Risk for developing Type 1 (insulin-dependent) diabetes mellitus and the presence of islet 64K antibodies

Summary First-degree relatives of Type 1 (insulin-dependent) diabetic patients are at increased risk for developing clinical diabetes. The presence of islet cell or insulin autoantibodies further identifies relatives at greater risk, but not all immunologic-marker-positive relatives progress to disease. Beta-cell dysfunction, however, seems to be more prevalent than clinical Type 1 diabetes, since stable subclinical pancreatic Beta-cell dysfunction may occur. Antibodies against a M_r 64,000 (64K) islet Beta-cell protein, identified as glutamic acid decarboxylase, have been reported both at and several years prior to the clinical onset of Type 1 diabetes. We measured 64K antibodies in first-degree relatives with varying degrees of Beta-cell dysfunction and risk for subsequent Type 1 diabetes to determine whether 64K antibodies improve the predictive power of islet cell antibodies and/or insulin autoantibodies. In the Seattle Family Study first-degree relatives of Type 1 diabetic patients are followed prospectively using detailed Beta-cell function tests, insulin sensitivity, quantitative evaluation of islet cell antibodies and fluid phase assay insulin autoantibodies. 64K antibodies were measured using dog islets. Relatives were selected, based on Beta-cell function to represent individuals at high (n=6) and low (n=30) risk for subsequent Type 1 diabetes. The 30 low-risk individuals followed-up for 78 months, had stable Beta-cell function, and six (20%) were negative for all autoantibodies, ten (33%) were positive for insulin autoantibodies, 16 (53%) were islet cell antibody positive while six (20%) were positive for 64K antibodies. In contrast, of the six subjects with progressively declining Beta-cell function who are therefore at high risk, two of whom have already developed Type 1 diabetes, two (33%) were positive for insulin autoantibodies, four (67%) were islet cell antibody positive, while all six (100%) were positive for 64K antibodies. We conclude that antibodies to the M_r 64,000 islet protein correlate with progressive Beta-cell dysfunction more closely than either islet cell antibodies or insulin autoantibodies, but can sometimes be present in individuals whose Beta-cell function remains stable over several years.