Clinical characteristics of patients with the initial diagnosis of NIDDM with positivity for antibodies to glutamic acid decarboxylase

The measurement of islet cell antibodies (ICA) and antibodies to glutamic acid decarboxylase (GAD-Ab) is clinically useful in evaluating patients with insulin-dependent diabetes mellitus (IDDM). Our objective was to correlate the clinical characteristics of patients with noninsulin-dependent diabetes mellitus (NIDDM) who exhibited positivity for GAD-Ab vs. patients who were negative for this enzyme. The serum level of GAD-Ab was measured by radiobinding assay (RBA) using pig brain GAD. The prevalence of GAD-Ab in the 181 patients was low; the 8 involved subjects (4.4%) were all females. The NIDDM patients who were GAD-Ab-positive were significantly younger, experienced diabetes onset at an early age, had a shorter duration of diabetes, a shorter interval between diabetes onset to initiation of insulin therapy, a lower body mass index (BMI), a lower serum C-peptide value, and required a higher dose of insulin. A higher proportion of the GAD-Ab-positive patients was receiving insulin therapy. Conclusions: Clinical characteristics of patients with NIDDM who were positive for GAD-Ab differed significantly from those of the patients negative for CAD-Ah The profile of the GAD-Ab-positive patients with NIDDM resembled that of those with IDDM.