GAD65 autoantibodies increase the predictability but not the sensitivity of islet cell and insulin autoantibodies for developing insulin dependent diabetes mellitus.

The clinical onset of insulin-dependent diabetes (IDD) can be predicted by determination of autoantibodies to several pancreatic-islet cell antigens. Islet-cell autoantibodies (ICA) and insulin autoantibodies (AA) are most commonly used. We have developed a recombinant human glutamic acid decarboxylase (GAD65) radioimmunoassay and measured autoantibodies to GAD65 (GAD65A) in the sera of 73 documented prediabetic individuals, 76 newly-diagnosed patients, 103 relatives of IDD probands at increased risk for the development of IDD because they were positive for ICA and/or IAA, 72 ICA and IAA negative relatives, and 207 healthy controls. Our data demonstrate that GAD65A are strongly associated with the currently established autoantibody markers of IDD. Their presence in prediabetic subjects with only ICA or IAA enhances their risk for progression to IDD, yet does not much enhance the screening sensitivity already available through conventional ICA and IAA for IDD prediction.