Value of Antibodies to Islet Protein Tyrosine Phosphatase–Like Molecule in Predicting Type 1 Diabetes

  1. R. David G Leslie
  1. Department of Diabetes and Metabolism, St. Bartholomew's HospitalLondon, U.K.
  2. Laboratory of Oral Medicine, National Institutes of HealthBethesda, Maryland
  3. Clinica Medica II, La Sapienza UniversityRome, Italy
  4. Department of Medicine, Kings College Hospital, London, U.K.
  1. Address correspondence and reprint requests to Dr. R.D.G. Leslie, Department of Diabetes, St. Bartholomew's Hospital, London EC1A 7BE, U.K.

Abstract

Islet antigens associated with type 1 diabetes include a recently identified protein tyrosine phosphatase–like molecule IA-2, which contains the intracellular fragment IA-2ic. To determine whether combinations of antibodies including those to IA-2 characterize and predict type 1 diabetes, we studied antibodies to IA-2, IA-2ic, glutamic acid decarboxylase (GAD65), and islet cell antibodies (ICAs) in 1) 60 newly diagnosed type 1 diabetic patients followed for 1 year, 2) 31 monozygotic twin pairs discordant for type 1 diabetes followed up to 12 years (11 twins developed diabetes), 3) 18 dizygotic twin pairs discordant for type 1 diabetes, and 4) normal healthy control subjects. Newly diagnosed type 1 diabetic patients frequently had antibodies to IA-2 (62%), IA-2ic (67%), GAD65 (77%), and ICAs (85%). The intracellular fragment of IA-2 probably contains the immunodominant epitope as 137 of 143 samples with IA-2 antibodies from type 1 diabetic patients also had IA-2ic antibodies. Monozygotic twins were usually discordant for antibody specificities. Concordance was higher in monozygotic than matched dizygotic twins for both antibody combinations (33 vs. 6%, P < 0.05) and the development of diabetes (33 vs. 0%, P < 0.01). In monozygotic twins, all the antibodies were highly predictive of type 1 diabetes (positive predictive values all >87%), although antibodies were also detected in twins at low risk of disease. In summary, IA-2 emerges as a major antigen associated with type 1 diabetes and distinct from GAD65. Type 1 diabetes–associated autoimmunity, which is probably induced by environmental factors, does not necessarily herald progression to the disease. However, genetic factors may influence the development of combinations of disease-associated antibodies and the progression to type 1 diabetes.

  • Received July 29, 1996.
  • Revision received March 26, 1997.
  • Accepted March 26, 1997.
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