Predictive value of autoantibodies to IA-2 for insulin requirements in Japanese subjects with type 1 diabetes

[A case of elderly-onset type 1 diabetes mellitus: negative for antiglutamic acid dehydrogenase antibody and positive insulinoma-associated tyrosine phosphatase-like protein-2 antibody]

An 83-year-old Japanese woman given a diagnosis of type 2 diabetes mellitus 3 years previously was hospitalized for markedly elevated plasma glucose (386 mg/dl) and glycated hemoglobin (9.3%) levels. Laboratory study results showed urinary connecting peptide immunoreactivity (CPR) concentrations of 8.9 μg/day and serum CPR levels <0.2 ng/ml before and 0.3 ng/ml 6 min after glucagon administration, indicating decreased insulin secretion. Although antiglutamic acid dehydrogenase (GAD) antibody levels were negative, insulinoma-associated tryrosine phosphatase-like protein-2 (IA-2) antibody levels were positive (50 U/ml), leading to a diagnosis of type 1 diabetes mellitus. Furthermore, human leukocyte antigen (HLA) typing revealed DRB1*0901, a diabetes-susceptibility gene. Intensive insulin therapy was initiated. This was a rare case of elderly-onset type 1 diabetes.

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.