A novel radioligand binding assay to determine diagnostic accuracy of isoform-specific glutamic acid decarboxylase antibodies in childhood IDDM
✍ Scribed by C. E. Grubin; T. Daniels; B. Toivola; M. Landin-Olsson; W. A. Hagopian; L. Li; A. E. Karlsen; E. Boel; B. Michelsen; Å. Lernmark
- Book ID
- 104761616
- Publisher
- Springer
- Year
- 1994
- Tongue
- English
- Weight
- 806 KB
- Volume
- 37
- Category
- Article
- ISSN
- 0012-186X
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✦ Synopsis
Insulin-dependent diabetes mellitus (IDDM) is associated with autoreactivity against GAD but the diagnostic sensitivity (positivity in disease) and specificity (negativity in health) of isoform-specific GAD antibodies have yet to be defined in assay systems suitable for screening large number of samples. One set of IDDM patient (n = 10) and control (n = 50) standard sera were used to develop quantitative antibody assays with in vitro synthesized recombinant 35Smethionine-labelled GAD65 and GAD67, respectively, and protein A-Sepharose to separate free from antibody-bound ligand. Binding levels were not normally distributed (p < 0.0001) and therefore, the diagnostic accuracy of GAD antibodies was analysed by the ROC plots in population-based, consecutively-diagnosed, recent onset, 0-14year-old patients (n = 105), and matched, healthy control subjects (n = 157). The ROC plots showed that the diagnostic sensitivity of GAD65 antibodies was 77 % and the specificity 92 % compared with 8 % and 98 %, respectively for GAD67 antibodies. In the IDDM sera, GAD65 and GAD67 antibodies were concordant in 7% (6 of 81) and GAD65 antibodies and ICA in 89 % (72 of 81) without a correlation between the autoantibody levels. Autoantibodies to recombinant human islet GAD65 are specific and sensitive markers for childhood IDDM in this immunoassay with in vitro synthesized 35S-methioninelabelled recombinant GAD. [Diabetologia (1994) 37: 344-350] Key words Glutamic acid decarboxylase, receiveroperating characteristic plot, diagnostic accuracy, islet cell antibodies, autoimmunity, diabetes mellitus Serum samples from recent onset patients with IDDM [1-3] or first degree relatives later developing this disease [4, 5], have been shown to immunoprecipitate a Mr 64,000 (64K) islet cell protein, later identified as GAD [6]. The human islet GAD was discovered to represent a new isoform, GAD65, which is coded for by a previously unidentified gene (GAD2) on chromosome