Check GAD antibody positivity with the Diamyd anti-GAD RIA plate*

ReferencesT1DM and LADA Differ inGADA Epitope SpecificityDChristiane Hampe, Rattan Juneja, Åke Lernmark, Jerry Palmeriabetes Mellitus is classifiedinto two major forms, Type1 and Type 2 diabetes. Type1 diabetes is characterizedby an autoimmune-mediateddestruction of betacells,leading to insulin deficiency. The autoimmunereaction involves both T cells and antibodies directedagainst islet cell autoantigens that can be detectedin the majority of Type 1 diabetes patients (1, 2).The main autoantigens identified are insulin (3), theMr 65,000 isoform of glutamic acid decarboxylase(GAD65) (4), and the tyrosine phosphatase-like IA-2antigen (5). These autoantibodies are often detectedlong before the clinical onset of Type 1 diabetes andare useful to predict disease risk (5, 6). GAD65 andIA-2 autoantibodies (Ab) are readily detected bynow standardized (7), precise and reproducible radioimmunoassays(4, 7, 8) suitable for large scale analysisand population screening (6, 9). In contrast, classicalType 2 diabetes patients do not show evidence ofautoimmune beta cell destruction. Patients withType 1 diabetes usually require insulin treatment atthe time of diagnosis whereas Type 2 patients can besuccessfully treated by diet and oral agents for manyyears. These patients do not show evidence of autoimmunebeta cell destruction. A third group of patientsis referred to as latent autoimmune diabetes inadults (LADA) (10), Type 1.5 diabetes (11), or slowlyprogressive insulin dependent diabetes mellitus(SPIDDM) (12). These patients lose beta cell function,fail oral agents early and require insulin treatment(13, 14). Evidence for an underlying autoimmmunepathogenesis is provided by the observationthat many of these patients have islet cell antibodies(ICA), autoantibodies to GAD65 (GAD65Ab) (10,15, 16), or both. The presence of GAD65Ab alone isa sufficient marker for future insulin requirementin younger patients (44 years or younger) while inolder patients positivity for both ICA andGAD65Ab is a stronger predictor of insulin requirement(17). The question has been raised whetherType 1.5 diabetes represents a separate clinical diseaseor is a slowly progressive form of Type 1 diabetes(18, 19). Epitope mapping of GAD65Ab can assist inthe classification of the underlying autoimmunity.Using both GAD65/67 fusion proteins (20, 21) andGAD65-specific recombinant Fab we and otherswere able to identify phenotype-specific GAD65Abepitopes. GAD65Ab in newly diagnosed young Type1 diabetes patients recognize restricted epitopes primarilylocated at the combined middle-carboxyterminalconformational epitope of GAD65, while bindingto GAD67 or the N-terminus of GAD65 isdetected only at a low level. In contrast, GAD65Abpositive Type 1.5 diabetes patients exhibit aGAD65Ab epitope pattern that is characterized bybinding to both the N-terminus of GAD65 and to atentative conformational epitope formed of themiddle and carboxyterminal part of GAD65 (22).This GAD65Ab epitope profile clearly differs fromthat found in Type 1 diabetes patients and moreresembles the broader GAD65Ab epitope specificityfound in GAD65Ab-positive healthy individuals andfirst-degree relatives (20). This difference in the bindingpattern of GAD65Ab of Type 1.5 diabetes patientscompared to that of Type 1 diabetes patientssupports the notion that the disease process maydiffer between these two types of patients. We thereforesuggest that Type 1.5 diabetes might be a subtypeof Type 1 diabetes characterized by separateimmunologic features. GAD65Ab epitope patternsmay be useful to identify Type 1.5.Christiane Hampe, Ph.D., has a position asjunior faculty at the University of Washingtonin Seattle. Her research interests are the disssectionof the role of GAD65 and its autoantibodiesin the pathogenesis of Type 1 diabetes.While these autoantibodies are widely acceptedas markers for the disease, preliminarydata indicate that disease-specific GAD65Abmodulate T cell responses. Hampe’s currentresearch goals are to understand the effect ofGAD65Ab on processing and presentation ofGAD65.1. Bonifacio E, et al,Islet autoantibody markers in IDDM: risk assessmentstrategies yielding high sensitivity.Diabetologia 38:816-822, 19952. Landin-Olsson M, et al,Islet cell and other organ-specific autoantibodies in allchildren developing Type 1 (insulin-independent) diabetesmellitus in Sweden during one year and in matchedcontrols.Diabetologia 32:387-395, 19893. Palmer JP, et al,Insulin antibodies in insulin-dependent diabetics beforeinsulin treatment. Science 222:1337-1339, 19834. Grubin CE, et al,A novel radioligand binding assay to determine diagnosticaccuracy of isoform-specific glutamic acid decarboxylaseantibodies in childhood IDDM.Diabetologia 37:344-350, 19945. Verge CF, et al,Prediction of Type I diabetes in first-degree relativesusing a combination6. Bingley PJ, et al,Prediction of IDDM in the general population:Strategies based on combinations of autoantibodymarkers.Diabetes 46:1701-1710, 19977. Mire-Sluis AR, et al,The development of a World Health Organisationinternational standard for islet cell antibodies: the aimsand design of an international collaborative study.Diabetes Metab Res Rev 15:72-77, 19998. Verge CF, et al,Combined use of autoantibodies (IA-2) autoantibody,GAD autoantibody, insulin autoantibody, cytoplasmicislet cell antibodies) in Type 1 diabetes: CombinatorialIslet Autoantibody Workshop.Diabetes 47:1857-1866, 19989. Rolandsson O, et al,Glutamate decarboxylase (GAD65) and tyrosine phosphatase-likeprotein (IA-2) autoantibodies index in aregional population is related to glucose intoleranceand body mass index.Diabetologia 42:555-559, 199910. Tuomi T, et al,Antibodies to glutamic acid decarboxylase reveallatent autoimmune diabetes mellitus in adults with anon-insulin-dependent onset of disease.Diabetes 42:359-362, 199311. Harris MI, et al,Classification of diabetes mellitus and other catagoriesof glucose intolerance. In: Keen H, DeFronzo R,Alberti K, Zimmet P, ed.The international textbook of diabetes mellitus.London: Wiley, 1992, 3-18.12. Ludvigsson J, et al,HLA-DR3 is associated with amore slowly progressiveform of Type 1 (insulin-dependent) diabetes.Diabetologia 29:207-210, 198613. Temple RC, et al,Insulin deficiency in non-insulin-dependent diabetes.Lancet 1:293-295, 198914. Gjessing HJ, et al,Fasting plasma c-peptide, glucagon stimulated plasmac-peptide, and urinary c-peptide in relation to clinicaltype of diabetes.Diabetologia 32:305-311, 198915. Groop LC, et al,Islet cell antibodies identify latent Type 1 diabetes inpatients aged 35-75 years at diagnosis.Diabetes 35:237-241, 198616. Rowley MJ, et al,Antibodies to glutamic acid decarboxylase discriminatemajor types of diabetes mellitus.Diabetes 41:548-551, 199217. Turner R, et al,UKPDS 25: autoantibodies to isle T cell cytoplasm andglutamic acid decarboxylase for prediction of insulinrequirement in Type 2 diabetes.UK Prospective Diabetes Study Group [published erratumappears in Lancet 1998 Jan 31;351 (9099): 376].Lancet 350:1288-1293, 199718. Juneja R, et al,Autoimmunity 29:65-83, 199919. Tuomi T, et al,Clinical and genetic characteristics of Type 2 diabeteswith and without GAD antibodies.Diabetes 48:150-157, 199920. Hampe CS, et al,Recognition of Glutamic Acid Decarboxylase (GAD)by Autoantibodies from Different GAD Antibody-Positive Phenotypes.J Clin Endocrinol Metab 85:4671-4679, 200021. Falorni A, et al,Diagnostic sensitivity of immunodominant epitopes ofglutamic acid decarboxylase (GAD65) autoantibodiesepitopes in childhood IDDM.Diabetologia 39:1091-1098, 199622. Hampe CS, et al,GAD65 antibody epitope patterns of Type 1.5 diabeticpatients are consistent with slow-onset autoimmunediabetes.Diabetes Care 25:1481-1482., 2002dmccad june 2003page 39