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Diagnostic sensitivity of immunodominant epitopes of glutamic acid decarboxylase (GAD65) autoantibodies in childhood IDDM

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Summary

The prevalence and titre of epitope-specific autoantibodies to glutamic acid decarboxylase (GAD65) in 155 insulin-dependent diabetic (IDDM) and 9 GAD65 antibody (Ab)-positive healthy children were determined using four GAD65/67 chimaeric molecules which discriminate among the N-terminal (N), middle (M) and C-terminal (C) epitopes of GAD65. Radioligand binding assays for IgG Ab used immunoprecipitation of in vitro translated 35S-GAD. We found autoantibodies to GAD65 in 116 of 155 (75%), to GAD67 in 19 of 155 (12%) (p<0.0001) and to the GAD65-N-67 chimaera in 25 of 155 (16%) (p<0.0001) IDDM sera. GAD67Ab were found almost exclusively (17 of 19, 89%) in GAD65Ab-positive sera and the levels of GAD67Ab correlated with those of GAD65Ab (r 2=0.5913; p=0.009). GAD65Ab directed to GAD65-M were found in 104 of 155 (67%), to GAD65-C in 104 of 155 (67%) and to GAD65-M + C in 116 of 155 (75%) of IDDM sera, and indicated reactivity to at least two distinct epitopes. Among the nine GAD65Ab-positive healthy children, two (22%) were also positive with GAD67, nine (100%) with GAD65-M + C, seven (78%) with GAD65-M, eight (89%) with GAD65-C and two (22%) with GAD65-N-67. Titres of GAD65Ab (p=0.007), GAD65-C-Ab (p=0.002) and GAD65C + M-Ab (p=0.003), but not of GAD65-M-Ab (p=0.101) were significantly higher in IDDM than in healthy children. We conclude that GAD65Ab in IDDM and healthy children are directed to middle and C-terminal epitopes, and propose that levels of antibodies specifically directed to the carboxy-terminal end of GAD65 may distinguish IDDM from healthy children.

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Abbreviations

Ab:

Antibodies

GAD:

glutamic acid decarboxylase

ICA:

islet cell antibodies

IDDM:

insulin-dependent diabetes mellitus

JDF:

Juvenile Diabetes Foundation

PC-2:

proinsulin-converting enzyme 2

TCA:

trichloroacetic acid

M:

middle terminal epitope

N:

N-terminal epitope

C:

C-terminal epitope

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Authors and Affiliations

  1. Department of Molecular Medicine, Karolinska Institute, Stockholm, Sweden

    A. Falorni, M. Ackefors, C. Carlberg & å. Lernmark

  2. Department of Medicine, University of Washington, Seattle, Washington, USA

    T. Daniels & å. Lernmark

  3. Department of Women and Child Health, Karolinska Institute, Stockholm, Sweden

    B. Persson

  4. Synectics Biotechnology, Stockholm, Sweden

    J. Robertson

Authors
  1. A. Falorni
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  2. M. Ackefors
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  3. C. Carlberg
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  4. T. Daniels
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  5. B. Persson
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  6. J. Robertson
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  7. å. Lernmark
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Falorni, A., Ackefors, M., Carlberg, C. et al. Diagnostic sensitivity of immunodominant epitopes of glutamic acid decarboxylase (GAD65) autoantibodies in childhood IDDM. Diabetologia 39, 1091–1098 (1996). https://doi.org/10.1007/BF00400659

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  • DOI: https://doi.org/10.1007/BF00400659

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