Clinical features of cases of seroconversion of anti-glutamic acid decarboxylase antibody during the clinical course of type 2 diabetes: a nationwide survey in Japan

The pathogenesis of type 1 diabetes is different from that of type 2 diabetes, and anti-glutamic acid decarboxylase antibody (GADA) helps to diagnose autoimmune type 1 diabetes. Some studies reported that GADA seroconversion occurs during the clinical course of type 2 diabetes, leading to development of “type 1 on type 2 diabetes”. To clarify the clinical characteristics and triggers of GADA seroconversion, we performed a nationwide questionnaire survey for clinical cases identified by literature search, and obtained information on 38 cases (24 with insulin therapy and 14 without it). The diabetes duration up to determination of GADA seroconversion was significantly longer in the group with insulin therapy than that without it. This finding was particularly noted in insulin-treated non-obese patients with lower serum C-peptide levels. In these patients, insulin therapy could have masked sudden increases in plasma glucose and HbA1c levels, possibly leading to delayed determination of GADA seroconversion. In non-obese patients without insulin therapy, an abrupt rise in the plasma glucose and HbA1c levels was observed at immediately before the determination, a finding which may help to predict GADA seroconversion. From the results of the present survey, we could not determine apparent triggers of GADA seroconversion. Thus, physicians may need to consider the possibility of concurrent type 1 diabetes during the therapeutic course of type 2 diabetes; GADA measurement should be considered when non-obese type 2 diabetic patients not receiving insulin therapy experience unexpected abrupt hyperglycemia and when those receiving insulin therapy show low serum C-peptide levels.