GAD65 Autoantibodies Identify High Risk for Type 1 Diabetes
GAD65 Autoantibodies Identify High Risk for Type 1 Diabetes
This article reports a major improvement in the diabetes-relevant GADA measurement by a new ECL-based assay among GADA-positive children by the standard NIDDK harmonized GADA radioassay. The specificity of GADA radioassay (98.0th percentile) was based on a much larger number of control subjects and was slightly less than the ECL-GADA assay (99.5th percentiles), and both assays showed identical specificity in DASP workshop participants. The current findings are consistent with our previous finding that an ECL-IAA assay is able to detect disease-relevant, high-affinity autoantibodies while ignoring a low-affinity signal that did not predict the development of multiple islet autoantibodies and progression to diabetes. This advance is likely to have important implications for population screening programs, cohort studies searching for environmental triggers, and clinical trials to prevent T1D. In the near future, applying these new ECL assays to adolescent and adult patients with late autoimmune diabetes in adults and hybrid or undetermined-type diabetes will also be helpful for improving clinical diagnosis.
In DAISY, TrialNet Pathway to Prevention, TEDDY (The Environmental Determinants of Diabetes in the Young), and other major programs, 30–60% of autoantibody positivity is attributable to a single islet autoantibody, with the majority of these single antibodies being GADA or IAA. Patients who express only a single islet autoantibody are at a low risk for developing T1D compared with those with multiple autoantibodies. Relatives expressing only IAA in the DPT-1 (Diabetes Prevention Trial of Type 1 Diabetes) study essentially did not progress to diabetes. The antibody affinity study by competition assay we used is very similar to previous reports, although it is an indirect measurement. Our previous and present studies demonstrate that most of the single IAA or GADA detected only by radioassay were low-affinity antibodies and failed to produce a signal with the bivalent ECL assay. A few laboratories previously reported that both IAA and GADA affinity in multiple antibody–positive children was significantly higher than in children who remained single autoantibody positive or became autoantibody negative. We hypothesized that most of these single antibodies may result from immunization with a cross-reactive molecule, whereas higher-affinity IAA or GADA result from immunization with an islet autoantigen itself. Both forms of antibody can be competed with native antigen molecule and thus are not biochemically false positive; however, in terms of biologic relevance, antibodies detected with only the radioassay appear not to predict diabetes.
A prospective follow-up study observed that the development of islet autoantibodies often happens sequentially; that is, the majority of subjects are initially single antibody positive. Thus, differentiation of high- from low-risk islet autoantibodies at that stage could be important in identifying truly high-risk subjects for prevention trials. The present study shows that individuals positive for only GADA by radioassay but negative by ECL assay remained ECL negative for years, even though they had multiple positive follow-up tests by radioassay. We did not see individuals who after being IAA or GADA positive only by radioassay develop a second islet autoantibody or diabetes. On the other hand, in prediabetic or high-risk subjects with multiple islet autoantibodies, ECL assay always detected IAA or GADA from the very beginning. Siljander et al. found that there was no affinity maturation observed over time from seroconversion to T1D diagnosis. Thus, the new ECL assays may make it possible to correctly identify high-risk IAA and GADA on the first positive sample. The major strength of this study was availability of well-characterized, prospectively collected DAISY samples. However, it would be ideal to confirm these results in additional cohorts with long-term follow-up (e.g., DPT-1, TrialNet Pathway to Prevention, TEDDY). Although we provide evidence that the disease-relevant ECL-GADA assay is of high affinity, full confirmation awaits a separate study. In conclusion, the ECL-GADA assay is, similarly to the ECL-IAA assay, able to differentiate high-risk islet autoantibodies from low-risk or nondisease-relevant antibodies at the earliest stage of screening.
Discussion
This article reports a major improvement in the diabetes-relevant GADA measurement by a new ECL-based assay among GADA-positive children by the standard NIDDK harmonized GADA radioassay. The specificity of GADA radioassay (98.0th percentile) was based on a much larger number of control subjects and was slightly less than the ECL-GADA assay (99.5th percentiles), and both assays showed identical specificity in DASP workshop participants. The current findings are consistent with our previous finding that an ECL-IAA assay is able to detect disease-relevant, high-affinity autoantibodies while ignoring a low-affinity signal that did not predict the development of multiple islet autoantibodies and progression to diabetes. This advance is likely to have important implications for population screening programs, cohort studies searching for environmental triggers, and clinical trials to prevent T1D. In the near future, applying these new ECL assays to adolescent and adult patients with late autoimmune diabetes in adults and hybrid or undetermined-type diabetes will also be helpful for improving clinical diagnosis.
In DAISY, TrialNet Pathway to Prevention, TEDDY (The Environmental Determinants of Diabetes in the Young), and other major programs, 30–60% of autoantibody positivity is attributable to a single islet autoantibody, with the majority of these single antibodies being GADA or IAA. Patients who express only a single islet autoantibody are at a low risk for developing T1D compared with those with multiple autoantibodies. Relatives expressing only IAA in the DPT-1 (Diabetes Prevention Trial of Type 1 Diabetes) study essentially did not progress to diabetes. The antibody affinity study by competition assay we used is very similar to previous reports, although it is an indirect measurement. Our previous and present studies demonstrate that most of the single IAA or GADA detected only by radioassay were low-affinity antibodies and failed to produce a signal with the bivalent ECL assay. A few laboratories previously reported that both IAA and GADA affinity in multiple antibody–positive children was significantly higher than in children who remained single autoantibody positive or became autoantibody negative. We hypothesized that most of these single antibodies may result from immunization with a cross-reactive molecule, whereas higher-affinity IAA or GADA result from immunization with an islet autoantigen itself. Both forms of antibody can be competed with native antigen molecule and thus are not biochemically false positive; however, in terms of biologic relevance, antibodies detected with only the radioassay appear not to predict diabetes.
A prospective follow-up study observed that the development of islet autoantibodies often happens sequentially; that is, the majority of subjects are initially single antibody positive. Thus, differentiation of high- from low-risk islet autoantibodies at that stage could be important in identifying truly high-risk subjects for prevention trials. The present study shows that individuals positive for only GADA by radioassay but negative by ECL assay remained ECL negative for years, even though they had multiple positive follow-up tests by radioassay. We did not see individuals who after being IAA or GADA positive only by radioassay develop a second islet autoantibody or diabetes. On the other hand, in prediabetic or high-risk subjects with multiple islet autoantibodies, ECL assay always detected IAA or GADA from the very beginning. Siljander et al. found that there was no affinity maturation observed over time from seroconversion to T1D diagnosis. Thus, the new ECL assays may make it possible to correctly identify high-risk IAA and GADA on the first positive sample. The major strength of this study was availability of well-characterized, prospectively collected DAISY samples. However, it would be ideal to confirm these results in additional cohorts with long-term follow-up (e.g., DPT-1, TrialNet Pathway to Prevention, TEDDY). Although we provide evidence that the disease-relevant ECL-GADA assay is of high affinity, full confirmation awaits a separate study. In conclusion, the ECL-GADA assay is, similarly to the ECL-IAA assay, able to differentiate high-risk islet autoantibodies from low-risk or nondisease-relevant antibodies at the earliest stage of screening.
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