A novel radioligand binding assay to determine diagnostic accuracy of isoform-specific glutamic acid decarboxylase antibodies in childhood IDDM.
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.
Grubin
C E
CE
Department of Medicine, University of Washington, Seattle.
Daniels
T
T
Toivola
B
B
Landin-Olsson
M
M
Hagopian
W A
WA
Li
L
L
Karlsen
A E
AE
Boel
E
E
Michelsen
B
B
Lernmark
A
A
D000293:Adolescent; D000328:Adult; D001323:Autoantibodies / Q000032:analysis*; D015551:Autoimmunity; D002648:Child; D003922:Diabetes Mellitus, Type 1 / Q000175:diagnosis* / Q000276:immunology; D005189:False Positive Reactions; D005260:Female; D005968:Glutamate Decarboxylase / Q000276:immunology*; D006801:Humans; D007515:Islets of Langerhans / Q000276:immunology; D007527:Isoenzymes / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011869:Radioligand Assay; D011994:Recombinant Proteins / Q000276:immunology; D012680:Sensitivity and Specificity
D001323:Autoantibodies; D007527:Isoenzymes; D011994:Recombinant Proteins; D005968:Glutamate Decarboxylase