Determination of Autoantibodies to Two Forms (65 kDa, 67 kDa) of Glutamic Acid Decarboxylase by Western Blot Analysis with Immunopurified Antigens and Its Clinical Evaluation

Abstract

To investigate the clinical significance of autoantibodies to two forms of glutamic acid decarboxylase (GAD), we used Western blot analysis to isolate then from rat brain on an immunoaffinity colums with anti-synthetic C-terminal GAD peptide antibodies which recognize both GAD₆₅ and GAD₆₇. The frequency of antibodies to GAD₆₅ and/or GAD₆₇ in 45 cases of insulin dependent diabetes mellitus (IDDM) was 88%(14/16) in ICA-positive subjects and 10%(3/29) in ICA-negative subjects. Antibodies to GAD₆₇ were detected in 1 ICA positive NIDDM patient and antibodies to GAD₆₅ were detected in 1 of 2 Stiff-man syndrome patients without IDDM, whereas no antibodies to GADs were detected in 20 patients with autoimmune thyroid disease or in 30 normal subjects. In this study, we found that some sera from IDDM patients recognized only GAD₆₅ or GAD₆₇, however, we found no obvious correlation between duration of illness or ICA-titers and the specificity of antibodies to either form of GAD. Antibodies to GAD₆₅ and GAD₆₇ are considered useful markers for the diagnosis of IDDM and for understanding its pathogenesis.