The objective was to determine the composition of the Cystic Fibrosis (CF) 
Population attending specialist UK CF centres in terms of age, gender, age at 
diagnosis, genotype and ethnicity. With the planned introduction of the national 
CF screening programme in the UK, cystic fibrosis transmembrane regulator (CFTR) 
mutations were compared between different ethnic groups enabling a UK-specific 
frequency of mutations to be defined. Data were analysed from the patient 
biographies held in the UK CF Database (see www.cystic-fibrosis.org.uk). The 
currently registered population of 5,274 CF patients is 96.3% Caucasian with a 
male preponderance that significantly increases with age. The majority of the 
196 non-Caucasian CF patients are from the Indian Subcontinent (ISC), of which 
one in 84 UK CF patients are of Pakistani origin. The commonest CFTR mutation, 
deltaF508, is found in 74.1% of all CF chromosomes. In the Caucasian CF 
population, 57.5% are deltaF508 homozygotes but the UK ISC CF population with 
only 24.7%, has significantly fewer deltaF508 homozygotes patients (95% 
confidence interval (CI) 0.2-0.4). The distribution of Caucasian patients with 
deltaF508/deltaF508, deltaF508/Other and Other/Other does not fit the expected 
distribution with a Hardy-Weinberg model unless those patients without a 
detected mutation are excluded (P<0.001). The UK CF Database has shown the UK CF 
population to have distinct characteristics separate from the North American and 
European CF Registries. The ISC group contains many mutations not recognised by 
current genetic analysis, and one in four ISC patients have no CFTR mutations 
identified. The CFTR analysis proposed for the screening programme would detect 
96% of patients registered in the database, but is unlikely to achieve the 
desired >80% detection rates in the ethnic minority groups. Screen-positive, 
non-Caucasian infants without an identifiable CFTR mutation should be referred 
for a sweat test and genetic counselling when serum trypsinogen concentrations 
remain elevated after birth.