• carriers
• cystic fibrosis
• screening

• CF, cystic fibrosis
• IRT, immune reactive trypsin
• CFTR, cystic fibrosis transmembrane regulator

A decision to introduce nationwide cystic fibrosis (CF) newborn screening in the United Kingdom has now been taken, although the exact procedure is still being determined, except in Scotland where screening began in February 2003. In Scotland, as well as in a number of regions in England and Wales where ad hoc newborn screening was started some time ago, an immune reactive trypsin (IRT)/DNA system of newborn screening is used, DNA analysis being undertaken on those above a cut off point of IRT. The multiplex DNA arm covers about 86% of the most common mutations in the native UK population.¹ There is evidence that the more severe mutations of the cystic fibrosis transmembrane regulator (CFTR) gene are the ones most likely to cause an increase in IRT.²

There are a number of advantages of IRT/DNA programmes: earlier full diagnosis within the first few weeks of life becomes possible for those in whom both mutations are found; there is a reduction in sweat testing and in the uncertainty that may follow inadequate sweat collection; also many fewer couples need to be faced with the worry that their baby might have CF than when IRT is used alone.^3,4 In those from ethnic minorities where the mutation spectrum is largely unknown, one has no choice other than to proceed to sweat test in those with a persistently raised IRT.

The disadvantage of the IRT/DNA method is that the genetic analysis step results in the discovery of some healthy carrier infants, with the spectre of CF raised for the parents before the situation is resolved by negative sweat test. Two or three carrier newborns are discovered for each child diagnosed with CF.^3,4

One issue that has concerned some is that one might …