[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.