No association of antibodies to glutamic acid decarboxylase and diabetic complications in patients with IDDM

OBJECTIVE - To evaluate the association of antibodies to glutamic acid decarboxylase (GAD-ab) and diabetic complications (neuropathy, retinopathy, and nephropathy) in patients with insulin-dependent diabetes mellitus (IDDM). RESEARCH DESIGN AND METHOD - We examined the prevalence of GAD-ab (immunoprecipitation assay) and islet cell antibodies (ICAs) (indirect immunofluorescence) in a representative sample of IDDM patients (n = 146) with different disease duration (2-52 years, median 13.2 years). Of all patients characterized for the existence of diabetic complications, 56 of 146 had peripheral neuropathy, 24 of 142 had autonomic neuropathy, 67 of 141 had retinopathy, and 39 of 146 had nephropathy. RESULTS - GAD-ab (> 2 SD) were detected more frequently than ICA (>5 Juvenile Diabetes Foundation units) in IDDM patients of different disease duration (GAD-ab⁺ 37% [54 of 146] vs. ICA⁺ 22% [32 of 146], P = 0.011; diabetes duration less than median: GAD- ab⁺ 47% vs. ICA⁺ 23%, P = 0.0046; diabetes duration greater than median: GAD-ab⁺ 27% vs. ICA⁺ 22%, P > 0.05). For GAD-ab and for ICA, respectively, no difference was observed in frequency of positivity or titers between patients with or without diabetic complications. CONCLUSIONS - Both GAD-ab and, to a lesser extent, ICA persist for a long time in several individuals. This persistence is not related to diabetic neuropathy or any other diabetic complication.