Adult-onset autoimmune diabetes identified by glutamic acid decarboxylase autoantibodies: a retrospective cohort study

AIMS/HYPOTHESIS

Patients with GAD antibodies (GADAb) showing clinical features of type 2 diabetes typically exhibit progression to an insulin-dependent state in several months or years. This condition is diagnosed as slowly progressive insulin-dependent (type 1) diabetes mellitus (SPIDDM) or latent autoimmune diabetes in adults, a subtype of adult-onset autoimmune diabetes. However, some patients diagnosed with adult-onset autoimmune diabetes do not progress to an insulin-dependent state. We conducted a retrospective cohort study to identify patients with non-insulin-dependent diabetes among those diagnosed with adult-onset autoimmune diabetes using measurable indicators in routine clinical practice.

METHODS

We surveyed data from the electronic medical records of all patients with GADAb from eight medical centres in Japan for selecting and analysing patients who matched the diagnostic criteria of SPIDDM.

RESULTS

Overall, 345 patients were analysed; of these, 162 initiated insulin therapy (insulin therapy group), whereas 183 did not (non-insulin therapy group) during the follow-up period (median 3.0 years). Patients in the non-insulin therapy group were more likely to be male and presented a later diabetes onset, shorter duration of diabetes, higher BMI, higher blood pressure levels, lower HbA_1c levels, lower GADAb levels and lesser antidiabetic agent use than those in the insulin therapy group when GADAb was first identified as positive. A Cox proportional hazards model showed that BMI, HbA_1c levels and GADAb levels were independent factors for progression to insulin therapy. Kaplan-Meier analyses revealed that 86.0% of the patients with diabetes having GADAb who presented all three factors (BMI ≥ 22 kg/m², HbA_1c < 75 mmol/mol [9.0%] and GADAb <10.0 U/ml) did not require insulin therapy for 4 years.

CONCLUSIONS/INTERPRETATION

Higher BMI (≥22 kg/m²), lower HbA_1c (<75 mmol/mol [9.0%]) and lower GADAb levels (<10.0 U/ml) can predict a non-insulin-dependent state for at least several years in Japanese patients with diabetes having GADAb.

Predictive value of titer of GAD antibodies for further progression of beta cell dysfunction in slowly progressive insulin-dependent (type 1) diabetes (SPIDDM)

Aims

Whether the titer of glutamic acid decarboxylase antibodies (GADAs), especially a low titer, is a marker of progression of beta cell dysfunction in patients with slowly progressive insulin-dependent (type 1) diabetes (SPIDDM) is unclear.

Materials and methods

Patients were subdivided as follows: patients with high GADA titers [≥10 U/ml (≥180 WHO U/ml): high GADA] (group 1, n = 37); those with low GADA titers [<10 U/ml (<180 WHO U/ml): low GADA] (group 2, n = 33); those without GADA and with islet cell antibodies (ICA) (group 3, n = 8); those without both GADA and ICA and with insulinoma-associated antigen 2 antibodies (IA-2A) (group 4, n = 6). We also allocated 198 type 2 diabetic patients without any GADA, ICA or IA-2A as group 5. Serum C-peptide responses to annual oral glucose tolerance tests (OGTTs) were followed up for a mean of 107 months from entry.

Results

The proportion of patients progressing to an insulin-dependent state in groups 1, 2, 3 and 4 was significantly higher than in group 5. C-peptide responses in OGTTs of patients in groups 1 and 2 were decreased at a significantly higher rate than in group 5. Multivariate Cox proportional hazard analysis revealed that factors including high GADA, low GADA, onset age <45 years, duration of diabetes <24 months, body mass index (BMI) <22.0 kg/m², low degree of preserved beta cell function and ICA were independent risk factors for progression to an insulin-dependent state.

Conclusions

SPIDDM patients with low GADA titers have a significantly higher risk of progression to an insulin-dependent state than type 2 diabetic patients, suggesting that the presence of GADA, irrespective of the titer, is a hallmark of beta cell failure. Other risk factors for further progression to an insulin-dependent state in SPIDDM patients were ICA, onset age, duration of diabetes, BMI and residual beta cell function.