CF screening

Sir-Ten Kate (Nature 342, 131; 1989) suggests that carrier screening for cystic fibrosis (CF) should be postponed until 96 per cent of the possible mutations have been detected, on the grounds that so long as a substantial proportion of CF is not associated with the now-identifiable mutation AF508, the risk for a couple only one of which is identified as a carrier would still be greater (at 1 in 300) than for unscreened couples (1 in 2,500). Were testing to be offered tomorrow to women in early pregnancy, it would perform rather better than the criteria now applied in the avoidance of Down's syndrome, where indicators such as maternal age, low serum alphafetoprotein and high human chorionic gonadotropin define those with risks greater than 1 in 250 and which, followed by amniocentesis, detect some 60 per cent of Down's syndrome cases. [...]we acknowledge that, as with other screening for autosomal recessive disease, the need for accurate information on paternity is a consideration of which those to whom testing is offered should be aware.