Glutamic acid decarboxylase antibodies in non-insulin-dependent diabetes patients with secondary sulfonylurea failure in Thailand

Abstract

The objective of this study was to determine the frequency of glutamic acid decarboxylase antibody (GAD-Ab) in Thai non-insulin-dependent diabetes (NIDDM) patients who had secondary sulfonylurea failure. Sera were collected from 40 NIDDM patients, who had history of secondary failure to treatment with sulfonylurea, for analysis of fasting c-peptide and GAD-Ab. Both c-peptide and GAD-Ab were measured using radioimmunoassay method. Of 40 patients, ten (25.0%) were positive for GAD-Ab with a mean level of 59.9 U/ml (median 58.5, range 3.4–127). Patients with GAD-Ab(+) had a significantly lower fasting c-peptide levels than those with GAD-Ab(−) albeit shorter duration of diabetes (0.21±0.19 (S.D.) versus 0.52±0.33 nmol/l; P=0.003). Duration of treatment with sulfonylurea in patients with GAD-Ab(+) was also shorter (4.6±3.5 versus 10.4±5.5 years; P=0.001). Age at onset of diabetes did not differ between these two groups. Among 40% of patients who had insulin deficiency (fasting c-peptide level <0.33 nmol/l), GAD-Ab was present in half and these GAD-Ab(+) patients had significantly shorter duration of sulfonylurea treatment (3.3±2.3 versus 10.0±7.9 years; P=0.018). In conclusion, the frequency of GAD-Ab in Thai NIDDM patients with secondary sulfonylurea failure in this study was 25%. Almost all GAD-Ab(+) patients had insulin deficiency and most had been initially treated with sulfonylurea for a few years before depending on insulin. This group of patients represents a slowly progressive type I or latent autoimmune diabetes in adult diabetic population.