Cystic Fibrosis Screening

What is Cystic Fibrosis?

Cystic fibrosis is a life-long illness that is usually diagnosed in the first few years of life. The disorder causes problems with breathing and digestion, because of altered mucus production in affected individuals. Cystic fibrosis (CF) does not affect intelligence. The average life expectancy of affected individuals approaches forty years.

How common is cystic fibrosis?

The rate of defective CF genes varies in different groups of people. In Caucasians, one in every twenty-nine individuals is a carrier of a CF mutation, and roughly one in every 3,300 newborns will have cystic fibrosis. In Hispanic populations, the carrier rate is lower, at one in forty six, with about one in 8,000 to 9,000 children being affected. In African-Americans, one in sixty-two are carriers, with a newborn rate of roughly one in 15,000. Among Asian-Americans, one person in ninety is a carrier, and among their newborns, only one in 32,000 will have CF.

How is cystic fibrosis inherited?

For CF to occur, a person has to inherit an altered gene from each parent. If a person inherits one copy of a CF gene with a mistake, that person is a “carrier” for CF, and does not have CF. There are no known health problems associated with being a carrier. To have CF, an individual must inherit a defective CF gene from both carrier parents. If both parents are carriers, there is a one in four chance that any one of their children will have CF.

How can I find out if I carry the gene for cystic fibrosis?

A DNA test on white cells from a blood sample can tell a patient whether they are likely to be a carrier of a defective CF gene. This DNA test looks for the most common defective genes but cannot detect every single abnormal gene. The detection rate for the problem is about 97% in Caucasians, while among other groups it can be as low as 57%. This means that among some ethnic groups with very low rates of being CF carriers, the blood test is only likely to detect this a little more than half the time.

What if the test is positive?

If the initial blood testing returns positive for a defective CF gene, your partner is then tested. If this test returns negative, the likelihood of having an affected child is very low.

If the testing should be positive for both the patient and her partner, the likelihood that any child born to them will have cystic fibrosis is one in four. Additional testing during the pregnancy can show whether or not the fetus will have cystic fibrosis. A test called “chorionic villus sampling” in which a small portion of the placenta is analyzed, can be performed at the 11th week of pregnancy. A more common test called “amniocentesis” may be performed at the 15th week. For amniocentesis, a thin needle is inserted under ultrasound guidance into the fluid surrounding the baby in the womb. A small amount of the fluid is then withdrawn and the cells found therein are analyzed for the CF genes.

These prenatal tests carry some degree of hazard to the pregnancy. If a patient decides not to have this prenatal testing, a simple test done on a sweat sample may be performed soon after birth.

Where can I obtain further information?

We will be happy to discuss cystic fibrosis screening further with you during your visits to our office. Other resources for additional information include:

Cystic Fibrosis Foundation, www.cff.org
Boomer Esiason Foundation, http://www.esiason.org
Canadian Cystic Fibrosis Foundation, http://www.cysticfibrosis.ca/home.cfm