Editor,—The paper describing screening for cystic fibrosis (CF) by Cunningham and Marshall1 has a number of important flaws. Any screening programme is targeted at a defined population. The title refers to a “population in one region” without being geographically precise, but the study is of children born in two hospitals. If the total number of screened pregnancies in the hospitals had been stated then the incidence of CF conceptions in this group could have been calculated.

The paper quotes without referencing a CF “gene frequency”, but the authors clearly mean CF carrier frequency of nearly 1 in 20. This gives an incidence of 1 in 1600 live births (not 1 in 2000). The only published long term population data estimating CF incidence in Scotland are the UK data, which at the time of this study was fractionally under 1 in 2500 live births. …