[The glutamic acid decarboxylase (GAD) antibodies and their clinical significance].

Since it was reported that the 64kD antigen that had been found to be the target of autoantibodies in the sera from IDDM patients was the same as GAD, GAD antibodies have been one of the focuses of many investigations. In this study, we developed a sensitive radioimmunoassay (RIA) system for GAD antibodies in human sera using native GAD purified from the pig brain. To confirm the relevance of pig GAD as the target antigen, we compared the sequences and antigenic activities among pig, rat and recombinant human GAD65. Based on the data from our and other laboratories, the homology of amino acid sequences between pig and human GAD65 was 96.4%. The coefficient of correlation between the results of human and pig GAD RIA was 0.948. The GAD antibody study group confirmed the clinical usefulness of GAD antibodies not only for the diagnosis of IDDM but also slowly progressive IDDM.