AIM: To investigate the characteristics of the progression of islet β cell function in Chinese latent autoimmune diabetes in adult (LADA) patients with glutamic acid decarboxylase antibody (GAD-Ab) positivity, and to explore the prognostic factors for β cell function.

METHODS: Forty-five LADA patients with GAD-Ab positivity screened from phenotypic type 2 diabetic (T2DM) patients and 45 T2DM patients without GAD-Ab matched as controls were followed-up every 6 mo. Sixteen patients in LADA1 and T2DM1 groups respectively have been followed-up for 6 years, while 29 patients in LADA2 and T2DM2 groups respectively for only 1.5 years. GAD-Ab was determined by radioligand assay, and C-peptides (CP) by radioimmune assay.

RESULTS: The percentage of patients whose fasting CP (FCP) decreased more than 50% compared with the baseline reached to 25.0% at 1.5 th year in LADA1 group, and FCP level decreased (395.8±71.5 vs 572.8±72.3 pmol/L, P< 0.05) at 2.5 th year and continuously went down to the end of follow-up. No significant changes of the above parameters were found in T2DM1 group. The average decreased percentages of FCP per year in LADA and T2DM patients were 15.8%(4.0-91.0%) and 5.2%(-3.5 to 35.5%, P= 0.000) respectively. The index of GAD-Ab was negatively correlated with the FCP in LADA patients (r s=-0.483, P= 0.000). The decreased percentage of FCP per year in LADA patients were correlated with GAD-Ab index, body mass index (BMI) and age at onset (r s= 0.408,-0.301 and-0.523 respectively, P< 0.05). Moreover, GAD-Ab was the only risk factor for predicting β cell failure in LADA patients (B= 1.455, EXP (B)= 4.283, P= 0.023).

CONCLUSION: The decreasing rate of islet β cell function in LADA, being highly heterogeneous, is three times that of T2DM patients. The titer of GAD-Ab is an important predictor for the progression of islet β cell function, and age at onset and BMI could also act as the predictors.