METABOLIC CHARACTERISTICS OF AUTOIMMUNE DIABETES-MELLITUS IN ADULTS

It is still a matter of debate whether patients who develop islet-cell antibody positive autoimmune diabetes during adulthood represent slowly evolving Type 1 (insulin-dependent) diabetes mellitus or a separate subgroup of Type 2 (non-insulin-dependent) diabetes. To address this question, we measured C-peptide response to a test meal, and energy metabolism in the basal state and during a euglycaemic, hyperinsulinaemic clamp in (1) 29 patients with Type 2 diabetes; (2) 10 patients with autoimmune diabetes developing after the age of 40 years; (3) 11 patients with Type 1 diabetes and (4) 15 non-diabetic control subjects. While C-peptide response to a test meal was lacking in Type 1 diabetes and nearly normal in Type 2 diabetes, the C-peptide response in autoimmune diabetes was markedly reduced. Patients with Type 2 diabetes, autoimmune diabetes and Type 1 diabetes showed a 47%, 45% and 42%, respectively, reduction in the rate of non-oxidative glucose metabolism compared with control subjects (p < 0.05-0.01). Similarly, patients with Type 2 diabetes (+ 52%), autoimmune diabetes (+ 27%) and Type 1 diabetes (+ 33%) presented with an enhanced basal rate of hepatic glucose production, which was less suppressed by insulin compared with healthy control subjects (p < 0.01). However, patients with autoimmune diabetes derived more energy from oxidation of glucose and proteins and less energy from oxidation of lipids than patients with either Type 1 or Type 2 diabetes (p < 0.05-0.01). In conclusion, patients who develop autoimmue diabetes during adulthood share the defects in hepatic glucose production and in non-oxidative glucose metabolism with both Type 1 and Type 2 diabetes. Oxidative energy metabolism in autoimmune diabetes, however, differs from that observed in Type 1 and Type 2 diabetes. Given the metabolic characteristics of these patients, it seems justified to consider autoimmune diabetes in adults as a subgroup of diabetes developing in adult age.