Predicting Type 1 Diabetes in the General Population

The study was done to evaluate the utility of GAD antibodies (GADAs) and islet antigen-2 antibodies (IA-2As) in prediction of Type 1 diabetes over 27 years in the general population and to assess the 6-year rates of seroconversion.  

A total of 3,475 nondiabetic subjects aged 3-18 years were sampled in 1980, and 2,375 subjects (68.3%) were resampled in 1986. All subjects were observed for development of diabetes to the end of 2007. GADAs and IA-2As were analyzed in all samples obtained in 1980 and 1986. 

Results: A total of 34 individuals (1.0%; 9 developed diabetes) initially had GADAs and 22 (0.6%; 9 developed diabetes) IA-2As. Seven subjects (0.2%) tested positive for both autoantibodies. 

The positive seroconversion rate over 6 years was 0.4% for GADAs and 0.2% for IA-2As, while the inverse seroconversion rates were 33 and 57%, respectively. Eighteen subjects (0.5%) developed Type 1 diabetes after a median pre-diabetic period of 8.6 years (range 0.9-20.3). Initial positivity for GADAs and/or IA-2As had a sensitivity of 61% (95% CI 36-83) for Type 1 diabetes. Combined positivity for GADAs and IA-2As had both a specificity and a positive predictive value of 100% (95% CI 59-100).  

From the results it was concluded that, one-time screening for GADAs and IA-2As in the general childhood population would identify approximately 60% of those individuals who will develop Type 1 diabetes over the next 27 years, and those subjects who have both autoantibodies carry an extremely high risk for diabetes. Both positive and inverse seroconversions do occur over time reflecting a dynamic process of beta-cell autoimmunity.