HIGH PREVALENCE OF GAD(65) (AND IA-2) ANTIBODIES IN JAPANESE IDDM PATIENTS BY A NEW IMMUNOPRECIPITATION ASSAY BASED ON RECOMBINANT HUMAN GAD(65)

Marked differences have been reported in the prevalence of glutamic ac id decarboxylase (GAD) antibodies between Caucasian (63-84 %) and Japa nese (30-50 %) or Asian (5-50 %) IDDM patients. Using a new immunoprec ipitation assay based on I-125-labelled recombinant human GAD(65), we have reassessed prevalence of GAD(65) antibodies in Japanese patients. We also assessed prevalence of IA-2 antibodies. GAD(65) antibodies we re detected in 83.3 % of sera taken within 1 year of onset, comparable to the prevalence reported in Caucasian patients. Positivity decrease d to 66.7 % after 2 to 3 years and to 54.3 % after 3 years from onset, still higher than previously reported Asian prevalence. Except in one patient, high antibody levels persisted chronically, up to 12 years. There was no difference in the prevalence of GAD(65) antibodies betwee n Japanese IDDM patients with and without autoimmune thyroid disease ( AITD). IA-2 antibodies were detected in 64.7 % of sera taken within 1 year of onset. Prevalence of IA-2 antibodies was lower than that of GA D(65) antibodies. The difference in positivity in Asian IDDM patients between present and previous reports arose from the sensitivity of our assay for GAD(65) antibodies. Additionally, the patients we studied h ad classic IDDM with a well-defined onset. We conclude that prevalence of GAD(65) antibodies in Japanese IDDM patients is comparable to that in Western studies. There was no relationship of GAD(65) antibody pos itivity to coexistence of AITD. Our results suggest that autoimmunity is the most significant cause of Japanese IDDM. (C) 1997 by John Wiley & Sons, Ltd.