Diabetes Metab J.  2020 Apr;44(2):260-266. 10.4093/dmj.2019.0007.

Glutamic Acid Decarboxylase Autoantibody Detection by Electrochemiluminescence Assay Identifies Latent Autoimmune Diabetes in Adults with Poor Islet Function

• Zhu Y
• Qian L
• Liu Q
• Zou J
• Zhou Y
• Yang T
• Huang G
• Zhou Z
• Liu Y

• KMID: 2502407
• DOI: http://doi.org/10.4093/dmj.2019.0007

Abstract

Background
The detection of glutamic acid decarboxylase 65 (GAD65) autoantibodies is essential for the prediction and diagnosis of latent autoimmune diabetes in adults (LADA). The aim of the current study was to compare a newly developed electrochemiluminescence (ECL)-GAD65 antibody assay with the established radiobinding assay, and to explore whether the new assay could be used to define LADA more precisely.
Methods
Serum samples were harvested from 141 patients with LADA, 95 with type 1 diabetes mellitus, and 99 with type 2 diabetes mellitus, and tested for GAD65 autoantibodies using both the radiobinding assay and ECL assay. A glutamic acid decarboxylase antibodies (GADA) competition assay was also performed to assess antibody affinity. Furthermore, the clinical features of these patients were compared.
Results
Eighty-eight out of 141 serum samples (62.4%) from LADA patients were GAD65 antibody-positive by ECL assay. Compared with ECL-GAD65 antibody-negative patients, ECL-GAD65 antibody-positive patients were leaner (P<0.0001), had poorer β-cell function (P<0.05), and were more likely to have other diabetes-associated autoantibodies. The β-cell function of ECLGAD65 antibody-positive patients was similar to that of type 1 diabetes mellitus patients, whereas ECL-GAD65 antibody-negative patients were more similar to type 2 diabetes mellitus patients.
Conclusion
Patients with ECL-GAD65 antibody-negative share a similar phenotype with type 2 diabetes mellitus patients, whereas patients with ECL-GAD65 antibody-positive resemble those with type 1 diabetes mellitus. Thus, the detection of GADA using ECL may help to identify the subtype of LADA.

Keyword

Autoantibodies; C-peptide; Glutamate decarboxylase; Latent autoimmune diabetes in adults

Figure

• 

  Fig. 1 Comparison of the radiobinding assay (RBA) and electrochemiluminescence (ECL) assay and differences in the affinity and number of autoantibodies, the area under the curve (AUC) for C-peptide in the various patient groups. (A) Glutamic acid decarboxylase antibodies (GADA) concentrations obtained using RBA and ECL assay were compared in latent autoimmune diabetes in adult (LADA) patients. (B) Affinity data for GADA-positive samples, classified according to ECL-GADA status. Serum samples with positive GADA by RBA from nine subjects (five ECL-GADA+ and four ECL-GADA−) were incubated with a range of concentrations of unlabeled glutamic acid decarboxylase 65 (GAD65) protein and analyzed using standard RBA. Positive samples detected by ECL-GADA assay (solid line) required less unlabeled GAD65 to reach a 50% maximal inhibition than those found to be negative (dotted line), which means positive samples are consistent with higher affinity. Results are expressed as percentages of the signal not absorbed. (C) The number of positive diabetes-associated autoantibodies in 88 ECL-GADA+ and 53 ECL-GADA− LADA samples. GADA was detected by ECL assay, IA2, and ZnT8 antibodies were detected by radioassay. (D) The AUC of C-peptide in LADA patients (ECL-GADA+ and ECL-GADA−), type 1 diabetes mellitus (T1DM) patients, and type 2 diabetes mellitus (T2DM) patients. aP<0.01 compared to T1DM, bP<0.05 compared to ECL-GADA+, cP<0.05 compared to ECL-GADA−.

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