How is prenatal diagnosis of cystic fibrosis (CF) made?

Updated: Oct 22, 2019
  • Author: Girish D Sharma, MD, FCCP, FAAP; Chief Editor: Kenan Haver, MD  more...
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Answer

Prenatal diagnosis allows the clinician to prepare for the medical and psychological needs of the parents, fetus, and newborn before, during, and after delivery.

Noninvasive CFTR analysis involves a technique for recovering DNA from cells obtained by buccal brushing. This technique can be used to determine the carrier status of the parents of a fetus with suspected CF based on sonographic findings of meconium ileus.

These tests are highly specific and are improving. One commercial test screens for 97 of the most common CF mutations. Although more than 1600 CF mutations exist, the 97 mutations covered by this test represent 98% of mutations responsible for the disease. In addition, results with this test are available in 5-8 days, versus 2-3 weeks with complete gene sequencing.

Screening tests do not screen for all possible mutations, and several types screen for just a few of the more common genetic mutations. Therefore, it is important to understand the implications of positive or negative results depending on the brand of screening test used.

Amniocentesis can provide subsequent fetal evaluation when both parents have identified CF mutations.

When only one or neither parent has an identified CF mutation but the couple has a previous child with CF, the status of the fetus can be predicted by restriction fragment length polymorphism (RFLP) analysis. Genetic material from both parents, the affected sibling, and the fetus must be available for RFLP testing. If the results predict CF in the fetus, referral to a tertiary care facility facilitates genetic counseling and consultation with specialists in maternal-fetal medicine.

If DNA analysis or amniocentesis tests are refused or if results are nondiagnostic, the authors recommend close sonographic follow-up at 6-week intervals.


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