A NEW SOLID-PHASE RADIOIMMUNOASSAY TO DETECT ANTI-GAD65 AUTOANTIBODIES

This paper describes a simple, rapid, routine method to detect anti-GA D65 autoantibodies by a solid-phase radioimmunoassay using human recom binant GAD65 coated microwells and I-125-protein A to reveal antibody binding. Both recombinant and radiolabelled proteins are commercially available. This new method was validated by investigating the presence of GAD65 autoantibodies in two different studies (A and B): the first including subjects originating from our own case histories (group A s era), the second made up of recoded subjects and standards sent to our lab by the Second International GAD Antibody Workshop organizers (gro up B sera). In study A we tested sera from 52 normal subjects, 25 newl y diagnosed type 1 diabetics and 3 stiff man syndrome (SMS) subjects d etecting GAD65 autoantibodies in 72% of IDDM and 100% of SMS patients. In study B we tested (in blind fashion) 89 recoded sample sera or sta ndards that were part of the larger group used in the Second Internati onal GAD Antibody Workshop, finding GAD65 autoantibodies in 3.3% of he althy control subjects (1/30), 60% of IDDM patients(18/30), 100% of IC A + nondiabetic subjects (3/3) but in none of 4 nondiabetic patients w ith Graves' disease. Comparing our solid-phase RIA results with those published for the same sera from the Second International GAD Antibody Workshop we obtained for our method a sensitivity of 85.7%, a specifi city of 93.9% and a consistency of 100%. These results indicate that o ur assay, which is based on commercially available reagents, should be a useful tool for the detection of GAD65 autoantibodies in large scal e studies. (C) 1997 Elsevier Science B.V.