ANTIBODIES TO GLUTAMIC-ACID DECARBOXYLASE IN THE PREDICTION OF INSULIN DEPENDENCY

Antibodies to glutamic acid decarboxylase (anti-GAD) predict the progr ession of adults masquerading as NIDDM to insulin dependency and predi ct the eventual occurrence of IDDM in healthy pregnant women in Finlan d. Almost 80% of prediabetic and newly diagnosed IDDM cases are positi ve for anti-GAD, However, approximately 20% of these groups do not hav e a humoral response to GAD so it cannot be claimed that anti-GAD is t he exclusive autoimmune phenomenon. Nevertheless, 94% of children with newly diagnosed IDDM that we studied had an autoimmune response to ei ther GAD, ICA or IAA, singly or in combination. The anti-GAD assay als o has a substantial role in the diagnosis and classification of diabet es presenting in adult life since a proportion of adults who present w ith apparent NIDDM actually have a slowly evolving autoimmune insuliti s, a condition we have called latent autoimmune diabetes in adults (LA DA), It appears likely that anti-GAD will be predictive for IDDM in bo th first degree relatives and the general population. As a result of t he cost and relative ease of performance, it will provide a practical alternative to ICA, particularly in population screening. Comparisons of testing for anti-GAD and ICA as predictors of IDDM using large popu lation groups are now in progress in our laboratory.