POPULATION-BASED STUDY OF PREVALENCE OF ISLET-CELL AUTOANTIBODIES IN MONOZYGOTIC AND DIZYGOTIC DANISH TWIN PAIRS WITH INSULIN-DEPENDENT DIABETES-MELLITUS

Objective: To study the comparative importance of environment and gene s in the development of islet cell autoimmunity associated with insuli n dependent diabetes mellitus. Design: Population based study of diabe tic twins. Setting: Danish population. Subjects: 18 monozygotic and 36 dizygotic twin pairs with one or both partners having insulin depende nt diabetes. Main outcome measures: Presence of islet cell antibodies, insulin autoantibodies, and autoantibodies to glutamic acid decarboxy lase (GAD65) in serum samples from twin pairs 10 years (range 0-30 yea rs) and 9.5 years (2-30 years) after onset of disease. Results: In tho se with diabetes the prevalence of islet cell antibodies, insulin auto antibodies, and autoantibodies to glutamic acid decarboxylase in the 2 6 monozygotic twins was 38%, 85%, and 92%, respectively, and in the di zygotic twins was 57%, 70%, and 57%, respectively. Ln those without di abetes the proportions were 20%, 50%, and 40% in the 10 monozygotic tw ins and 26%, 49%, and 40% in the 35 dizygotic twins. Conclusion: There is no difference between the prevalence of islet cell autoantibodies in dizygotic and monozygotic twins without diabetes, suggesting that i slet cell autoimmunity is environmentally rather than genetically dete rmined. Furthermore, the prevalence of islet cell antibodies was highe r in the non-diabetic twins than in other first degree relatives of pa tients with insulin dependent diabetes. This implies that the prenatal or early postnatal period during which twins are exposed to the same environment, in contrast with that experienced by first degree relativ es, is of aetiological importance.