Reactivity to N-Terminally Truncated GAD65(96–585) Identifies GAD Autoantibodies That Are More Closely Associated With Diabetes Progression in Relatives of Patients With Type 1 Diabetes

GAD autoantibodies (GADAs) identify individuals at increased risk of developing type 1 diabetes, but many people currently found to be GADA positive are unlikely to progress to clinical disease. More specific GADA assays are therefore needed. Recent international workshops have shown that the reactivity of sera from healthy donors varies according to assay type and indicated that the use of N-terminally truncated GAD65 radiolabels in GADA radiobinding assays is associated with higher specificity. To determine whether a radiobinding assay using radiolabeled GAD65(96–585) identified individuals who are at higher risk of developing diabetes, samples from recent-onset patients and GADA-positive first-degree relatives participating in the Bart’s-Oxford type 1 diabetes family study were reassayed with full-length or N-terminally truncated GAD using the National Institute of Diabetes and Digestive and Kidney Diseases harmonized protocol. The sensitivity in patients was the same with both labels, but fewer relatives retested positive with truncated GAD. Among relatives who progressed to diabetes, similar proportions were found to be GADA positive when tested with either label, but because of their higher specificity the cumulative risk of diabetes was higher in those with autoantibodies to GAD65(96–585). Autoantibodies to GAD65(96–585) in relatives are more closely associated with diabetes risk than those to full-length GAD, suggesting that assays using N-terminally truncated GAD should be used to select participants for intervention trials.

[1]  Marian Rewers,et al.  The cation efflux transporter ZnT8 (Slc30A8) is a major autoantigen in human type 1 diabetes , 2007, Proceedings of the National Academy of Sciences.

[2]  P. Bingley,et al.  GAD65 autoantibody titres at diagnosis in Latent Autoimmune Diabetes in Adults (LADA) differ from Type 1 diabetes (T1D) and together with epitope specificity predict insulin requirement , 2004 .

[3]  P. Bingley,et al.  Optimized autoantibody-based risk assessment in family members. Implications for future intervention trials. , 1999, Diabetes care.

[4]  M. Knip,et al.  GAD65 antibody isotypes and epitope recognition during the prediabetic process in siblings of children with type I diabetes , 2004, Clinical and experimental immunology.

[5]  S. Baekkeskov,et al.  Autoreactive epitopes defined by diabetes-associated human monoclonal antibodies are localized in the middle and C-terminal domains of the smaller form of glutamate decarboxylase. , 1993, Proceedings of the National Academy of Sciences of the United States of America.

[6]  E. Bonifacio,et al.  Maturation of the humoral autoimmune response to epitopes of GAD in preclinical childhood type 1 diabetes. , 2000, Diabetes.

[7]  P. Bingley,et al.  Rising Incidence of Type 1 Diabetes Is Associated With Altered Immunophenotype at Diagnosis , 2012, Diabetes.

[8]  M. Christie,et al.  Relationship of the 37,000- and 40,000-M(r) tryptic fragments of islet antigens in insulin-dependent diabetes to the protein tyrosine phosphatase-like molecule IA-2 (ICA512). , 1995, The Journal of clinical investigation.

[9]  P. Bingley,et al.  HLA class II typing of whole genome amplified mouth swab DNA. , 2000, Tissue antigens.

[10]  E. Bonifacio,et al.  GAD Autoantibody Affinity and Epitope Specificity Identify Distinct Immunization Profiles in Children at Risk for Type 1 Diabetes , 2007, Diabetes.

[11]  P. Bingley,et al.  Humoral Responses to Islet Antigen-2 and Zinc Transporter 8 Are Attenuated in Patients Carrying HLA-A*24 Alleles at the Onset of Type 1 Diabetes , 2013, Diabetes.

[12]  P. Bingley,et al.  Prediction of IDDM in the General Population: Strategies Based on Combinations of Autoantibody Markers , 1997, Diabetes.

[13]  P. Bingley.  Clinical applications of diabetes antibody testing. , 2010, The Journal of clinical endocrinology and metabolism.

[14]  B. Rees Smith,et al.  Glutamic acid decarboxylase autoantibody assay using 125I-labelled recombinant GAD65 produced in yeast. , 1996, Clinica chimica acta; international journal of clinical chemistry.

[15]  P. Mueller,et al.  Detection of Antibodies Directed to the N-Terminal Region of GAD Is Dependent on Assay Format and Contributes to Differences in the Specificity of GAD Autoantibody Assays for Type 1 Diabetes , 2015, Diabetes.

[16]  M. Rewers,et al.  GAD65 Autoantibodies Detected by Electrochemiluminescence Assay Identify High Risk for Type 1 Diabetes , 2013, Diabetes.

[17]  G. Eisenbarth,et al.  Accepting clocks that tell time poorly: fluid-phase versus standard ELISA autoantibody assays. , 2007, Clinical immunology.

[18]  P. Bingley,et al.  Harmonization of glutamic acid decarboxylase and islet antigen-2 autoantibody assays for national institute of diabetes and digestive and kidney diseases consortia. , 2010, The Journal of clinical endocrinology and metabolism.

[19]  C. Betterle,et al.  A sensitive non-isotopic assay for GAD65 autoantibodies. , 2003, Clinica chimica acta; international journal of clinical chemistry.

[20]  A. Ziegler,et al.  GAD autoantibody affinity in schoolchildren from the general population , 2014, Diabetologia.