefits of screening for cystic fibrosis carriers and affected fetuses are not clearcut. The primary economic benefit of screening is in termination of pregnancies that are positive for cystic fibrosis. However, many couples use the screening results to plan for the care of their child, rather than termination. The cost-effectiveness of prenatal screening has thus been found to be highly dependent on the couple’s plans for the pregnancy.
References
Further Reading
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