HIGH DIAGNOSTIC SENSITIVITY OF GLUTAMATE-DECARBOXYLASE AUTOANTIBODIESIN INSULIN-DEPENDENT DIABETES-MELLITUS WITH CLINICAL ONSET BETWEEN AGE 20 AND 40 YEARS

Patients with adult-onset Type 1 (insulin-dependent) diabetes mellitus (IDDM) are more difficult to identify than young patients, as their c linical onset is often less acute with a questionable state of insulin dependency. Classification may be facilitated by the detection of aut oantibodies that are associated with IDDM. The prevalence of islet cel l autoantibodies (ICA) and insulin autoantibodies (IAA) is, however, m arkedly lower in adult than in young patients. The present study asses ses the usefulness of antibodies against glutamate decarboxylase (GAD) , as a complementary marker. Sera from 312 recent-onset IDDM patients under age 40 and 163 age-matched controls were assayed for IAA ICA, an d antibodies against recombinant GAD65 (M(r) 65,000) or GAD67 (M(r) 67 ,000). IAA or ICA occurred in over 90% of patients diagnosed under age 20 but only in 65% of patients between age 20 and 40. Determination o f GAD65-Ab did not increase the percent antibody positive patients und er age 10, but did so at older ages: from 92-98% in the 10-19 years ag e group, and from 65-85% in the 20-39 years age group. The determinati on of GAD67-Ab did not add to the information provided by the GAD65-Ab assay. Our results indicate that, alone or in combination with ICA, t he GAD65-Ab assay identified more patients with an IDDM marker in the age group 20-39 years than in the group under age 20.