Screening could halve CF births

Prenatal diagnosis can save parents a lot of grief

By Robb Beattie

Cystic fibrosis (CF) can be a devastating disease for children and parents alike. But genetic testing programs are now making headway alerting pregnant women who are CF gene mutation carriers. In the US, the largest CF screening program in the country has just released results showing a halving of CF births in women counselled over the program's four-year existence.

The screening program is run by Kasier Permanente, a three-million-member health maintenance organization in California. Focused on people of direct European descent (the highest risk group for CF), the program screens the DNA of pregnant women using a panel of 37 common or relatively common CF mutations. Patients with positive results are offered genetic counselling and CF screening of their partners, and prenatal diagnosis is then made available to parents at high risk of carrying a fetus with CF. To date, 56,000 clients have been screened and 2,003 carriers identified, for a carrier identification rate of one in 28.

Speaking at the 2003 annual meeting of the American Society of Human Genetics in Los Angeles, Dr David R Witt, director of the San Jose-based program, described how the program followed pregnancies in 57 couples where both partners were found to be CF carriers. The most commonly identified mutant combination was F508 in both parents. In nine cases, prenatal testing predicted severe CF, and the parents opted to end the pregnancies. All but two of the other pregnancies were carried to term. During the four years of the screening program, nine children were born with two CF mutations; of them, six were diagnosed with severe CF. In total, nine of 15 predicted cases of severe CF and two of five cases predicted to be mildly affected or unaffected were prevented.

In Canada, CF testing in pregnancy is recommended only when the parents have an increased risk due to family history or clinical manifestations.