Genetic Determinants and Epidemiology of Cystic Fibrosis–Related Diabetes

OBJECTIVE Longer survival of patients with cystic fibrosis has increased the occurrence of cystic fibrosis-related diabetes (CFRD). In this study we documented the incidence of CFRD and evaluated the association between mutations responsible for cystic fibrosis and incident CFRD, while identifying potential risk factors. RESEARCH DESIGN AND METHODS This was a population-based longitudinal study of 50 cystic fibrosis speciality clinics in the U.K. Subjects included 8,029 individuals aged 0-64 years enrolled in the U.K. Cystic Fibrosis Registry during 1996-2005. Of these, 5,196 with data and without diabetes were included in analyses of incidence, and 3,275 with complete data were included in analyses of risk factors. Diabetes was defined by physician diagnosis, oral glucose tolerance testing, or treatment with hypoglycemic drugs. RESULTS A total of 526 individuals developed CFRD over 15,010 person-years. The annual incidence was 3.5%. The incidence was higher in female patients and in patients with mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene in classes I and II. In a multivariate model of 377 cases of 3,275 patients, CFTR class (relative risk 1.70 [95% CI 1.16-2.49], class I or II versus others), increasing age, female sex, worse pulmonary function, liver dysfunction, pancreatic insufficiency, and corticosteroid use were independently associated with incident diabetes. CONCLUSIONS The incidence of CFRD is high in Britain. CFTR class I and II mutations increase the risk of diabetes independent of other risk factors including pancreatic exocrine dysfunction.