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

Diabetologia. 1994 Apr;37(4):344-50. doi: 10.1007/BF00408469.


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 35S-methionine-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, 0-14 year-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-methionine-labelled recombinant GAD.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Autoantibodies / analysis*
  • Autoimmunity
  • Child
  • Diabetes Mellitus, Type 1 / diagnosis*
  • Diabetes Mellitus, Type 1 / immunology
  • False Positive Reactions
  • Female
  • Glutamate Decarboxylase / immunology*
  • Humans
  • Islets of Langerhans / immunology
  • Isoenzymes / immunology*
  • Male
  • Middle Aged
  • Predictive Value of Tests
  • Radioligand Assay
  • Recombinant Proteins / immunology
  • Sensitivity and Specificity


  • Autoantibodies
  • Isoenzymes
  • Recombinant Proteins
  • Glutamate Decarboxylase