Glutamic Acid Decarboxylase (GAD) Autoantibody

Overview:

This test is intended for the semiquantitative determination of glutamic acid decarboxylase (GAD) antibody in human serum; it is useful as an aid in the diagnosis of type 1 diabetes mellitus (autoimmune mediated diabetes).1

This test allows for the detection of the presence of antibodies to glutamic acid decarboxylase, which provides early evidence of autoimmune disease activity; its measurement has been shown to be useful in assisting the physician in the prediction, diagnosis, and management of patients with diabetes.2-6

Glutamic acid decarboxylase (GAD65) is an enzyme that is produced primarily by pancreatic islet cells. A number of recent studies indicate that patients with insulin-dependent diabetes mellitus (IDDM) often have antibodies to GAD65 and several other islet cell antigens.7 This is consistent with the hypothesis that IDDM is an autoimmune disease and that autoantibody production is an early step in the development of IDDM.8 Autoantibodies can be detected in many cases prior to the onset of glucose intolerance. The presence of GAD65 autoantibodies can be detected in many cases prior to the onset of glucose intolerance. The presence of GAD65 autoantibodies has been shown to be a strong predictive marker for the eventual onset of IDDM. Measurement of GAD65 antibody can also be of use in distinguishing insulin-dependent from non−insulin-dependent diabetics when the clinical history is ambiguous. GAD65 autoantibodies are often markedly elevated in patients with the stiff-person syndrome (also referred to as stiff-man syndrome), a condition that is associated with fluctuating stiffness and paroxysmal spasms of the trunk and legs.9,10

1. Glutamic Acid Decarboxylase Autoantibody ELISA [package insert]. Star, Idaho: Kronus; 2009. P/N 174g 09/09.

2. Pihoker C, Gilliam LK, Hampe CS.Lernmark A. Autoantibodies in diabetes. Diabetes. 2005 Dec; 54(Suppl 2):S52-61. PubMed 16306341

3. Winter WE, Schatz DA. Autoimmune markers in diabetes. Clin Chem. 2011 Feb; 57(2):168-175. PubMed 21127152

4. Tuomilehto J, Zimmet P, Mackay IR, et al. Antibodies to glutamic acid decarboxylase as predictors of insulin-dependent diabetes mellitus before clinical onset of disease. Lancet. 1994 Jun; 343(8910):1383-1385. PubMed 7910881

5. Verge CF, Gianani R, Kawasaki E, et al. Prediction of type I diabetes in first-degree relatives using a combination of insulin, GAD, and ICA512bdc/IA-2 autoantibodies. Diabetes. 1996 Jul; 45(7):926-933. PubMed 8666144

6. Bingley PJ, Bonifacio E, Gale EA. Can we really predict IDDM? Diabetes. 1993 Feb; 42(2):213-220 (review). PubMed 8425658

7. Pietropaolo M, Peakman M, Pietropaolo SL, et al. Combined analysis of GAD(65) and ICA512(IA-2) autoantibodies in organ and non-organ-specific autoimmune diseases confers high specificity for insulin-dependent diabetes mellitus. J Autoimmun. 1998 Feb; 11(1):1-10. PubMed 9480718

8. Bach JF. Insulin-dependent diabetes mellitus as an autoimmune disease. Endocr Rev. 1994 Aug; 15(4):516-542 (review) PubMed 7988484

9. Stayer C, Meinck HM. Stiff-man syndrome: An overview. Neurologia. 1998 Feb; 13(2):83-88. PubMed 9578675

10. Dalakas MC, Li M, Fujii M, Jacobowitz DM. Stiff person syndrome: Quantification, specificity, and intrathecal synthesis of GAD65 antibodies. Neurology. 2001 Sep 11; 57(5):780-784. PubMed 11552003