Distribution of autoantibodies to glutamic acid decarboxylase across the spectrum of diabetes mellitus seen in South Africa

Aims This study investigated the association between glutamic acid decarbox ylase antibodies (GAD-AB) and Type 1, Type 2, pancreatic and lipoatrophic d iabetes mellitus (DM) in South African patients. Methods Four groups were selected: group A, 100 Black Type 1 DM patients (a ge at onset < 35 years, body mass index (BMI) < 27 kg/m(2) and insulin depe ndent within 1 year of presentation); group B, 80 Black Type 2 DM patients (age at onset > 35 years, BMI > 27 kg/m(2) and controlled on oral hypoglyca emic agents for at least 1 year after presentation); group C, 10 patients o f varying ethnicity with DM or impaired glucose tolerance secondary to chro nic pancreatitis; group D, five patients of varying ethnicity with DM assoc iated with total lipodystrophy. Fifty healthy Black control subjects were a lso studied (group E). Serum GAD-AB and random C-peptide levels were measur ed by radioimmunoassay. Results Mean C-peptide concentration was significantly lower in Type 1 DM p atients than Type 2 DM patients (P < 0.00001). Forty-four patients with Typ e 1 DM were GAD-AB-positive compared to two patients with Type 2 DM. Two co ntrol subjects were also GAD-AB-positive. No patient in the other groups ha d a titre > 1 U/ml. Type 1 DM patients who were GAD-AB-positive did not dif fer from those who were GAD-AB-negative for age at onset, duration of DM or C-peptide concentrations. Conclusions Auto-immune beta-cell destruction has an important role in the pathogenesis of Type 1 DM amongst African patients. However, Type 2 African DM patients and other diabetes subtypes are largely GAD-AB-negative.