CONCORDANCE RATES OF INSULIN-DEPENDENT DIABETES-MELLITUS - A POPULATION-BASED STUDY OF YOUNG DANISH TWINS

Objective-To study the genetic contribution to the aetiology of insuli n dependent diabetes mellitus. Design-Historical cohort study of twins , with information on diabetes being gathered by questionnaire, verifi cation of the diagnosis by the subject's diabetologist or general prac titioner, and clinical examination in available twins. Setting-Danish twin register and diabetic clinics and general practices throughout De nmark. Subjects-20 888 twin pairs born during 1953-82, included in a p opulation based nationwide register. Main outcome measures-Crude and c umulative concordance rates and heritability in monozygotic and dizygo tic twins. Results-The crude probandwise concordance rate was 0.53 (95 % confidence interval 0.33 to 0.73) for monozygotic twin pairs and 0.1 1 (0.05 to 0.21) for dizygotic twin pairs. When adjusted for age at on set of diabetes and age at last observation among unaffected twin part ners the cumulative probandwise risk from birth to age 35 was estimate d as 0.70 (0.45 to 0.95) for monozygotic twins and 0.13 (0.05 to 0.20) for dizygotic twins. The correlations of liability for monozygotic an d dizygotic twin pairs were estimated as 0.96 (SE 0.09) and 0.58 (0.07 ), with a heritability estimate of 0.72 (0.21). Conclusions-The risk o f insulin dependent diabetes in monozygotic twins is higher than previ ously thought and for dizygotic twins is higher than in ordinary first degree relatives. Based on the findings of this study the genetic com ponent to the disease seems more important than hitherto believed.