Islet-cell antibodies as predictors of the later development of type 1 (insulin-dependent) diabetes. A study in identical twins.

To determine the value of islet-cell antibodies, both complement-fixing and non-complement-fixing, in predicting the later development of Type 1 (insulin-dependent) diabetes, we studied different groups of identical twins. Twelve twins have developed diabetes and 11 of these had non-complement-fixing islet-cell antibodies before diagnosis, and eight out of nine tested had complement-fixing islet-cell antibodies. Of the twins who have remained non-diabetic for many years and are now unlikely to develop diabetes, twelve have had non-complement-fixing islet-cell antibodies at some stage but only four have ever had complement-fixing antibodies. In 29 non-diabetic co-twins tested within 5 years of the diagnosis of diabetes in the affected twin the presence of islet-cell antibodies, especially complement-fixing, predicted the progression to frank diabetes with a high specificity (100%), sensitivity (88%) and predictive value (100%). In pairs remaining discordant the antibodies were found more frequently in the diabetic than the non-diabetic twin. We conclude that the presence of islet-cell antibodies is not genetically determined and can occur without progression to diabetes. However, the presence of islet-cell antibodies, especially complement-fixing, in non-diabetic twins tested soon after the diagnosis of their co-twin, indicates a high risk for the development of diabetes.