Prevalence of autoantibodies to the 65- and 67-kD isoforms of glutamate decarboxylase in insulin-dependent diabetes mellitus.

Abstract

We investigated the presence of autoantibodies to baculovirusexpressed human recombinant 65-and 67-kD isoforms of glutamate decarboxylase (GAD65 and GAD67) in insulin-dependent diabetes mellitus (IDDM). In the immunoprecipitation test using I35Slmethionine-labeled GADs antibodies to GAD65 were detected in 13/15 (87%) islet cell antibody (ICA)-positive and in 1/35 (2.9%) ICA-negative first-degree relatives of patients with IDDM, in 6/11 (54.5%) ICA-positive nondiabetic schoolchildren, and in 35/50 (70%) patients with newly diagnosed IDDM. GAD67 antibodies were positive only in five (33%) of the ICA-positive relatives (P < 0.05) and in nine (18%) IDDM patients at onset (P < 0.00001). After onset of IDDM antibodies to GAD65 and GAD67 declined but were still positive in 25 and 9.4% of subjects with long-standing IDDM (> 10 yr). In all study groups antibodies to GAD67 were only detected in GAD65 antibody-positive sera. An immunotrapping enzyme activity assay for GAD65 antibodies was positive in 64/75 (85.3%) of sera that were GAD antibody positive in the immunoprecipitation test (r = 0.870, P < 0.0001). In two (2.7%) sera GAD65 antibodies that block GAD enzyme activity were found. Our data suggest that antibodies to GAD65 but not to GAD67 represent sensitive markers for preclinical and overt IDDM. The immunotrapping assay here described represents a valuable technique for specific and sensitive screening for GAD antibodies. (J.

A novel radioligand binding assay to determine diagnostic accuracy of isoform-specific glutamic acid decarboxylase antibodies in childhood IDDM

“…The present study supports previous demonstrations that the GAD65 mRNA [7] codes for the 64K antigen [12,21,37]. The results of this study also confirm other studies [12,18,20] but fail to support investigations showing that IDDM sera have significant reactivity to GAD67 [13] or GAD67 peptide fragments [16]. This discrepancy remains to be explained but may be due to the formation of GAD65/GAD67 heterodimers [38] in extracts of brain or rat islet [14] or recombinant mixtures which contain both isoforms.…”

“…GAD65 (but not GAD67) is expressed in human islets [11,14], however, variable reactivity of patient sera has been reported [12,13,[15][16][17][18][19]. GAD65 specificity of IDDM sera was first demonstrated in our immunoprecipitation assay with recombinant GAD expressed in transfected cells [12] and recently confirmed in other assays with recombinant antigens [18,20]. The use of different assay systems and species-specific GAD65 and GAD67 may explain the lower frequency of GAD67 antibodies in these compared to previous reports [13,16].…”

Association between Antibodies to the MR 67,000 Isoform of Glutamate Decarboxylase (GAD) and Type 1 (Insulin-Dependent) Diabetes Mellitus with Coexisting Autoimmune Polyendocrine Syndrome Type II

“…Part of these sera had been previously characterized for ICA and GAD antibodies 12 . 50 healthy individuals without a family history of endocrine diseases served as controls.…”

Type 1 Diabetes Mellitus and Drug-resistant Epilepsy: Presence of High Titer of Anti-Glutamic Acid Decarboxylase Autoantibodies in Serum and Cerebrospinal Fluid

“…Anti-GAD antibodies are now considered to be a marker of type 1 diabetes, since they can be found in the sera of the majority of individuals with preclinical and early phase type 1 diabetes (4,5). Although GAD has initially been regarded as an important -cell antigen able to induce type 1 diabetes in non-obese diabetic (NOD) mice, its pathogenic role in the initiation of type 1 diabetes remains controversial (6).…”