Significance of IA-2 antibody in Japanese type 1 diabetes: its association with GAD antibody.

To investigate the presence and level of serum antibodies to IA-2 (IA-2A) in Japanese patients with adult type 1 diabetes in order to clarify its association with glutamic acid decarboxylase (GAD) antibody. Serum samples were obtained from 101 Japanese patients with type 1 diabetes, including 37 patients with slowly progressive form of type 1 diabetes. Serum levels of IA-2A and GADA were determined by radioimmunoassay. The study had a cross-sectional design. IA-2A and GADA were detected in 37 and 59% of these patients, respectively. Of the 37 slowly progressive form of patients, IA-2A and GADA were present in 49 and 86%, respectively (NS). GADA levels were significantly higher (P<0.05) in IA-2A positive than in IA-2A negative patients in slowly progressive form, but IA-2A levels did not differ significantly between GADA positive and GADA negative patients. Measuring IA-2A in combination with GADA is useful for the diagnosis and prognosis of type 1 diabetes in Japanese.