Proinsulin/Insulin Autoantibodies Measured With Electrochemiluminescent Assay Are the Earliest Indicator of Prediabetic Islet Autoimmunity

OBJECTIVE

We evaluated a novel electrochemiluminescent assay for insulin/proinsulin autoantibodies (ECL-IAA) as a new marker of the onset of islet autoimmunity and as a predictor of type 1 diabetes.

RESEARCH DESIGN AND METHODS

The Diabetes Autoimmunity Study in the Young (DAISY) prospectively follows children at increased genetic risk for development of islet autoimmunity (defined as presence of autoantibodies to insulin, GAD65, IA-2, or zinc transporter 8 ZnT8]) and type 1 diabetes (general population of children and first-degree relatives). Serial serum samples from subjects who progressed to type 1 diabetes and who had their first islet autoantibodies measured by age 18 months (N = 47) were tested using ECL-IAA.

RESULTS

Almost all prediabetic children tested positive for ECL-IAA (46 of 47, 98%) during follow-up. ECL-IAA was almost always the first autoantibody to appear (94% total; 21% very first by itself]; 23% with only mIAA; 19% with another islet autoantibody GAD or ZnT8]; and 30% with ≥2 other antibodies mIAA, GAD, IA-2, or ZnT8]). Among the 46 subjects who were ECL-IAA positive, ECL-IAA antedated the onset of other islet autoantibodies by a mean of 2.3 years (range, 0.3–7.2 years). Both the age of appearance of autoantibody and IAA levels (but not GAD65, IA2, or ZnT8 levels) are major determinants of the age of diabetes onset.

CONCLUSIONS

This new ECL-IAA assay defines more precisely the onset of prediabetic autoimmunity and may help identify events triggering islet autoimmunity, as well as allow earlier intervention for type 1 diabetes. Nearly all young children progressing to diabetes are insulin autoantibody positive.Anti-islet autoimmunity currently detected by measurement of islet autoantibodies almost always precedes by years the development of type 1A diabetes. If the autoimmunity is triggered by time-correlated factors such as acute viral infections, then the discovery of pathogenic viruses may depend on accurate timing of the appearance of islet autoantibodies. Most of the trials to prevent type 1A diabetes target persons in the preclinical phase of the disease marked by the presence of persistent islet autoantibodies (1). Because this preclinical period is quite variable, accurate prediction of the time to progression to overt diabetes is critical for the design and implementation of preventive trials. Although genetic markers can identify varying risk, it is only once autoimmunity has begun (marked by the presence of multiple autoantibodies to pancreatic β-cell antigens) that a high positive predictive value (>90%) can be achieved. Multiple autoantibodies are present in the majority of prediabetic individuals (2–4). Screening for risk of type 1 diabetes uses “biochemical” autoantibody assays for specific islet autoantigens (1). These include insulin autoantibodies (IAA) (5), GAD65 (6), protein tyrosine IA-2 (ICA512) (7), and, most recently, zinc transporter 8 (ZnT8) (8). Individuals having a single positive autoantibody (insulin, GAD65, IA-2, or ZnT8 autoantibodies) are at low risk for progression to diabetes, whereas individuals expressing two or more positive autoantibodies, especially on multiple tests over time, are at very high risk for progression to diabetes (9,10).IAA are usually extremely high at the onset of diabetes in young children but usually negative in individuals first presenting with diabetes after age 12 years. There is a log-linear inverse relationship between these levels and the age of onset of diabetes (11), as well as between levels of IAA and time of progression from first appearance of islet autoantibodies to diagnosis of diabetes in prospectively followed Diabetes Autoimmunity Study in the Young (DAISY) children (10). We recently have reported (12) development of an electrochemiluminescence assay for IAA (ECL-IAA) using Meso Scale instrumentation and ruthenium-labeled proinsulin. This assay detects high-affinity IAA and is more sensitive than the micro-IAA (mIAA) radioassays in the last Diabetes Autoantibody Standardization Program (DASP) workshop, yet is equally specific.In this study we evaluated ECL-IAA as a new marker of the onset of islet autoimmunity and as a predictor of progression to diabetes among antibody-positive subjects. We found that this novel nonradioactive IAA assay is more sensitive and defines the timing of the initial autoantibody appearance earlier than the previously used mIAA radioassay. We report the predictors of progression to diabetes and the determinants of age at diagnosis among children at high risk participating in the prospective DAISY.