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Scotet et al report an analysis of ten years’ experience of neonatal screening for cystic fibrosis in the four regions of Brittany [Scotet, V. et al (2000) Lancet 356, 789-794 (see Cystic fibrosis summary for background information on cystic fibrosis genetics)]. Between 1989 and 1998, 343,756 neonates were screened. The identification of the CFTR gene in 1989 led, in 1992, to a change in the screening protocol to a method involving direct mutation analysis on all blood samples with an immunoreactive trypsin concentration in the highest 0.5-1.0% of the range. During the 10-year period, 118 children born in the region were diagnosed with cystic fibrosis: 112 by the screening test and six by clinical symptoms (these false-negative cases all occurred before the introduction of the mutation test). The cost of screening was estimated at US$6825 per affected child. The screening programme enabled prenatal diagnosis in subsequent pregnancies to be offered to couples who had an affected child. 39 couples took up this offer, some in more than one pregnancy; in all 18 cases where an affected fetus was identifed, the couple opted for abortion. In the case of 12 of these couples, the second pregnancy began before any clinical symptoms were evident in the older child.

Comment: The clinical benefit, to the affected child, of neonatal screening for cystic fibrosis remains highly controversial. The authors of this study quote evidence in favour of early diagnosis and treatment, but other studies have found no such evidence. Perhaps the biggest benefit of screening may be in enabling informed choice, in subsequent pregnancies, to couples who have an affected child and may conceive again before the child’s symptoms are apparent. It could be debated, however, whether this benefit outweighs some disadvantages of screening. One such disadvantage, which became apparent in this study, is that there are some combinations of CFTR mutations that are so mild that no clinical symptoms develop at all, at least during childhood. It is unclear whether it is an advantage to such individuals to be diagnosed as having cystic fibrosis, or to their parents in trying to make decisions about prenatal diagnosis in subsequent pregnancies.