title: Cumulative incidence of type 1 diabetes in 10,168 siblings of Finnish young-onset type 1 diabetic patients.
abstract: The aims of our analysis were to obtain the empirical risk estimates for type 1 diabetes in the siblings of a Finnish population-based cohort of childhood-onset diabetic patients and search for demographic and other factors predicting the risk of type 1 diabetes in siblings. We defined the diabetes status of all siblings of all probands who are included in the nationwide register of Finnish cases for whom type 1 diabetes was diagnosed before age 18 years between 1965 and 1979. Siblings' diabetes status was ascertained by a record search of nationwide registries through 2001, and the type of diabetes and date of its manifestation were obtained from medical records. The total number of person-years during the follow-up was 405,685. Of the 10,168 siblings at risk, 647 (6.4%) had been diagnosed with type 1 diabetes by 2001. The cumulative incidence of type 1 diabetes by ages 10, 20, 30, 40, and 50 years in all siblings was 1.5, 4.1, 5.5, 6.4, and 6.9%, respectively. A young age at diagnosis in the index case, paternal young-onset diabetes, male sex, and older parental age at delivery considerably increased the risk of type 1 diabetes for siblings. This large prospective family study of type 1 diabetes in siblings of childhood-onset diabetic patients provides reliable empirical estimates for the sibling recurrence risk.
authors.affiliation: Diabetes and Genetic Epidemiology Unit, Department of Epidemiology and Health Promotion, National Public Health Institute, Mannerheimintie 166, FIN-00300, Helsinki, Finland. valma.harjutsalo@ktl.fi
authors.forename: Valma
authors.initials: V
authors.lastname: Harjutsalo
authors.forename: Toomas
authors.initials: T
authors.lastname: Podar
authors.forename: Jaakko
authors.initials: J
authors.lastname: Tuomilehto
mesh_terms: D000293:Adolescent; D017668:Age of Onset; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology* / Q000235:genetics*; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D008423:Maternal Age; D008499:Medical Records; D010331:Paternal Age; D012042:Registries; D012307:Risk Factors; D035781:Siblings